Australasian Science Magazine

By Stephen Luntz

The ankle bone of an Australian ceratosaur has been found near San Remo on Victoria’s east coast, placing the major group of carnivorous dinosaurs on this continent for the first time.

“Until now, this group of dinosaurs has been strangely absent from Australia, but now at last we know they were here – confirming their global distribution,” says Dr Erich Fitzgerald, a palaeontologist at Museum Victoria.

The exact species of ceratosaur is unknown, although Fitzgerald says it was not a member of the genus Ceratosaurus, from which the group gets its name. “Unfortunately from relatively fragmentary parts of the skeleton we can’t identify the species, although we think it was potentially from the family of abelisauroids.”

The Abelisauridae flourished in the southern hemisphere, but Australia’s poorly studied dinosaur record had previously shown no sign of them, nor other ceratosaurs.

The fossil is recognisably a ceratosaur due to a distinctive ridge of bone and the fusion of two bones that are separate in most other predatory dinosaurs. Fitzgerald says the evolutionary pressures that caused ceratosaurs’ fused tarsis is unknown.

Mike Cleeland, who Fitzgerald describes as a “very talented amateur”, made the discovery. Cleeland has found many fossils where others see nothing, and was investigating the area as part of an ongoing Museum of Victoria project studying Victoria’s coastal rocks.

The individual in question would have been up to 2 metres high, but Fitzgerald considers 1–1.5 metres more likely. It could also have been up to 3.5 metres long and weigh about as much as an adult human.

Ceratosaur fossils have sharp needle-like teeth that weren’t suited to tearing chunks off large herbivores or biting through bone. Consequently, the Museum’s artist has drawn the individual from which the fossil came capturing a juvenile (see above), but Fitzgerald says we can only speculate on this species’ diet.

The bone is dated to around 125 million years ago, when Australia’s southern coastline would have been near the Antarctic Circle. “There was probably seasonal snow cover, but the world was much warmer then, and crocodiles, lungfish and turtles have been found in nearby rocks of the same age,” Fitzgerald says.

“At the time, Australia was almost bisected by an inland sea where the Great Artesian Basin now lies, so there were probably close ceratosaur relatives living down the eastern side.” Fitzgerald is less certain whether Western Australia would also have hosted the predators.