Thursday, 2 February 2012

The New Oldest Ancestor Of All Modern Alligators And Crocodiles

The snout of Aegisuchus witmeri
A few months ago, I reported on the discovery of a new species of crocodile which was believed to be the oldest crocodilian on Earth. It was named Stomatosuchus. Its most prominent feature was a thick plate of bone, muscle and nerve endings on its snout which led to its nickname 'shield croc.'

A few years ago, a team of palaeontologists, excavating at a fossiliferous formation in the country found some mysterious reptile remains. They were put into storage in the vaults at the Royal Ontario Museum of Toronto, until researchers, led by Professor Casey Holliday from the University of Missouri, analysed the bones. Their findings revealed that the 95 million year old bones were from a shield croc. The earliest ancestor of all modern crocodiles and alligators.

They named it Aegisuchus witmeri. Further analysis of its 'shield' revealed the presence of tiny dents and tubes which would have delivered blood to the tissues. Such a structure is unknown in modern crocodilians, but its similarity to the large sails of the Permian Dimetrodon or even the Cretaceous Spinosaurus, led the team to believe that the structure was used in mating rituals and as a biological thermostat, regulating the creature's body temperature.

Unusually, the jaws were very long but quite weak, suggesting that it was in fact an ambush predator; and on the basis of skull to body length ratio, would have been around 10 metres. 'We believe shield croc may have used its long face as a fish trap,' said Nick Gardner, an undergraduate researcher at Marshall University, who collaborated with Holliday on the study. 'It is possible that it lay in wait for any unsuspecting fish which swam in front of it.'

'Then, if it was close enough, shield croc simply opened its mouth and ate the fish without a struggle, eliminating the need for strong jaws.' Its morphological similarities to Stomatosuchus, but superior age formed the basis for Holliday's argument that Aegisuchus is the oldest ancestor of the crocodilians. The shield croc fossil studied by Holliday and Gardner is being returned to the Royal Ontario Museum, where it will be put on display later in the year.