A recent thorough study, combining radio-carbon dating and genetic evidence, suggests elk did not cross the Bering Landbridge and colonize North America until about 15,200 years ago. According to this study, “there is no unequivocal fossil evidence that elk lived in North America prior to this date.” However, not every elk fossil in North America has been radio-carbon dated, and I’ll explain later how it’s possible elk could have colonized North America before this date without contradicting the data in this study. But first, I’ll summarize the pertinent findings of this paper which was published in The Proceedings of the Royal Society of Biological Sciences last year.
The authors of this study had difficulty even finding North American elk fossils that were thought to be older than 15,000 years. They did find 5 but determined from tests of bone collagen that 3 had been misidentified and were either bison or horse. The radiocarbon date on the 1 that was correctly identified as coming from a member of the deer family was 13,100 BP…within the proposed timespan.
Radio-carbon dating shows that elk have lived in northeast Asia for over 50,000 years. (Radio-carbon dating can’t date fossils older than this.) Scientists examined the DNA of almost 100 Pleistocene-aged and modern elk specimens from northeast Asia and North America. They found that all living North American elk are descended from elk originating in east Asia. North American elk apparently split from their Siberian ancestors about 15,000 years ago.
The environment of the Bering Landbridge experienced many changes over time. It was underwater from 135,000 BP- 70,000 BP. It rose above sea level between 70,000 BP-60,000 BP. Between 60,000 BP-30,000 BP, sea levels fluctuated so that some times the region was inundated and at other times it re-emerged. From 30,000 BP-11,000 BP the landbridge re-emerged, but since the latter date, it has been submerged once again. However, until about 16,000 BP the environment of the landbridge had little favorable elk habitat. A relatively warmer and drier climate occurred here between 16,000 BP- 11,000 BP, and elk were able to inhabit the landbridge and colonize the rest of North America from this starting point. Curiously, elk no longer live in Alaska because a cooler wetter climate pattern has caused their favored habitats to deteriorate here.
Archaeologists believe humans also crossed the Bering landbridge during the same time period as the elk migration, but archaeological evidence is scarce. The presence of elk fossils in Alaska during this time period and the timing of this migration as a proxy for human migration supports their belief. Because the climate was warmer and drier, these paleo-indians may not have been as culturally adapted to living in arctic conditions as the more recent native American inhabitants are here.
Elk in Tennessee. This species may be a relatively recent member of North America’s fauna. There is no unequivocal evidence of their presence on this continent until 15,200 BP.
Range map of elk. Elk no longer occur in Alaska because habitat is not favorable there for their survival. However, between ~16,000 BP- ~11,000 BP, climate there was relatively warmer than it is today, and elk were able to live in the region. This is when scientists believe they crossed the Bering Landbridge and began colonizing North America. Humans without an arctic-adapted culture also crossed the Bering Landbridge during this time period.
I don’t dispute the data and conclusions of this fine study. However, I’m not entirely convinced that elk did not occur in some regions of North America prior to 15,200 BP. The unique environmental conditions on the Bering Landbridge between 16,000 BP-11,000 BP that allowed elk to migrate to North America probably occurred and re-occurred periodically throughout the Pleistocene. It’s possible and even likely that elk would have crossed the landbridge during an earlier incarnation of this climate phase. Scientists have been wrong before about the exact dating of animal migrations into North America. Formerly, scientists assumed grizzly bears (Ursus arctos) did not colonize North America south of the Ice Sheets until about 13,000 BP when the glaciers receded. But a few years ago, fossil evidence of a grizzly bear, dating to 21,000 BP, was found in Edmonton, Alberta. All it would take to prove that elk lived in North America prior to 15,200 BP would be 1 specimen dating to a greater age than that. I’m aware of 1 candidate. There is an elk vertebrae in the Charleston Museum of Natural History that was recovered from sediments thought to be of early Pleistocene age. It was found associated with Eremotherium, a species of ground sloth thought to have become extirpated from the region 30,000 years ago. As far as I know, this specimen has never been radio-carbon dated. I think it merits dating. Would the date support the findings of the new study or would it suggest a more complicated history for Pleistocene elk in North America?
Photo of elk fossils found in South Carolina from the book Additions to the Pleistocene Mammal Faunas of South Carolina, North Carolina, and Georgia by Albert Sanders. The vertebrae comes from sediments thought to pre-date 15,200 BP.
The DNA evidence from the study make it clear–all North American elk alive today descend from the elk migration across the Bering Landbridge that began about 15,000 years ago. But this doesn’t rule out the possibility that a now extinct Pleistocene ecomorph of the elk occurred in North America prior to this date. Both cougars and jaguars lived in North America during the Pleistocene. DNA evidence proves the North American ecomorphs of these 2 big cats went extinct about 11,000 years ago. (See: https://markgelbart.wordpress.com/2014/04/11/extinct-pleistocene-ecomorphs-of-the-cougar-puma-concolor-and-the-timber-wolf-canis-lupus/) All modern individuals of these 2 species descend from populations that lived in eastern South America at the end of the Pleistocene. It’s not unprecedented for populations of a species to become extirpated, then replaced by other populations of the same species.
Reference:
Meirav, Meiri; et. al.
“Faunal Record Identifies Bering Isthmus Conditions as Constraint to end-Pleistocene Migrations to the New World”
Proceedings of the Royal Society of Biological Sciences 281 (1776) December 2013
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