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Monday, January 7, 2013

Can broken teeth explain big cat extinction?

Why did American lions (Panthera atrox, top left) and saber-toothed cats (alluringly named Smilodon fatalis, bottom left) go extinct some 12,000 years ago? One hypothesis is that the predators fell on hard times as their prey was either culled by competing humans or decimated by climate change. The rational behind this idea is that the carnivores found at the La Brea tar pits (yes, I know how redundant this is) in California had a lot of broken teeth. About 7% of modern big cats and 9% of modern hyenas have broken teeth, whereas 36% of the extinct lion and 11% of saber-toothed cats had broken teeth. This led researchers to wonder if the large cats were forced to consume high amounts of bone as their prey diminished.

To be clear, the idea isn’t that the cats died out because they kept breaking their teeth while eating bones. Rather, the broken teeth are an indication that prey was scarce enough to discourage the predators from wasting any part of a carcass. It was the scarcity of prey that drove the carnivores to extinction.

So, is this idea correct? To find out, Larisa DeSantis from Vanderbilt University and her colleagues studied the fossilized teeth of the extinct cats. They used high-resolution scanning electron microscope (SEM) plus dental microwear texture analysis to determine whether the carnivores regularly consumed bones as well as flesh. The teeth of bone-avoiding carnivores (like cheetahs) have fewer pits and more long scratches than the teeth of animals that consume a lot of bone (like hyenas).

Both the American lion and the saber-toothed cat consumed less bone than all modern cats except for cheetahs. In addition, when the paleontologists compared the oldest specimens to the more recent ones (just before the species went extinct) they found that bone consumption had gone down, not up. The predators were not consuming more parts of their prey.

However these creatures were breaking their teeth, it wasn’t by eating bones. More significantly, this means that times were not lean enough to force the large cats to consume every part of their prey. So it’s back to the drawing board for both the cause of the tooth breakage and the extinctions.

American lion skull photo by By Claire H., 10/10/2008.

Larisa R. G. DeSantis, Blaine W. Schubert, Jessica R. Scott, & Peter S. Ungar (2012). Implications of Diet for the Extinction of Saber-Toothed Cats and American Lions PloS ONE, 7 (12) : doi:10.1371/journal.pone.0052453.