Tuesday, 17 July 2012

A very important ankle!

It came to my attention today that there has been a wonderful discovery right on our doorstep. In October 2006 a lump of fossilised dinosaur bone was discovered at San Remo, 87km southeast of Melbourne. It turned out to be the calcaneous (heel bone) connected to part of the astralgus (also known as the Talus or ankle bone) of a carnivorous dinosaur from the ceratosaur group. The bone is named the astragalocalcaneum, due to the fact the bones, which are normally separate, are fused in ceratosaurs. This means the fossil is recognisably a ceratosaur. Because only the one bone fragment was found it has been impossible to identify the exact species, although scientists think it may have been from the family of abelisauroids (for more info see abelisaurid on wiki.)
The ceratosaur specimen is particularly important due to the fact that it is the first one to be found in Australia. Australia now has evidence for five major theropod groups in the Early Cretaceous; Ceratosauria, Spinosauridae, Carcharodontosauria, Tyrannosauroidea, Deinonychosauria and Avialae. Theropods gave rise to modern birds.
The bone was found in a deposit known as the Wonthaggi Formation which dates at around 121-125 Million years old, in a time within the Early Cretaceous known as the Aptian. During the time the ceratosaur lived Australia (which was part of the bigger Gondwana) was virtually cut in two by an inland sea, so there may have been ceratosaur relatives living all down the eastern side. There was likely seasonal snow in the region, however, the world was much warmer at that time and the fossils of lungfish, turtles and crocodiles have been found in nearby rocks of the same age. Ceratosaurs have very pointy 'needle-like' teeth, and currently there is only speculation on their diet.
If you would like to read the more technical aspects of this find, it was recently published in Naturwissenshaften: The Science of Nature. There were also articles published by the ABC found here, by Australian Geographic here and in the July/August issue of Australasian Science magazine (Volume 33, Number 6), reporting the find.
The original paper can be found online in PDF format here.

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