- Friday, February 27, 2015
- 1:30 PM–2:20 PM
- Science Building 010
Michael Cherney Ph.D. Candidate Department of Earth & Environmental Sciences University of Michigan
Around 10,000 years ago, proboscideans (elephants and their relatives) disappear from the continental fossil records of Europe, northern Asia, and the Americas. All that remain of the once diverse and widespread group are three elephant species living in Africa and southern Asia. Evidence of human hunting and utilization of fossil proboscideans along with consistent correlation between influxes of substantial populations of humans into new areas and subsequent extirpations of proboscideans suggests that humans played a direct role in their extinctions. However, lack of independent evidence for ‘overhunting’ by humans supports the idea that dramatic climate change may be a more likely culprit. The two hypotheses are not mutually exclusive – both mechanisms may have played a role. This middle ground may seem sensible given the issue’s undeniable complexity, but the various factors are unlikely to have the same relative importance.
Fortunately, each of these contrasting hypotheses makes different testable predictions. If climate change were the main factor, populations would be expected to show effects of long-term and increasingly extreme nutritional stress leading up to regional extirpations.
On the other hand, over-hunting causes attrition of a population without degrading the health of individuals. Fossil tusks provide a means of assessing the nature of stresses on populations. Tusks contain a nearly life-long record of an individual’s growth history that includes proxies for nutritional status and physical health. Among other details, rate and variability of growth, as well as timing of certain life events, such as weaning, reflect an individual’s well-being. Wild African elephants wean later during extended times of drought and we might expect a similar scenario in the last woolly mammoths if they were driven to extinction by climate changes.
This presentation will highlight results of my attempts to determine whether weaning ages determined from analyses of juvenile Siberian woolly mammoth tusks fit better with the expectations of climate-change-driven extinction or with those of extinction caused by over-hunting by humans.