June 30, 2009

Hadrosaur Had Unusual Jaw

A new study suggests that a hadrosaur's jaw wasn't hinged in the same way as modern people and animals, answering a question that researchers have long wondered about how these ancient animals handled food.

The researchers reported in Tuesday's edition of Proceeding of the National Academy of Sciences that the study focused on scratch marks on hadrosaur teeth.

"For millions of years, until their extinction at the end of the Cretaceous, duckbilled dinosaurs "” or hadrosaurs "” were the world's dominant herbivores. They must have been able to break down their food somehow, but without the complex jaw joint of mammals they would not have been able to chew in the same way," paleontologist Mark Purnell of the University of Leicester in England said in a statement.

The scratch patterns on the hadrosaur teeth indicates that the movements of the teeth were complex, involving up and down, sideways and front to back motion.

A paleontologist at the Natural History Museum in London, Paul Barrett, said that the findings show how the dinosaur chewed in a completely different way than anything alive today.

The findings prove that they had a hinge between the upper jaws and the rest of the skull so that "when they bit down on their food the upper jaws were forced outwards, flexing along this hinge so that the tooth surfaces slid sideways across each other, grinding and shredding food in the process," he said in a statement.

Hadrosaurs are also known as duck-billed dinosaurs because of the similarity of their head compared to that of a modern duck.


Image 1: These are teeth from the lower jaw of a hadrosaur, Edmontosaurus, showing its multiple rows of leaf-shaped teeth. The worn, chewing surface of the teeth is towards the top. Credit: Vince Williams, University of Leicester

Image 2: This is a highly magnified Scanning Electron Microscope view of the surface of one of the hadrosaur teeth, showing the scratches created about 67 million years ago by tooth movements and feeding. The small black boxes show the areas, each less than half a millimeter wide.


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