Researchers have recently discovered remains of a mammal that was only as large as a kitten, but was still a fierce predator. The research was completed by Russell Engelman and Darin Croft of Case Western Reserve University in Ohio and the results were published in the Journal of Vertebrate Paleontology.
The skull was recovered in Bolivia, where the animal lived 13 million years ago. It is believed to be in the order Sparassodonta, which has no living members but is considered a sister taxa to marsupials. They are currently holding off on naming a species. While many sparassodont species have only been identified through their teeth, this skull—which is about 3 inches (7.6 cm) long—is lacking teeth that are adequate to compare to other closely-related species.
Though they don’t have good tooth samples in the skull to identify the species, the researchers were still able to tease out a lot of information about the dentition. The animal had large, round canine teeth, perfect for attacking some fairly ambitious prey. "Most predators don't go after animals of equal size, but these features indicate this small predator was a formidable hunter," Croft said in a press release.
When it was first collected in 1978, it hadn’t been analyzed very thoroughly and was initially assumed to be an extinct species of carnivorous opossums. However, the species that is currently documented to be the oldest meat-eating opossum is about half as old as this mystery skull, putting strain on that connection. Additionally, the morphology of the eye socket in relation to the nasal bone was more like a sparassdont than an opossum.
"No single feature found in the skull was so distinctive that we could say one way or the other what it was," Croft explained in the press release, "but the combination of features is unique and says this is a sparassodont."
However, things aren’t really that clear-cut when comparing this skull to sparassodonts. Its features are more reminiscent of larger animals than those of similar size. The skull has a short snout and no gaps between its teeth, which is similar to animals the size of a jaguar. Smaller animals typically have gapped teeth as well as longer fox-like snouts.
Croft will be returning to the area where the skull was recovered this summer in hopes of finding more clues about the identity of this small-yet-mighty animal.