A new analysis of the distinctive canines of the saber-toothed tiger (Smilodon fatalis) suggests that the baby tooth — one of the deciduous teeth all mammals grow and lose by adulthood — that preceded each saber stayed in place for years to stabilize the growing permanent saber tooth, perhaps allowing adolescents to learn how to hunt without breaking them.
The canine of saber-toothed predators represents one of the most specialized dental structures known. Hypotheses about the function of hypertrophied canines range from display and conspecific interaction, soft food processing, to active prey acquisition. Recent research on the ontogenetic timing of skull traits indicates the adult canine can take years to fully erupt, but the consequences of prolonged eruption on inferences of canine functional morphology are missing from current discourse and have not been quantified. In his new study, Tseng evaluates hypotheses about adult canine bending strength and stiffness, respectively, during eruption in Smilodon fatalis. Image credit: Massimo Molinero.
This new study provides the first evidence that the saber tooth alone would have been increasingly vulnerable to lateral breakage during eruption, but that a baby or milk tooth alongside it would have made it much more stable.
The evidence consists of computer modeling of saber-tooth strength and stiffness against sideways bending, and actual testing and breaking of plastic models of saber teeth.
“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,” said study author Dr. Jack Tseng, a plaeontologist at the University of California, Berkeley.
“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 unusual presence of the baby canine long after the permanent saber tooth erupted protected the saber while the maturing tigers learned how to hunt without damaging them.”
“Eventually, the baby tooth would fall out and the adult would lose the saber support, presumably having learned how to be careful with its saber.”
Paleontologists still do not know how saber-toothed animals like Smilodon hunted prey without breaking their unwieldy sabers.
“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,” Dr. 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.”
According to the researcher, the same canine stabilization system may have evolved in other saber-toothed animals.
While no examples of double fangs in other species have been found in the fossil record, some skulls have been found with adult teeth elsewhere in the jaws but milk teeth where the saber would erupt.
“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,” Dr. Tseng said.
The study was published in The Anatomical Record.
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Z. Jack Tseng. Bending performance changes during prolonged canine eruption in saber-toothed carnivores: A case study of Smilodon fatalis. The Anatomical Record, published online April 8, 2024; doi: 10.1002/ar.25447
