This Marsupial Sabertooth Was No Killer Cat

The extinct saber-toothed cat Smilodon fatalis prowled Pleistocene North America sporting seven-inch, blade-like canines that paleontologists say may have allowed it to slit gaping wounds across throats and bellies to swiftly bleed out its prey, reports Riley Black for National Geographic.

Understandably, when paleontologists discovered an ancient Argentine marsupial the size of a leopard with fangs that were even larger, relative to its body size, they assumed its huge canines were also for slashing and impaling writhing prey. But now, new research suggests that the marsupial sabertooth, Thylacosmilus atrox, was more likely a scavenger than a death-dealing predator.

Thylacosmilus didn’t just carry its young inside a pouch like modern marsupials, it also kept its saber-teeth sheathed by bony protrusions from its lower jaw that may have protected the fangs when its mouth was closed, reports Matt Kaplan for the New York Times.

The re-evaluation of how Thylacosmilus made its living as a carnivore came from an array of observations regarding its anatomy that appeared to have been lost in the shadow cast by the creature’s fearsome-looking teeth.

“Those big canines had everyone mesmerized, nobody seemed to notice that they were actually shaped like claws rather than blades. We almost named the paper ‘Blinded by the Tooth,’” Christine Janis, a paleontologist at the University of Bristol and lead author of the new research, tells the Times. Janis and her co-authors published “An eye for a tooth: Thylacosmilus was not a marsupial ‘saber-tooth predator’” last month in the journal PeerJ.

Besides the triangular, claw-shape of the marsupial’s teeth in cross section it also lacked upper incisors, which would have filled the space between the canines. According to Janis, those upper-incisors are essential tools for scraping meat from bone in today’s big cats as well as Smilodon. Moreover, the two sides of Thylacosmilus’ lower jaw weren’t even fused together by bone.

To get a clearer idea of what Thylacosmilus’ fangs might have been good for, the team conducted biomechanical studies comparing them to Smilodon.

"Previous studies by other researchers have shown Thylacosmilus to have had a weaker bite than Smilodon,” says Stephan Lautenschlager, a paleontologist at the University of Birmingham who worked on the analyses, in a statement. "But what we can show is there was probably a difference in behaviour between the two species: Thylacosmilus' skull and canines are weaker in a stabbing action than those of Smilodon, but are stronger in a 'pull-back' type of action. This suggests that Thylacosmilus was not using its canines to kill with, but perhaps instead to open carcasses."

The wear and tear on Thylacosmilus’ molars also didn’t match up with the patterns seen on modern big cats or Smilodon, per the Times. Instead of shearing meat from bone, the tooth surfaces of Thylacosmilus suggest it was eating very soft food.

“Thylacosmilus is not simply a marsupial version of a saber-tooth cat,” Larisa DeSantis, a paleontologist at Vanderbilt University and co-author of the paper, tells National Geographic.

Hans-Dieter Sues, a paleontologist at the Smithsonian’s National Museum of Natural History and who was not involved in the research, says the new findings show that even “striking similarities” in form, especially in species that are not closely related, must be examined in detail before scientists can infer “similarity in function.”

DeSantis tells National Geographic that the evidence suggests the ecology of Thylacosmilus “may have been very different than anything alive today—a carnivore that specialized on soft organs.”

In the statement, Janis says that this preference for guts may have also been facilitated by a large tongue: "It may have employed those canines to open carcasses and perhaps also used a big tongue to help extract the innards: other mammals that have lost the incisors, like walruses and anteaters, also have big tongues that they use in feeding."

But some other researchers think painting Thylacosmilus as an organ-slurper might be a stretch. Speaking with the Times, Blaire Van Valkenburgh, a paleontologist at the University of California, Los Angeles says she is “willing to entertain the notion that Thylacosmilus was a scavenger, but calling it a specialist organ feeder may be going a bit far.” And though Van Valkenburgh tells the Times she had the same thought concerning the extinct creature’s potentially prodigious tongue, she laments “I am not sure how we could ever confirm this.”

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