Think "saber-toothed" and meat-eating predators like cats probably come to mind. But Brazil was once home to a saber-toothed vegetarian with teeth so scary that rivals probably backed away after seeing them.
Paleontologists also believe the 260-million-year-old animal, described in the latest issue of Science, was one of the first of its kind to sport upper and lower teeth that fit together when it bit down, a handy feature called "dental occlusion" that we humans and many other animals today enjoy.
The new species, named Tiarajudens eccentricus, was part of a group of ancient animals called therapsids, many of which are relatives of today's mammals.
"Tiarajudens was an animal the size of a large dog," project leader Juan Carlos Cisneros told Discovery News. Its general appearance was bizarre: a slightly robust animal with a short snout from which large saber teeth came out."
Cisneros, a Federal University of Piaui paleontologist, and his team analyzed the animal's remains, which consist of a smashed-up skull and some teeth. They calculate it had a total of 21 teeth on just one side of its skull. In addition to the long, pointy sabers, these included spoon-shaped incisors associated with modern herbivores, as well as large crowned teeth linked to animals like today's grass-eating cows.
"Grasses are rich in fiber and modern ruminants eat them, but in the Permian grasses didn't exist so this new therapsid probably ate stems or leaves rich in fiber that existed at the time," Cisneros said.
While the saber teeth might have helped to move or pull soft branches, the researchers suspect this "eccentric" plant eater was very territorial, showing its impressive teeth to rivals while defending land and protecting itself from predators.
Dinosaurs did not live in this animal's realm, but other large predators were around, such as 13 to 20-foot-long dinocephalians (meaning "terrible heads"), biarmosuchians and the gorgonopsians -- named after the Gorgons of Greek mythology. Each was formidable in its own right.
As human boxers today often attest, teeth can fall out after battles and for other reasons, so Tiarajudens "was constantly replacing its molar-like teeth," Cisneros said. He explained that it did this as crocodiles and most modern reptiles do today. For every three teeth, a new one popped out behind, ready to serve as a replacement.
"The process happens in waves that may take a few days," he continued. "During each wave of replacement, the animal replaces several teeth at once. Because the animal replaces every three teeth, it manages to have at least two thirds of its set of molar-like teeth always fully operational."
We don't benefit from such a system, but we do share the top-meets-bottom teeth feature. Although some therapsids evolved into mammals, this particular species was in a lineage called anomodonts, which became extinct. This means, Cisneros said, that "dental occlusion evolved independently many times, which is interesting. It means that nature was doing experiments with this."
As for the saber teeth, many prehistoric animals sported them. Some modern animals have them too, such as musk deer and water deer.
Jorg Frobisch is a palaeozoologist at the Museum of Natural History, Leibniz Institute for Research on Evolution and Biodiversity at Humboldt University Berlin. He wrote a commentary on the new animal, published in the same issue of Science.
Frobisch told Discovery News, Tiarajudens eccentricus is an "extremely interesting animal" due to its teeth.
He added that the find "provides a wealth of new information" on early tooth development, especially on enlarged canines.