Thriving long before the dinosaur age, Tiarajudens eccentricus was armed with an incredible arsenal of teeth for grinding, tearing, and even scaring. But the newly discovered saber-toothed mammal ancestor was a vegetarian, a new study says.
Not only did the big-dog-size animal have huge canines—each as large as a crayon—but the roof of the animal's mouth appears to have been studded with teeth, which allowed for rapid replacement of lost teeth, as in sharks, researchers say.
Part of the Anomodontia suborder within the Therapsida order—often called mammal-like reptiles—the 260-million-year-old fossil vegetarian "looks like a combination of different animals, and it takes some time to believe it when you see this animal in front of you," said paleontologist Juan Carlos Cisneros, who discovered the fossil in Brazil.
"It has the incisors of a horse, which are very good for cutting and pulling plants; the big molars of a capybara (picture), for grinding; and the canines of a saber-toothed cat."
Paleontologist Jörg Fröbisch said the saber teeth are a particular surprise, considering the animal's diet of fibrous plants.
"You would usually expect saber teeth in a carnivore," said Fröbisch, of the Humboldt University of Berlin.
"The best known animals are obviously saber-toothed cats or tigers, but there are also some [extinct] forms known among the marsupials, relatives of kangaroos and wombats," added Fröbisch, who wasn't involved in the Tiarajudens eccentricus study, to be published tomorrow in the journal Science.
T. eccentricus' saber teeth might have deterred predators or intimidated or wounded rivals of the same species, the study authors speculate.
"Saber teeth used for display or fighting between members of the same species is something that we thought appeared in herbivores less than 60 million years ago," said study leader Cisneros, of Brazil's Federal University of Piauí.
"If Tiarajudens eccentricus [used them this way], then it appeared much earlier, when terrestrial communities were ... dominated by herbivores."
Tooth Trials: Secret of Evolutionary Success?
Why did plant-eating Tiarajudens eccentricus—"the eccentric tooth of the Tiarajú region"—have idiosyncratic dentition? The answer may lie in evolutionary experimentation.
No matter how unusual, Tiarajudens eccentricus' wildly differing teeth fit closely together during a bite—the better to grind up and process fibrous leaves and stems. This early example of a tight tooth fit in a therapsid may offer insights into why humans and other mammals are so equipped today, since mammals evolved from therapsids.
"This animal was already capable of eating like a modern ruminant, and that's very interesting," Cisneros said. Ruminants are animals such as cows and goats, which chew their cud and have complex, multichambered stomachs.
These unique dental adaptations may also offer some clues to the striking success of the anomodonts during the middle Permian era, before dinosaurs dominated Earth. (See a prehistoric time line.)
"Anomodonts were the most successful group of terrestrial vertebrates, with the most species, most diverse morphologies, and most ecological adaptations during this time," the University of Humboldt's Fröbisch said.
"There were burrowing forms, climbing forms, semiaquatic forms, small rat-sized animals, and large cow-sized animals in this same group, and this is unique in the ancestral lineage of mammals," he said.
"This early experimentation in different teeth, I'm sure, is part of why this group became so successful."