вторник, 26 января 2016 г.

Ozraptor

Ozraptor ("Australian thief") is an abelisauroid theropod dinosaur from the Middle Jurassic (Bajocian) Colalura Sandstoneof Australia. Ozraptor was a medium-sized theropod with a length about 7 m, a weight of 400 kg and a height of 2.5 m


In 1967 a group of four twelve-year-old Scotch College schoolboys found a fossil at the Bringo Railway Cutting site near Geraldton, which they showed to Professor Rex Prider of the University of Western Australia. He had a cast made that he sent to experts of the British Museum of Natural History in London who thought it likely belonged to an extinct turtle. Re-evaluation of the bone in the nineties after being prepared out of the rock by John Albert Long and Ralph Molnar showed that it actually was the shinbone of some sort of theropod.

In 1998 Long and Molnar named and described the type (and only) species Ozraptor subotaii. The generic name is derived from "Ozzies", the nickname for Australians, and a Latin raptor, "seizer". The specific name honours a fictional character, the swift-running thief and archer "Subotai" from the movie Conan the Barbarian.

The holotype, UWA 82469, was found from layers of the Colalura Sandstone Formation, dating to the middle Bajocian, about 170 million years old. It consists of the distal or lower end of a left tibia. Together with Rhoetosaurus, Ozraptor belongs to the oldest known Australian dinosaurs.

The specimen is eight centimetres long and four centimetres wide at the lower end. From this a total length for the shinbone was estimated of about seventeen to twenty centimetres and for the animal as a whole of about two metres. Three diagnostic features were established enabling it to be upheld as a distinct species of dinosaur: the ascending process of the astragalus had a rectangular shape with a straight upper end; the astragalar facet had a vertical ridge; the medial condyle was weakly developed.

Only known from one partial leg bone, Ozraptor is difficult to classify. In 1998 the describers could not more precisely determine the classification than a Theropoda incertae sedis. In 2004 Thomas Holtz thought it was a member of the Avetheropoda. In 2005 another study, by Oliver Rauhut, suggested that it was indeed a theropod, and more specifically, a member of the Abelisauroidea based on the presence of the distinct vertical median ridge on the astragalar groove. If so, it would be the oldest known abelisauroid.

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