for National Geographic News
It's small, it's fast, and it's bizarre-looking. Paleontologists in China have discovered the skull of a new dinosaur species with beaver-like buck teeth on its upper jaw and the beginnings of a beak on its lower jaw.
The skull is around 128 million years old and was found in Liaoning Province, a region in northeastern China that has proven to be a spectacular treasure trove of dinosaur fossils.
Named Incisivosaurus gauthieri for its mouthful of weird teeth, it is the oldest fossil of an oviraptorosaur yet found. It also goes a long way toward solving the puzzle of what they ate.
"This early skull is the first hard evidence scientists have that at one point oviraptorosaurs were herbivorous," said Xu Xing, a paleontologist at the Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China. Xu and colleagues report on the find in the September 19 issue of the journal Nature. The National Geographic Society has been a long-time sponsor of Xu's work.
Oviraptorosaurs evolved sometime in the Early Cretaceous (144 to 127 million years ago) and belong to a group of meat-eating dinosaurs known as theropods. Up until now, fossils of oviraptorosaurs came primarily from the Late Cretaceous (89 to 65 million years ago) and were considered a somewhat bizarre branch of the theropod family. They were toothless, had beaks and many had a high-domed parrot-like head. These features are quite different from those of other theropods.
The four-inch (100-millimeter) Incisivosaurus skull is longer and lower than that of later oviraptorosaurs, and more closely resembles more traditional theropods, providing scientists with a bridge between early and later forms.
Mouthful of Teeth
The most striking feature of the Incisivosaurus, which was probably around three to four feet (one meter) long, is its mouthful of teeth.
"It doesn't have a true beak," said Peter Makovicky, a paleontologist at the Field Museum in Chicago who has done extensive work on dinosaurs with beaks. "It has a beak at the edge of the lower jaw, but the upper jaw has two enormous, beaver-like incisors [front teeth]. Behind them are small, pointy teeth. The cheek teeth, if you can call them that, are leaf-shaped. It's a very complex and weird dentition."
The teeth would be more suitable for gnawing than for slicing or cutting. Over time, oviraptorosaurs lost all their teeth and evolved a full beak, and paleontologists have long been curious as to what they ate.
Early fossils were found near nests, giving them their name, oviraptorosaur, which means egg thief. Later finds made it more likely that they were sitting on the nestshatching, not eating the eggs. A lizard skeleton found in the gut of one fossil suggested that they were indeed carnivores.
But the tooth structure and wear patterns of the Incisivosaurus show the best evidence found to date for herbivory among theropods, said Makovicky.
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