Saber-toothed cats may be best known for their supersized canines, but they also had exceptionally strong forelimbs for pinning prey before delivering the fatal bite, says a new study in the journal PLoS ONE.
Commonly called the "saber-toothed tiger," the extinct cat Smilodon fatalis roamed North and South America until 10,000 years ago, preying on large mammals such as bison, camels, mastodons and mammoths. Telltale clues from bones and teeth suggest they relied on their forelimbs as well as their fangs to catch and kill their prey.
The size and shape of sabertooth canines made them more vulnerable to fracture than cats living today, said author Julie Meachen-Samuels, a paleontologist at the National Evolutionary Synthesis Center in Durham, NC.
"Cats living today have canines that are round in cross-section, so they can withstand forces in all directions. If the prey is struggling it doesn't matter which way it's pulling — their teeth are unlikely to break," she explained.
In contrast, the elongated canines of saber-toothed cats were oval in cross-section, which made them more vulnerable to breaking than their conical-toothed cousins. "Many scientists infer that saber-toothed cats killed prey differently from other cats because their teeth were thinner side-to-side," said Meachen-Samuels.
Despite their vulnerable canines, prominent muscle attachment scars on sabertooth limb bones suggest the cat was powerfully built. Saber-toothed cats may have used their muscular arms to immobilize prey and protect their teeth from fracture, she explained.
"When I looked at the arm bones, Smilodon fatalis was way out in left field," said Meachen-Samuels.
Sabertooth arm bones were not only larger in diameter than other cats, they also had thicker cortical bone, the dense outer layer that makes bones strong and stiff. Thicker cortical bone is consistent with the idea that sabertooth forelimbs were under greater stress than would be expected for cats their size, Meachen-Samuels explained. Just like weight-bearing exercise remodels our bones and improves bone density over time, the repeated strain of grappling with prey may have resulted in thicker and stronger arm bones in saber-toothed cats.
"As muscles pull on bones, bones respond by getting stronger," said Meachen-Samuels. "Because saber-toothed cats had thicker arm bones we think they must have used their forelimbs more than other cats did."
"The findings give us new information about how strong their forelimbs were and how they were built," she added. "This is the first study to look inside sabertooth arm bones to see exactly how much stress and strain they could handle."
The findings will be published online in the June 30 issue of PLoS ONE.
Blaire Van Valkenburgh of the University of California, Los Angeles was also an author on this study.
CITATION: Meachen-Samuels, J. and B. VanValkenburgh (2010). "Radiographs reveal exceptional forelimb strength in the saber-toothed cat, Smilodon fatalis." PLoS ONE.
The National Evolutionary Synthesis Center (NESCent) is a nonprofit science center dedicated to cross-disciplinary research in evolution. Funded by the National Science Foundation, NESCent is jointly operated by Duke University, The University of North Carolina at Chapel Hill, and North Carolina State University. For more information about research and training opportunities at NESCent, visit www.nescent.org.
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