The fearsome saber-toothed cat teeth may have fully emerged later in life than those of modern big cats, but they grew at a rate about double that of their living relatives, according to a study published July 1, 2015 in the open-access journal PLOS ONE by Aleksander Wysocki from Clemson University, and colleagues.

The saber-toothed cat lived in North and South America until going extinct about 10,000 years ago. The cats are famous for their protruding canines, which could grow to be about 7 inches long. Although well-preserved fossils are available to researchers, very little is known about the ages at which the animals reached key developmental stages.

Using saber-toothed cat specimens recovered from the La Brea Tar Pits in Los Angeles, the authors of the study combined data from stable oxygen isotope analyses, micro-computed tomography, and previously published studies to establish the eruption rate for the saber-toothed cat's permanent upper canines and to calculate the timing of other growth events.

The authors of the study estimate that the permanent dentition of saber-toothed cats was fully erupted by 14 to 22 months, with the exception of the upper canines. These weren't fully developed until about three years of age, which is delayed in comparison to similar-sized living members of the cat family. The eruption rate of the saber-toothed cat's permanent upper canines was 6 millimeters per month - double the growth rate of an African lion's teeth.

The researchers suggest that the technique used in the study could be applied to a variety of extinct species to better understand the manner and rate by which different animals grew, for example, by looking at the tusks of extinct elephants or marine mammals.

"Despite having canine crown heights that were more than twice those of the lion, it didn't require twice as much time to develop its canines," added lead author Aleksander Wysocki.

Wysocki MA, Feranec RS, Tseng ZJ, Bjornsson CS (2015) Using a Novel Absolute Ontogenetic Age Determination Technique to Calculate the Timing of Tooth Eruption in the Saber-Toothed Cat, Smilodon fatalis. PLoS ONE 10(7): e0129847. doi:10.1371/journal.pone.0129847