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With long, thin blades protruding from their mouths, saber-toothed cats roamed the Earth during the last ice age, alongside woolly mammoths, giant ground sloths and mastodons. They lived from the Eocene to Pleistocene epochs, which spanned over 50 million to about 11,700 years ago.
Not all saber-toothed creatures were felids, or “true cats,” which are the animals we consider to be “cats” today, such as lions, tigers and housecats. Sabers, the long knife-like canine teeth that grew from the upper jaw, appeared in many mammals over evolutionary time, including some animals called nimravids that looked a lot like cats, but weren’t felids. Within the felids, however, the stocky, muscular Smilodon fatalis is often thought of as the iconic example of a saber-toothed cat because of its extremely long canines—up to about seven inches long.
The cats’ range spanned the globe and included North America, where many of them became forever stuck and preserved in California’s La Brea Tar Pits.
Now, recent studies on the skulls and teeth of these long-extinct creatures are shedding light on how they developed and grew up from cubs to adults. It turns out that the saber-toothed cats may have had a delayed transition to adulthood, postponing the loss of baby teeth and remaining in an extended weaning stage.
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Baby saber teeth as training wheels
As paleontologists sifted through the bones mired in the thick, sticky La Brea Tar Pits, they noticed something peculiar. Some juvenile Smilodon fatalis skulls had two sets of sabers—four blade-like teeth. One set appeared to be baby teeth, also called milk teeth, while the others were adult teeth.
That curious observation led paleontologist Jack Tseng of the University of California, Berkeley, to wonder how young saber-toothed S. fatalis cats learned to wield their extreme teeth properly. “Even the animals we know today are not born fully equipped to do everything they need to do as adults,” says Tseng. “Humans can appreciate that—that’s why we have people saying, ‘adulting is hard.’”
Previous studies suggested that the overlap of baby and adult teeth persisted for as long as a year and a half. “I thought there were probably biomechanical or engineering consequences of having four knives in the mouth instead of two, so that’s really what got this study started,” says Tseng.
For his April paper published in the Anatomical Record, Tseng scanned and digitized three adult saber teeth and created physical and virtual models of them. In reference to an artificial gum line that he set in these models, he virtually reversed the growth process, slowly seeing what would happen if he were to move the teeth back into the gums. Along the way, Tseng realized that the long, thin sabers resembled beams used in construction, so he applied beam theory equations to the data to understand the forces that the teeth could withstand at various growth stages.
The results showed that as adult sabers grew from the gumline, the teeth increased in strength, but they also became much more flexible. “That is not a great thing for function, because the more you bend, the more microfractures or other types of damage can be introduced,” says Tseng. But beam theory calculations showed that adding a baby saber beside the adult tooth as it grew down provided a stabilizing or buttressing effect.
Hans Sues of the Smithsonian’s National Museum of Natural History, a vertebrate paleontologist who was not involved in the study, says, “It is not only an unusual structure, but when you look at it from a biomechanical point of view, you can see that this would be really liable to be damaged, particularly if the cat bit into prey and hit bone.” Tseng’s “discovery that the milk canine basically stays in place for a while and creates a structural brace—that’s a really neat thing,” he says. Sues points out that many avenues for further research in this area remain. “There are still so many unresolved questions—for instance, to what extent was that tooth fully exposed when not in use?”
According to Tseng, the prolonged double-fang period might have given young cubs time to practice their killing technique. “Think of those baby sabers as training wheels—once the training wheels are off, they only have adult sabers,” he says. The adult teeth are weaker on their own, but the cubs “are now seasoned predators with a perfected technique that might prevent those teeth from getting to the point of risking breakage,” he explains.
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A longer time with mom
Paleontologist Narimane Chatar of the University of Liège in Belgium says researchers have been debating whether Smilodon fatalis had an extended period of maternal care. A paper published in iScience in 2021 stoked the fires by reporting on fossils from three of these cats in Ecuador—an adult female and two adolescents that were probably a mother and her two cubs. Because the cubs were at least two years old, an age at which some modern big cats have already set out on their own, the work suggested that S. fatalis had a lengthy maternal care period. Chatar wanted to take a closer look at S. fatalis bones to see if they could shed light on the debate.
In her May paper, published in the Anatomical Record, Chatar found and scanned 22 mandibles of S. fatalis cats of different growth stages from the tar pits and the Natural History Museum of Los Angeles County, which she compared to 23 jaws of modern lions.
“We saw that both species exhibited a shift in mandibular shape when the lower carnassial erupted,” says Chatar. Lower carnassial teeth appear near the back of the mouth and are designed for cutting meat, so they signal the switch from a milk-based diet to a meat-based one. And in the lion, the appearance of this tooth at ten months of age signals the end of the weaning period. In addition, S. fatalis mandibles showed more changes, which could have made more room for larger chewing muscles. Combined with previous studies suggesting the saber-toothed cat’s teeth erupted later compared to modern big cats, Chatar concluded that S. fatalis probably had a longer weaning period.
The team, which included Tseng, also studied the possible functionality of the young jaws. The animals are thought to have used an anchor bite on the throat of their prey to hold them in place, and they would have done this with their mandibles. “Juvenile Smilodon were less efficient at performing this kind of bite than juvenile lions, and that was surprising,” she says. Although Smilodon fatalis cats eventually outshone lions at using the steadying anchor bite, they gained this skill at a later age, suggesting a longer duration of maternal care.
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“In paleontology, I think we pay a little bit more attention to juvenile specimens compared to those who study animals living today, but even then, this focus on how we get from a little tiny ball of nothing to a big scary predator is not something that is as well understood,” says Ashley Reynolds, who is a postdoctoral fellow at the Canadian Museum of Nature and the University of Ottawa.
Reynolds was not involved with Chatar’s study, but she produced the iScience paper on S. fatalis fossils found in Ecuador. “It’s really nice to see this work being approached from such an interesting angle, looking at the biomechanics of how that develops and how things change, and especially how things are different between these saber-tooth cats and the extant cats that we have today,” she says.
The research is still ongoing, with Chatar now working as a postdoc in Tseng’s lab. Chatar says that the one message people should take away from this study is, “Even fearsome and scary animals like Smilodon needed their mom until quite a late age.”