Did sabre-toothed cats have double fangs?

The sabre-toothed cat Smilodon is one of the most iconic of prehistoric creatures, with its pair of elongated canine fangs, but new research suggests this is only half the story.

Smilodon fatalis is one species of sabre-toothed cats – a group which was common around the world until about 10,000 years ago.

Smilodon lived in the Americas during the Pleistocene epoch (2.5 million to 11,700 years ago). S. fatalis would have been about the size of a modern male lion at about a metre tall and reaching 160–280kg. It is smaller than the largest member of the genus, Smilodon populator, which lived in South America and is estimated to have reached weights of more than 400kg.

Despite thousands of Smilodon skulls being found, especially in California’s La Brea tar pits, very few have sabres attached.

Among the few skulls with sabres connected, a small number show a surprising feature: the socket for the sabre is occupied not by a single elongated tooth, but 2 teeth. The permanent adult tooth slots into a groove in the baby tooth.

Smilodon skull fossil teeth fang sabre-toothed cat
A portion of the right maxilla of a saber-toothed cat, Smilodon fatalis, showing a fully erupted baby saber tooth with the adult tooth just erupting. Credit: Jack Tseng, UC Berkeley.

Up until recently, these were thought to be rare cases of Smilodon with delayed loss of the baby tooth.

It was first speculated in 2015 that the double fang in adolescent Smilodon instead played an important role in supporting the adult tooth. Sabre-toothed cat growth data implies that the pair of teeth existed side by side for 24–30 months before the baby tooth finally fell out.

New research published in the Anatomical Record uses computer modelling to lend weight to this theory by simulating the stresses that would have been placed on the fang.

“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,” says author Jack Tseng, an associate professor at the University of California, Berkeley.

Tseng found that the narrow new adult sabre would be too weak to withstand breaking.

“According to beam theory, when you bend a blade-like structure laterally sideways in the direction of their narrower dimension, they are quite a lot weaker compared to the main direction of strength,” Tseng said.

“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 sabre, the overall stiffness more closely aligned with theoretical optimal.”

Model of sabre-toothed cat skull
A finite element model of an adult sabre tooth indicating sabre bending stress. The warmer the colour, the higher the stress and the more likely failure will occur in a particular area of the tooth model. The red dot near the tip is where the force was applied to measure the sideways bending stress. Credit: Jack Tseng, UC Berkeley.

Even so, sabre-toothed cats weren’t immune from breaking their knife-like teeth. Fossils found at La Brea show that Smilodon broke their teeth far more often than other large carnivores, including dire wolves.

Given the fangs’ fragility, palaeontologists still aren’t sure how sabre-toothed cats used them.

“Hypotheses about the function of hypertrophied [elongated] canines range from display and conspecific [within the same species] interaction, soft food processing, to active prey acquisition,” Tseng writes.

Tseng says the fact Smilodon would have to adjust to changing teeth for more than 2 years as their permanent teeth grew may help in explaining their main function in adult individuals.

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