Drastic ecological restructuring, species redistribution and extinctions mark the Pleistocene–Holocene transition, but an insufficiency of numbers of well-dated large mammal fossils from this ...transition have impeded progress in understanding the various causative links. Here I add many new radiocarbon dates to those already published on late Pleistocene fossils from Alaska and the Yukon Territory (AK–YT) and show previously unrecognized patterns. Species that survived the Pleistocene, for example, bison (Bison priscus, which evolved into Bison bison), wapiti (Cervus canadensis) and, to a smaller degree, moose (Alces alces), began to increase in numbers and continued to do so before and during human colonization and before the regional extinction of horse (Equus ferus) and mammoth (Mammuthus primigenius). These patterns allow us to reject, at least in AK–YT, some hypotheses of late Pleistocene extinction: ‘Blitzkrieg’ version of simultaneous human overkill, ‘keystone’ removal, and ‘palaeo-disease’. Hypotheses of a subtler human impact and/or ecological replacement or displacement are more consistent with the data. The new patterns of dates indicate a radical ecological sorting during a uniquely forage-rich transitional period, affecting all large mammals, including humans.
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About 70% of North American large mammal species were lost at the end of the Pleistocene epoch. The causes of this extinction-the role of humans versus that of climate-have been the focus of much ...controversy. Horses have figured centrally in that debate, because equid species dominated North American late Pleistocene faunas in terms of abundance, geographical distribution, and species variety, yet none survived into the Holocene epoch. The timing of these equid regional extinctions and accompanying evolutionary changes are poorly known. In an attempt to document better the decline and demise of two Alaskan Pleistocene equids, I selected a large number of fossils from the latest Pleistocene for radiocarbon dating. Here I show that horses underwent a rapid decline in body size before extinction, and I propose that the size decline and subsequent regional extinction at 12,500 radiocarbon years before present are best attributed to a coincident climatic/vegetational shift. The present data do not support human overkill and several other proposed extinction causes, and also show that large mammal species responded somewhat individualistically to climate changes at the end of the Pleistocene.
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Island colonization and subsequent dwarfing of Pleistocene proboscideans is one of the more dramatic evolutionary and ecological occurrences, especially in situations where island populations ...survived end-Pleistocene extinctions whereas those on the nearby mainland did not. For example, Holocene mammoths have been dated from Wrangel Island in northern Russia. In most of these cases, few details are available about the dynamics of how island colonization and extinction occurred. As part of a large radiocarbon dating project of Alaskan mammoth fossils, I addressed this question by including mammoth specimens from Bering Sea islands known to have formed during the end-Pleistocene sea transgression. One date of 7,908 ± 100 yr bp (radiocarbon years before present) established the presence of Holocene mammoths on St Paul Island, a first Holocene island record for the Americas. Four lines of evidence-265 accelerator mass spectrometer (AMS) radiocarbon dates from Alaskan mainland mammoths, 13 new dates from Alaskan island mammoths, recent reconstructions of bathymetric plots and sea transgression rates from the Bering Sea-made it possible to reconstruct how mammoths became stranded in the Pribilofs and why this apparently did not happen on other Alaskan Bering Sea islands.
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Human colonization of the New World is generally believed to have entailed migrations from Siberia across the Bering isthmus. However, the limited archaeological record of these migrations means that ...details of the timing, cause and rate remain cryptic. Here, we have used a combination of ancient DNA, 14C dating, hydrogen and oxygen isotopes, and collagen sequencing to explore the colonization history of one of the few other large mammals to have successfully migrated into the Americas at this time: the North American elk (Cervus elaphus canadensis), also known as wapiti. We identify a long-term occupation of northeast Siberia, far beyond the species’s current Old World distribution. Migration into North America occurred at the end of the last glaciation, while the northeast Siberian source population became extinct only within the last 500 years. This finding is congruent with a similar proposed delay in human colonization, inferred from modern human mitochondrial DNA, and suggestions that the Bering isthmus was not traversable during parts of the Late Pleistocene. Our data imply a fundamental constraint in crossing Beringia, placing limits on the age and mode of human settlement in the Americas, and further establish the utility of ancient DNA in palaeontological investigations of species histories.
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To account for the vastness of the northern arid steppes during Glacial episodes, I propose the proximate key variable was simply frequent clear skies. This hitherto under-emphasized point is the hub ...which best explains many questions. Low maritime cloud cover best accounts for today's tundra, and in a related way, the cloudy Polar Front accounts for the whole of the taiga. Even during Glacial maxima, the proximity of the sea to the Bering isthmus created intermittent maritime cloud cover. This regional cloud cover produced an ecological interruption, or buckle, of the arid steppe belt. While this Beringian mesic buckle did not serve as an intercontinental ecological barrier to most steppe-adapted species, it does seem to have limited the distributions of woolly rhinos, camels, American kiangs, short-faced bears, badgers, and some others. At the beginning of the Holocene, this narrow refugium seems to have been a source of some mesic-adapted species which colonized westward into the now tundra vegetation of northern Asia and eastward into northern North America. This Holocene expansion from a limited and regional Pleistocene refugium created our present misconceptions about Beringia. The mid-strait mesic ecological conditions were the exception to the more extensive, arid-adapted, communities of the Mammoth Steppe.
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6.
Dry Creek Powers, W. Roger; Guthrie, R. Dale; Hoffecker, John F ...
2017, 2017-05-31
eBook
With cultural remains dated unequivocally to 13,000 calendar years ago, Dry Creek assumed major importance upon its excavation and study by W. Roger Powers. The site was the first to conclusively ...demonstrate a human presence that could be dated to the same time as the Bering Land Bridge. As Powers and his team studied the site, their work verified initial expectations. Unfortunately, the research was never fully published. Dry Creek: The Archaeology and Paleoecology of a Late Pleistocene Alaskan Hunting Camp is ready to take its rightful place in the ongoing research into the peopling of the Americas. Containing the original research, this book also updates and reconsiders Dry Creek in light of more recent discoveries and analysis.
Analyses of fossil mammal faunas from 2945 localities in the United States demonstrate that the geographic ranges of individual species shifted at different times, in different directions, and at ...different rates in response to late Quatemary environmental fluctuations. The geographic pattern of faunal provinces was similar for the late Pleistocene and late Holocene, but differing environmental gradients resulted in dissimilar species composition for these biogeographic regions. Modern community patterns emerged only in the last few thousand years, and many late Pleistocene communities do not have modern analogs. Faunal heterogeneity was greater in the late Pleistocene.
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Frozen mammals of the Ice Age, preserved for millennia in the tundra, have been a source of fascination and mystery since their first discovery over two centuries ago. These mummies, their ecology, ...and their preservation are the subject of this compelling book by paleontologist Dale Guthrie. The 1979 find of a frozen, extinct steppe bison in an Alaskan gold mine allowed him to undertake the first scientific excavation of an Ice Age mummy in North America and to test theories about these enigmatic frozen fauna.The 36, 000-year-old bison mummy, coated with blue mineral crystals, was dubbed "Blue Babe." Guthrie conveys the excitement of its excavation and shows how he made use of evidence from living animals, other Pleistocene mummies, Paleolithic art, and geological data. With photographs and scoresof detailed drawings, he takes the reader through the excavation and subsequent detective work, analyzing the animal's carcass and its surroundings, the circumstances of its death, its appearance in life, the landscape it inhabited, and the processes of preservation by freezing. His examination shows that Blue Babe died in early winter, falling prey to lions that inhabited the Arctic during the Pleistocene era.Guthrie uses information gleaned from his study of Blue Babe to provide a broad picture of bison evolutionary history and ecology, including speculations on the interactions of bison and Ice Age peoples. His description of the Mammoth Steppe as a cold, dry, grassy plain is based on an entirely new way of reading the fossil record.
Dung from a mammoth was preserved under frozen conditions in Alaska. The mammoth lived during the early part of the Late Glacial interstadial (ca 12,300 BP). Microfossils, macroremains and ancient ...DNA from the dung were studied and the chemical composition was determined to reconstruct both the paleoenvironment and paleobiology of this mammoth. Pollen spectra are dominated by Poaceae,
Artemisia and other light-demanding taxa, indicating an open, treeless landscape (‘mammoth steppe’). Fruits and seeds support this conclusion. The dung consists mainly of cyperaceous stems and leaves, with a minor component of vegetative remains of Poaceae. Analyses of fragments of the plastid
rbcL gene and
trnL intron and nrITS1 region, amplified from DNA extracted from the dung, supplemented the microscopic identifications. Many fruit bodies with ascospores of the coprophilous fungus
Podospora conica were found inside the dung ball, indicating that the mammoth had eaten dung. The absence of bile acids points to mammoth dung. This is the second time that evidence for coprophagy of mammoths has been derived from the presence of fruit bodies of coprophilous fungi in frozen dung. Coprophagy might well have been a common habit of mammoths. Therefore, we strongly recommend that particular attention should be given to fungal remains in future fossil dung studies.
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