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26-Nov-2004

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Can bison DNA explain the disappearance of sabre-toothed cats?



Steppe bison skull. Image courtesy of Henry Wellcome Ancient Biomolecules Centre, Oxford University.
Click here for a high resolution photograph.

Sabre-toothed cats, short-faced bears, camels, wild horses, mammoths and many other large creatures disappeared from Siberia, Alaska and Canada at about the same time thousands of years ago. While scientists don't agree on the cause of these extinctions, climate/environmental change and human hunting pressures are two of the most popular possible causes of these extinctions.

Researchers recently sampled DNA from about 350 fossilized bison bones in an attempt to help clear up the confusion. Their study suggests that climate and environmental change not human hunting was the primary cause of the extinctions.

This research appears in the 26 November 2004 issue of the journal Science.

Science author Beth Shapiro from Oxford University in Oxford, United Kingdom and her colleagues show that the numbers of ancient bison living in present-day Siberia, Alaska and Canada shrunk dramatically about 37 thousand years ago. The bison population drop occurred well before large numbers of humans lived in North America. This timing suggests that human hunting was not the primary cause of the bison population crash.



Extracting ancient mitochondrial DNA from a bison bone. Image courtesy of Henry Wellcome Ancient Biomolecules Centre, Oxford University.
Click here for a high resolution photograph.

What's the connection between bison and sabre-tooth cats?

The scientists say that this new bison information lets us see what was probably happening to big animals besides bison that lived in the same areas at the same time. If the bison were having problems, then the sabre-toothed cats, camels, wild horses, mammoths and many other large mammals were probably having troubles as well, the scientists propose. Because the fossils of sabre-tooth cats and other big animals are rare, scientists are looking at bison fossils in an attempt to understand a larger story.

The ancient bison populations plummeted just before huge sheets of ice moved across much of North America. During this time, both the climate and the environment were changing. For example, some grasslands changed over to forests. It is these kinds of changes that may have pushed many large mammals toward extinction, though additional less influential causes probably contributed as well. For example, hunting pressure from humans thousands of years after the documented bison population crash could have been "the straw the broke the camels back" for some of the big animals, including North American camels!

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