Health and Science Story

04 July 2009 06:47 BST

Tiny dino skull reveals evolution secrets

One of the smallest dinosaur skulls ever found is shedding new light on the evolution of plant-eaters.

A team of scientists from London, Cambridge and Chicago have concluded the skull, which would have been just 45mm in length, reveals information about the transition phase between earlier carnivores and the herbivores which developed later.

"This discovery is important because for the first time we can examine how Heterodontosaurus changed as it grew," the study's lead author, Richard Butler of the Natural History Museum said in the Journal of Vertebrate Paleontology.

"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."

The team's attention was attracted by the unusual combination of teeth of the very young Heterodontosaurus.

Its large fang-like canines at the front of their jaws and worn molar-like grinding teeth at the back contrasted with most reptiles, which changed little in shape along the length of the jaw.

The study's co-authors dismissed the theory that the canines are sexually dimorphic, which involves them being used as weapons in disputes with males over mates and territories, because the canines were not present at the early stage of growth.

This "strongly suggests that this is not a sexually dimorphic character because such characters tend to appear later in life," Dr Butler said.

Instead it is believed 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.

This characteristic is described as "occasional omnivory" and provides a crucial bridging point between the early carnivores and later evolution of herbivores.