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Heterodontosaurus skull. Natural History Museum

A tiny dinosaur skull with an unusual set of teeth has been identified by a team of scientists from London, Cambridge and Chicago, writes Sarah Day. 

Geoscientist Online 24 October 2008

At just 45 millimetres long, the skull is one of the smallest ever discovered, and has been identified as a baby Heterodontosaurus, one of the earliest dinosaurs known to have existed on Earth. The discovery has allowed scientists to solve one of the mysteries surrounding the species – its unusual combination of teeth.

While most reptiles have teeth that are the same size all the way along their jaws, Heterodontosaurus has fang-like canines at the front of its jaw, and worn, molar-like grinding teeth at the back. These have been the cause of debate between scientists about what the dinosaur’s diet might have been.

So far, researchers had thought that the canine teeth were possessed only by adult males, used in fighting for territory or females. However, the discovery of the canines in a baby Heterodontosaurus suggests the teeth may have had other functions.

The team, led by Dr Richard Butler, a palaeontologist at the Natural History Museum, London, publish their research in the latest issue of the Journal of Vertebrate Palaeontology.

copyright Society of Vertebrate Paleontology
Reconstruction Herterodontosaurus model, Copyright NHM Butler says "the fact that the skull of such a young Heterodontosaurus has a fully developed set of canines suggests they were not restricted to males and used for fighting for territory or females, but instead were probably present in both sexes and may just have been used for eating or defence."

The skull, which Butler and his colleagues examined using X-ray technology and CT scanning, is also the first to give an insight into how one of the first dinosaurs on Earth matured into adulthood.

"This discovery is important because for the first time we can examine how Heterodontosaurus changed as it grew" says Butler. "The juvenile dinosaurs of this type had relatively large eyes and a short snout when compared to an adult – similar to the differences we see between puppies and fully grown dogs."

Heterodontosaurus means 'different-toothed lizard'. The species lived during the Early Jurassic Period, around 190 million years ago, in a part of Gondwanaland that is now South Africa. There are only two known fossils, both from South Africa - so the find is an important one in adding to our relatively small amount of knowledge about the species and its relatives.

Butler’s co-author is Laura Porro, a postdoctoral student at the University of Chicago. "I didn’t recognise it as a dinosaur at first’ she says, ‘but when I turned it over and saw the eye looking straight at me, I knew exactly what it was."