Duck-billed dinosaurs had unique chew

30 June 2009

The duck-billed dinosaurs, called hadrosaurs, could chew in a very unusual way, scientists announce in the Proceedings of the National Academy of Sciences (PNAS) today.

As the dominant herbivores on Earth for millions of years, this major group of dinosaurs were obviously successful

Highly magnified Scanning Electron Microscope view of the surface of one of the hadrosaur teeth

Highly magnified scanning electron microscope view of surface of one of the hadrosaur teeth. The scratches are inside the boxes, which are less than 0.5mm in width. © Vince Williams, University of Leicester

However, they did not have the complex jaw joint found in mammals and so scientists had wondered how they ate, until now.

Scientists, led by palaeontologist Mark Purnell of the University of Leicester, and including those from the Natural History Museum, discovered hadrosaurs had a unique way of eating, unlike any other creature alive.

Examining scratches

They examined tiny scratches on 67-million-year-old fossil teeth of an Edmontosaurus, a specimen from the Natural History Museum.

The scratches were preserved from the time the dinosaur died and they reveal the movements the teeth made while the animal was eating and the type of food it most likely ate.

A different chew

The results showed the teeth movements were complex and involved up and down, sideways and front to back motion. Natural History Museum dinosaur fossil expert Paul Barrett explains.

Teeth from the lower jaw of a hadrosaur, Edmontosaurus, showing its multiple rows of leaf-shaped tee

Teeth from the lower jaw of a hadrosaur showing its multiple rows of leaf-shaped teeth. The worn, chewing surface of the teeth is towards the top. © Vince Williams, University of Leicester

‘The results show that hadrosaurs did chew, but in a completely different way to anything alive today. Rather than a flexible lower jaw joint, they had a hinge between the upper jaws and the rest of the skull.'

'As 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.’

‘The lower jaws could also be moved back and forth, giving a second grinding action.’

Highly magnified scans

The team used a new approach to analyse the teeth. The specimens were moulded and coated with gold and then examined using a scanning electron microscope. 

The result was a set of highly magnified images of the teeth surfaces, revealing the details of the minute scratches.

What they ate

The research also sheds light on what the dinosaurs ate. Vince Williams of the University of Leicester says, ‘Although the first grasses had evolved by the Late Cretaceous they were not common and it is most unlikely that grasses formed a major component of hadrosaur diets.’

‘We can tell from the scratches that the hadrosaur’s food either contained small particles of grit, normal for vegetation cropped close to the ground, or, like grass, contained microscopic granules of silica.' 

'We know that horsetails were a common plant at the time and have this characteristic; they may well have been an important food for hadrosaurs.’

Great from small

As well as giving clues to the life of the hadrosaurs and helping understand more about the ecosystems of the Late Cretaceous, this study also shows how such a large amount of information can be gained from such a tiny specimen. 

Williams concludes, ’By looking at the pattern of scratches in an area that is only about as wide as a couple of human hairs we can work out how and what these huge herbivores were eating.’

‘And because we can analyse single teeth, rather than whole skeletons, the technique has the potential to tell us a lot more about dinosaur feeding and the ecosystems in which they lived.’

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