Saber-toothed kittens were born bruisers

One of the most well-known and charismatic mammals from the Ice Age of North America is the saber-toothed cat, Smilodon fatalis. Famous for its oversized teeth, Smilodon is also notable for its extremely robust and muscular forelimbs. Smilodon and other saber-toothed cats are thought to have ambushed prey and wrestled it to the ground, using their heavy bodies and strong forelimbs to immobilize the unlucky victim. From there, they used their long teeth to slash killing wounds. Struggling or bucking prey would have been very dangerous for such long-toothed predators, possibly breaking its teeth, so they needed very strong forelimbs.

Living big cats have comparatively thin, or gracile, limb bones, that get more gracile as they grow up. In contrast to the pattern in living cats, saber-toothed cats were suspected to have grown more robust as they reached adulthood. Research on Smilodon published by Katherine Long and colleagues in 2017 aimed to determine if that was actually true.

They studied every complete limb bone of Smilodon discovered at Rancho La Brea, in Los Angeles, including many kittens. They compared the Smilodon bones to living cougars, lions, and tigers, as well as the extinct American lion, Panthera atrox. Their results confirmed that the forelimbs of Smilodon adults were much more robust than similarly sized lions and tigers. They also found that P. atrox grew more gracile as it grew up, as expected.