Monday 23 January 2012

The fore-limbs of Majungasaurus.

Majungasaurus crenatissimus was a species of Abelisaurid Therapod Dinosaur, native to Madagascar in the Late Cretaceous (70 to 65.5 million years ago). The first partial specimens was first discovered in 1896 by a French army officer and recorded by the French palaeontologist Charles Depéret, since when numerous partial skeletons have been found and a good picture of the overall animal built up. The species was formally described by another French palaeontologist, René Lavocat, in 1955.

The Abelisaurs were an unusual group of therapods known from South America, Africa, Madagascar, India and Southern Europe. They were typically large animals, with short, wide skulls with elaborate ornamentation. In this Majungasaurus was typical, with a length of 6-7 meters, and an average weight in excess of 1100 kg. It had a short snout for such a large animal, with a skull length of 60-70 cm in adult individuals, and exceptionally wide, even for an Abelisaur. In addition it had fused nasal bones that formed a ridge on its snout, and fused frontal bones that formed a dome shaped horn on the top of its skull; it has been suggested that these might have been further enlarged by keratin sheaths.

Prior to now the fore-limbs have only been described from two Abelisaurs, Carnotasaurus sastrei and Aucasaurus garridoi, both South American species known only from single specimens. In both these species the fore-limbs were highly reduced, leading to speculation that this might be the case in all Abelisaurs, but there has been no evidence from outside South America to confirm or deny this.

The January edition of the Journal of Vertebrate Paleontology contains a paper by Sara Burch of the Department of Anatomical Sciences at Stoney Brook University and Matthew Carrano of the Department of Paleobiology at the Smithsonian Institution describing for the first time the forelimbs of Majungasaurus crenatissimus. As with the South American Albelisaurs these were notably reduced on the Therapod norm, more so than was the case even in the famous Tyranosaurus rex, causing Burch and Carrano to speculate that the limb may have been enclosed in some sort of flipper, though what the use of a small flipper to such a large (and apparently terrestrial) animal was it is hard to say.

Reconstruction of the fore-limb and scapulocoracoid of Majungasaurus. From Burch and Carrano (2012).