Extinct Sabercat Brought to Life

Using software designed for stress testing in engineering, researchers have modeled an American sabercat's skull in the highest resolution vertebrate animal model to date.

Wildlife biologists can watch a lion stalk its prey, but paleontologists must examine fossils to understand how the extinct saber-toothed cat hunted. Researchers now have modeled an American sabercat's skull with software designed for stress testing in engineering, building the highest resolution vertebrate animal model to date. They found that the sabercat’s massive teeth belied a surprisingly weak bite.

 

On a computer, “you can crash test a biological design,” says Colin McHenry, a doctoral candidate at the University of Newcastle, and lead author of the work. His team built a virtual sabercat skull that could display the effects of stress down to cubic millimeter resolution. Stress resistance indicates how hard the cat could bite and which muscles contributed the most force. The study appeared in the October 9, 2007 issue of the Proceedings of the National Academy of Sciences.

 

A high-resolution model of a lion’s skull (A) shows little stress compared to a model of an American sabercat skull (B) when researchers apply lateral forces to simulate thrashing prey. Twisting forces (C) and forces pulling forward on the canine teeth (D) also illustrate the  stresses a sabercat might have encountered while killing animals. Courtesy of Colin McHenryDespite more than 150 years spent studying sabercats, scientists have yet to agree on the animal’s biting power and the relative importance of head and neck muscles. In recent years, researchers have turned to computer simulations to reconstruct the musculature of extinct animals. They use the finite element method (FEM), a system originally designed to test aeronautical designs under stress. Until now, FEM studies featured animal skulls modeled as though bone has the same strength and density throughout—which it doesn't. And they didn't account for moving jaws.

 

To create a more lifelike simulation, McHenry’s team used a standard medical imaging technology, computed tomography, to build high-resolution FEM models of sabercat and (for comparison) lion skulls. The individual elements that make up this 3D model mimicked realistic bits of bone with different strengths. The team then added musculature, estimating the sabercat’s muscle sizes and strengths from the skull’s geometry. After subjecting both models (sabercat and lion) to the forces of struggling prey and the pull of the animal’s own muscles, they mapped the resulting stresses.

 

The sabercat skull generally handled forces poorly, while the lion skull took them like a tank. The researchers concluded that the sabercat didn’t land powerful bites, and that the jaw muscles may have required help from the neck muscles to puncture prey. These results support existing arguments that sabercats killed with piercing canine tooth bites, but there was still debate about the bite force, says McHenry. The sabercat probably bit one-third as hard as a comparably sized lion, the team concluded.

 

The next step is to account for the way bone responds to pressure from different directions, a method called anisotropic modeling, says Lior Horesh, PhD, a post-doctoral research fellow in Emory University’s department of mathematics and computer science. Horesh calls the team's research “one good step forward.”

 

McHenry and his colleagues soon will apply FEM modeling to biomedical questions, including mechanical evaluation of surgical planning procedures and stress-testing of prosthetic devices. “I think the medical community can learn a lot from paleontologists and biologists,” he says.

 



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