Abstract: The ability to identify the ecological role an organism plays is fundamental to modern ecology and is an important goal of palaeontological studies. Morphometrics has the potential to be a statistically robust means of futhering this goal, identifying ecomorphological trends within a group of organisams. The dramatic morphological and ecological diversity of modern and fossil birds makes them ideal for ecomorphological studies, and the vast increase in known Mesozoic avian diversity opens numerous possibilities for applying modern ecomorphology to enhance our understanding of avian diversification in the Mesozoic. This study presents a large morphometric database of modern birds analysed using a multivariate statistical approach, in order to identify correlations between ecology and morphology. These relationships were also examined in a number of Mesozoic birds in order to investigate both the ecological diversification of early birds as a whole and the specific ecological roles individual taxa may have played.
Abstract: The exquisitely preserved longipterygid enantiornithine Rapaxavis pani is redescribed here after more extensive preparation. A complete review of its morphology is presented based on information gathered before and after preparation. Among other features, Rapaxavis pani is characterized by having an elongate rostrum (close to 60% of the skull length), rostrally restricted dentition, and schizorhinal external nares. Yet, the most puzzling feature of this bird is the presence of a pair of pectoral bones (here termed paracoracoidal ossifications) that, with the exception of the enantiornithine Concornis lacustris, are unknown within Aves. Particularly notable is the presence of a distal tarsal cap, formed by the fusion of distal tarsal elements, a feature that is controversial in non-ornithuromorph birds. The holotype and only known specimen of Rapaxavis pani thus reveals important information for better understanding the anatomy and phylogenetic relationships of longipterygids, in particular, as well as basal birds as a whole.
Abstract: We provide a detailed study of the morphology of the holotype of Juravenator starki from the Late Jurassic of the Solnhofen area of southern Germany. The incompletely ossified surface of multiple bones and lack of several skeletal fusions indicate that Juravenator starki is based on an immature specimen. Nonetheless, numerous unique morphologies and bone proportions distinguish this taxon from Compsognathus longipes, the only previously named non-avian theropod dinosaur from the Late Jurassic of the Solnhofen Archipelago. Yet, its skeletal anatomy is most similar to that of Compsognathus and other theropods that have often been regarded as closely related to the latter - sometimes within a monophyletic Compsognathidae. Juravenator is characterized by having a small size (∼ 0.75-meter-long in the holotype) with few maxillary teeth, lack of a premaxillary-maxillary diastema, an antorbital fenestra subequal in length to orbit, an elongate scapula that is narrowest at its neck, a proportionally short humerus and high and abruptly tapered manual claws, and bow-like zygapophysial articulations in the mid-caudal vertebrae. Portions of the epidermis preserved mainly along the tail provide the only glimpse of the morphology of the skin of basal coelurosaurs, and structures newly revealed under UV light hint at the possibility of filamentous integumentary structures - akin to those interpreted as proto-feathers in other basal coelurosaurs - also covering the body of this dinosaur. The discovery of Juravenator has provided evidence of morphologies - from details of the skull to the epidermis - that are poorly known in other theropods interpreted as at or near the base of Coelurosauria, and thus contributes significantly to our understanding of the evolutionary history of this clade. The exquisitely preserved holotipic skeleton adds significantly to the meager record of small-bodied Late Jurassic theropods.
Abstract: The ability to identify the ecological role an organism plays is fundamental to modern ecology and is an important goal of palaeontological studies. Morphometrics has the potential to be a statistically robust means of furthering this goal, identifying ecomorphological trends within a group of organisms. The dramatic morphological and ecological diversity of modern and fossil birds makes them ideal for ecomorphological studies, and the vast increase in known Mesozoic avian diversity opens numerous possibilities for applying modern ecomorphology to enhance our understanding of avian diversification in the Mesozoic. This study presents a large morphometric database of modern birds analysed using a multivariate statistical approach, in order to identify correlations between ecology and morphology. These relationships were also examined in a number of Mesozoic birds in order to investigate both the ecological diversification of early birds as a whole and the specific ecological roles individual taxa may have played.
Abstract: Confuciusornis sanctus stands out among the remarkable diversity of birds of the Jehol biota (Lower Cretaceous, Liaoning Province, China). Its basal position in the phylogenetic tree of birds, combined with the exceptional number of well-preserved, largely complete and articulated specimens, makes it a perfect model system for studying the variation, development and life history of early Mesozoic birds. A comprehensive morphometric study (measurements of humerus, ulna, radius, femur and tibia) previously identified two distinct size classes of C. sanctus, while demonstrating the lack of statistical support of the association between this size dimorphism and the characteristic pair of long tail feathers present in some specimens. Four plausible explanations were discussed to account for the resultant size classes: the existence of more than one species in the sample; sexual size dimorphism; two size classes corresponding to attritional death assemblages; and/or a particular growth pattern similar to that inferred for non-avian dinosaurs. Here we present an expanded statistical analysis based on a larger sample of C. sanctus that substantiates previous interpretations, but also addresses the statistical association between the presence/absence of tail feathers and fore- and hind-limb allometry. We discuss the implication of the resulting quantitative patterns of morphological variation to understand better confuciusornithid taxonomy and the life history of C. sanctus.
Abstract: Viviparity is known in several clades of Mesozoic aquatic reptiles, but evidence for it is lacking in the Plesiosauria. Here, we report a Late Cretaceous plesiosaur fossil consisting of a fetus preserved within an adult of the same taxon. We interpret this occurrence as a gravid female and unborn young and hence as definitive evidence for plesiosaur viviparity. Quantitative analysis indicates that plesiosaurs gave birth to large, probably single progeny. The combination of viviparity, large offspring size, and small brood number differs markedly from the pattern seen in other marine reptiles but does resemble the K-selected strategy of all extant marine mammals and a few extant lizards. Plesiosaurs may have shared other life history traits with these clades, such as sociality and maternal care.
Abstract: Enantiornithines are the most speciose avian clade in the Mesozoic, with a fossil record that nearly spans the Cretaceous;
however, with less than half of known taxa preserving skull material, our understanding of their cranial morphology remains
incomplete. Herewe present a comprehensive overviewof the current knowledge of enantiornithine skull anatomy and discuss
the range of morphologies known for each of the main cranial elements. The typical enantiornithine skull retains numerous
ancestral features such as the absence of fusion among bones, the presence of a postorbital bone, a primitive quadrate with a
single headed otic process, an unforked dentary, and teeth. The postorbital in at least one taxon is unreduced, suggesting the
existence of a complete infratemporal fenestra and thus an unmodified diapsid skull as in confuciusornithids. The rostrum is
well known and shows considerable variation, typical of theropods; however, in terms of rostral proportions, enantiornithines
are extremely limited within the modern avian spectrum. Although Late Cretaceous skull material is extremely fragmentary,
when compared to Early Cretaceous material it reveals a trend towards more specialized morphologies in younger taxa. The
foramen magnum in all taxa points caudally, indicating that the ‘flexed’ type skull morphology may not have evolved in this
group. Enantiornithine teeth show considerable diversity in numbers, size, morphology and placement, ranging from taxa
with large teeth found throughout the jaws to taxa with small, rostrally restricted teeth, to the fully edentulous. Despite limited
preservation of skull material, a number of trophic specializations can be deduced from the range of preserved morphologies,
further hinting at the morphological and ecological diversity of the Cretaceous Enantiornithes.
Abstract: A new fossil bird is described from the Early Eocene Fur Formation of Denmark. Pellornis mikkelseni gen. et sp. nov. is represented by a single specimen that consists of three-dimensionally preserved elements of the wing and pectoral girdle together with associated parts of the left hindlimb. Comparisons based on general morphology and particular characters of the wing and most elements of the pectoral girdle indicate that the new specimen is morphologically similar to the extinct taxon Messelornithidae (Messel rails). This similarity is also expressed by a phylogenetic analysis, which supports a close relationship between the new fossil and Messel rails. The morphology of the sternum, in particular, shows that the new fossil is distinguishable from other Messelornithidae. An interesting aspect of its morphology is the presence of limb specializations such as the extensive ossification of tendons—well known among running birds—that suggest the new Danish fossil may have been a ground bird with cursorial habits, a condition that was also previously hypothesized as typical for other Messel rails.
Abstract: Mosasaurs (family Mosasauridae) are a diverse group of secondarily aquatic lizards that radiated into marine environments
during the Late Cretaceous (98–65 million years ago). For the most part, they have been considered to be simple
anguilliform swimmers – i.e., their propulsive force was generated by means of lateral undulations incorporating the greater
part of the body – with unremarkable, dorsoventrally narrow tails and long, lizard-like bodies. Convergence with the
specialized fusiform body shape and inferred carangiform locomotory style (in which only a portion of the posterior body
participates in the thrust-producing flexure) of ichthyosaurs and metriorhynchid crocodyliform reptiles, along with
cetaceans, has so far only been recognized in Plotosaurus, the most highly derived member of the Mosasauridae. Here we
report on an exceptionally complete specimen (LACM 128319) of the moderately derived genus Platecarpus that preserves
soft tissues and anatomical details (e.g., large portions of integument, a partial body outline, putative skin color markings, a
downturned tail, branching bronchial tubes, and probable visceral traces) to an extent that has never been seen previously
in any mosasaur. Our study demonstrates that a streamlined body plan and crescent-shaped caudal fin were already well
established in Platecarpus, a taxon that preceded Plotosaurus by 20 million years. These new data expand our understanding
of convergent evolution among marine reptiles, and provide insights into their evolution’s tempo and mode.
Abstract: Mosasaurs (family Mosasauridae) are a diverse group of secondarily aquatic lizards that radiated into marine environments
during the Late Cretaceous (98–65 million years ago). For the most part, they have been considered to be simple
anguilliform swimmers – i.e., their propulsive force was generated by means of lateral undulations incorporating the greater
part of the body – with unremarkable, dorsoventrally narrow tails and long, lizard-like bodies. Convergence with the
specialized fusiform body shape and inferred carangiform locomotory style (in which only a portion of the posterior body
participates in the thrust-producing flexure) of ichthyosaurs and metriorhynchid crocodyliform reptiles, along with
cetaceans, has so far only been recognized in Plotosaurus, the most highly derived member of the Mosasauridae. Here we
report on an exceptionally complete specimen (LACM 128319) of the moderately derived genus Platecarpus that preserves
soft tissues and anatomical details (e.g., large portions of integument, a partial body outline, putative skin color markings, a
downturned tail, branching bronchial tubes, and probable visceral traces) to an extent that has never been seen previously
in any mosasaur. Our study demonstrates that a streamlined body plan and crescent-shaped caudal fin were already well
established in Platecarpus, a taxon that preceded Plotosaurus by 20 million years. These new data expand our understanding
of convergent evolution among marine reptiles, and provide insights into their evolution’s tempo and mode.
Abstract: The Chinese Early Cretaceous bird Confuciusornis sanctus
is notable because among the many wellpreserved
specimens, some exhibit a pair of remarkably
long, blade-like tail feathers absent in other specimens.
The Peters & Peters (2009) study provides confirmation
of the main conclusion of Chiappe et al. (2008), namely
that there is no statistical correlation between size (limb
bone lengths) and presence/absence of the long tail
feathers of C. sanctus. Peters & Peters (2009) also concluded
that the two distinct size classes identified by
Chiappe et al. (2008)—each containing long-tailed
specimens—were the expression of sexual size dimorphism,
in which the large class was interpreted as females.
We argue that such a conclusion is not substantiated by
the available data and that interpretations of the size
variability of C. sanctus may involve other biological or
taphonomic phenomena.
Abstract: We provide a detailed study of the morphology of the holotype of Juravenator starki from
the Late Jurassic of the Solnhofen area of southern Germany. The incompletely ossified surface of
multiple bones and lack of several skeletal fusions indicate that Juravenator starki is based on an
immature specimen. Nonetheless, numerous unique morphologies and bone proportions distinguish
this taxon from Compsognathus longipes, the only previously named non-avian theropod dinosaur
from the Late Jurassic of the Solnhofen Archipelago. Yet, its skeletal anatomy is most similar to that
of Compsognathus and other theropods that have often been regarded as closely related to the latter –
sometimes within a monophyletic Compsognathidae. Juravenator is characterized by having a small
size (~ 0.75-meter-long in the holotype) with few maxillary teeth, lack of a premaxillary-maxillary
diastema, an antorbital fenestra subequal in length to orbit, an elongate scapula that is narrowest at its
neck, a proportionally short humerus and high and abruptly tapered manual claws, and bowlike
zygapophysial articulations in the mid-caudal vertebrae. Portions of the epidermis preserved
mainly along the tail provide the only glimpse of the morphology of the skin of basal coelurosaurs,
and structures newly revealed under UV light hint at the possibility of filamentous integumentary
structures – akin to those interpreted as proto-feathers in other basal coelurosaurs – also covering the
body of this dinosaur. The discovery of Juravenator has provided evidence of morphologies – from
details of the skull to the epidermis – that are poorly known in other theropods interpreted as at
or near the base of Coelurosauria, and thus contributes significantly to our understanding of the
evolutionary history of this clade. The exquisitely preserved holotipic skeleton adds significantly to
the meager record of small-bodied Late Jurassic theropods.
Abstract: The extremes of dinosaur body size have long fascinated scientists. The smallest (,1 m length) known
dinosaurs are carnivorous saurischian theropods, and similarly diminutive herbivorous or omnivorous
ornithischians (the other major group of dinosaurs) are unknown. We report a new ornithischian
dinosaur, Fruitadens haagarorum, from the Late Jurassic of western North America that rivals the smallest
theropods in size. The largest specimens of Fruitadens represent young adults in their fifth year of development and are estimated at just 65–75 cm in total body length and 0.5–0.75 kg body mass. They are
thus the smallest known ornithischians. Fruitadens is a late-surviving member of the basal dinosaur
clade Heterodontosauridae, and is the first member of this clade to be described from North America.
The craniodental anatomy and diminutive body size of Fruitadens suggest that this taxon was an ecological
generalist with an omnivorous diet, thus providing new insights into morphological and
palaeoecological diversity within Dinosauria. Late-surviving (Late Jurassic and Early Cretaceous)
heterodontosaurids are smaller and less ecologically specialized than Early (Late Triassic and Early
Jurassic) heterodontosaurids, and this ecological generalization may account in part for the remarkable
100-million-year-long longevity of the clade.
Abstract: We describe a new, exceptionally well-preserved
fossil bird recovered from marine deposits of the Early
Eocene Fur Formation of Denmark. Morsoravis sedilis gen. et
sp. nov. is known by a single specimen that consists of a
three-dimensional skull, vertebral column, ribs, pelvis, and
left hindlimb and associated parts of the right hindlimb.
Comparisons based on overall morphology and particularly
characters of the skull, vertebrae and pelvis indicate that the
new specimen is morphologically similar to charadriiform
birds (the shorebirds and relatives). This similarity is also
expressed by a phylogenetic analysis of higher neornithine
(modern birds) taxa, which supports a close relationship
between the new fossil and modern charadriiforms. The
morphology of the hindlimbs, in particular, shows that the
new fossil corresponds to a new taxon that is distinguishable
from modern charadriiform clades. One interesting aspect of
its morphology is the presence of hindlimb specializations
that are most commonly found among perching birds –
these suggest that ecologically the new Danish fossil bird
may have differed from the wading habits typical of most
charadriiforms.
Abstract: We report on a new species of enantiornithine bird from the Lower Cretaceous Qiaotou formation of Northern Hebei, China. The new taxon, Shenqiornis mengi gen. et sp. nov., posses several enantiornithine synapomorphies but is unique from other known species. The specimen has a well-preserved skull that reveals new information about enantiornithine cranial morphology. The new taxon possesses a large postorbital with a long tapering jugal process indicating that some enantiornithines may have had a fully diapsid skull, as in Confuciusornis. The tooth morphology of the specimen is unique and likely represents a previously unknown trophic specialization within Enantiornithes.
Abstract: Avian fossils from the Upper Cretaceous of Mongolia provide significant scientific insight into the
evolution of early birds, primarily due to the scarcity of continental interiors with a well-documented
avifauna in the Cretaceous record. This paper describes in detail the anatomy and histology of a new
taxon of early ornithuromorph bird, Hollanda luceria, from the Barun Goyot Formation at Khermeen Tsav
in the Gobi Desert of Mongolia. The new taxon is represented exclusively by hindlimb elements, and is
characterized by having elongated hindlimbs with an extremely reduced metatarsal IV and an unusual
tibiotarsal-femoral articulation centered on a highly peaked lateral articular facet of the tibiotarsus.
Cladistic and ecospace analyses were also carried out in order to infer evolutionary relationships and
ecology of this primitive bird. These analyses indicate that the new taxon is a previously undescribed
lineage of basal ornithuromorph and an outgroup of Ornithurae (sensu Chiappe, 2002), which may have
had a cursorial lifestyle similar to that of the modern roadrunner, Geococcyx californianus.
Abstract: We present new remains from the Campanian Maastrichtian beds of the Allen Formation, in Salitral Ojo de Agua (RÃo Negro, Argentina) which are assignable to Alvarezsauridae indet. This clade of small coelurosaurian theropods is known from strata of similar age in Mongolia and from similar sediments (Turonian and Coniacian in age) in Argentina. Thus, the material presented here extends the temporal record of the alvarezsaurids from the Southern Hemisphere up to the latest Cretaceous. The fossil bones reported were associated to eggshells of the oofamily Elongatoolithidae, which are actually attributed to Therapoda.
Abstract: Living birds are the most diverse land vertebrates
and the heirs of a rich chapter in the evolution of life. The
origin of modern birds from animals similar to Tyrannosaurus
rex is among the most remarkable examples of an
evolutionary transition. A wealth of recently discovered
fossils has finally settled the century-old controversy about
the origin of birds and it has made the evolutionary saga
toward modern birds one of the best documented transitions
in the history of life. This paper reviews the evidence in
support of the origin of birds from meat-eating dinosaurs,
and it highlights the array of fossils that connect these
fearsome animals with those that fly all around us.
Abstract: We describe the first American stegosaur track of the ichnospecies Deltapodus brodricki, collected in the Upper
Jurassic Morrison Formation of San Juan County, southeastern Utah, United States. The track is preserved as a natural
cast on the underside of a slab of fluvial sandstone and consists of a well-preserved pes track and the eroded remains
of a manus track. Previously, Deltapodus was known only from the Middle Jurassic Yorkshire coast of England and
the Upper Jurassic of Portugal and Spain. The new discovery thus substantially extends the geographic record of this
ichnospecies and highlights the similarities between the Late Jurassic dinosaur faunas of North America and those
of Western Europe.
Abstract: A new species of enantiornithine bird from the Lower Cretaceous Yixian Formation of northeastern
China is reported. The new taxon, Shanweiniao cooperorum, possesses several enantiornithine synapomorphies as well
as the elongate rostral morphology (rostrum equal to or exceeding 60% the total length of the skull) of the Chinese early
Cretaceous enantiornithines, Longipteryx chaoyangensis and Longirostravis hani. The discovery of this new specimen
highlights the existence of a diverse clade of trophically specialized enantiornithines, Longipterygidae, for which we
present phylogenetic support in a new comprehensive cladistic analysis of Mesozoic birds. Shanweiniao provides new
information on the anatomy of longipterygids, and preserves a rectricial morphology previously unknown to enantiornithines,
with at least four tail feathers closely arranged. This supports the hypothesis that enantiornithines were strong
fliers and adds to the diversity of known tail morphologies of these Cretaceous birds.
Abstract: We calculated water vapor conductance (a product of eggshell porosity) from the first
definitively identified sauropod egg (Megaloolithus patagonicus) from the Auca Mahuevo locality in
Argentina. We then compared the results with those from M. siruguei (an egg type long associated
with sauropod dinosaurs) from the Pinyes locality in Spain. The 14-cm Auca Mahuevo egg has a
thinner eggshell and 47 times fewer pores than the 22-cm M. siruguei specimen. The resultingwater
vapor conductance ( ) of the titanosaur GH2O and M. siruguei eggs is 341 and 3979 mg H2O per day
per Torr respectively; these values are two and ten times greater than in avian eggs of comparable
size, but lower than in eggs ofmostmodern reptiles. Clutches fromAucaMahuevo typically contain
20–40 eggs; in contrast, M. siruguei clutches from the Pinyes site average nine eggs. The GH2O of M. sirugueri
exceeds that of the Argentine egg by an order of magnitude, supporting previous inferences of egg burial.
The GH2O of the Argentine titanosaur egg closely approximates that of Troodon and
some oviraptorid eggs, previously calculated as equal to or two times greater than, respectively,
the GH2O of avian eggs of similar size. Higher embryonic growth rates (relative to modern reptiles),
especially in some dinosaurs with large clutch mass, may have required incubation in a more open
environment, where water conservation represented a more critical factor than in a buried clutch.
The lower GH2O calculated for the two megaloolithid eggs is consistent with previous interpretations
of nesting mode that are based on site taphonomy and nesting traces. This study indicates that at
least some dinosaurs did not fully bury their eggs.
Abstract: Confuciusornis sanctus stands out among the remarkable diversity of Mesozoic birds recently unearthed from China. Not only is this primitive beaked pygostylian (birds with abbreviated caudal vertebrae fused into a pygostyle) much more abundant than other avian taxa of this age but differences in plumage between specimens--some having a pair of long stiff tail feathers--have been interpreted as evidence for the earliest example of sexual dimorphism in birds. We report the results of a multivariate morphometric study involving measurements of more than 100 skeletons of C. sanctus. Our analyses do not show any correlation between size distribution and the presence or absence of blade-like rectrices (tail feathers), thus implying, that if these feathers are sexual characters, they are not correlated with sexual size dimorphism. Our results also provide insights into the taxonomy and life history of confuciusornithids, suggesting that these birds may have retained ancestral dinosaurian growth patterns characterized by a midlife exponential growth stage.
Abstract: Life-history parameters of pterosaurs such as growth and ontogenetic development represent an enigma. This aspect of pterosaur biology has remained perplexing because few pterosaur taxa are represented by complete ontogenetic series. Of these, Pterodaustro is unique in that besides being represented by hundreds of individuals with wing spans ranging from 0.3 to 2.5 m, it includes an embryo within an egg. Here we present a comprehensive osteohistological assessment of multiple skeletal elements of a range of ontogenetic sizes of Pterodaustro, and we provide unparalleled insight into its growth dynamics. We show that, upon hatching, Pterodaustro juveniles grew rapidly for approximately 2 years until they reached approximately 53% of their mature body size, whereupon they attained sexual maturity. Thereafter, growth continued for at least another 3–4 years at comparatively slower rates until larger adult body sizes were attained. Our analysis further provides definitive evidence that Pterodaustro had a determinate growth strategy.
Abstract: Megaloolithid dinosaur eggs are distributed nearly worldwide in Late Cretaceous terrestrial sediments, the most important regions of occurrence being southwestern Europe, central India, and the spectacular Auca Mahuevo site in Argentina. Based on finds from the Argentinian site, eggs classified within the oogenus Megaloolithus of the traditional fossil egg parataxonomy are believed to have been produced by titanosaurian sauropods.
Here we review the geologic context, taphonomy, nest structure, clutch morphology, shell thickness variation, and shell porosity of Megaloolithus occurrences from Europe, India, and Auca Mahuevo, Argentina. We focus on the implications of the data for the reproductive biology of sauropod dinosaurs. Although virtually all occurrences are from paleosols of varying maturity, there are striking differences between the European and Indian sites on one hand and Auca Mahuevo on the other. Clutch size is <8 in the former and <40 in the latter, shell porosity is very high in the former and low in the latter. Eggs at Auca Mahuevo are also smaller than those in Europe and India. Based on detailed data for inter-clutch variation of shell thickness and porosity in clutches from the Spanish site of Coll de Nargó, all Megaloothithus eggs from Spain and probably from southern France pertain to a single oospecies, M mammilare. Those from Auca Mahuevo belong to M. patagonicus.
Clutches from Europe and India were buried in the substrate and incubated by environmental heat, whereas those from Auca Mahuevo were deposited in an open nest structure and remained uncovered by sediments or plant material. Colonial nesting cannot be proven for the Indian and European occurrences, high density of clutches being the result of prolonged use of a site. Colonial nesting seems likely at Auca Mahuevo, but contradictions in the interpretation of this site remain.
Very small clutch size and clutch mass compared to estimated adult female mass suggests that the European and Indian titanosaurs produced multiple clutches per nesting season. In both the European and Indian as well as the Auca Mahuevo occurrence, small egg size and inferred large egg number suggests that titanosaurian sauropods were r-strategist. This reproductive strategy was obligatory due to the obligatory ovipary imposed by the calcareous eggshell combined with biomechanical limitations on maximum egg size.
Abstract: Wings flying at low Reynolds numbers enter a stalled flow regime by laminar boundary
layer separation at the leading edge. A way to improve the flying performance of these wings at
the angle of attack close to stalling is by forcing the transition of the upper-side wing boundary
layer from laminar flow to turbulent flow. To force such a transition several devices can be used,
the simplest one being a wire parallel to the wing leading edge.The efficiency of such a turbulence
generator has been checked by testing two wing models in a low turbulence wind tunnel. One of
the wings is of elliptic planformand is equipped with a leading edge wire placed along 62 per cent
of the wing span. The second model simulates the wing of the very primitive bird Archaeopteryx,
and it is also equipped with a wire at the leading edge which simulates one of the long fingers
emerging fromthe leading edge of the wings of this bird. In both cases, experimental results show
that these leading-edge devices are effective in delaying wing stall.
Abstract: An incomplete braincase from the Upper Cretaceous Portezuelo Formation of northwestern Patagonia (Neuque´n Province, Argentina) is
described. The specimen preserves the lateral walls formed by the laterosphenoid, probably part of the orbitosphenoid, prootic, the exoccipitalopisthotic
complex and fragments of the frontal, parietal and basisphenoid. Both inner ears are preserved allowing the production of latex
endocasts. The external and internal morphology of the laterosphenoid and the prootic, the absence of a floccular recess, and the morphology
and position of the cranial nerves VeVII, the oval window and the metotic foramen indicate that the new braincase belongs to a sauropod
dinosaur, probably a titanosaur. The morphology of the inner ear is also reminiscent of that of Sauropoda, which is characterized by the presence
of a simple, short and conical lagena, a posterior semicircular canal that is larger than the lateral semicircular canal, an anterior semicircular
canal that is larger than the other two, and an angle between the vertical semicircular canals (anterior and posterior) of approximately 90.
Abstract: We report on a new Early Cretaceous bird from
China that sheds significant light on the evolutionary transition
between primitive birds with a long bony tail and those
with a short tail ending in a pygostyle. A cladistic analysis of
basal birds supports the placement of the new fossil as the
sister-taxon of all pygostylians. Possessing a unique hand
morphology with a phalangeal formula of 2-3-3-x-x and a
reduced number of caudal vertebrae lacking a pygostyle, the
new specimen reveals anatomical information previously
unknown and increases the taxonomic diversity of primitive,
non-pygostylian birds. We infer from the specimen that during
the evolution of the avian tail, a decrease in relative caudal
length and number of vertebrae preceded the distal
fusion of caudals into a pygostyle.
Abstract: We describe the integumentary anatomy of titanosaur sauropod embryos from the Auca Mahuevo nesting site. Natural (calcitic)
casts of the skin show the non-imbricating, tuberculate scales (i.e., tubercles) typical of other non-avian dinosaurs. However, a variety of scale
patterns previously unknown for the skin of these animals is reported. The observed integumentary patterns include ground tubercles, large and
elongated tubercles, parallel rows of large tubercles, tubercles in rosette-like and flower-like arrangements, and in striate-like rows. Ground tubercles and rosette-like patterns resemble the few examples of skin known for adult sauropods. The former pattern also resembles the
arrangement of osteoderms of the armored titanosaur Saltasaurus. Although the embryonic skin does not show definitive evidence of armor,
the posthatching development of osteoderms cannot be ruled out. This material, the only available evidence of the embryonic skin of non-avian
dinosaurs, contributes significantly to our knowledge of the integumentary morphology of these animals.
Abstract: We report on a new species of enantiornithine bird from the Late Cretaceous of the Mongolian Gobi Desert, which adds to the meager record of birds from the latest part of the Mesozoic in this region. The exceptional, three-dimensional bones of the new fossil increase the known anatomical diversity of enantiornithine birds, providing information about previously unreported morphologies such as a pneumatised furcula. Several synapomorphies nest the new bird within an enantiornithine clade of proficient fliers, but the anatomy and proportions of its flight apparatus imply significant aerodynamic restrictions. The combination of phylogeny and our functional interpretation suggests that this new fossil bird is a representative of a flightless lineage. This discovery thus provides the first evidence of a trend towards more limited flying capabilities among Enantiornithes, a group of Cretaceous birds otherwise believed to be represented by competent fliers.
Abstract: The anatomy of a new, enormous phorusrhacid (Aves: Cariamae) from the Middle Miocene Collón Curá
Formation of northwestern Patagonia (RÃo Negro province, Argentina) is described. The new phorusrhacid is known by
a single specimen that consists of a nearly complete skull associated with a tarsometatarsus and a pedal phalanx. The new
fossil is the largest known phorusrhacid and its morphology resembles more that of taxa traditionally grouped within
phorusrhacines. Its skull—by far the best preserved among large phorusrhacids—provides a great deal of previously
unknown anatomical information and indicates that reconstructions of the skull of gigantic phorusrhacids based on their
smaller relatives are unwarranted.
Abstract: Cretaceous continental Tetrapods from Argentina: An updated synthesis. The Argentinean territory has the most extensive and informative record of tetrapods of the Southern Hemisphere. The increase of finds produced in recent years has permitted us to devise an adequate systematic framework to reinterpret the evolution of the faunas during more than 70 million years. in this work, an updated synthesis of the knowledge about the continental tetrapod fauna from the Cretaceous of Argentina is presented, based on the record of anurans, turtles, lepidosaurs, crocodiles, pterosaurs, dinosaurs, and mammals.
Abstract: We present an anatomical description, photographic documentation, basic metrical data, and osteological comparisons of the small-sized theropod dinosaur Juravenator starki from the Upper Jurassic of the Franconian Alb. Although discovered in 1998, the exquisite skeleton of this dinosaur, the second known theropod from the Franconian Alb after the famed Compsognathus, remained under preparation for several years. The systematic position of Juravenator, its relationship to other theropods, and its environmental and taphonomical contexts are also briefly discussed. The most recent investigations of the soft tissue of the fossil under UV light are presented and interpreted.
Abstract: Three-dimensional specimens of the volant fossil bird Gansus yumenensis from the Early Cretaceous Xiagou Formation of northwestern China demonstrate that this taxon possesses advanced anatomical features previously known only in Late Cretaceous and Cenozoic ornithuran birds. Phylogenetic analysis recovers Gansus within the Ornithurae, making it the oldest known member of the clade. The Xiagou Formation preserves the oldest known ornithuromorph-dominated avian assemblage. The anatomy of Gansus, like that of other non-neornithean (nonmodern) ornithuran birds, indicates specialization for an amphibious life-style, supporting the hypothesis that modern birds originated in aquatic or littoral niches.
Abstract: The new Schamhaupten fossil Juravenator starki is the second dinosaur found in the laminated limestones of the late Jurassic of Bavaria, after the discovery of the celebrated Compsognathus nearly 150 years ago. The schamhaupten Limestones are slightly older than the Solnhofen Lithographic Limestone containing Compsognathus and the famous bird Archaeopteryx. Being exquisitely preserved and complete from the snout to the distal third of the tail, the new fossil is the best-preserved predatory non-avian dinosaur in Europe. Evidence from the surface of its bones and the existence of open centroneural sutures in its tail vertebrae suggest that the fossil corresponds to a very young individual. Remains of soft tissue are preserved surrounding several portions of the skeleton, although they are best observed along the tail.
Abstract: Fossil bird material is exceptionally rare in the Mesozoic of western Asia. With the notable exception of the Upper Cretaceous foot-propelled diving bird Asiahesperornis bazhanovi from northern Kazakhstan, the only bird fossils described from this region have been bone fragments from the Upper Cretaceous of Uzbekistan. In this paper, all material referred to date to the hesperornithiform Asiahesperornis is reviewed and re-described. New postcranial elements of this taxon from the holotype Kushmurun locality (Maastrichtian Zhuravlovskaya Svita) are presented, and the taxonomic history and likely affinities of this ocean-going bird are discussed.
Abstract: Dalingheornis liveii gen. et sp. nov., a new enantiornithine bird was collected from the early Cretaceous Yixian Formation in northeastern China. It is the first record of a highly specialized heterodactyl foot in Mesozoic birds. The Y-shaped furcula with short hypocleidum is different from that of other enantiornithines. The minor metacarpal is robust and longer than the major metacarpal. A long ony tail composed of 20 caudal vertebrae with chevrons resembling those of dromaeosaurids and thus, highlighting again the evolutionary relationship between birds and non-avian theropods. Well-preserved alula feathers and a heterodactyl foot provide strong evidence for the arboreal habit of Dalingheornis.
Abstract: Small Late Jurassic theropod dinosaurs are rare worldwide. In Europe these carnivorous dinosaurs are represented primarily by only two skeletons of Compsognathus, neither of which is well preserved. Here we describe a small new theropod dinosaur from the Late Jurassic period of Schamhaupten in southern Germany. Being exquisitely preserved and complete from the snout to the distal third of the tail, the new fossil is the best-preserved predatory, non-avian dinosaur in Europe. It possesses a suite of characters that support its identification as a basal coelurosaur. A cladistic analysis indicates that the new taxon is closer to maniraptorans than to tyrannosauroids, grouping it with taxa often considered to be compsognathids. Large portions of integument are preserved along its tail. The absence of feathers or feather-like structures in a fossil phylogenetically nested within feathered theropods indicates that the evolution of these integumentary structures might be more complex than previously thought.
Abstract: Although dinosaur eggs were first discovered and identified in the late 1800s, limited attention was given to the scientific value of
oological fossils in contrast to observations based on skeletal features. Here, we offer a review of Mesozoic saurischian egg materials,
in comparison with extant crocodilians and avians, and their paleobiological interpretation based either on the presence of embryos in
ovo or brooding adults on egg clutches. Our study focuses on the eggs of the oviraptorid Citipati osmolka (Mongolia), the troodontid
Troodon formosus (North America), the theropod oospecies Macroelongatoolithus xixiaensis (China), the ornithothoracine bird
(Argentina), an indeterminate theropod (Thailand), and titanosaurs (Argentina). Results show that (1) many oological characters and
reproductive behaviors associated with modern birds are rooted among non-avian theropods, (2) there is a reproductive evolutionary
cline from crocodilians to modern birds with (3) a noticeable pattern of coeval development between the accretion of eggshell layers,
origination and size increased of larger air cells (inferred from egg polar asymmetry), and brooding/incubating behaviors. Most of
these pre-adaptations are grouped in two main clades of the saurischian cladogram: one at the level of Oviraptorosauridae and the
other at Troodontidae. Although undeniably these two theropod taxa seem to represent two important phases for the evolution of avian
reproduction, the phylogenetic distance between these clades and Titanosauria cannot be ignored. As such, the reproductive features
that appeared in concert in oviraptorids might have gradually evolved across more basal theropod clades. Although Troodon formosus
by its egg shape and nesting behavior seems to be in this study the precursors of modern avian reproduction, the importance of smallbodied
theropods such as those who laid the Phu Phok eggs cannot be dismissed and the eggs of such dinosaurs could suggest a closer
phylogenetic ties to Aves than troodontids. At a higher level of inferences, there is a strong possibility that the evolution of these
reproductive features is concurrent with profound physiological and metabolic changes that occurred in saurischian dinosaurs
throughout their evolution.
Abstract: Macelognathus vagans was described by O.C. Marsh in 1884, based on a mandibular symphysis from the
Upper Jurassic Morrison Formation of Wyoming. Often considered a dinosaur but later tentatively referred to the
Crocodylia, its phylogenetic identity has until now been enigmatic. New material of this species from the Morrison
Formation of western Colorado demonstrates its affinities with basal crocodylomorphs commonly grouped together as
the Sphenosuchia, which are characterized by a gracile postcranial skeleton with erect limb posture. Macelognathus
shares features with Kayentasuchus from the Lower Jurassic Kayenta Formation of Arizona and Hallopus, which may
be from the Morrison Formation of eastern Colorado. The new material constitutes the youngest definitive occurrence
of a sphenosuchian, previously known from the Late Triassic to the Middle or Late? Jurassic.
Abstract: We present the first records of Mesozoic fossil birds to be described from British Columbia. New fossil avians
from the Campanian Northumberland Formation on Hornby Island (Strait of Georgia) add to the known distributions of
two groups of fossil birds during the latter stage of the Mesozoic. New specimens referred to the clades Ornithurae and
Enantiornithes demonstrate the presence of a diverse marine avifauna in Canadian Pacific marine sediments prior to the
Cretaceous–Tertiary (K–T) boundary. These new fossil bird remains from coastal rocks on the west coast of British
Columbia lend further support to suggestions that ocean-going birds were important constituents of marine ecosystems
in the terminal stages of the Mesozoic.
Abstract: A detailed description of the anatomy, in particular of the skull, of Eoenantiornis is provided. This description
reveals many morphological characters previously unknown for enantiornithine birds, such as presence of a distinct facet
for the intramandibular articulation between the dentary and postdentary bones. Eoenantiornis documents an intermediate
stage in the abbreviation of the alular digit among Ornithothoraces, which paralleled a similar transformation within
Ornithuromorpha. Our analysis also indicates that Eoenantiornis belongs to the Euenantiornithes.
Abstract: We report on the discovery of an Early Cretaceous bird from northwestern Gansu Province, in northwestern China.
Represented by a nearly complete left wing and shoulder girdle the size of a rock dove, the new bird was quarried from
laminated yellowish mudstones of the Xiagou Formation (Xinminpu Group) near Changma, in the Jiuquan area. These
deposits have previously yielded the only known specimen of Gansus yumenensis, a basal ornithuromorph represented by the
distal half of a hind limb with long and slender digits. Several derived characters of the new occurrence supports its allocation
within Enantiornithes: (1) a convex lateral margin of the coracoid, (2) a minor metacarpal that projects distally more than the
major metacarpal and (3) a proximal phalanx of the major digit longer than the intermediate (second) phalanx. The general
proportions of the wing suggest it was a flier comparable to most other known enantiornithine birds. Although, direct
comparisons between the new fossil and Gansus are not possible, phylogenetic based inferences supports their placement into
two different clades. While the new fossil falls definitively within the enantiornithines, G. Yumenensis falls within the
ornithuromorphs. The new occurrence thus adds to the taxonomic diversity of Early Cretaceous birds from Gansu Province in
particular and central Asia in general.
Abstract: Our knowledge of the eggs and embryos of pterosaurs, the Mesozoic flying reptiles, is sparse. Until now, the recent discovery of an ornithocheirid embryo from 121-million-year-old rocks in China constituted the only reliable evidence of an unhatched pterosaur. Here we describe an embryonic fossil of a different pterosaur from the Early Cretaceous lacustrine deposits of Loma del Pterodaustro (the Lagarcito Formation, which is about 100 million years old) in central Argentina. This new fossil provides insight into the eggshell morphology, early growth and nesting environments of pterosaurs.
Abstract: We report on a new Mesozoic bird, Longirostravis hani, from the Early Cretaceous Jehol Biota of northeastern China. The new taxon has a long, slender rostrum and mandible, and a small number of rostralmost teeth. Postcranial characters such as a furcular ramus wider ventrally than dorsally, a centrally concave proximal margin of the humeral head, and a minor metacarpal that projects distally more than the major metacarpal, support the placement of Longirostravis within euenantiornithine Enantiornithes, the most diverse clade of Mesozoic birds. The morphology of the skull, however, suggests that Longirostravis had a probing feeding behavior, a specialization previously unknown for Enantiornithes. Indeed, this discovery provides the first evidence in support of the existence of such a foraging behavior among basal lineages of Mesozoic birds.
Abstract: We report here two crocodyliform specimens from Lower Cretaceous beds of the Tugulu Group (Xinjiang Uygur Autonomous
Region, People’s Republic of China). One of them consists of postcranial material, while the other is a nicely preserved skull. The
latter is assigned to Edentosuchus tienshanensis, a previously poorly know taxon from the Tugulu Group. The new specimen adds
novel information on this unusual crocodyliform and allows us to test previously proposed phylogenetic relationships of
Edentosuchus tienshanensis through a parsimony analysis within the context of Crocodyliformes. Edentosuchus is found to be
a member of Protosuchidae, the most basal clade of crocodyliforms, thus extending the stratigraphic record of this clade from the
Early Jurassic to the Early Cretaceous.
Abstract: A sedimentological study of the Albian (Early Cretaceous) Lagarcito Formation and the description of new fish fossils from several stratigraphic levels are presented. The recognized facies and the facies association are interpreted as deposited in a shallow perennial lake, and they are subordinately combined with facies representing an ephemeral lake with fluvial and eolian deposits. The vertebrate material is preserved in medium grained, reddish sandstones, and consists of partially articulated fish vertebrae, scales and a fragmentary shoulder girdle. These remains are referred to non-Halecomorphi Halecostomi, based on the morphology of the vertebrae and scales. This is the first record of fish material preserved in three dimensions in the Lagarcito Formation, in contrast to the two dimension previous records from the same unit.
Abstract: Exceptionally preserved sauropod eggshells discovered in Upper Cretaceous (Campanian) deposits in
Patagonia, Argentina, contain skeletal remains and soft tissues of embryonic Titanosaurid dinosaurs.
To preserve these labile embryonic remains, the rate of mineral precipitation must have superseded postmortem
degradative processes, resulting in virtually instantaneous mineralization of soft tissues. If so,
mineralization may also have been rapid enough to retain fragments of original biomolecules in these
specimens. To investigate preservation of biomolecular compounds in these well-preserved sauropod
dinosaur eggshells, we applied multiple analytical techniques. Results demonstrate organic compounds
and antigenic structures similar to those found in extant eggshells.
Abstract: Abnormal, multilayered eggshells are frequently reported in fossil specimens. However, previous reports
of this pathological condition pertain to taxonomically unidentified fossil eggs or eggshell fragments rather than in situ
clutches. A survey of 393 in situ clutches, referable to titanosaur sauropod dinosaurs, from Upper Cretaceous rocks in
northwestern Patagonia, Argentina, revealed that six of these clutches contain both normal eggs and abnormal, multilayered
eggs within the same clutch. Excavation of one clutch exposed 30 eggs, distributed in three levels, including 27
normal eggs and 3 multilayered eggs. The three abnormal eggs occupied the highest level within the clutch and represent
the last eggs laid by the female sauropod. The innermost eggshell layer in multilayered eggs from all six clutches exhibits
typical megaloolithid calcite structure. The structure of the overlying, abnormal shell layer(s), however, varies among the
clutches and within a single egg. Three types of abnormal eggshell morphology are documented. All previous studies that
link abnormal eggshells to dinosaur physiology and the terminal Cretaceous extinction event are incomplete in terms of
taphonomy, taxonomic identification, and lack rigorous statistical methods.
Abstract: The origin of birds, the clade originating from the common ancestor of the Late Jurassic
Archaeopteryx and extant birds, has been at the center of a heated debate throughout the history of evolutionary
biology. Although many disparate hypotheses of bird origins have been proposed in the last two
centuries, an overwhelming consensus exists in support of the idea that birds evolved from maniraptoran
theropod dinosaurs. Osteological support for this hypothesis is plentiful. The skeletons of such maniraptoran
dinosaurs as dromaeosaurids, troodontids, and oviraptorids, share a great deal of similarity with those
of birds. In addition, a series of spectacular discoveries in the last decade has provided new lines of evidence
that supplement the already overwhelming osteological data. This recent evidence is derived primarily
from the study of egg morphology and integumentary anatomy but also includes behavioral inferences
based on a handful of rare fossils. These discoveries have documented the presence of feathers, brooding
behavior, autochronous ovideposition, and other avian attributes among basal maniraptoran dinosaurs.
The available evidence strongly supports the classification of birds within theropods and indicates that
many avian attributes previously thought to be unique to birds (from brooding behavior to flight) first
evolved among maniraptoran dinosaurs. Although dissenters of the Maniraptoran hypothesis of bird origins have countered by highlighting temporal and developmental limitations, these criticisms are clearly
spurious. The most frequently voiced arguments, the so called “temporal paradox†and the homology of
the digits of the avian hand, are tainted by logical inconsistencies. Perhaps the most important is the fact
that these dissenters have been unable to produce alternative phylogenetic hypotheses that could explain,
within the methodological framework of cladistic parsimony, the vast amount of similarity between nonavian
theropods and birds.
Abstract: We report on two juvenile specimens of Pterodaustro guinazui, a medium-sized, filter-feeding pterodactyloid
pterosaur from the Lower Cretaceous (Albian) lacustrine deposits of the Lagarcito Formation of central Argentina (Sierra
de Las Quijadas, San Luis Province). Both specimens lack the skull, but one is otherwise nearly complete and articulated,
and the other is more fragmentary. Their small size (300 mm of wingspan), the lack of fusion of several postcranial
bones, the minimal epiphyseal ossification, and the porous appearance of the periosteal surfaces indicate the specimens
died at a very early stage of postnatal development. The presence of derived characters unique, within Pterodactyloidea,
to P. guinazui (e.g., caudal vertebrae exceeding 16 elements) supports the proposed specific identification of the specimens.
The new material provides anatomical information previously unknown for P. guinazui and sheds light on allometric
transformations during the growth of this pterosaur. Comparisons with more mature and much larger individuals support
two major allometric trends: (i) the negative allometric growth of the proximal portion of the forelimb, and (ii) the positive
allometric growth of the metacarpal IV.
Abstract: Six egg-filled depressions discovered in the Upper Cretaceous
Anacleto Formation (Campanian) of Patagonia, Argentina,
and interpreted as dinosaur nests, provide the only
known evidence of titanosaurid sauropod nest construction.
These nest trace fossils show truncation of sedimentary
structures as well as differences in texture between the host
substrate and in-filling sediment. Titanosaurid sauropods
excavated and laid eggs in open nests rather than burying
clutches in sediment. In addition, this paper establishes criteria
for definitive recognition of excavated nests in the
stratigraphic record.
Abstract: FEATHERING DINOSAURS: THE TRANSITION FROM THEROPODS TO BIRDS.— Since the beginning
of evolutionary thinking, the origin of birds has constituted one of the most debated problems
in evolutionary biology. Today, a large body of evidence indicates that such a problem is to
a great extent solved. Osteological, oological, ethological, and integumentary evidence strongly
supports the hypothesis that birds evolved from theropod dinosaurs, in particular from dinosaurs
classified within Maniraptora. TodayÂ’s handful of researchers opposing this hypothesis
have either based their criticisms on mistaken observations or they have framed them within
dated methodologies. This paper provides a brief discussion of both the evidence in support to
this hypothesis and the main arguments against it.
Abstract: Fossil birds from the Mesozoic of Gondwana are exceedingly
rare (Chiappe, 1996a; Forster et al., 1998; Clarke and Chiappe,
2001). We report on a new avian specimen from the upper
Cretaceous of Lebanon, which represents the only known Mesozoic
bird skeleton of northern Gondwana and the first such
occurrence for the African-Arabic Plate. Although recovered
from marine limestones, the new fossil reveals anatomical features
diagnostic of Enantiornithes, a group of Cretaceous flying
birds mainly known from continental environments (Chiappe,
1995; Padian and Chiappe, 1998; Chiappe and Walker, 2002).
Characteristics of its preservation and the existence of amber
corpuscles scattered between its bones suggest the new Lebanese
bird was transported to its marine burial from a non-marine,
probably insular habitat.
Abstract: Until recently, most knowledge of the early history of birds and the evolution of their unique specializations was based on just a handful of diverse Mesozoic taxa widely separated in time and restricted to marine environments. Although Archaeopteryx is still the oldest and only Jurassic bird, a wealth of recent discoveries combined with new phylogenetic analyses have documented the divergence of a number of lineages by the beginning of the Cretaceous. These and younger Cretaceous fossils have filled much of the morphological chasm that existed between Archaeopteryx and its living counterparts, providing insights into the evolutionary development of feathers and other important features of the avian flight system. Dramatic new perceptions of the life history, growth and development of early birds have also been made possible by the latest data. Although no primitive birds are known to have survived beyond the end of the Cretaceous, the present fossil record provides no evidence for a sudden disappearance. Likewise, a Mesozoic origin for extant birds remains controversial.
Abstract: Birds known from more than isolated skeletal elements are rare in the fossil record, especially from the European Mesozoic. This paucity has hindered interpretations of avian evolution immediately prior to, and in the aftermath of, the Cretaceous-Tertiary (K-T) extinction event. We report on a specimen of a large ornithurine bird (closely related to Ichthyornis) from the uppermost Cretaceous (Maastricht Formation) of Belgium. This is the first record of a bird from these historic strata and the only phylogenetically informative ornithurine to be recovered from the Mesozoic of Europe. Because this new specimen was collected from 40 m below the K-T boundary (approximate age of 65.8 Ma), it is also the youngest non-neornithine (= non-modern) bird known from anywhere in the world.
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Abstract: In 1992, a field party led by Storrs L. Olson (National Museum of
Natural History) recovered several bird bones from the marine Upper
Cretaceous Mooreville Chalk Formation of western Alabama. In addition
to a few remains of the ornithurine Ichthyornis, the only avian
taxon previously reported for the Mesozoic of Alabama (Wetmore,
1962; Olson, 1975; Lamb, 1993, 1997; Lamb et al., 1993), the party
collected several small bones, which proximity and taphonomic characteristics
support that they belong to a single individual. The new
specimen shares synapomorphies with Enantiornithes, a Cretaceous
group of volant birds mostly known from continental deposits (Walker,
1981; Chiappe and Walker, in press). The occurrence of this new specimen
in offshore deposits is thus significant. Most importantly, comparisons
to other enantiornithines reveal characters justifying the erection
of a new species, thus increasing the known taxonomic diversity
of this major clade of basal birds.
Abstract: Birds known from more than isolated skeletal elements are rare in the fossil record,
especially from the European Mesozoic. This paucity has hindered interpretations of avian evolution
immediately prior to, and in the aftermath of, the Cretaceous-Tertiary (K-T) extinction event. We
report on a specimen of a large ornithurine bird (closely related to Ichthyornis) from the uppermost
Cretaceous (Maastricht Formation) of Belgium. This is the first record of a bird from these historic
strata and the only phylogenetically informative ornithurine to be recovered from the Mesozoic of
Europe. Because this new specimen was collected from 40 m below the K-T boundary (approximate
age of 65.8 Ma), it is also the youngest non-neornithine (=non-modern) bird known from anywhere in
the world.
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Abstract: Abelisaur dinosaurs, theropods with unusual horned skulls
such as Majungatholus (Sampson et al., 1998) and Carnotaurus
(Bonaparte, 1985), are the most abundant land predators from
the Late Cretaceous of Gondwana (Bonaparte, 1996; Novas,
1997; Sampson et al., 1998; Coria and Salgado, 1998). Although
a number of abelisaur species are known from Argentina
(Bonaparte, 1996), as well as India and Madagascar (Sampson
et al., 1998), much of their anatomy and evolutionary relationships
remains poorly understood.
In March of 1999, a joint expedition from the Museo Municipal
Carmen Funes and the Natural History Museum of Los
Angeles County recovered a nearly complete and articulated
skeleton of a large theropod from Auca Mahuevo, a Patagonian
Late Cretaceous site famous for its abundant sauropod eggs and
embryos (Chiappe et al., 1998, 2000). In spite of being 30%
smaller, the Auca Mahuevo theropod is remarkably similar to
Carnotaurus sastrei (Bonaparte, 1985). Nonetheless, a unique
combination of characters distinguishes the new skeleton from
Carnotaurus sastrei. Thus, following the predicates of the phylogenetic
species concept (Nixon and Wheeler, 1992), the Auca
Mahuevo skeleton forms the basis for a new abelisaur species,
Aucasaurus garridoi.
Abstract: The eggshell microstructure of some Late Cretaceous nonavian
theropod eggs closely resembles that of the most primitive
group of extant birds, the paleognaths (Mikhailov, 1992).
It has been proposed, therefore, that the parataxonomic ornithoid-
ratite structure is plesiomorphic for Aves (Mikhailov,
1992; Norell et al., 1994). The purported presence of this eggshell
structure in Cretaceous enantiornithine birds (Mikhailov,
1997) would seem to support this hypothesis. However, all eggshell
previously ascribed to basal avian lineages is either diagenetically
recrystallized or not associated with an egg containing
an embryo (Kurochkin, 1996; Mikhailov, 1997). Hence, no
unaltered basal avian eggshell structure has ever been reported
from an egg containing an embryo.
We describe here well-preserved eggs from non-marine sandstone
units of the Bajo de la Carpa Member of the Upper Cretaceous
Rı´o Colorado Formation in the city of Neuque´n, Argentina.
Age estimates for the Rı´o Colorado Formation range
from Coniacian (Heredia and Calvo, 1997) to Campanian (Cruz
et al., 1989) but recent biochronologic and magnetostratigraphic
correlations indicate a Campanian age (Dingus et al., 2000).
The egg described here contains partially articulated embryonic
bones, allowing the first unequivocal assignment of prismatic,
trilaminate eggshell structure found in extant neognaths to a
basal avian lineage.
Abstract: Little is known about the cranial anatomy of the taxonomically diverse and
geographically widespread titanosaurs, a paucity that has hindered inferences
about the genealogical history and evolutionary development of the latest
sauropod dinosaurs. Newly discovered fossil eggs containing embryonic remains
from the Late Cretaceous of Argentina provide the Þrst articulated skulls
of titanosaur dinosaurs. The nearly complete fetal skulls shed light on the
evolution of some of the most notable cranial features of sauropod dinosaurs,
including the retraction of the external nares, the forward rotation of the
braincase, and the abbreviation of the infraorbital region.
Abstract: Little is known about the cranial anatomy of the taxonomically diverse and geographically widespread titanosaurs, a paucity that has hindered inferences about the genealogical history and evolutionary development of the latest sauropod dinosaurs. Newly discovered fossil eggs containing embryonic remains from the Late Cretaceous of Argentina provide the first articulated skulls of titanosaur dinosaurs. The nearly complete fetal skulls shed light on the evolution of some of the most notable cranial features of sauropod dinosaurs, including the retraction of the external nares, the forward rotation of the braincase, and the abbreviation of the infraorbital region.
Abstract: Anatomy and tooth replacement mechanisms observed in a sauropod dinosaur left premaxilla from the Late Cretaceous of Patagonia are described. The specimen is assigned to Neosauropoda, and with doubts to Titanosauridae, due to the presence of a stepped anterior margin, and long and cylindrical teeth with no denticles. The specimen presents a dental settlement pattern performed by intra-alveolar packages of four dental elements, one functional and three germinal, which compose a comb-like arrangement only recorded in diplodocid and titanosaurid sauropods.
Abstract: A newly discovered cervical vertebra from the Upper Cretaceous Lecho Formation of northwestern Argentina (Estancia El Brete) bears pneumatic foramina and epipophyses, and is assigned to the Theropoda. Although isolated, this specimen is significant because it is different from all described theropod cervical material from South America, most likely representing a new taxon. The El Brete specimen most closely resembles the cervical vertebrae of Chirostenotes, oviraptorids, and therizinosaurids. A cladistic analysis of cervical morphology groups the new specimen with those of the Laurasian oviraptorosaurs, suggesting the presence of this group of nonavian theropods in the Cretaceous of Gondwana.
Abstract: During the last few years, rocks from the Late Jurassic-Early Cretaceous transition in the northeastern Chinese province of Liaoning have yielded a plethora of early bird specimens and their dinosaurian forebears. These specimens, often articulated and preserving portions of their integument and other soft tissues, have shed unprecedented light onto the origin of birds and their early evolution. Many of these recent discoveries, including Sinosauropteryx prima, Protarchaeopteryx robusta, Caudipteryx zoui, and Confuciusornis sanctus, came from the fine deposits of the Chaomidianzi Formation, a lithostratigraphic unit formerly regarded as the lower section of the Yixian formation.
In the Sihetun-Jianshangou area, the Chaomidianzi Formation unconformably overlies the Middle Jurassic Tuchengzi Formation. The Chaomidianzi Formation is subdivided into (from the oldest to youngest) the Sihetun, Jiulongsong, and Hengdaozi Members. While the Jiulongsong Member has yielded most of the dinosaurs (including birds) from the Chaomidianzi Formation, the lacustrine grayish-yellow and grayish-green tuffaceous sandstones, siltstones, and silty mudstones of the Hengdaozi Member have yielded a large variety of plants, insects, fishes, turtles, and birds.
Among the specimens of primitive birds from the Hengdaozi Member housed at the National Geological Museum of China, in Beijing, one specimen (represented by a slab and a counterslab) initially thought to be of Confuciusornis sanctus, displays morphological differences with the latter that distinguish it as a new taxon. This new bird, Changchengornis hengdaoziensis, is preliminarily described here and issues concerning its anatomy and phylogentic relationships are discussed. A detailed description of its morphology will be provided elsewhere.
Abstract: We report small fibrous structures associated with a new specimen of Shuvuuia deserti, which we hypothesize are remnants of feather-like epidermal appendages. Multiple analyses suggest that these structures are epidermally derived and contain epitopes consistent with beta-keratin, a protein expressed only in extant “reptiles†and birds. Morphological, microscopic, mass spectrometric, and immunohistochemical studies are consistent with the interpretation that these structures are related to feathers. These data suggest that proteinaceous components may survive across geological time and support the view that alvarezsaurids (Shuvuuia and its allies) are either a lineage of birds or are a lineage phylogenetically close to them.
Abstract: Since the late 1800s, the debate on the origin of flight in birds has
centred around two antagonistic theories: the arboreal (take-off
from trees) and cursorial (take-off from running) models.
Despite broad acceptance of the idea that birds evolved from
bipedal and predominantly terrestrial maniraptoriformdinosaurs,
the cursorial model of flight origins has been less successful than
the arboreal model. Three issues have contributed to this lack of
success: the gap between the estimated maximum running speed
of Archaeopteryx (2 metres per second) and its estimated minimum
flying speed (6 metres per second); the high energy
demands of evolving flight against gravity; and the problem of
explaining the origin of the `flight' stroke in an earthbound
organism. Here we analyse the take-off run of Archaeopteryx
through lift-off from an aerodynamic perspective, and emphasize
the importance of combining functional and aerodynamic considerations
with those of phylogeny. Our calculations provide
a solution to the `velocity gap' problem and shed light on how a
running Archaeopteryx (or its cursorial maniraptoriform ancestors)
could have achieved the velocity necessary to become airborne by
flapping feathered wings.
Abstract: A partial skeleton of a primitive bird, Rahona ostromi, gen. et sp. nov., has been discovered from the Late Cretaceous of Madagascar. This specimen, although exhibiting avian features such as a reversed hallux and ulnar papillae, retains characteristics that indicate a theropod ancestry, including a pubic foot and hyposphene-hypantra vertebral articulations. Rahona has a robust, hyperextendible second digit on the hind foot that terminates in a sicklelike claw, a unique characteristic of the theropod groups Troodontidae and Dromaeosauridae. A phylogenetic analysis places Rahona with Archaeopteryx, making Rahona one of the most primitive birds yet discovered.
Abstract: Anatomical and aerodynamic analysis of fossils and living birds show that birds evolved from small, predatory dinosaurs that lived on the ground.
Abstract: In joint expeditions, researchers from the American Museum of
Natural History and the Mongolian Academy of Sciences have
recovered over 20 alvarezsaurid (Theropoda: Aves) specimens in
the Late Cretaceous beds of Mongolia’s Gobi Desert1. Here we
describe a new taxon that is closely related to Mononykus2,3. This
new taxon is represented by two exquisitely preserved skulls—the
first known for Alvarezsauridae—details of which support the
theory that the group is related to birds4,5. This theory was first
put forward on the basis of primarily postcranial evidence2,3,
including the presence of avian characteristics such as the absence
of a contact between the jugal and postorbital, and between the
quadratojugal and squamosal, articulations. Other earlier evidence
that suggested that the alvarezsaurids were birds included
the presence of a movable joint between the quadratojugal and
quadrate, separate squamosal and braincase articulations of the
quadrate, confluence between the caudal tympanic recess and
columellar recess, a triradiate palatine, an unusually large foramen
magnum, and the loss of a coronoid bone. The configuration of
the temporal region of the skull and its articulation with the
rostrum indicate the capability for prokinetic movement in which
flexing occurs at the junction of the upper jaw and neurocranium,
and support the idea that prokinesis preceded other types of avian
intracranial kinesis.
Abstract: Definitive non-avian dinosaur embryos, those contained inside
fossil eggs, are rare1,2. Here we describe the first known unequivocal
embryonic remains of sauropod dinosaurs--the only
known non-avian dinosaur embryos from Gondwana--from a
nesting ground in the Upper Cretaceous stage of Patagonia,
Argentina. At this new site, Auca Mahuevo (Fig. 1), thousands
of eggs are distributed over an area greater than 1 km2. The
proportion of eggs containing embryonic remains is high: over
a dozen in situ eggs and nearly 40 egg fragments encasing
embryonic material were recovered. In addition to bone, these
specimens contain large patches of fossil skin casts, the first
definitive portions of integument ever reported for a non-avian
dinosaur embryo. As morphology of the eggs enclosing these
osseous and integumentary remains is identical, we propose that
these specimens belong to the same sauropod species. This
discovery allows the confident association of the megaloolithid
type of dinosaur eggshell3 with sauropod dinosaurs.
Abstract: A sedimentological analysis of the basal section of the Early Cretaceous, lacustrine Lagarcito formation at “Loma del Pterodaustro†(San Luis, Argentina) and a summary of its biological components are presented. Three sedimentological facies can be recognized in the basal sequence of the Lagarcito Formation. Fossil remains are particularly abundant in laminated claystones of a facies interpreted as deposits formed in offshore areas of the lake. The preservation of delicate structures allows recognition of these deposits as a Konservat Lagerstätte. Up to now, rocks at “Loma del Pterodaustro†have yielded plants, conchostracans, semionotid and pleuropholid fishes, pterodactyloid pterosaurs, and a variety of invertebrate traces. The chronology of the Lagarcito Formation is discussed and it is concluded that this unit is of Albian age. The palaeoenvironment of deposition of the basal sequence of the Lagarcito Formation at “Loma del Pterodaustro†is interpreted as a perennial, shallow lake developed within an alluvial plain, under semiarid climatic conditions
Abstract: Birds evolved from and are phylogenetically recognized as members of the theropod dinosaurs; their ®rst
known member is the Late Jurassic Archaeopteryx, now represented by seven skeletons and a feather, and their
closest known non-avian relatives are the dromaeosaurid theropods such as Deinonychus. Bird ¯ight is widely
thought to have evolved from the trees down, but Archaeopteryx and its outgroups show no obvious arboreal
or tree-climbing characters, and its wing planform and wing loading do not resemble those of gliders. The
ancestors of birds were bipedal, terrestrial, agile, cursorial and carnivorous or omnivorous. Apart from a
perching foot and some skeletal fusions, a great many characters that are usually considered `avian' (e.g. the
furcula, the elongated forearm, the laterally ¯exing wrist and apparently feathers) evolved in non-avian
theropods for reasons unrelated to birds or to ¯ight. Soon after Archaeopteryx, avian features such as the
pygostyle, fusion of the carpometacarpus, and elongated curved pedal claws with a reversed, fully descended
and opposable hallux, indicate improved ¯ying ability and arboreal habits. In the further evolution of birds,
characters related to the ¯ight apparatus phylogenetically preceded those related to the rest of the skeleton
and skull. Mesozoic birds are more diverse and numerous than thought previously and the most diverse
known group of Cretaceous birds, the Enantiornithes, was not even recognized until 1981. The vast
majority of Mesozoic bird groups have no Tertiary records: Enantiornithes, Hesperornithiformes,
Ichthyornithiformes and several other lineages disappeared by the end of the Cretaceous. By that time, a few
Linnean `Orders' of extant birds had appeared, but none of these taxa belongs to extant ` families ', and it
is not until the Paleocene or (in most cases) the Eocene that the majority of extant bird `Orders' are known
in the fossil record. There is no evidence for a major or mass extinction of birds at the end of the Cretaceous,
nor for a sudden `bottleneck' in diversity that fostered the early Tertiary origination of living bird `Orders'.
Abstract: A feathered skeleton of a Lower Cretaceous enantiornithine bird from Spain indicates that
the modified diapsid skull of modern birds did not evolve until late in their evolution: Basal
birds retained an essentially primitive diapsid design. The fossil provides data clarifying
long-standing debates on the cranial morphology of the basalmost bird, Archaeopteryx.
It also reemphasizes the notion that the early morphological transformations of birds
were focused on the flight apparatus. This fossil was a nestling and suggests that early
postnatal developments in the Cretaceous enantiornithine birds and those in their extant
counterparts are comparable.
Abstract: We report the discovery of two exquisitely preserved specimens of a new, very primitive bird from the Late Cretaceous period of Madagascar. The new taxon, Vorona berivotrensis, is provisionally placed phylogenetically in an unresolved trichotomy with Enantiornithes and a clade consisting of Patagopteryx and Ornithurae. These specimens are the first known pre-Holocene birds from Madagascar and the first avian skeletal remains from the Mesozoic era of a large portion of Gondwana.
Abstract: Avian flight is one of the most remarkable achievements of vertebrate evolution, yet there is little evidence of its early phases. Specimens of Archaeoptex shed important (albeit controversial) light on this evolutionary phenomenon, but the large morphological (and almost certainly functional) gap between Archeopteryx and modern avians remained virtually empy until recently. Here we report a new, exquisitely preserved, bird from the Lower Cretaceous Konservat-Lagerstätte of Las Hoyas (Cuenca, Spain) which provides evidence for the oldest known alula (bastard wing). Crustacean remains found inside its belly also provide the oldest direct evidence of feeding habits in birds. The new specimen has numerous synapomorphies with the Enantiornithes, but its unique sternal morphology, along with other autopomorphies in the furcula and vertebral centra, support the recognition of a new enantiornithine taxon, Eoalulavis hoyasi. The combination in Eoalulavis of a decisive aerodynamic feature, such as the alula, with the basic structures of the modern flight apparatus indicates that as early as 115 million years ago, birds had evolved a sophisticated structural system that enabled them to fly at low speeds and to attain high manoeurvrability.
Abstract: In order to assess the phylogenetic relationships of Mononykus, a cladistic analysis was performed. Using velociraptorine theropods as outgroups, the analysis resulted in a single most parsimonious cladogram. In this cladogram the monophyletic Alvarezsauridae (including Mononykus and the Argentine Alvarezsaurus and Patagonykus) is the sistergroup of all other birds except Archeopteryx. The monophyly of Aves (=Avialae sensu Gauthier) is supported by seven unambiguous synapomorphies, four of which are present in Mononykus. These characters include fewer than 26 caudal vertebrae, caudal vertebrae with short distal prezygapophyses, teeth with unserrated crowns and a caudal tympanic recess opening only inside the tympanic cavity. The mononophyly of Metornithes (Aves exclusive of Archaeopteryx) is supported by six unambiguous synapomorphies all of which occur in Mononykus. Among these characters are the presence of prominent ventral processes on the cervicodorsal vertebrae, a carpometacarpus, a prominent antitrochanter in the pelvis and a rectangular, carinate sternum. Furthermore, six synapomorphies (all present in Mononykus) unambiguously diagnose both Aves and Metomithes. the distribution among avain and nonavian taxa of all these characters is discussed. Several authors have criticized the hypothesis of avian relationships for Mononykus. In this paper we address those criticisms. We also discuss the rationale of testing phylogenetic hypotheses within a cladistic framework and establish that our critics have not furnished much beyond a prior speculation.
Abstract: In order to assess the phylogenetic relationships of Mononykus a cladistic analysis was performed. Using velociraptorine theropods as outgroups, the analysis resulted in a single most parsimonious cladogram. In this cladogram the monophyletic Alvarezsauridae (including Mononykus and the Argentine Alvarezsaurus and Patagonykus) is the sistergroup of all other birds except Archeopteryx. The monophyly of Aves (=Avialae sensu Gauthier) is supported by seven unambiguous synapomorphies, four of which are present in Mononykus. These characters include fewer than 26 caudal vertebrae with short distal prezygapophyses, teeth with unserrated crowns and a caudal tympanic recess opening only inside the tympanic cavity. The monophyly of Metornithes (Aves exclusive of Archaeopteryx) is supported by six unambiguous synapomorphies all of which occur in Mononykus. Among these characters are the presence of prominent ventral processes on the cervicodorsal vertebrae, a carpometacarpus, a prominent antitrochanter in the pelvis and a rectangular, carinate sternum. Furthermore, six snyapomorphies (all present in Mononykus) ambiguously diagnose both Aves and Metomithes. the distribution among avian and nonavian taxa of all these characters is discussed. Several authors have criticized the hypotheses of avian relationships for Mononykus. In this paper we address those criticisms. We also discuss the rationale of testing phylogenetic hypotheses within a cladistic framework and establish that our critics have not furnished much beyond a priori speculation
Abstract: The record of Gondwanan Mesozioic birds, including osteological specimens, feathers and traces, is critically reviewed. Data regarding the paleoenvironment and associated biota of each record is provided. Several occurrences of controversial status in the Late Triassic-Early Jurassic of Africa and the Cretaceous of Australia and Africa, and misguided reports from the Cretaceous of South America are also discussed. The Mesozoic record of Gondwanan birds is limited, although it has provided relevant insights about the early evolution of birds. Undisputable records are known from the Cretaceous of South America, Australia, Africa, and Antarctica. This material indicates that during the Cretaceous, Gondwanan birds were widely distributed, inhabiting a broad range of environments and developing various modes of life.
Abstract: With a wing span of 1-2.5 metres, a long, thin, upward-curved skull, and jaws bearing up to 1,000 filament-like teeth, the filter-feeding, Early Cretaceous Pterodaustro guiñazui is among the most peculiar pterosaurs ever found. Pterodaustro’s bizarre mandibular teeth have long puzzled paleontologists. The fine structure and baleen-like arrangement of the teeth led some to regard them as keratin-like or bristle-like structures that were not actual teeth. Our study, based on new specimens from the laminated shales of the Lagarcito Formation of central Argentina, provides a description of the intriguing filter-feeding apparatus of Pterodaustro and confirms its dental nature.
Abstract: Avain flight is one of the most remarkable achievements of vertebrate evolution, yet there is little evidence of its early phases. Specimens of Archaeopteryx shed important (albeit controversial) light on this evolutionary phenomenon, but the large morphological (and almost certainly functional) gap between Archaeopteryx and modern avians remained virtually empty until recently. Here we report a new, exquisitely preserved, bird from the Lower Cretaceous Konservat-Lagerstätte of Las Hoyas (Cuenca, Spain) which provides evidence for the oldest known alula (bastard wing). Crustacean remains found inside its belly also provide the oldest direct evidence of feeding habits in birds. The new specimen has numerous synapomorphies with the Enantiornithes, but its unique sternal morphology, along with other autopomorphies in the furcula and vertebral centra, support the recognition of a new enantiornithine taxon, Eoalulavis hoyasi. The combination in Eoalulavis of a decisive aerodynamic feature, such as the alula, with the basic structures of the modern flight apparatus indicates that as early as 115 million years ago, birds had evolved a sophisticated structural system that enabled them to fly at low speeds and to attain high manoeuvrability.
Abstract: More than half of the evolutionary history of birds is played out in the Mesozoic. A recent burst of fossil discoveries has documented a tremendous diversity of early avians. Clarification of the Phylogenetic structure of this diversity has provided clues for a better understanding of the evolution of functional, developmental and physiological characteristics of modern birds. Yet their long Mesozoic history is only beginning to be deciphered.
Abstract: We report on the bone microstructure of the Late Cretaceous birds Patagopteryx deferrariisi and members of the Enantiornithes. These birds represent the most primitive birds ever studied histologically. The occurrence of growth rings indicating alternating periods of slowed and fast growth suggests that these basal birds had slower growth rates, and differed physiologically from their modern relatives. Our findings also call into question previous ideas suggesting that nonavian theropods developed a full avian degree of homeothermic endothermy, which was later inherited by birds. On the contrary, our findings suggest that birds developed classic endothermy relatively late in their phylogenetic history.
Abstract: A spectacular fossil specimen that suggests the presence of an avian type of nesting behavior in oviraptorids, a clade of non-avian maniraptoran theropods, is reported here. The substantial evidence indicating that birds are a type of theropod dinosaur has led to copious discussion concerning the origin and possible presence of advanced avian reproductive behavior in non-avian dinosaurs. Although the inference of behavior from fossils is problematic, some remarkable discoveries, such as the incontrovertible evidence of dinosaur nests, and more controversial claims made on the basis of dinosaur nesting grounds and juvenile morphology, hint at the occurrence of advanced reproductive behaviour in a variety of non-avian dinosaurs. But there is no direct fossil evidence implying advanced parental systems such as those found in modern birds. The closest associations between presumed parents and nests occur in ovirapotorid dinosaurs from Late Cretaceous deposits of the Gobi Desert. The specimen described here is the first preserved well enough to determine its precise relationship with the nest. It is a large oviraptorid positioned over a nest of oviraptorid eggs in the same posture taken by many living birds when brooding. This provides the strongest evidence yet for the presence of avian brooding behavior in non-avian dinosaurs.
Abstract: The record of enantiornithine birds from the United States was previously restricted to Avisaurus archibaldi from the Maastrichtian Hell Creek Formation of eastern Montana and a fragmentary humerus from the Upper Cretaceous of new Mexico. This distinctive group of Volant birds was first recognized on the basis of a collection of bones from the Maastrichtian Lecho Formation of northwestern Argentina, including two tarsometatarsi that were later assigned to the genus Avisaurus. Although, Brett-Surman and Paul (1985) regarded Avisaurus as a non-avian theropod, the characters supporting this hypothesis have been recognized as either being misinterpreted or shared by a variety of theropods, Archaeopteryx lithographica, and some Cretaceous birds. In contrast, the enantiornithine affinity of the Avisauridae is strongly supported by the fact that the isolated A. archibaldi and the Argentine form (recently named Soroavisaurus australis) share synapomorphies with Neuquenornis australis, a Patagonian enantiornithine known by a nearly complete skeleton. In this paper we describe a new species of Avisauridae based on a small tarsometatarus discovered in the summer of 1991 while excavating a dinosaur bone bed in the Campanian Two Medicine Formation of western Montana. The anatomical nomenclature follows Baumel et al. using the English equivalents of the Latin terminology. The phylogenetic species concept in which a species is diagnosed on the basis of a unique combination of characters is adopted.
Abstract: We report here a new locality, Ukhaa Tolgod (‘brown hills’), from the Upper Cretaceous of the Gobi Desert of Mongolia, which shows an unmatched abundance of well preserved vertebrate fossils, including the highest concentration of mammalian skulls and skeletons from any Mesozoic site. In the main collecting area (about 4 km square), recovered and uncollected articulated skeletons of theropod, ankylosaurian and protoceratopsian dinosaurs represent over 100 individuals. Specimens collected also include skulls (many with associated skeletons) of over 400 mammals and lizards, skeletons (including the first known skull) of the bird Mononykus, and nest sites that preserve the first known theropod dinosaur embryos. In contrast to other Mesozoic localities, the diversity and abundance of theropods, mammals and lizards are unusually high. The exceptional preservation of vertebrates from the red-bed facies of the Gobi Upper Cretaceous has been attributed to arid conditions, possibly involving catastrophic death and burial during major sandstorms. Although fossils are found in fluvial facies at Ukhaa Tolgod, high concentration of excellent specimens in Aeolian facies support the argument for rapid entombment in sand. This contrasts with conditions for the terrestrial Upper Cretaceous in North and South America, where accretionary preservation of fossils in fluvial deposits predominates.
Abstract: The continental Upper Cretaceous record of birds from Argentina is composed mainly of two distinct clades: the flying Enantiornithes, and the flightless Patagopteryx deferrariisi. Regarding the phylogenetic position of the Enantiornithes, several different hypotheses have been proposed, whereas the phylogenetic relationships of P. deferrariisi were only briefly explored. In this paper a cladistic analysis of 73 cranial and postcranial features is performed, and characters supporting all previous phylogenetic hypotheses of these two groups are discussed. These results strongly support P. deferrariisi as the sister-group of Ornithurae (14 synapomorphies diagnose this clade), developing flightlessness independent from the ratites and all other flightless taxa. The present study also indicates that the Enantiornithes is the sister-group of P. deferrariisi + Ornithurae (29 synapomorphies diagnose this relationship). The sequence of character transformation derived from the cladistic analysis suggests that during the evolutionary history of birds the thoracic limb and girdle elements acquired early and rapidly the structures enabling active flight, whereas a modern-aspect pelvic limb and girdle was not developed until the rise of the Ornithurae.
Abstract: A new genus and species of Late Cretaceous (Coniancian-Santonian)birds, Neuquenornis volans, is described. This new taxon is known from a fairly complete, articulated specimen from the Rio Colorado Formation of northwestern Patagonia. Synapomorphies of the humerus, radius, ulna, coracoid, femur, tibiotarsus, tarsometatarsus, and thoracic vertebrae, support its allocation to the Enantiornithes. The tarsometatarsal structure of Neuquenornis refers it to the Late Cretaceous family Avisauridae. The structure of the wing and pectoral girdle of Neuquenornis and Soroavisaurus from El Brete, indicates that avisaurids were capable of perching in trees.
Abstract: New discoveries of dinosaurs, together with cladistic procedures, have provided further insights into the morphological transition from nonavian dinosaurs to modern birds. Until now, however, the bone histology associated with this evolutionary transition has remained undocumented. Here we report the occurrence of growth rings in the Cretaceous birds Patagopteryx deferrariisi and Entiornithes, which are phylogenetically intermediate between nonoavian dinosaurs and ornithurine birds, thus documenting for the first time this histological pattern among birds.
Abstract: An embryonic skeleton of a nonavian theropod dinosaur was found preserved in an egg from Upper Cretaceous rocks in the Gobi Desert of Mongolia. Cranial features identify the embryo as a member of Oviraptoridae. Two embryo-sized skulls of dromaeosaurids, similar to that of Velociraptor, were also recovered in the nest. The eggshell microstructure is similar to that of ratite birds and is of a type common in the Djadokhta Formation at the Flaming Cliffs (Bayn Dzak). Discovery of a nest of such eggs at the Flaming Cliffs in 1923, beneath the Oviraptor philoceratops holotype, suggests that this dinosaur may have been a brooding adult.
Abstract: The Late Cretaceous rock of Mongolia have produced unusual and phylogenetically important dinosaurs. Here we report a startling new example. Mononychus olecranus gen. et sp. nov., an avialian theropod dinosaur with a short, robust forelimb possessing a single stout claw. Several features, including a carinate sternum and reduced fibula, suggest that Mononychus olecransus is more closely related to modern birds than is archaeopteryx lithographica. The two skeletons are among the best preserved fossils known of a primitive bird, and emphasize the complexity of the morphological transformation from nonavialian theropods to modern birds. The occurrence of such a primitive bird in the Late Cretaceous reflects the paucity of Mesozoic bird fossils and suggests that the early radiation of avialians is only beginning to be sampled.
Abstract: The fossil record of Passeriformes from South America had previously been restricted to the Pleistocene of Argentina, Brazil and Venezuela. In this contribution we report the first passeriform fossil from the Miocene of South America.
Abstract: Several characters of the tarsometatarsus of the Cretaceous enantiornithine birds are discussed, with emphasis on the genus Avisaurus, which was considered a non-avian theropod taxon by its authors. Two synapomorphies (metatarsal IV reduced with respect to metatarsals II and III; well-developed knob on the anterior face of metatarsal II) relate Avisaurus to the remaining enantiornithine tarsometatarsi types and support reference of this taxon within the Enantiornithes. Three other synapomorphies (laterally compressed, J-shaped metatarsal I; anterior surface of the mid-shaft of metatarsal III strongly convex transversely; strong posterior projection of the internal rim of trochlea on metatarsal III) shared by Avisaurus and a Late Cretaceous enantiornithine from northwestern Patagonia further support its avian affinities. Avisaurus and the family Avisauridae are assigned to the avian subclass Enantiornithes.
Abstract: The purpose of this application is to conserve the name Phororhacos Ameghino, 1889, which has been widely used for a genus of fossil gian flightless birds from South America. The name was first published as Phorusrhacos Ameghino, 1887, based on a single bone then thought to be mammalian, but although this spelling did not appear again for 75 years and was rejected in 1968 as a nomen oblitum it has had extensive recent usage.
Abstract: Amargasuchus minor is described from the Early Cretaceous (Neocomian) of the La Amarga Formation of northwest Patagonia (Argentina). This species possesses a moderately high and narrow snout, strong festooning, a relatively large number of maxillary teeth and a well-developed antorbital fenestra, and it lacks hypertrophied teeth, a combination of characters which suggests that it belongs to the crocodile family Trematochampsidae. Amargasuchus differs, however, from Trematochampsa in several respects. These include an almost straight lateral edge of the maxilla in dorsal aspect, a different distribution of the largest teeth, a longer snout, and laterally compressed alveoli. The new material supports a Gondwanan origin of the Trematochampsidae and agrees with a new phylogenetic hypothesis which considers trematochampsids to be the ancestral group of certain lineages of ziphodont mesosuchian crocodiles.
Abstract: Unraveling stages in the early evolution and diversification of birds seems simple enough, given the fact that large numbers of new and exceptionally well-preserved fossils have become available for study in recent years. Complications still remain, however; the history of this vertebrate lineage has been central to several heated debates since the earliest days of evolutionary biology. Are birds the extant descendants of theropod dinosaurs? How have new fossil discoveries helped to fill in the gap between Archaeopteryx and it extant counterparts? In this review, we focus renewed attention on fossil birds and their relatives—specific lines of evidence that can be used to support the theropod hypothesis for avian origins and update some recent areas of contention. Related to this, we provide a general synopsis of recent fossil discoveries from the Mesozoic, especially the Cretaceous.
Abstract: Recent discoveries of dinosaur eggs containing embryos have furnished data to confidently anchor oological characters and in some instances reproductive behavioral strategies to specific dinosaurian taxa. Here we examine the egg morphology and nesting behaviors of hard-shelled turtles, crocodilians, and a variety of dinosaurs (hadrosaurid, titanosaur, troodontid, and oviraptoroid), and present comparisons to those found in extant birds. Our study documents the greatest similarity between the eggs and nest attendance of non-avian theropod dinosaurs (i.e. troodontids and oviraptorids) and those of birds, thus adding support to the hypothesis that birds originated among non-avian theropods.
Abstract: INTRODUCTION
Although more than half of bird evolution occurred during the Mesozoic (Chiappe, 1995a), our understanding of this long, historical process focused on the spectacular specimens of the Late Jurassic Archaeopteryx lithographica and the more derived Late Cretaceous hesperornithiforms and ichthyornithiforms for over a century of paleontological research. In the last decade, however, a tremendous burst of new evidence—perhaps unparalleled in the field of vertebrate paleontology—has been uncovered. Indeed, the number of species of early birds described during the 1990s nearly tripled the number of taxa discovered during the previous 130 years elapsed since the discovery of Archaeopteryx in the mid-1800s (Chiappe, 1997a; Padian and Chiappe, 1998).
While this new evidence has offered an unprecedented opportunity for better understanding the evolutionary transformations of several remarkable biological bird attributes (e.g., feathers, uninterrupted growth, active flight), it has also made obsolete the previous phylogenetic analyses of basal birds, which had been based on far fewer taxa (e.g., Cracraft, 1986; Chiappe and Calvo, 1994; Sanz et al., 1995; Chiappe et al., 1996). Clearly, a comprehensive phylogenetic hypothesis of the new diversity of basal avians is needed before the evolutionary history of these attributes can be fully explained. While this major task is beyond the scope of this paper and is the subject of ongoing research, this study aims to provide the phylogenetic framework for most of the taxa addressed in this volume and, in doing so, to substantially increase the number of taxa ever to be included in a cladistic analysis of basal birds.
Abstract: INTRODUCTION
Our knowledge of the early evolutionary history of birds has changed dramatically since the early 1980s (Chiappe, 1995a). The increasing information about the Mesozoic diversification of birds is generating insightful hypotheses on their phylogenetic structure and evolutionary history. Since 1986, the Konservat-Lagerstätte of Las Hoyas (Province of Cuenca, Spain) has provided exceptional evidence contributing to the flourishing revision on this paleobiological issue. In this paper we describe the avian taxa from Las Hoyas: Iberomesornis romerali, Concornis lacustris, and Eoalulavis hoyasi. We review how these taxa have been interpreted and discussed according to recent phylogenetic hypotheses. We also discuss the contribution made by the birds from Las Hoyas to our current understanding of the early phases of avian flight.
The first report on Iberomesornis romerali (referred to as “the Las Hoyas bird†in literature prior to 1992) appeared in 1988 (Sanz et al., 1988). This preliminary paper stressed the significance of this primitive bird in regard to early avian diversification. Iberomesornis, lacking the skull, the cranial portion of the neck, and most of the hands (see Anatomy, below), presents apomorphic characters (e.g., pygostyle, strut-like coracoid) with respect to Archaeopteryx and plesiomorphic characters (e.g., primitive sacropelvic elements, unfused metatarsus) with respect to neornithine birds. Therefore, Iberomesornis was proposed to be the closest known sister-group of Ornithurae, a suggestion promptly accepted by several authors (Cracraft, 1988; Chiappe, 1991). This conclusion was presented in the II International Symposium of the Society of Avian Paleontology and Evolution, held in Los Angeles, California (USA) in September, 1988. Four years later, a formal denomination of the Las Hoyas bird, along with a further description and discussion, was published in the Proceedings of the above mentioned Symposium (Sanz and Bonaparte, 1992).
At the end of the 1980s, a new bird skeleton was discovered at Las Hoyas. This new specimen was published by Sanz and Buscalioni (1992) with the name Concornis lacustris. Concornis, roughly twice the size of Iberomesornis, is known by an almost complete skeleton with some feather evidence, although it lacks the skull and neck. Sanz et al. (1995) fully described the holotype (and only known) specimen and provided strong evidence in support of its placement within Enantiornithes. One of the most striking features of Concornis is the presence of a broad, notched sternum with a caudal carina, similar to that described for Cathayornis (Zhou, 1995a).
In 1994, a third avian skeleton was found at Las Hoyas. This new bird specimen is better preserved than the other two, and consists of the part of the skeleton, lacking the skull. Wing feathers are preserved in position. It was interpreted as a new enantiornithine taxon and named Eoalulavis hoyasi (Sanz et al., 1996). Here, we place more emphasis on this last specimen, which to date has been only preliminarily described.
Abstract: The genealogical relationship of birds--members of the class Aves--to other vertebrates has been debated throughout the history of evolutionary biology. These days, despite a few poorly substantiated proposals suggesting that birds may be the descendants of a variety of basal archosaurian reptiles (reptiles that predated the dinosaurs), the overwhelming consensus is that Aves are living representatives of the carnivorous theropod dinosaurs. This hypothesis has its roots in the nineteenth century, but in the last decade it has received a great deal of persuasive paleontological support. Despite disagreement regarding the specific theropod taxon that can be placed closest to birds (candidates include the sickle-clawed dromaeosaurids, parrot-headed oviraptorids, and ostrichlike ornitomimids), studies in areas as disparate as osteology (bones), behavior, oology (eggs), and integument (skin) converge to sustain the origin of birds within the maniraptoriform theropods, no longer leaving any reasonable doubt that extant birds are indeed short-tailed, feathered dinosaurs. In addition, the great amount of fossil information discovered over the last 20 years has revealed that the avian taxa that have evolved since their origin are much more diverse than had been expected.
Abstract: INTRODUCTION
The first Mesozoic avian remains from the Iberian Peninsula were reported by Vidal (1902), who mentioned the accidental destruction of a fossil bird from the Lower Cretaceous quarry of “ La Pedrera de Meiá†(42 01’ N; 4 35’ W) in the Spanish Province of Lleida, Catalonia (Lacasa-Ruiz, 1985). In subsequent years, this site yielded a large number of isolated feathers (Lacasa-Ruiz, 1985; Gómez Pallerola, 1986; Kellner, this volume). However, the first significant discovery–the skeletal remains of Noguerornis gonzalezi–was not made until the 1980’s (Lacasa-Ruiz, 1986, 1989a, b, 1991a).
The discovery of Early Cretaceous avians from Spain provided relevant new information about the early evolution of birds, clarifying the early pattern of morphological transformation (see Sanz et al., 1988, this volume; Chiappe, 1991, 1995a), and establishing the earliest records of volant birds with enhanced aerodynamic specializations (Sanz et al., 1988, 1996, this volume; Chiappe, 1995b). The significance of the spectacular specimens of Iberomesornis romerali (Sanz and Bonaparte, 1992; Sanz et al., this volume), Concornis lacustris (Sanz and Buscalioni, 1992; Sanz et al., 1995, this volume), and Eoalulavis hoyasi (Sanz et al., 1996, this volume) was immediately recognized (see Cracraft, 1988; Milner, 1993; Padian, 1996); this was not the case, however, for the less complete Noguerornis gonzalezi. Although several papers by Lacasa-Ruiz (e.g., Lacasa-Ruiz, 1986, 1989a, b, 1991a) remarked upon the peculiarities and significance of Noguerornis (one of the earliest known avian members), this information has remained virtually unnoticed. In this paper, after further mechanical preparation, we provide a detailed description of the holotype—and still unique specimen—of Noguerornis, and discuss both its relationships to other basal birds and its contribution to our understanding of early avian evolution.
Abstract: The phylogenetic position of Avimimus is a puzzle that is yet to be solved. Since its description by Kurzanov in 1981, Avimimus has been alternatively regarded as a non-avian theropod close to the ancestry of birds (e.g., Thulborn, 1984; Norman, 1990; Holtz, 1994) or as a flightless, basal avian (e.g., Chatterjee, 1991, 1995, 1999). It is hoped that the comments and the high-quality stereo photographs provided in this short paper (see Figs. 3.1-3.19) will yield some clues that will eventually help the relationships of Avimimus to be decoded.
Abstract: INTRODUCTION
The first Mesozoic avian remains from the Iberian Peninsula were reported by Vidal (1902), who mentioned the accidental destruction of a fossil bird from the Lower Cretaceous quarry of “ La Pedrera de Meiá†(42 01’ N; 4 35’ W) in the Spanish Province of Lleida, Catalonia (Lacasa-Ruiz, 1985). In subsequent years, this site yielded a large number of isolated feathers (Lacasa-Ruiz, 1985; Gómez Pallerola, 1986; Kellner, this volume). However, the first significant discovery–the skeletal remains of Noguerornis gonzalezi–was not made until the 1980’s (Lacasa-Ruiz, 1986, 1989a, b, 1991a).
The discovery of Early Cretaceous avians from Spain provided relevant new information about the early evolution of birds, clarifying the early pattern of morphological transformation (see Sanz et al., 1988, this volume; Chiappe, 1991, 1995a), and establishing the earliest records of volant birds with enhanced aerodynamic specializations (Sanz et al., 1988, 1996, this volume; Chiappe, 1995b). The significance of the spectacular specimens of Iberomesornis romerali (Sanz and Bonaparte, 1992; Sanz et al., this volume), Concornis lacustris (Sanz and Buscalioni, 1992; Sanz et al., 1995, this volume), and Eoalulavis hoyasi (Sanz et al., 1996, this volume) was immediately recognized (see Cracraft, 1988; Milner, 1993; Padian, 1996); this was not the case, however, for the less complete Noguerornis gonzalezi. Although several papers by Lacasa-Ruiz (e.g., Lacasa-Ruiz, 1986, 1989a, b, 1991a) remarked upon the peculiarities and significance of Noguerornis (one of the earliest known avian members), this information has remained virtually unnoticed. In this paper, after further mechanical preparation, we provide a detailed description of the holotype—and still unique specimen—of Noguerornis, and discuss both its relationships to other basal birds and its contribution to our understanding of early avian evolution.
Abstract: INTRODUCTION
The discovery of “Mononychus†olecranus (Perle et al., 1993a; later emended to Mononykus olecranus—see Perle et al., 1993b) from the Late Cretaceous of the Gobi Desert stimulated a fruitful new discussion about the origin and early diversification of birds, and the evolution of their flight. Mononykus not only led to the recognition of a previously unknown clade of early birds but also suggested, through its phylogenetic placement as the sister-taxon of all birds except Archaeopteryx, the possibility (heretical to some) that flight may have evolved twice within birds (Perle et al., 1993a).
The study of Mononykus also helped to fine-tune the phylogenetic placement of certain enigmatic Cretaceous taxa. Novas (1996, 1997) convincingly argued for a common relationship between Mononykus and the Patagonian Late Cretaceous Patagonykus puertai and Alvarezsaurus calvoi, placing all of them within Alvarezsauridae (Bonaparte, 1991), a formerly monospecific taxon regarded by Bonaparte (1991) as a group of non-avian theropods. More recently, Karkhu and Rautian (1996) described Parvicursor remotus from the Late Cretaceous of the Gobi Desert. Although they placed it in a unique family, they recognized its strong similarity to Mononykus. We believe that this similarity is due to common descent and that Parvicursoridae is a junior synonym of Alvarezsauridae.
In addition to the taxa above mentioned, several specimens (e.g., MGI N 100/99, MGI 100/975, MGI 100/977, MGI 100/1001; listed as Mononykus in Perle et al. [1993a] and Chiappe et al. [1996]) that were collected between 1992 and 1995 by the American Museum of Natural History-Mongolian Academy of Sciences Paleontological Expeditions to the Upper Cretaceous red beds of southern Mongolia (Djadohkta and Barun Goyot Formations and their equivalents)
Abstract: With nearly 10,000 known living species, birds are the most taxonomically diverse land vertebrates. Evidence from bone morphology, integuementary structures, microstructure of eggshells, and behaviors inferred from preserved life-poses of fossils collected over the last three decades indicates that living birds, and their extinct relatives, are evolutionarily nested within a subset of predatory dinosaurs known as maniraptoriform theropods. The known evolutionary history of birds extends over the last 150 million years of the earth's rock record. More than half of this long history is played out in the Mesozoic era--the age of large dinosaurs--which ended at the end of the Cretaceous period, 65 million years ago. This article briefly summarizes our current knowledge of bird evolution during the first 85 million years of their recorded history.
Abstract: A cladistic numerical analysis using a large number of characters and Mesozoic avian taxa is presented and the phylogenetic relationships of the Alvarezsauridae, the Confuciusornithidae and the Enantiornithes are discussed in light of this new study. It is concluded that (1) the Alvarezsauridae are the sister group of Aves, (2) the Confuiciusornithidae share a sister group relationship with the Ornithothoraces (Enantiornithomorpha and Ornithuromorpha), and (3) the Enantiornithes are not closely related to Archaeopteryx, and thus “Sauriurae†is a paraphyletic group.
Abstract: Few areas of vertebrate paleontology have advanced more over the last few years than that of the early evolution of birds. Recent findings of primitive, non-neornithine birds have been so numerous that we have more than doubled the number of valid taxa described between 1861, when the first early bird, Archaeopteryx lithographica von Meyer, was reported, and 1990. Thus, to address the plethora of new ideas and discussions that all these new findings have triggered, in the single hour of roundtable discussion that I had been assigned to moderate, was a daunting, if not impossible, task. With this in mind, and after discussing possible topics of debate with other colleagues, I decided to center the discussion on only three topics within this new profusion of evidence. The aim of this report is not to provide a review of the new data on early bird evolution, nor is it to defend my own views over those of others. Much of the new evidence has already been reviewed, and a variety of choices are available for the interested reader. Wellnhofer (1994) and Feduccia (1996) provide reviews based on a traditional “evolutionary†approach, whereas I have reviewed the new data from a strict cladistic perspective (Chiappe, 1995a).
Abstract: Mesozoic remains of embryonic and early juvenile birds are rare. To date, a handful of in ovo
embryos and early juveniles of enantiornithines from the Early Cretaceous of China and Spain and
the Late Cretaceous of Mongolia and Argentina have comprised the entire published record of
perinatal ontogenetic stages of Mesozoic birds. We report on the skeletal morphology of three
nearly complete early juvenile avians from the renowned Early Cretaceous Yixian Formation of
Liaoning Province in northeastern China. Evidence of the immaturity of these specimens is
expressed in the intense grooving and pitting of the periosteal surfaces, the disproportionately
small size of the sterna, and the relative size of the skull and orbits. Size notwithstanding,
anatomical differences between these three specimens are minimal, leaving no basis for
discriminating them into separate taxa. Numerous osteological synapomorphies indicate that
they are euenantiornithine birds, the most diverse clade of Enantiornithes, but their identification
as members of a particular euenantiornithine taxon remains unclear. Their early ontogenetic stage,
however, provides important information about the postnatal development of this specious clade
of Cretaceous birds. The presence of pennaceous wing feathers suggests that fledging occurred very
early in ontogeny, thus supporting a precocial or highly precocial strategy for enantiornithine
hatchlings. The morphology of these new early-stage juveniles is also significant in that they allow
a better understanding of the homologies of several avian compound bones because the
components of these skeletal compounds are preserved prior to their coossification. The general
morphology of the wrist and ankle of these juveniles highlights once again the striking similarity
between nonavian theropods and early birds.
Abstract: Several isolated bones of tinamous from Miocene deposits of Santa Cruz Province (southern
Patagonia, Argentina) are the oldest known remains of this paleognath lineage. The specimens include an
incomplete coracoid, proximal end of four coracoids, distal ends of two tibiotarsi, and distal ends of two
humeri. They represent at least two species but cannot be assigned to any known taxon. A detailed description
and phylogenetic interpretation of this material is provided here. Morphological data of the fossils
are included in a matrix of 63 osteological characters and 34 terminal taxa incorporating 24 living species
of Tinamidae in addition to the fossils under study. The cladistic analysis produced 81 optimal trees, in
which the fossils are more closely related to the open-area tinamous (Nothurinae). Placement of the Santa
Cruz fossil tinamous between the open-area (Nothurinae) and the forest-dwelling (‘‘Tinaminae’’) tinamous
is consistent with the paleoenvironmental conditions inferred from the associated fossil fauna.
Abstract: A partial skeleton of an immature individual of the alvarezsaurid mononykine theropod
Shuvuuia deserti from the Late Cretaceous (Campanian) To¨ gro¨ giin Shiree locality of southern Mongolia
exhibits a number of features, most importantly in the manus, pes, and caudal series, previously unknown
for this taxon and all other alvarezsaurids. The well-preserved and articulated right hand of this new
specimen confirms the presence of manual digits II and III among alvarezsaurids. The nearly complete tail
of the new specimen indicates that previous calculations for the number of caudal vertebrae in mononykines (i.e., 25 or 26 vertebrae) underestimated this number by at least 10 elements. Complete and articulated pedal digits I (hallux) provide additional morphological information, which when added to new data from other skeletal regions strengthens the diagnosis of Shuvuuia deserti. Competing hypotheses for alvarezsaurid phylogenetic relationships have depicted these taxa either within Aves, or as nonavian theropods. These hypotheses are briefly summarized, and in particular, a critical evaluation of the character evidence in support of the ornithomimoid affiliation of this theropod clade is provided. We demonstrate that the evidence in support of this latter hypothesis is largely unsubstantiated.
Abstract: An embryonic oviraptorid skeleton is described within an egg from the Late Cretaceous
Djadokha Formation of Ukhaa Tolgod, Mongolia. The specimen comprises the ventral part of
the skull and most of the mandible, a poorly preserved axial skeleton missing most of the tail,
and portions of the forelimbs, shoulder girdles, pelvis, and hindlimbs. The skull is readily
referable to the theropod dinosaur clade Oviraptoridae on the basis of several skull specializations
(edentulous, vertically oriented premaxilla, a sinusoidally shaped lower jaw, and an
unusual articulation of the vomer and premaxilla), and the postcranial skeleton is consistent
with this identification. The egg is equivalent in overall shape and microstructure to those
found beneath several oviraptorid skeletons recovered from the same formation. The skeleton
is well ossified and, in comparison with ossification patterns in living Aves, the evidence
suggests that this species was closer to the precocial end of the precocial-altricial spectrum of
developmental patterns.
Abstract: We describe an exquisitely preserved new skull of a bird from the Late Cretaceous sandstones
of Ukhaa Tolgod, southern Mongolia. Derived similarities shared between this skull
and the holotype of Gobipteryx minuta, also from the Late Cretaceous of the Gobi Desert,
support the assignment of the new cranial material to this avian taxon. The new skull also
proves indistinguishable from that of the enantiornithine Nanantius valifanovi from the Late
Cretaceous of Mongolia. The identification of the new skull as that of Gobipteryx minuta and
its correspondence to that of Nanantius valifanovi indicate that the latter taxon is a junior
synonym of Gobipteryx minuta. This taxonomic conclusion is crucial for understanding the
phylogenetic relationships of Gobipteryx minuta because the undoubtedly enantiornithine postcranial
morphology of Nanantius valifanovi provides the first uncontroversial evidence of the
enantiornithine relationship of Gobipteryx minuta. The new skull from Ukhaa Tolgod and our
reinterpretation of cranial aspects of the previously published material of Gobipteryx minuta
and Nanantius valifanovi permit an accurate reconstruction of the palate of this enantiornithine
bird, thus adding significant data for understanding the poorly known palatal structure of
Mesozoic birds.
Abstract: A new bird from the Late Cretaceous of Patagonia (Argentina), known from associated
wing elements, is described and its phylogenetic position evaluated. Fossil taxa as well as
representatives of species of extant birds sampled from lineages considered to be basal within
the crown clade were included in a cladistic analysis of 72 characters primarily from the
thoracic limb. Based on the results of the phylogenetic analysis and identification of autapomorphies
in the specimen, we name a new taxon Limenavis patagonica.
Limenavis patagonica is identified as closer to the crown clade than Enantiornithes by the
presence of three unambiguous synapomorphies: a fossa (sometimes with two distinguishable
subparts) on the dorsal, distalmost extremity of the humerus; distal fusion of metacarpals II
and III; and an extensor process on metacarpal I. It is placed closer to the crown clade than
Ichthyornis, and, thus, unambiguously as a carinate (see Methods for terminology), by two
further synapomorphies: the abruptly truncate contact of the dorsal trochlear surface of the
ulna with the ulnar shaft and the loss of a tubercle adjacent to the tendinal groove on the
distal ulna. Finally, Limenavis patagonica is diagnosed by three autapomorphies: the attachment
of the pars ulnaris of the trochlea humeroulnaris on the proximal ulna developed as a
pit-shaped fossa; the location of the pisiform process with its proximal surface at approximately
the same level as the proximal surface of metacarpal I; and a scar of the ligamentum
collaterale ventrale of the ulna proximodistally elongate and extending down the caudal margin
of the brachial impression.
Limenavis patagonica is placed just outside the avian crown clade. The shortest tree with
the new taxon as part of the crown clade is five steps longer than the most parsimonious
topology.
Abstract: With hundreds of filamentlike teeth in its mandibles and several other unique cranial features, the Argentine Early Cretaceous Pterodaustro guinazui ranks among the most specialized of pterosaurs. Based on the newly collected specimens, this study provides a detailed description of the peculiar skull morphology of Pterodaustro and discusses its phylogenetic position within pterosaurs. An overview of the stratigraphy, sedimentology, and chronology of the Lagarcito Formation from which Pterodaustro comes is provided, along with an interpretation of the paleoenvironment. Cranial morphology corroborates the sister-taxon relationship between Pterodaustro and the Late Jurassic Ctenochasma proposed by most previous authors.
Abstract: The stratigraphy and age of a sauropod nesting ground containing the first definitive embryonic
remains of sauropods preserved inside their eggs is analyzed. The fossil locality, called
Auca Mahuevo, occurs in the Anacleto Member of the Rı´o Colorado Formation in Neuque´n
Province, Argentina. The 5 m thick interval of overbank mudstones containing the fossilized
eggs and embryos occurs near the middle of a 35 m sequence of thin, fluvial, concretionary
sandstones and thicker units of silty sandstone. Flooding of shallow stream channels deposited
overbank silt and mud on the eggs, killing the embryos and initiating the process of fossilization.
Egg fragments containing patches of fossilized integument were found as float weathering
out of the mudstone on local flats. Complete eggs containing embryonic bones and teeth
were quarried from a steep ridge where the mudstone was exposed.
Twelve paleomagnetic samples collected throughout the lower 30 m of the section establish
the presence of a Reverse geomagnetic polarity interval. This constitutes the first magnetostratigraphic
characterization for this part of the Rı´o Colorado Formation and for the late
Cretaceous sequence of formations that comprise the Neuque´n Group. Biochronologic age
estimates for the Rı´o Colorado fauna combined with the Reverse polarity determinations for
the fossiliferous sediments in the Anacleto Member argue for an age younger than the long Cretaceous C34 Normal, which ends at the upper boundary of the Sartonian and older than
the late Campanian. The Reverse interval containing the fossils at Auca Mahuevo is therefore
considered to be early or middle Campanian in age, most likely correlative with C33R between
83.5 and 79.5 Ma.
Abstract: With humdreds of filamentlike teeth in its mandibles and several other unique cranial features, the Argentine Early Cretaceous Pterodaustro guinazui ranks among the most specialized of pterosaurs. Based on newly collected specimens, this study provides a detailed description of the peculiar skull morphology of Pterodaustro and discusses its phylogenetic position within pterosaurs. An overview of the stratigraphy, sedimentology, and chronology of the Lagarcito Formation from which Pterodaustro comes is provided, along with an interpretation of the paleoenvironment. Cranial morphology corroborates the sister-taxon relationship between Pterodaustro and the Late Jurassic Ctenochasma proposed by most previous authors.
Abstract: The osteology and plumage of Confuciusornis sanctus and Changchengornis hengdaoziensis
from the Chaomidianzi Formation (previously referred to as the lower section of the Yixian
Formation) of western Liaoning Province (China) are described in detail.
Confuciusornis sanctus and Changchengornis hengdaoziensis have toothless, beaked skulls
(the tomial crest is straight in the former species and strongly curved in the latter) and retain
the dorsal portion of the nasal process of the maxilla. The skull of Confuciusornis sanctus is
of typical diapsid plan. It possesses a triradiate postorbital that with the squamosal forms a
complete supratemporal arcade. Furthermore, a robust jugal–postorbital contact completely
separates the infratemporal fenestra from the orbit. Although the postorbital region is not
preserved in Changchengornis hengdaoziensis, it likely resembles that of Confuciusornis sanctus.
Both species have abbreviated tails with long pygostyles, not the long, bony tail originally
reconstructed in Confuciusornis sanctus. Scapulae and coracoids are fused to form scapulocoracoids.
The coracoids are strutlike but much shorter than the scapulae. The furculae are
robust and boomerang shaped. The sterna are long and nearly flat. A complete basket of
gastralia follows the sternum caudally. The wing elements are short, and proportions among
individual bones are primitive in that the hand is longer than either the humerus or the ulna
and the ulna is shorter than the humerus. The pelvis is opisthopubic. The postacetabular wing
of the ilium is much shorter than the preacetabular wing. Differences in plumage, namely the
presence or absence of two very long tail feathers, are observed among several well-preserved
specimens of Confuciusornis sanctus. This difference is likely the expression of sexual dimorphism,
although other biological attributes known for extant populations (e.g., differential
molting, correlation between sexual maturity and ornamental plumage) indicate that alternative
explanations may also account for the observed plumage variation among specimens of Confuciusornis
sanctus.
Given the latest Jurassic–earliest Cretaceous age of the Chaomidianzi Formation, Confuciusornis
sanctus and Changchengornis hengdaoziensis are surely among the oldest known birds
after the Early Tithonian Archaeopteryx lithographica. Confuciusornis sanctus and Changchengornis
hengdaoziensis thus furnish the earliest record of beaked birds.
The fully diapsid skull of Confuciusornis sanctus, and presumably of Changchengornis
hengdaoziensis, and the absence of a bending zone on the base of the snout suggest that earlier
interpretations of the skull of Confuciusornis sanctus as prokinetic are incorrect. Confuciusornis
sanctus probably had very limited cranial kinetic capabilities, if any. Optimization of
the postorbital–jugal contact, a character intimately correlated with intracranial kinesis, in a
phylogeny of basal avians indicates that the essentially akinetic condition of the skull of
Confuciusornis sanctus is a reversal derived from forms possessing kinetic properties.
Recent recognition of two additional species of Confuciusornis—Confuciusornis chuonzhous
and Confuciusornis suniae—are based on anatomical misinterpretations. Thus, Confuciusornis
suniae and Confuciusornis chuonzhous are regarded as junior synonyms of Confuciusornis
sanctus. Confuciusornis sanctus is the sister-taxon of Changchengornis hengdaoziensis,
and both are placed within the Confuciusornithidae. Some of the synapomorphies
supporting this grouping include the presence of edentolous jaws, a rostrally forked mandibular
symphysis, a reduced claw of manual digit II, and a V-shaped caudal margin of the sternum.
The Confuciusornithidae is considered to be the sister-group of a clade composed of the
Enantiornithomorpha and the Ornithuromorpha. This phylogenetic interpretation is far more
parsimonious than previous systematic hypotheses placing the Confuciusornithidae as either
within the Enantiornithes or as its sister-group.
Purported climbing specializations of Confuciusornis sanctus are evaluated in light of the
available anatomical evidence. We conclude that both Confuciusornis sanctus and Changchengornis
hengdaoziensis were ill suited for tree climbing. The foot of Changchengornis
hengdaoziensis, however, suggests a greater grasping ability than that of Confuciusornis sanctus.
It is argued that both Confuciusornis sanctus and Changchengornis hengdaoziensis were
able to fly and take off from the ground.
The remarkable concentration of specimens of Confuciusornis sanctus from a relatively
small quarry near the village of Sihetun (Liaoning Province) suggests several events of mass
mortality and, perhaps, a gregarious behavior.
Abstract: The articulated postcranial skeleton of an oviraptorid dinosaur (Theropoda, Coelurosauria) from the late Cretaceous Djadokhta Formation of Ukhaa Tolgod, Mongolia, is preserved overlying a nest. The eggs are similar in size, shape, and ornamentation to another egg from this locality in which an oviraptorid embryo is preserved, suggesting that the nest is of the same species as the adult skeleton overlying it and was parented by the adult. The lack of a skull precludes specific identification, but in several features the specimen is more similar to Oviraptor than to other oviraptorids. The ventral part of the thorax is exceptionally well preserved and provides evidence for other avian features that were previously unreported in oviraptorids, including the articulation of the first three thoracic ribs with the costal margin of the sternum and the presence of a single, ossified ventral segment in each rib as well as ossified uncinate processes associated with the thoracic ribs. Remnants of keratinous sheaths are preserved with four of the manal claws, and the bony and keratinous claws were as strongly curved as the manal claws of Archaeopteryx and the pedal claws of modern climbing birds. The skeleton is positioned over the center of the nest, with its limbs arranged symmetrically on either side and its arms spread out around the nest perimeter. This is one of four known oviraptorid skeletons preserved on nests of this type of egg, comprising 23.5% of the 17 oviraptorid skeletons collected from the Djadokhta Formation before 1996. The lack of disturbance to the nest and skeleton indicate that the specimen is preserved in the position in which the adult died. Its posture is the same as that commonly taken only by birds among tetrapods that brood their nest, and its close proximity to the eggs indicates that the nest was not covered, indicating that the behavior of sitting on open nests in this posture evolved before the most recent common ancestor of modern birds
Abstract: Additional preparation of the holotype of Concornis
lacustris from the Lower Cretaceous (Barremian)
deposits of Las Hoyas (Spain) has provided
abundant new osteological data. This specimen
is superbly preserved and anatomical details
are available for most skeletal regions except the
skull and neck. The forelimb has "modem" proportions
but it retains large claws. The sternum is
carinate and deeply notched. The carina, however,
does not reach the cranial margin but is developed
in the caudal halfofthe sternum. The dorsal, synsacral
and caudal vertebrae are amphicoelous. The
dorsal vertebrae have deep lateral grooves and
parapophyses in a central position. The ischium
has large obturator and dorsal processes; the pubes
form a distal symphysis. The hind limb is gracile,
elongate, and longer than the forelimb.
Cladistic analysis of various ornithothoracine
taxa supports the allocation of Concornis lacustris
within the Enantiornithes, a major clade of Cretaceous
birds mostly recognized from continental
deposits. This new interpretation is substantially
supported by 12 synapomorphies shared by C.
lacustris and the remaining enantiornithines. Within the Enantiornithes, tarsometatarsal data
support a sister-group relationship between C. lacustris
and the Avisauridae.
Concornis lacustris is the oldest enantiornithine
bird from the Western Hemisphere. The interpretation
of this species as an enantiornithine emphasizes
the wide geographical and stratigraphical
distribution of this clade during the Cretaceous,
and its large taxonomic diversity.
Abstract: A detailed description ofthe holotype specimen
of Mononykus olecranus, a basal flightless bird
from the Late Cretaceous Nemegt Formation of
Mongolia, is presented. The holotype comprises a
fragmentary skull, most precaudal vertebrae, fore
and hindlimbs, the thoracic girdle, and fragments
of the pelvis and synsacrum. In the skull, caudal,
dorsal, and rostral tympanic recesses are well developed.
The maxilla is toothless, and the anterior
margin of the antorbital fossa lacks accessory fenestrae.
The only dental element found is a tiny
isolated tooth that lacks serrations and has a constricted
base. The axial skeleton is remarkable in
having a biconvex posterior dorsal vertebra, and
keeled posterior synsacral vertebrae. The forelimb
is short and extremely robust. The humerus bears
a prominent deltopectoral crest. The olecranon
process of the ulna is hypertrophied. The carpometacarpus
is very short, subquadrangular, and
massive. The alular digit is extremely robust, bearing
a robust ungual phalanx. The sternum is stout
and carinate. In the pelvis, the ilium bears a strong
antitrochanter and the pubis is retroverted. The
hindlimb is gracile. In the femur the trochanteric
crest is undivided, and the popliteal fossa is
bounded distally by projections from both condyles.
The tibia and proximal tarsals are partially
fused. Two cnemial crests are present on the tibio-tarsus. The metatarsals are unfused; metatarsal III ity of the transition between nonavialian therois
completely reduced proximally and does not pods and modem birds, witnessing the differenreach
the tarsus. tiation of a totally new group ofbasal birds during
Mononykus olecranus emphasizes the complex- the Cretaceous.
Abstract: Enantiornithine tarsometatarsi from the Maastrichtian
Lecho Formation at the locality of El
Brete (northwestern Argentina) are described together
with their associated material. Three new
species, namely Yungavolucris brevipedalis, Lectavis
bretincola, and Soroavisaurus australis, are
recognized. Y. brevipedalis is distinguished by having
a short and broad tarsometatarsus with a pulleylike
trochlea of metatarsal II, and equally long
metatarsals III and IV with the distal end of the
former laterally curved. The long and slender tarsometatarsus
of L. bretincola is characterized,
among other features, for bearing a hypotarsus developed
primarily over the metatarsal II. In turn,
S. australis exhibits a long and narrow fenestra
between the proximal halves ofmetatarsals III and
IV, and the plantar surface of the proximal half of
metatarsal II forms a sharp edge (convergent with
those of L. bretincola).
The relationships among these three species, and
their interrelationships with respect to other Late
Cretaceous enantiornithine taxa, are explored. A
character analysis based on tarsometatarsal features
is presented. This analysis supports the hypothesis
that Soroavisaurus australis is the sister
group of a clade formed by Avisaurus archibaldi
and a new form from the Two Medicine Formation
of Montana. This clade is in turn the sister
group of Neuquenornis volans. These four taxa
compose the monophyletic taxon Avisauridae. In
the present analysis, the relationships among Lectavis
bretincola, Yungavolucris brevipedalis, and
Avisauridae remain unresolved.
Abstract: The results of three recent paleontological expeditions to the lacustrine deposits of the “Loma del Pterodaustro†fossil site of the Lagarcito Formation, in the Argentine Province of San Luis, are briefly summarized. Different types of plant impressions, ostracods, conchostracans, and diverse invertebrate traces, along with semionotid and pleuropholid fishes, abundant pterosaur remains, and a fragmentary portion of an anuran, were collected from these deposits. Paleontological and stratigraphical data support an Albian age for the Lagarcito Formation.
