Buck-toothed fossil reveals the dietary diversity of dinosaurs.
If the Looney Tunes animators had crossed Roadrunner with Bugs Bunny they'd have drawn something a lot like Incisivosaurus. This new-found, 128-million-year-old dinosaur fossil looks like a chicken with buck teeth1.
From a distance, Incisivosaurus would have had an air of one of the smaller, two-legged dinosaurs, such as Velociraptor. Close-up you'd have seen that its jaws, instead of being stuffed with razor-sharp teeth for dispatching hapless prey, boasted a variety of dental equipment suited to a vegetarian lifestyle.
Most prominent was a pair of front teeth like those of today's rabbits, of the extinct rodent-like mammals called multituberculates, and of some primates.
Xing Xu from the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, China, and colleagues found Incisivosaurus in the same rocks in northeastern China that have yielded a wealth of spectacular fossils over the past few years, including dinosaurs with feathers.
Is it a bird?
Xu's team thinks that Incisivosaurus, for all its distinctive appearance, is a primitive member of a peculiar group of dinosaurs called oviraptorosaurs, named after their most characteristic member, Oviraptor. This dinosaur had a short, deep skull and toothless jaws covered with a birdlike beak.
Oviraptor also behaved like a bird. There is a poignant fossil from Mongolia of a female Oviraptor buried while trying to shield her nest of eggs from a sandstorm.
The researchers believe that Incisivosaurus is primitive in that it had teeth rather than a beak, and a body that is less birdlike than some of its relatives. This conclusion questions recent claims that oviraptorosaurs are birds' closest relatives, or were even birds that lost the power of flight.
Xu and colleagues also reckon that the strange teeth of Incisivosaurus strengthen a previously suspected link between oviraptorosaurs and a little-known group of herbivorous dinosaurs, the therizinosaurs. Both groups claim an ancestry among meat-eating dinosaurs, but became adapted to a diet of plants.
In oviraptorosaurs, these adaptations are mainly found in the head. Therizinosaurs went further. Although still bipedal, many of these dinosaurs became extremely large; their huge, round bellies were slung between enormous, tree-trunk-like hind legs.
Their heads, on the ends of disproportionately skinny necks, were tiny. As if in compensation, their front feet sported three huge claws. Each claw was 70 centimeters long - the largest seen on any animal, anywhere.
Nobody has any idea how such strange creatures made a living. Certainly, their weirdness outstrips anything drawn by any animator. Looneytunesaurus anyone?
Henry Gee is the paleontology editor of the journal Nature.
Xu, X., Cheng, Y.-N., Wang, X.-L., Chang, C.-H. An unusual oviraptorosaurian dinosaur from China.. Nature, 419, 291 - 293, (2002).