Dixon Lane-Meadow Creek, CA, United States
Dixon Lane-Meadow Creek, CA, United States

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Sertich J.J.W.,Denver Museum of Nature and Science | Stucky R.K.,Denver Museum of Nature and Science | McDonald H.G.,Denver Museum of Nature and Science | McDonald H.G.,National Park Service | And 9 more authors.
Quaternary Research (United States) | Year: 2014

The vertebrate record at the Ziegler Reservoir fossil site (ZRFS) near Snowmass Village, Colorado ranges from ~140 to 77. ka, spanning all of Marine Oxygen Isotope Stage (MIS) 5. The site contains at least 52 taxa of macro- and microvertebrates, including one fish, three amphibian, four reptile, ten bird, and 34 mammal taxa. The most common vertebrate is Ambystoma tigrinum (tiger salamander), which is represented by >. 22,000 elements representing the entire life cycle. The mastodon, Mammut americanum, is the most common mammal, and is documented by >. 1800 skeletal elements making the ZRFS one of the largest accumulations of proboscidean remains in North America. Faunas at the ZRFS can be divided into two groups, a lake-margin group dating to ~140-100. ka that is dominated by woodland taxa, and a lake-center group dating to ~87-77. ka characterized by taxa favoring more open conditions. The change in faunal assemblages occurred between MIS 5c and 5a (vertebrates were absent from MIS 5b deposits), which were times of significant environmental change at the ZRFS. Furthermore, the ZRFS provides a well-dated occurrence of the extinct Bison latifrons, which has implications for the timing of the Rancholabrean Mammal Age in the region. © 2014 University of Washington.

Miller I.M.,Denver Museum of Nature and Science | Pigati J.S.,U.S. Geological Survey | Scott Anderson R.,Northern Arizona University | Johnson K.R.,Denver Museum of Nature and Science | And 43 more authors.
Quaternary Research (United States) | Year: 2014

In North America, terrestrial records of biodiversity and climate change that span Marine Oxygen Isotope Stage (MIS) 5 are rare. Where found, they provide insight into how the coupling of the ocean-atmosphere system is manifested in biotic and environmental records and how the biosphere responds to climate change. In 2010-2011, construction at Ziegler Reservoir near Snowmass Village, Colorado (USA) revealed a nearly continuous, lacustrine/wetland sedimentary sequence that preserved evidence of past plant communities between ~. 140 and 55. ka, including all of MIS 5. At an elevation of 2705. m, the Ziegler Reservoir fossil site also contained thousands of well-preserved bones of late Pleistocene megafauna, including mastodons, mammoths, ground sloths, horses, camels, deer, bison, black bear, coyotes, and bighorn sheep. In addition, the site contained more than 26,000 bones from at least 30 species of small animals including salamanders, otters, muskrats, minks, rabbits, beavers, frogs, lizards, snakes, fish, and birds. The combination of macro- and micro-vertebrates, invertebrates, terrestrial and aquatic plant macrofossils, a detailed pollen record, and a robust, directly dated stratigraphic framework shows that high-elevation ecosystems in the Rocky Mountains of Colorado are climatically sensitive and varied dramatically throughout MIS 5. © 2014 University of Washington.

Springer K.,San Bernardino County Museum | Scott E.,San Bernardino County Museum | Sagebiel J.C.,San Bernardino County Museum | Murray L.K.,University of Texas at Austin
Quaternary International | Year: 2010

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. © 2009 Elsevier Ltd and INQUA.

PubMed | San Bernardino County Museum and U.S. Geological Survey
Type: Journal Article | Journal: Proceedings of the National Academy of Sciences of the United States of America | Year: 2015

Desert wetlands are keystone ecosystems in arid environments and are preserved in the geologic record as groundwater discharge (GWD) deposits. GWD deposits are inherently discontinuous and stratigraphically complex, which has limited our understanding of how desert wetlands responded to past episodes of rapid climate change. Previous studies have shown that wetlands responded to climate change on glacial to interglacial timescales, but their sensitivity to short-lived climate perturbations is largely unknown. Here, we show that GWD deposits in the Las Vegas Valley (southern Nevada, United States) provide a detailed and nearly complete record of dynamic hydrologic changes during the past 35 ka (thousands of calibrated (14)C years before present), including cycles of wetland expansion and contraction that correlate tightly with climatic oscillations recorded in the Greenland ice cores. Cessation of discharge associated with rapid warming events resulted in the collapse of entire wetland systems in the Las Vegas Valley at multiple times during the late Quaternary. On average, drought-like conditions, as recorded by widespread erosion and the formation of desert soils, lasted for a few centuries. This record illustrates the vulnerability of desert wetland flora and fauna to abrupt climate change. It also shows that GWD deposits can be used to reconstruct paleohydrologic conditions at millennial to submillennial timescales and informs conservation efforts aimed at protecting these fragile ecosystems in the face of anthropogenic warming.

Scott E.,San Bernardino County Museum | Thomas Jr. W.S.,Stafford Research Incorporated | Graham R.W.,Pennsylvania State University | Martin L.D.,University of Kansas
Journal of Vertebrate Paleontology | Year: 2010

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. © 2010 by the Society of Vertebrate Paleontology.

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. © 2009 Elsevier Ltd and INQUA.

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