March 25, 2011 | 7
Some extinct animals have anatomical oddities that seem destined to be confined to the marginalia of history. Questionable characters, such as the single-fingered dinosaur and the flightless, club-winged bird, ultimately died off despite—if not because of—their idiosyncratic adaptations.
Now, researchers have described a perplexing, long-extinct creature, this time with some dubious dental assets: large saber teeth. A seemingly strange adaptation for a plant eater.
This Middle Permian creature exhibits what Jörg Fröbisch, of the Humboldt Museum in Berlin, kindly describes as "a unique dentition."
The aptly named Tiarajudens eccentricus (Tiaraju for its location, "dens" for teeth—and eccentricus, well, you can gather that bit) was a dog-sized animal that lived some 260 million years ago in what is now Brazil.
"Large saber canine [teeth] are unexpected in a herbivore," wrote the authors of the study that describes the new anomodont, a member of the therapsid group (which produced some lines that eventually led to mammals).
And these fangs weren’t subtle. The saber teeth were more than half the length of the animal’s 22.5-centimeter-long skull—proportionally bigger even than those of a carnivorous contemporary, the Inostrancevia.
Among four-legged animals, a plant-based diet had only emerged some 40 million years earlier, but the sizable teeth do not appear to be a holdover from carnivorous ancestors.
So if it wasn’t tearing meat like a saber-tooth tiger, what was it doing with these two outsized teeth? "The function of the saber teeth is unknown," wrote authors of the new study. But they might have used them to scare away predators, fight among each other or show off for potential mates—or perhaps all three.
Saber teeth are not totally unknown in the herbivore world. There are a few living deer, such as the water deer Hydropotes and musk deer Moschus, that have protruding teeth. But before this little anomodont was uncovered, the earliest known example was the Titanoides, which didn’t emerge until 57 million years ago.
These saber teeth are not, apparently, to be confused with the tusks simultaneously sprouting from a sister anomodont group, the dicynodonts.
With this distinction, Fröbisch poses an existential question—for T. eccentricus, at least: "When is a saber tooth a saber tooth, and when is it a tusk or simply an enlarged canine?"
The answer, actually, still seems unclear and, he notes, "appears to be vague and primarily based on length." But perhaps it will be worth chewing over, as he points out that it should help explain a bit about the evolution of herbivores and their "complex social interactions"—or lack thereof.
The study, led by Juan Carlos Cisneros, of the Universidade Federal do Piauí in Teresina, Brazil, and accompanying essay by Fröbisch were published in the March 25 issue of Science.
Images of T. eccentricus courtesy of Juan Cisneros