Smilodon casts a long shadow. The last and largest of the sabercats, this Ice Age beast has been the focus of our curiosity about how long-fanged predators used their extraordinary cutlery for decades. But, as paleontologists and fossil fans know, Smilodon only represents one particular form in a much greater sabercat family. There were others - so often neglected that a technical volume about them was called The Other Saber-tooths - and it seems that they nabbed dinner on the hoof in a different way than our beloved Smilodon.
Paleontologist Borja Figueirido and colleagues break it down. The researchers employ Smilodon fatalis as the iconic example of a dirk-toothed sabercat. These carnivores typically had burly physiques and relatively longer canines, the combination making them adept ambush predators. For comparison, the researchers tapped Homotherium serum - a scimitar-toothed sabercat with a lankier, leggier build and shorter canines, often interpreted as more of a pursuit predator.
The differences between these cats go beyond their general proportions. When Figueirido and coauthors investigated details like bone thickness and how the different skull shapes responded to stress, they found that Smilodon and Homotherium probably handled their prey in different ways.
Part of the story involves distinct types of bone tissue. At the front of the Smilodon skull, for example, the researchers found a larger amount of cortical bone than in Homotherium. This is a specific type of bone that is relatively stiff - as compared to more flexible trabecular bone - and would have reinforced the skull of Smilodon against the stresses involved in sinking canines into flesh yet would have been relatively weak against the side-to-side stresses of a prey animal trying to escape.
Homotherium showed a different pattern. In addition to having less cortical bone at the front of the skull, this scimitar cat had a greater amount of trabecular bone towards the back of the skull. The overall pattern of bone types resembles what’s seen in lions, Figueirido and colleagues note. Homotherium was handling prey differently.
But how? Figueirido and colleagues suggest that Homotherium may have preferentially used slashing bites to the throat - like what's been proposed for Smilodon - but that the scimitar cat’s skull was better suited to handling the stress of struggling prey. This might indicate a different way of biting, and it also hints at an evolutionary trade off in terms of subduing prey. The skull of Smilodon could became more adapted to the classic shear bite because the cat’s arms were doing most of the grappling and struggling. Homotherium, by contrast, kept its runner’s build and instead had a skull that could handle more stress from the struggles of its chosen prey items.
There are other sabertooths the same type of analysis could be carried out on. The “alien knife” Xenosmilus is often mentioned as a kind of mash-up between the dirk-toothed and scimitar-toothed cats, for example, and there are many species of the cat-like nimravids that could be investigated to see how they differed from each other. Smilodon represents only the tip of the sabertoothed iceberg.