Abstract: The Diamond Valley Lake local fauna from southwestern Riverside County, California is characterized by a classic suite of well-preserved late Pleistocene (Rancholabrean NALMA) vertebrates, including over 100,000 identifiable fossils representing more than 105 vertebrate, invertebrate and plant taxa from 2646 localities. The fauna is the largest open-environment, non-asphaltic late Pleistocene assemblage known from the American southwest. Located within the northern Peninsular Range physiographic province of southern California, the Diamond and Domenigoni Valleys contain bedded silts and clays intercalated with coarse-grained channel fill representing a braided stream environment. These fluvial sediments, yielding AMS dates from 19 ka to 13 ka, unconformably truncate older silts, clays and an organic black clay at depth. The clay is lacustrine in origin, with AMS dates from 46 ka to 41 ka. Numerous diagnostic vertebrate remains occur in both of these sediment packages. The Diamond Valley Lake local fauna constitutes a valuable source of new data on the relative density and diversity of late Pleistocene species from a geographic area where such data are largely absent. The assemblage differs dramatically in preservation and composition from other late Pleistocene coastal and desert localities in southern California.
Abstract: Direct radiocarbon dating and stable isotope and biometric analyses are evidence that the holotype of Equus laurentius Hay, 1913 comprises the skull and jaw of two different horses that are less than 500 years old. The size and morphology of the specimens fall within the range of like elements of modern Equus caballus Linnaeus, 1758. The mandibular cheek teeth exhibit bit wear, demonstrating that the mandible is that of a domestic animal. The taxonomy of the purportedly late Pleistocene species is therefore resolved, and Equus laurentius Hay is a junior synonym of Equus caballus Linnaeus. Equus laurentius and its holotype are neither taxonomically nor phylogenetically pertinent to studies of North American Pleistocene
Equus.
Abstract: Proposed explanations for the terminal Pleistocene large mammal extinction event in North America include climate warming and/or cooling, overhunting by early humans, disease, and bolide detonation or impact. A key assumption common to all these scenarios is that large mammals present in North America near the end of the Pleistocene were also present in similar abundance, with similar geographic distributions, during earlier, equally severe periods of climate change (e.g., 130 ka BP). This assumption is challenged here. An important difference in the latest Pleistocene was the profusion and geographic extent of the genus Bison, particularly in the American West. During the late Pleistocene, south of the glacial ice, the species Bison antiquus was more widely distributed and present in greater profusion than earlier species such as the larger B. latifrons. The increased abundance of these large, aggressive, herd-dwelling ruminants in the late Pleistocene constitutes a critical difference between this time period and earlier, similarly intense interglacials. Extinction scenarios for Pleistocene North America should avoid assuming a relatively static long-term faunal component, and account for the impacts of non-human immigrant species on natives, particularly when immigration events are close in time and space with climate changes.
Abstract: A review of fossils of extinct Bison from the Mojave Desert of California and Nevada demonstrates that the genus is even rarer in the region than was previously thought. The presence of fossils resembling Bison antiquus is confirmed only from the Las Vegas Valley, China Lake, Lake Manix (high in the section), and Dove Spring Wash. Additionally, a magnum of a very large Bison is present from a locality at Twentynine Palms. Other published records of Bison from the Mojave are problematic. Fossils assigned to Bison cf. B. antiquus from older (,290 Ka) sediments at Lake Manix are actually Camelops. A reported occurrence of Bison from the Pinto Basin is also Camelops. Fossils previously assigned to Bison sp. from the Piute Valley are an indeterminate large bovid and a large Equus. Bison is presently considered to have arrived in North America south of the ice between 210 +/- 60 Ka and approximately 160 Ka. Radiometric dates for confirmed occurrences of the genus Bison in the Mojave Desert range from less than 144 to 15 Ka and possibly 11 Ka in the Las Vegas Valley to between approximately 35 and 19 Ka at Lake Manix, about 19 Ka at China Lake, and approximately 16 Ka at Dove Spring Wash. The observed date range accords well with the age of coastal and inland Southern California records of extinct Bison (e.g., Rancho La Brea, Diamond Valley Lake, etc.), which are also relatively young. Fossils of Bison in the Mojave Desert have no older dates. The observed distributions and ages of Bison in the Mojave Desert and the southwest suggest that the genus might have had a more restricted temporal range than previously thought. This has important implications for biostratigraphy, for regional paleoecological reconstructions, and for correct interpretations of megafaunal
representation and diversity at the end of the Pleistocene.
Abstract: The rich fossil record of horses has made them a classic example of evolutionary processes. However, while the overall picture of equid evolution is well known, the details are surprisingly poorly understood, especially for the later Pliocene and Pleistocene, c. 3 million to 0.01 million years (Ma) ago, and nowhere more so than in the Americas. There is no consensus on the number of equid species or even the number of lineages that existed in these continents. Likewise, the origin of the endemic South American genus Hippidion is unresolved, as is the phylogenetic position of the âstilt-leggedâ horses of North America. Using ancient DNA sequences, we show that, in contrast to current models based on morphology and a recent genetic study, Hippidion was phylogenetically close to the caballine (true) horses, with origins considerably more recent than the currently accepted date of c. 10 Ma. Furthermore, we show that stilt-legged horses, commonly regarded as Old World migrants related to the hemionid asses of Asia, were in fact an endemic North American lineage. Finally, our data suggest that there were fewer horse species in late Pleistocene North America than have been named on morphological grounds. Both caballine and stilt-legged lineages may each have comprised a single, wide-ranging species.
Abstract: Mid-Pleistocene vertebrates in North America are scarce but important for recognizing the ecological effects of climatic change in the absence of humans. We report on a uniquely rich mid-Pleistocene vertebrate sequence from Porcupine Cave, Colorado, which records at least 127 species and the earliest appearances of 30 mammals and birds. By analyzing >20,000 mammal fossils in relation to modern species and independent climatic proxies, we determined how mammal communities reacted to presumed glacialâinterglacial transitions between 1,000,000 and 600,000 years ago. We conclude that climatic warming primarily affected mammals of lower trophic and size categories, in contrast to documented human impacts on higher trophic and size categories historically. Despite changes in species composition and minor changes in small-mammal species richness evident at times of climatic change, overall structural stability of mammal communities persisted >600,000 years before human impacts.
Abstract: Analysis of a buried deposit in the Diamond Valley of southern California has revealed well-preserved pollen, wood, and diatom remains. Accelerator mass spectrometry dates of 41,200±2100 and 41,490±1380 14C yr B.P. place this deposit in marine isotope stage 3. Diatoms suggest a shallow lacustrine environment. Pollen data suggest that several plant communities were present near the site, with grassland, scrub, chaparral, forest, and riparian communities represented. Comparison with modern pollen suggests similarities with montane forests in the nearby San Bernardino and San Jacinto ranges, indicating vegetation lowering by at least 900 m elevation and temperatures 4°â5°C cooler than today. An increase in high-elevation conifer pollen documents climatic cooling near the profile top. Early-profile diatoms are typical of warm water with high alkalinity and conductivity, whereas later diatoms suggest a higher flow regime and input of cooler water into the system. We suggest that the sequence is part of the cooling phase of an interstadial DansgaardâOeschger cycle. Records of the middle Wisconsin period are rare in southern California, but the Diamond Valley site is similar to records from Tulare Lake in the San Joaquin Valley and the ODP Site 893A record from Santa Barbara Basin. It is probable that the Diamond Valley assemblage is a local expression of a vegetation type widespread in the ranges and basins of southwestern California during the middle Wisconsin.
Abstract: Non-articular periostosis involving the distal end of a proximal phalanx of Equus conversidens is described. While not uncommon in fossil and recent equids, this is the first report of this paleopathology in E. conversidens. Based on remnants of epiphyseal plates, the animal was between one and two years of age at time of death.
Abstract: The Pinto Basin in Joshua Tree National Park is a recognized but largely unexplored site for Quaternary
fossil remains. Sediments in this area have yielded abundant but fragmentary Pleistocene vertebrate fossils.
Remains consist primarily of isolated dental and distal appendicular elements. Large and small horses and camels
are most commonly represented, but specifically diagnostic fossils are rare. New investigations initiated by the San
Bernardino County Museum, in cooperation with Joshua Tree National Park and the Joshua Tree National Park
Association, focus on renewed recovery and preservation of vertebrate fossils as well as their geologic, stratigraphic
and taphonomic contexts. More than 80 fossil localities have been identified since early 2003. Global
Positioning System data were acquired for all new localities, for inclusion in the parkâs digital overlay. New
discoveries include remains of Anas (duck), Canis (wolf-sized canid), Mammuthus (mammoth) and Odocoileus
(deer), as well as probable records of Accipitridae (hawk or eagle), Lepus (jackrabbit), Taxidea taxus (badger) and
Capromeryx (dwarf pronghorn), all new records for the fauna. The presence of Mammuthus demonstrates a
Pleistocene age for the fauna, although previous suggestions of a late Pleistocene (Rancholabrean North American
Land Mammal Age) date for the assemblage are not currently supported. Recommendations for future efforts to
manage, conserve and interpret fossil resources adequately include the creation of a park-wide paleontology
sensitivity overlay, cyclic field inspection, ongoing laboratory analysis, long-term curation in the park and implementation
of interpretive programs in paleontology.
