As its name implies, Tiarajudens eccentricus was a bit of an oddball. This mammal ancestor had huge, blade-like canines and a slew of teeth all along the roof its mouth – yet it was an herbivore. The big-dog-sized animal lived 270 million years ago in the Middle Permian, long before dinosaurs appeared on the scene. Now, a new fossil analysis reveals that they likely bared their outsized canines during visual displays and one-on-one combat. The findings were published in Royal Society Open Science this week.

First described in 2011, this mammal relative (or a therapsid to be exact) “looks like a combination of different animals, and it takes some time to believe it when you see this animal in front of you," Juan Cisneros from Universidade Federal do Piaui told National Geographic at the time. "It has the incisors of a horse, which are very good for cutting and pulling plants; the big molars of a capybara, for grinding; and the canines of a saber-toothed cat." The saber-caniniforms of these mammal forerunners were at least 12 centimeters (nearly 5 inches) long.

Now, Cisneros and colleagues have conducted a more in-depth analyses of fossils – half a skull, partial lower jaw, limb bones – recovered from sandstone blocks in the Rio do Rasto Formation of Brazil. They found the oldest evidence of herbivores using their canines during visual displays and fights with rivals.

"It is incredible to think that features found in deer such as the water deer, musk deer, and muntjacs today were already represented 270 million years ago," Cisneros says in a statement. These tusked deer, who all look rather vampiric, used their canines to scratch body surfaces of their opponents during mating season. Not using the teeth to inflict deep wounds might explain the absence of wear in T. eccentricus.

In fact, two forms of combat we see today – canine display and head-butting – appeared in the Permian. Head-butting was an alternative strategy used by dinocephalians, another herbivore during that time; these had massively thickened bones in their foreheads. Behavioral specializations that are considered so characteristic of more recent, Cenozoic mammals, they say, likely evolved when "Earth's first complex herbivore terrestrial communities were constituted."

The team also reanalyzed a recently described, closely related species called Anomocephalus africanus, which lived in South Africa when it was still part of Gondwana. The roof of its mouth was also studded with replacement teeth, though it lacked the conspicuous saber-like canines of its Brazilian cousin.



Anomocephalus and Tiarajudens. Wits University