Washington, Oct 24 : A team of scientists has discovered the fossilized skull of a tiny juvenile dinosaur, which may shed light on the evolution of plant eaters.
Discovered by a team of scientists from London, Cambridge and Chicago, the skull, which would have been only 45 millimeters (less than two inches) in length, belonged to a very young Heterodontosaurus, an early dinosaur.
This juvenile weighed about 200 grams, less than two sticks of butter.
The teeth suggest that Heterodontosaurus practiced occasional omnivory: the canines were used for defense or for adding small animals such as insects to a diet composed mainly of plants.
The researchers describe important findings from this skull that suggest how and when the ornithischians, the family of herbivorous dinosaurs that includes Heterodontosaurus, made the transition from eating meat to eating plants.
"It's likely that all dinosaurs evolved from carnivorous ancestors," said study co-author Laura Porro, a post-doctoral student at the University of Chicago.
"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," she added.
"This juvenile skull indicates that these dinosaurs were still in the midst of that transition," she further added.
Heterodontosaurus lived during the Early Jurassic period (about 190 million years ago) of South Africa. Adult Heterodontosaurs were turkey-sized animals, reaching just over three feet in length and weighing around five to six pounds.
"This discovery is important because for the first time we can examine how Heterodontosaurus changed as it grew," said the study's lead author, Richard Butler of the Natural History Museum, in London.
"The juvenile Heterodontosaurus 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," he added.
This bizarre suite of teeth has led to debate over what heterodontosaurs ate.
Porro and colleagues found that the juvenile already had a fully-developed set of canines.
"The fact that canines are present at such an early stage of growth strongly suggests that this is not a sexually dimorphic character because such characters tend to appear later in life," said Butler.
Instead, the researchers suspect that the canines were used as defensive weapons against predators, or for adding occasional small animals such as insects, small mammals and reptiles to a diet composed mainly of plants - what the authors refers to as "occasional omnivory."
The researchers found out that Heterodontosaurus was more similar to mammals, not only in the specialized, variable shape of its teeth, but also in replacing its teeth slowly, if at all, and developing tight tooth-to-tooth contact.
"Tooth replacement must have occurred during growth," the authors concluded.