Thursday, 22 December 2011

On The Evolutionary History Of The Dicynodonts

The Tasmanian fossil dicynodont tusk
The dicynodonts were perhaps the most succesful pre-dinosaur reptiles to walk the Earth. While not top predators or even carnivores, they dominated the Permian landscape. The group was first named in 1859 by the British palaeontologist Sir Richard Owen. Since then, over 70 different genera have been described. The very fact that fossils from many different species have been found across the world has contributed to our view of the dicynodonts as dominant.

Yet there was a geographical problem with this: the only known Australian specimen was a single fragment of bone discovered 30 years ago in Queensland. If the dicynodonts were a global group, then why was there an extreme lack of evidence for their existence in Australia? The discovery of a single tusk from the island of Tasmania, now gives the dicynodont a geographical range of over 2000 kilometres down the east cost of the southern continent.

An artist's impression of the Tasmanian dicynodont,
a cow sized animal which roamed the Triassic deserts
of Pangaea
Bob and Penny Tyson, two amateur palaeontologists, were taking a walk along a beach on the Tasman peninsula when they discovered a series of rare amphibian skulls, and the aforementioned tusk buried under a clump of seaweed. 'It was sitting on top of the rock surface, so all the surrounding rock had been worn away. It was just sitting there waiting to be knocked off.'

The fossils were taken to the University of Tasmania for analysis. Where sedimentologist, Professor Stuart Ball, found that they predated the first dinosaurs by around 20 million years, making them a late Triassic species. It seems that the dicynodonts survived in Australia far longer than anywhere else on Earth, even out-running the Permian extinction itself. Ball believes that floods may have washed the remains of the dicynodonts into billabongs - large ponds of water - which would account for the apparent lack of fossils.