Saber-Toothed Tigers' Skulls Reveal How They Grew Their Fangs

Saber-toothed tigers may have had two sets of their famous fangs for a period of their adolescence, fossil evidence reveals.

One species of these ancient and extinct cats, famed for their large and powerful saber-like teeth, is named Smilodon fatalis. The discovery of over 2,000 of these cats' skulls at the La Brea Tar Pits near Los Angeles established them as California's state fossil.

Many of these skulls were found with double fangs, which were initially thought to be a fluke. But it turns out that these famous sabers may have had their baby tooth counterparts for several years, according to a study in the journal The Anatomical Record.

In humans, baby teeth are lost as the adult tooth grows below, pushing the baby tooth out of the gum. Many other species of animals, including cats, undergo a similar process as juveniles approach adulthood.

A few of the La Brea saber-toothed cat skulls showed a strange feature: the saber tooth socket was occupied by two teeth, with the adult tooth slotted into the baby tooth. According to the paleontologists, this wasn't a freak of nature but instead a regular part of the maturing process of this species.

"What we do see is milk canines preserved on specimens with otherwise adult dentition, which suggests a prolonged retention of those milk canines while the adult tooth, the sabers, are either about to erupt or erupting," said paleontologist Jack Tseng, an associate professor of integrative biology at the University of California, Berkeley, in a statement. He is also a co-author of the study.

Smilodon fatalis is one of the most well-known and extensively studied species of saber-toothed cats, along with others like Smilodon gracilis and Smilodon populator. Smilodon fatalis lived in the Americas during the Pleistocene epoch, from about 2.5 million to about 10,000 years ago, and is known for its long, curved canine teeth, which could grow up to 7 inches long.

These teeth adapted to deliver deep, fatal blows to the neck or belly of its prey, which likely included large herbivores such as bison, camels and young mammoths or mastodons. Smilodon fatalis was similar in size to a modern large lion, weighing between 350 and 620 pounds, making it one of the largest predators of its time.

These cats may have had both their baby and adult saber teeth simultaneously for around 30 months of their adolescence, after which the baby tooth would fall out and leave only the adult fang, according to the researchers.

This strange system helped stabilize the growing adult tooth, protecting it from lateral breakage during its eruption, the theory goes.

"This new study is a confirmation—a physical and simulation test—of an idea some collaborators and I published a couple of years ago: that the timing of the eruption of the sabers has been tweaked to allow a double-fang stage," Tseng said.

He continued: "Imagine a timeline where you have the milk canine coming out, and when they finish erupting, the permanent canine comes out and overtakes the milk canine, eventually pushing it out. What if this milk tooth, for the 30 or so months that it was inside the mouth right next to this permanent tooth, was a mechanical buttress?"

The researchers modeled the strength of the growing saber tooth and also tested the strength of plastic model teeth. They suggest that the milk tooth helped to stabilize the tooth as the animal got used to wielding such a long saber.

"During the time period when the permanent tooth is erupting alongside the milk one, it is around the time when you switch from maximum width to the relatively narrower width, when that tooth will be getting weaker," Tseng said. "When you add an additional width back into the beam theory equation to account for the baby saber, the overall stiffness more closely aligned with theoretical optimal."

In the paper, the researchers said this development may also have evolved in other species of saber-toothed cats, though no examples have yet been discovered in the fossil record.

This study also changes the way researchers think about how these cats hunted during their adolescence and adulthood, as their canines would have become more vulnerable after the milk tooth fell out. They therefore may have relied more on predatory stealth or muscular strength to overwhelm their prey, using their sabers only for a major offensive when there was less danger of them breaking during their adolescent years.

"The double-fang stage is probably worth a rethinking now that I've shown there's this potential insurance policy, this larger range of protection," Tseng said.

"It allows the equivalent of our teenagers to experiment, to take risks, essentially to learn how to be a full-grown, fully fledged predator. I think that this refines, though it doesn't solve, thinking about the growth of saber tooth use and hunting through a mechanical lens," he said,

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