22 June 2009

Parrot-beaked dino was ancient nutcracker

Cosmos Online
Palaeontologists have found evidence that a parrot-beaked dinosaur ate nuts and seeds, and that it chewed its food in a novel way not known in any living animal.
Psittacosaurus gobiensis

Artistic rendering of a newly discovered species of parrot-beaked dinosaur, Psittacosaurus gobiensis. Psittacosaurs evolved their strong-jawed, nut-eating habits 60 million years before the earliest parrot. Credit: Todd Marshall

SYDNEY: Palaeontologists have for the first time found evidence that a parrot-beaked dinosaur ate nuts and seeds, and that it chewed its food in a novel way not known in any living animal.

Psittacosaurs are dinosaurs with parrot-like beaks that lived during the Cretaceous period about 100 to 130 million years ago.

Despite the resemblance of their jaws, they are unrelated to parrots, but may have developed the same nut-cracking habits 60 million years before parrots evolved, new research shows.

Stomach full of stones

“We make a strong case for having figured out the riddle of the unusual psittacosaur skull and may have narrowed its main food source to hard nuts and seeds,” palaeontologist Paul Sereno, of the University of Chicago,U.S., told Cosmos Online.

He is lead author of a paper detailing the find in the journal the Proceedings of the Royal Society B.

Psittacosaurs were first discovered in the Gobi Desert in southern Mongolia in 1922. These relatively small dinosaurs have short, deep snouts and projecting cheek horns. Sereno’s team unearthed a new species, Psittacosaurus gobiensis, in the Gobi desert in 2001.

The new fossil is just over a metre in length, but was found to contain what appear to be a “huge pile” of more than 50 stomach stones to grind up its food. The number of stones was “totally out of proportion to its body length,” said Sereno, who explained that in birds, a large number of gizzard stones indicate a diet of hard foods such as nuts and seeds.

Novel chewing technique

The researchers analysed the fossil’s well-preserved skull and concluded that this psittacosaur chomped on its food in a way previously unseen in animal jaws. Instead of biting up and down, or sliding the jaw from side to side in the way that plant eaters do, it drew it jaw upwards and backwards, in what the researchers call ‘inclined angle’ chewing.

This could explain the puzzling features previously noted in psittacosaur skulls. Psittacosaurs have long been a riddle to palaeontologists because their skulls are rigid, like those of meat eaters, but wear patterns show their jaws slid across each other in the same way that flexible-skulled herbivores do.

Different positions of the jaw would have been ideal for cropping, shelling and crushing nuts, the researchers believe. “It shows another remarkable solution to chewing invented by dinosaurs. It remains to be seen if any animals do it today. It is just a remarkable thing, to find a new chewing mechanism that is neither up and down nor fore and aft,” said Sereno.

Alex Cook, senior curator of palaeontology at the Queensland Museum, in Brisbane, said the find was interesting but not surprising. “It shows that where there is a niche to fill, something will evolve to fill it,” he said.

Cook added that a computer-tomography scan to work out the bite force of the skull would help to confirm what the dinosaur used its bite for. “This group had [rigid] skulls to maintain maximum force. It would have been nice to get a model of the force behaviour,” he said.

Sereno said that his team was currently sending the skull for a CT scan for that purpose. “We will reconstruct the estimated volume of jaw muscle and then calculate the force… I think they had quite a bite!”


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