"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 carnivoroushawks 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.
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 evolutiontwo 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 faunathey'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 differentlycarnivores eating plants, for instanceand 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 knowdinosaurs are really a big family with great diversity."
More National Geographic News Stories on Dinosaurs:
Dinosaur Tracks Preserved on Scottish Island
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
"Tidal Giant" Roamed Coastal Swamps of Ancient Africa
"Feathered" Fossil Bolsters Changing Image of Dinosaurs Oddly Angled Teeth Make Masiakasaurus
New Find: Pterosaur Had Strange Crest, Fishing Style
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
Destinations: Dinosaur National Monument
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