Sunday, July 31, 2016

Progressive Westward Expansion of North American Continental Ice Sheets During The Quaternery and Implications for the Timing of Initial Human Overland Migration Into the Americas

Chief Mountain (Ninaistakis), viewed from never glaciated Del Bonita, Alberta.

Western limit (Taber, Alberta) of pre-OIS 2 glaciation along the Oldman River.


Figure illustrating southern limit of glaciations (Illinoian and Wisconsinan).
Note that Del Bonita, Alberta lies at the southern boundary of
maximum glaciation.

Progressive Westward Expansion of North American Continental Ice Sheets During The Quaternery and Implications for the Timing of Initial Human Overland Migration Into the Americas
Jackson Jr, Lionel E.,
2014 Annual Meeting,
The Geological Society of America
19-22 October, 2014
Paper No. 137-3


There is extensive and robust stratigraphic and geomorphic evidence of progressive enlargement of North American (NA) continental ice sheets in a westerly direction during successive glaciations of the Quaternary Period. This culminated in a one-time coalescence of the Laurentide Ice sheet and valley glaciers from the Rocky and Mackenzie mountains and outlet glaciers from the Cordilleran Ice Sheet during marine isotope stage (MIS) 2. This singular coast-to-coast ice (CCI) event ended the pattern of broad ice-free corridors between Cordilleran and continental glaciers that was the norm during all previous Quaternary glacial maxima in North America. Recent discoveries of human settlements above the Arctic Circle in eastern Siberia during MIS 3 (~30 C14 ky BP) and an accumulation of archaeological sites in NA south of the limit of glaciation dating to MIS 3 (specifically <30 C14 ky BP to ~22 C14 ky BP) or contemporaneous with the CCI event during MIS 2 (specifically ~22 C14 ky BP to ~14 C14 ky BP) suggest that the limiting event for initial overland human migration into the Americas was the closing of the ice-free corridor rather than its opening as has been the orthodoxy.

Thursday, July 14, 2016

Mammuthus Population Dynamics in Late Pleistocene North America: Divergence, Phylogeography, and Introgression

Jacob Enk, Alison Devault, Christopher Widga, Jeffrey Saunders, Paul Szpak, John Southon, Jean-Marie Rouillard, Beth Shapiro, G. Brian Golding, Grant Zazula, Duane Froese, Daniel C. Fisher, Ross D. E. MacPhee, and Hendrik Poinar
Frontiers in Ecology and Evolution
published 26 April, 2016
doi: 10.3389/fevo.2016.00042
(Link) open access pdf


After evolving in Africa at the close of the Miocene, mammoths (Mammuthus sp.) spread through much of the northern hemisphere, diversifying morphologically as they entered various habitats.  Paleontologically, these morphs are conventionally recognized as species.  In Pleistocene North America alone, several mammoth species have been recognized, inhabiting environments as different as cold tundra-steppe in the north and the arid grasslands or temperate savanna-parklands of the south. Yet mammoth phylogeographic studies have overwhelmingly focused on permafrost-preserved remains of only one of these species, Mammuthus primigenius (woolly mammoth).  Here we challenge this bias by performing a geographically and taxonomically wide survey of mammoth genetic diversity across North America.  Using a targeted enrichment technique, we sequenced 67 complete mitochondrial genomes including non-primigenius specimens representing Mammuthus columbi (Columbian mammoth), Mammuthus jeffersoni (Jeffersonian mammoth), and Mammuthus exilis (pygmy mammoth), including specimens from contexts not generally associated with good DNA preservation.  While we uncovered clear phylogeographic structure in mammoth matrilines, their phylogeny as recovered from mitochondrial DNA is not compatible with existing systematic interpretations of their paleontological record.  Instead, our results strongly suggest that various nominal mammoth species interbred, perhaps extensively. We hypothesize that at least two distinct stages of interbreeding between conventional paleontological species are likely responsible for this pattern—one between Siberian woolly mammoths and resident American populations that introduced woolly mammoth phenotypes to the continent, and another between ecomorphologically distinct populations of woolly and Columbian mammoths in North America south of the ice.