Smilodon fatalis has its name for a reason. With swordlike canines, the saber-tooth cat is widely thought to have waited in silence before lunging and dealing devastating wounds to the soft throats of the large animals that it preyed upon. But paleontologists have long believed that this super-ambush predator was not alone in its way of life. A predatory marsupial known as Thylacosmilus also had long blades projecting from its mouth. But new research suggests that this notion is wrong.
Thylacosmilus was discovered in Argentina in 1926 when paleontologists excavated a fossil of an animal that looked remarkably similar to Smilodon. It had two main differences from the saber-tooth cat. First, it carried its young in a pouch like a kangaroo. And the canines of Thylacosmilus and Smilodon rested in different places.
Instead of having its teeth fully exposed outside of its mouth like Smilodon, Thylacosmilus had flanges formed from its lower jaw. These protrusions of bone functioned somewhat like scabbards, protecting the animal’s canines when its mouth was closed.
Beyond these differences, the animals were thought to have filled the same ecological ambush niche. Yet, upon closer examination, Christine Janis of the University of Bristol in England had doubts.
After more Thylacosmilus fossils were uncovered in South America, it became clear that the marsupial lacked the upper incisors that sit between the sharp canines. This struck Dr. Janis as strange, because great cats today like lions and jaguars depend on these teeth to get meat off bones. She also knew from previous work conducted by other labs that the canines of Thylacosmilus were structurally different from the teeth of Smilodon because of their triangular shape.
“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,’” Dr. Janis said. These differences raised questions and led her to collaborate with other researchers to conduct a detailed analysis of the ancient marsupial.
After simulations of skull and tooth performance were run with models of skulls generated from computed tomography, the researchers discovered that the marsupial’s skull was considerably weaker than that of Smilodon and was not robust enough to support a saber-tooth-style stabbing bite.
Instead, the simulations suggested that Thylacosmilus was excellent at making the strong pulling actions that are commonly used by scavengers, like hyenas, to rip carcasses apart.
The microscopic wear marks on the marsupial’s other teeth were also odd. Rather than showing evidence of biting and chewing bones, as is commonly found in large cats today and seen on the teeth of Smilodon, the teeth of Thylacosmilus show wear marks consistent with a diet of very soft meat, but not bones, similar to what cheetahs eat today.
Dr. Janis reported in the journal PeerJ last month that the findings reveal an animal that was definitely not a marsupial version of Smilodon. As for what it was actually doing, she proposes that Thylacosmilus was a scavenger that employed its huge canines to rip carcasses apart and then gobbled up organs.
She further suggests that, like walruses and anteaters that lack incisors and have very long tongues, Thylacosmilus slid its tongue into bodies to extract these innards. In essence, she argues it was a specialist organ feeder unlike anything living today.
Others in the field are not quite ready to embrace all that Dr. Janis is proposing.
“I am willing to entertain the notion that Thylacosmilus was a scavenger, but calling it a specialist organ feeder may be going a bit far,” said Blaire Van Valkenburgh, a paleontologist at the University of California, Los Angeles.”
The trouble is with the tongue.
“As I was reading about the missing incisors in the paper, I too thought that maybe these animals had a spectacular tongue with lots of stiff papillae that allowed them to rapidly clean bones of flesh,” Dr. Van Valkenburgh said. Unfortunately, unlike bones, tongues rot away when animals die. “I am not sure how we could ever confirm this.”