Late Pleistocene Large Mammals that Went Extinct Had No Distinguishing Features

Lorenzen et al. (2011) state that "despite decades of research, the roles of climate and humans in driving the dramatic extinctions of large-bodied mammals during the Late Quaternary period remain contentious." From about 50,000 years ago until today, Eurasia lost approximately 36% of its large mammals, while North American lost 72% of its Late Pleistocene mega-fauna. The animals examined for this study were the woolly rhinoceros (Coelodonta antiquitatis), woolly mammoth (Mammuthus primigenius), wild horse (wild Equus ferus and living domestic Equus caballus), reindeer/caribou (Rangifer tarandus), bison (Bison priscus/Bison bison) and musk ox (Ovibos moschatus). This was the first study to combine genetic, archaeological and climate data to try and answer a nagging question: why did some Ice Age mammals become extinct over time while others survived?

Ancient DNA extracted from radio-carbon dated fossil remains of six large-bodied Ice Age mammals were compared to paleoclimatic data on temperature and precipitation and to the distribution of prehistoric humans over the last 50,000 years, with a focus on four critical time periods: 42, 30, 21 and 6 thousand years ago (kya) -- pre-LGM (Last Glacial Maximum), peak LGM, end LGM and mid-Holocene, respectively. Demographic histories for each species were inferred from ancient mitochondrial DNA (control region) sequences that were analyzed three different ways: "Bayesian skyride," serial coalescent simulation and isolation-by-distance analysis.

All of the cold-adapted mammals studied by this research team managed to survive the long, relatively warm period (ca. 50-30kya) that preceded the LGM, apparently by finding small pockets of suitable habitat and climate-refugia-where individuals could persist for centuries in sufficient numbers that once conditions improved (i.e. got colder), populations rebounded. Such bottlenecks were evident in all species except bison. Mammoths, for example, were estimated to have rebounded ten-fold by 26kya, from a low of about 5,000 individuals-evidence that dramatic population declines do not necessarily lead to species extinction.

The wooly rhinoceros was widely distributed across Eurasia but went extinct rapidly during the intense warming that characterized the end of the LGM (about 14kya), with no evidence that humans hunters affected this outcome. Musk ox were similarly more affected by climate than by humans and while their range and population size has contracted, they have persisted despite Holocene warming (Campos et al. 2010). Muskox, like reindeer, have found suitable Holocene refugia across the Arctic: while musk ox numbers are currently rather low, wild and domestic reindeer number in the millions. Woolly mammoth went extinct after the Ice Age ended but more gradually, perhaps due to a combination of climate change and human hunting.

The authors suggest this study has implications for predicting the possible fates of living large-bodied, cold-adapted mammals should forecasted anthropogenic global warming come to pass. It is significant that the study found no distinguishing characteristics in the rate or pattern of decline in those species that went extinct compared to those that have survived and that all six species survived-and rebounded from-marked declines in their populations. As the authors conclude, such outcomes emphasize "the challenges associated with predicting future responses of extant mammals to climate and human-mediated habitat change."

Additional References
Campos, P.F., Willerslev, E., Sher, A., Orlando, L., Axelsson, E., Tikhonov, A., Aaris-Sørensen, K., Greenwood, A.D., Kahlke, R.-D., Kosintsev, P., Krakhmalnaya, T., Kuznetsova, T., Lemey, P., Macphee, R., Norris, C.A., Shepherd, K., Suchard, M.A., Zazula, G.D., Shapiro, B. and Gilbert, M.T.P. 2010. Ancient DNA analyses exclude humans as the driving force behind late Pleistocene musk ox (Ovibos moschatus) population dynamics. Proceedings of the National Academy of Sciences 107: 5675-5680.