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CHICAGO - A RARE juvenile skull of a 190 million-year-old dinosaur may help explain when an important group of plant eaters branched off from carnivorous cousins, US and British researchers said on Thursday.
The tiny skull belonged to a young Heterodontosaurus. Its tooth structure - sharp canine teeth for biting and tearing and flat grinding teeth - suggest the tiny creature was evolving from a meat eater to a plant eater, the scientists said.
'This juvenile skull indicates that these dinosaurs were still in the midst of that transition,' said Dr Laura Porro, a post-doctoral student at the University of Chicago, who described the skull in the Journal of Vertebrate Paleontology.
Dr Porro came across the skull in a drawer in the Iziko South African Museum in Cape Town, South Africa, while researching the eating habits of adults of this type of dinosaur, which belonged to the herbivore order ornithischians that lived during the Early Jurassic period of South Africa.
It was dug up in the 1960s but never identified.
Heterodontosaurus had an unusual combination of teeth, with large fang-like canines at the front of their jaws and worn, molar-like grinding teeth at the back.
Dr Porro said paleontologists had thought the canines were sexually dimorphic - a characteristic present only in adults of one gender in a species like antlers in male deer.
But the presence of long, serrated canines in the juvenile suggest they were common to both genders, Dr Porro said.
'They have these really long canine teeth, which don't look like the teeth of a plant eater,' Dr Porro, who worked with scientists from the Natural History Museum in London, said in a telephone interview.
'They almost look like little saber-toothed tiger teeth.'
The first dinosaurs appeared about 230 million years ago, and the earliest known ones were meat eaters.
There were other plant-eating dinosaurs at the time of Heterodontosaurus including the long-necked sauropods. But this little creature was one of the earliest of the ornithischians that soon become very important in the Age of Dinosaurs.
Later ornithischians included the duck-billed dinosaurs, horned dinosaurs such as Triceratops and tank-like dinosaurs such as Ankylosaurus.
While adult Heterodontosaurus were turkey-sized creatures that reached just over 1 metre in length and weighed about 2.5 kilogrammes, the juvenile likely weighed less than 200 grammes and would have been just about 40 to 45 centimetres long.
The find also offers a rare chance to compare a young dinosaur to adults in the species. Dr Porro said the eyes in the juvenile skull are much bigger, and the nose is much shorter.
'It's the same things that makes puppies and kittens appealing,' she said. 'I think it's adorable.'
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