Megafauna Extinction in Eurasia

Eurasia (Eurasia and Northern Asia) lost 35% of its megafauna during the late Pleistocene, relatively fewer than North America and Australia. Extinction patterns here differed from those in North America; not all the extinctions occurred synchronously at the end of the Pleistocene (Grayson 2007). For example, mammoths disappeared from many parts of Eurasia at around 12,000 radiocarbon years ago, but lasted as late as 4,000 radiocarbon years ago on Wrangel Island. Similarly, giant deer disappeared from Southwestern France between 12,000 and 11,000 radiocarbon years ago but not from western Siberia until 7,000 years ago Stuart et al 2004).

The consensus is that Man was unlikely to have caused megafauna extinction in Eurasia, as the first modern humans (with sophisticated hunting tools) entered Eurasia around 50,000 radiocarbon years ago, and there were no apparent extinctions then (Grayson 2007). However, Stuart (1999) argues that the human role in Eurasia is not insignificant. For example, according to radiocarbon-calibrated pollen profiles, vegetation able to support mammoth was present more than 1,000 radiocarbon years after these animals disappeared in the region, weakening the argument that environmental change was the sole cause of extinction. Instead, he suggests that the asynchronous nature of extinction in Eurasia could mean that extinctions only occurred when animal populations were already undergoing significant stress from climate change, and human hunting provided the last straw. This probably also explains why there were 2 distinct waves of extinction in Eurasia which coincided with periods of climate change (40,000 to 20,000 radiocarbon years before present and 14,000 to 10,000 radiocarbon years before present), the latter of which is the focus of this blog.

While Stuart’s argument is convincing, I think an interesting counterargument can be found in Anthony Barnosky’s 1986 paper. He argues that Irish deer, which became extinct at around 10,000 to 12,000 radiocarbon years ago, before the arrival of humans in Ireland, were wiped out not by Holocene warming but a brief cold spell just before warming. This cold spell shortened feeding seasons for the Irish elk, which were also unable to migrate to any refugia quickly enough as Ireland is an island. The evidence is in lake sediment layers where pollen records suggest changes in vegetation associated with colder weather and fewer elk bones, during a period called the Nahanagan Stadial. He suggests that the accumulation of many local causes of extinction could have led to the total extinction of megafauna. Nevertheless, more work remains to be done on this fascinating hypothesis.

Figure 1: Irish Elk

Finally, I return to a discussion of the climate change that occurred during the late Pleistocene. In my previous blog post ‘Humans in the Wild West’, I discussed research showing that the late Pleistocene-Holocene glacial transition was unique in the Northern Hemisphere compared to other previous interglacials, both in climate and biological terms. This caused megafauna extinction due to climate unsuitability. Nogues-Bravo et al (2008) constructed a model which shows this for one species – the woolly mammoth in Europe.

Figure 2: Maps of Projected Climatic Suitability for the Woolly Mammoths in the Late Pleistocene and Holocene (Nogues-Bravo et al 2008)

The increasing intensities of red show increasing suitability of mammoth habitat while increasing intensities of green show decreasing suitability. Black dots show mammoth presence while black lines show the northern limit of early humans. The figure shows that climate and habitat suitability for mammoths decreased during the late Pleistocene. Although humans did move Northwards, their presence did not seem to affect mammoth presence as drastically as habitat suitability; even in areas untouched by humans (north of black line), mammoth populations declined as habitat suitability decreased.

The causes of megafauna extinction in Europe are certainly extremely complex. Climate change appears to be the main culprit, since human populations coexisted with megafauna for over 50,000 radiocarbon years while accelerated extinctions only occurred in 2 distinct phases which were periods of distinct climate change. Extinctions in at least some specific geographical locations, such as the Irish elk in Ireland, were certainly distinct from the role of humans.  

References

Barnosky, A. (1986) “Big game” extinction caused by late Pleistocene climatic change: Irish elk (Megaloceros giganteus) in Ireland’, Quaternary Research, Vol. 25, 1, pp. 128-135

Grayson, D. K. (2007) ‘’Deciphering North American Pleistocene extinctions’’, Journal of Anthropological Research, Vol. 63, No. 2, pp. 185-213

Nogues-Bravo, D. et al (2008) ‘’Climate change, humans and the extinction of the woolly mammoth’’, PLOS Biology, 6(4), e79

Stuart, A. J. (1999). Late Pleistocene megafaunal extinctions in MacPhee, R. D. E. (ed.) Extinctions in Near Time: Causes, Contexts, and Consequences, New York: Plenum, pp. 257-269.