New research shows that the fearsome teeth of the saber-toothed cat Smilodon fatalis grew at a rate about double that of their living relatives, but still took years to fully emerge. The findings, published today in the journal PLOS ONE and based on a new technique that combines isotopic analysis and x-ray imaging, for the first time provide specific ages for developmental events in Smilodon, notably in their teeth.

This fossilized jaw of an adult Smilodon fatalis shows the fully erupted canine. © AMNH/J. Tseng

The study estimates that the eruption rate of S. fatalis’spermanent upper canines was 6 millimeters per month—double the growth rate of an African lion’s teeth. But the extinct cat’s dagger-like canines weren’t fully developed until about three years of age.

“For predators such as big cats, an important determinant of an individual’s full hunting ability is the time required to grow their weapons—their teeth,” said Z. Jack Tseng, a National Science Foundation and Frick Postdoctoral Fellow in the American Museum of Natural History’s Division of Paleontology and a coauthor on the new paper. “This is especially crucial for understanding sabertoothed predators such as Smilodon.”


The partial fossilized jaw of a baby Smilodon fatalis. One of its adult canines (inside, left) was erupting alongside the baby canine. © AMNH/J. Tseng

Smilodon fatalis lived in North and South America until going extinct about 10,000 years ago. About the size of a modern tiger or lion but bulkier, the cats are famous for their protruding canines, which could grow to be 18 centimeters (about 7 inches) long. Although well-preserved fossils of these cats are available to researchers—including those in the Museum’s own collection—little is known about the absolute ages at which the animals reached key developmental stages.


Life reconstruction of a family group of Smilodon fatalis. Illustration by and courtesy of Mauricio AntĂłn, from his 2013 book Sabertooth.

By using the eruption rate to calibrate a previously published tooth-replacement sequence for the saber-toothed cat, the researchers calculated the timing of various growth events in months. The researchers say that the technique they demonstrate in the paper could be applied to a variety of extinct species to better understand the manner and rate at which other extinct animals grew.

This story was originally published on the Museum blog.