"Weird" Bucktoothed Dino Found in China

Hillary Mayell
for National Geographic News
September 18, 2002
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 nests—hatching, 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.

"These teeth are totally inappropriate for eating meat," said Philip Currie, a paleontologist at the Royal Tyrell Museum of Palaeontology in Canada. "Even with the beak, we had always assumed that oviraptorosuars were still carnivorous—hawks and eagles do it quite well. But these teeth are teeth you expect to see in an herbivore."

The pattern of tooth loss that led to the eventual development of a full beak in later forms is different from patterns seen in birds, and suggests there are more complex evolutionary scenarios for beak development than previously thought, said Makovicky.

Dinosaur-Bird Connection

Most paleontologists believe that modern birds evolved from small non-flying theropods around 150 million years ago. The theory is backed by the fact that theropod dinosaurs and birds share more than 100 anatomical features, and by the feathered theropod fossils found in the last several years in China. Dromaeosaurs, a group of small, fleet-footed dinosaurs in the theropod family, are thought to be the closest known relatives of birds.

Several recent studies have suggested that instead, birds evolved from oviraptorosaurs, based on a series of characteristics shared by both, including toothless jaws, short nasals, and other morphological similarities.

But the fact that Incisivosaurus, an early oviraptorosaur at 128 million years old, doesn't have any of the birdlike features at a time when birds had already evolved, suggests that it may be more a case of convergent evolution—two groups evolving similar features at the same time but independently, Currie said.

"Lots of species that aren't birds have evolved beaks; turtles, for instance," he said.

The Incisivosaurus fossil comes from the Yixian Formation, layers of volcanic and sedimentary rock deposited between 145 and 120 million years ago. The region has yielded an enormous variety of fossils, including feathered dinosaurs, fish, birds, insects, crocodiles, lizards, turtles, flowers, and mammals, and is changing how we view dinosaurs.

"The ideas that there were only 500 species of dinosaurs spanning 150 million years. And most were small," said Currie. "In Liaoning, we're seeing an explosion of fauna—they've found something like 30 species already and all from the same time period. The shapes are a lot more bizarre than we ever imagined, they're doing things differently—carnivores eating plants, for instance—and most are small.

"The worlds of the past are opening up to us and changing what we thought we knew. It's just mind-boggling, and very exciting."

Xu Xing said the significance of the Incisivosaurus fossil is how little is known about dinosaurs. "There is a lot that we don't know—dinosaurs are really a big family with great diversity."

More National Geographic News Stories on Dinosaurs:
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Comets May Have Led to Birth and Death of Dinosaur Era
Dinosaur Tracks Shed Light on Sauropod Evolution
Fossil of Dog-Size Horned Dinosaur Unearthed in China
Tyrannosaurus rex Was a Slowpoke
Researchers Rethink Dinosaur Die Off Scenario
Researchers Melt Polar Dinosaur Mysteries
Scientist's Finds Spur New Thinking on Dino Evolution
Dino-Era Vomit Fossil Found in England
Study Paints New Picture of Dinosaur's Nose
Skeleton of New Dinosaur "Titan" Found in Madagascar
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"Feathered" Fossil Bolsters Changing Image of Dinosaurs Oddly Angled Teeth Make Masiakasaurus
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Dinosaur Beak Probably Used to Strain Food, Not Kill Prey

Additional Dinosaur Resources from National Geographic:
Paul Sereno: National Geographic Explorer-in-Residence and Dinosaur Hunter
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Destinations: Dinosaur National Monument

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