Saber-tooth cats (Smilodon fatalis) had extraordinarily strong front limbs for tackling and subduing prey before they slashed throats or bellies with their saber-like canine teeth. But little was known about their kittens and growth patterns due to the fragility of juvenile bones.
A new study by researchers at Cal Poly Pomona published in PLOS ONE found that saber-toothed kittens started out with very robust bones and Hulk-like bodies.
“We were expecting the bones to show that the kittens grew stronger with age,” said Donald Prothero, a lecturer at Cal Poly Pomona and a research associate at the Natural History Museum of Los Angeles. “But it turns out that they started out with the thickest limbs of any cat ever known.”
To figure out how saber-tooth kittens were built and their growth pattern, Katherine Long, who earned a Bachelor of Science in animal science in 2016 and is now a master’s student in geological sciences, measured the length and circumference of approximately 200 S. fatalis leg bones from the La Brea Tar Pits, home to a highly unusual collection of juvenile fossils from predators who became stuck in the tar seeps.
Because the S. fatalis limb bones were from kittens of different ages, Long was able to create a growth chart of the species, showing how the bones grew in length and robustness as they aged.
The co-authors then compared S. fatalis growth to those of the cougar, tiger, lion, American cave lion, wildcat and serval.
They found that saber-tooth cats didn’t become more robust as they grew up, but instead began that way and retained the stereotypical cat family growth pattern where the limbs grow longer more quickly than they grow thick.
“Working in the tar pits is an amazing experience,” says Long. “In the collections, the walls are filled from floor to ceiling with shelving that houses the huge magnitude of ice age fossils. When you work with the bones, your hands get dark from the residual asphalt [and] you can even smell the ‘tar’ at times. Even some of the larger specimens, like those of the Mastodon and Mammoth, have asphalt still draining out of them! Even so, I’ve never seen more pristine specimens ever before, and it’s really exciting to start out in the paleontological community in such an awesome locality.”
The study, “Did saber-tooth kittens grow up musclebound? A study of postnatal limb bone allometry in felids from the Pleistocene of Rancho La Brea” by Long, Prothero, Meena Madan (Univ. Bristol, UK), and Valerie J.P. Syverson (Univ. Wisconsin), was published in PLOS ONE on Sept. 27.
Later this month Long will present her research at the Geological Society of America meeting in Seattle. Four other Cal Poly Pomona students will be presenting posters on their paleontological research using bones from the La Brea Tar pits: graduate student Patrick Gillespy on the lack of evolutionary change in teratorn vultures; Thien Htun B.S., environmental biology ‘17 and a current graduate student, on the growth rate of ice age camels; senior Tahsin Annoor, on the growth rates of horses; and Saul Galvez, a senior in geological sciences, on bison.
Long hopes to continue conducting paleontological research after graduating.
“I find extinction absolutely fascinating and plan learn as much as I can about it,” she said “I want to learn more about not only what once was, but apply it to modern conservation efforts as well. If all goes as planned, I hope to pursue a Ph.D. in the realm of veterinary research or integrative biology, and continue working with extinct mammals.”