Meat and veg: A model reconstructing how Heterodontosaurus may have looked in life.

Credit: NHM

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SYDNEY: The discovery of a skull of a baby fanged dinosaur may reveal a key transitional phase between meat-eating and plant-eating dinosaurs.

The tiny 4.5 cm-long skull of the species Heterodontosaurus is described in the latest issue of the Journal of Vertebrate Palaeontology.

"It's likely that all dinosaurs evolved from carnivorous ancestors," said Laura Porro, co-author of the study and a palaeontologist at the University of Chicago, USA. "Since heterodontosaurs are among the earliest dinosaurs adapted to eating plants, they may represent a transition phase between meat-eating ancestors and more sophisticated, fully-herbivorous descendents."

Omnivorous species

Prior to this study, there were only two known fossils of Heterodontosaurus, both of which are adults. Porro made the latest discovery by poking around in the collections of the Iziko South African Museum in Cape Town.

While searching through drawers of material excavated in the 1960s, she turned up two more specimens including the baby's skull.

The species is particularly unusual, said co-author Richard Butler, a palaeontologist with the Natural History Museum in London, England, because it has both fang-like canines at the front of the jaw and molar-like grinding teeth at the back of the jaw.

Experts had thought that Heterodontosaurus was an exclusive vegetarian, and males alone possessed the exaggerated canine teeth for display or defence. But the new skull "demonstrates that large canines were present very early in growth," said Butler, suggesting the fangs were more widespread in the species.

The palaeontologists now believe that the animals fed upon small vertebrates and insects in addition to vegetation.

Different toothed lizard

Using CT and X-ray images the research team were also able to compare the juvenile skull with the adult specimens, which has given them a better understanding of the how the animals developed.

Heterodontosaurus means 'different toothed lizard' and is one of the earliest-known dinosaurs. In life it would have been a small, bipedal species about the size of a turkey and is known from South African deposits dated to the Early Jurassic Period, 190 million years ago.

Butler said the discovery is important because it improves the picture we have of dinosaur biology and evolution: "Understanding the early evolution of dinosaurs is crucial to understanding why they became so successful, so large, and so diverse."

Robert Jones palaeontology collection manager at the Australian Museum, in Sydney, said the discovery has provided new insight into one of the most controversial dinosaur species. "It adds to the continuously growing body of knowledge gathered from often rare or poorly preserved fossils that accumulates over time as new material is discovered and described," he said.