Wednesday, 19 September 2012

A New Species Of Marine Reptiles

The fossil of Diandongosuchus fuyuanensis
250 million years ago, a large split occurred in the main group of reptiles. On one side were the ancestors of modern reptiles, dinosaurs and their avian descendants. On the other were the marine reptiles. As with almost all first members of a group, the early forms were small, lying close to the bottom of their respective food chains. They soon became more diverse, however, spreading out and occupying new ecological niches, growing larger to become, eventually, the dominant creatures in the Triassic oceans.

Earlier this year, a team of palaeontologists, led by Li Chun from the Institute of Vertebrate Palaeontology and Palaeoanthropology, uncovered the bones of a crocodile-like formation from the mid Triassic rocks of the Falang formation in the Yunnan Province of China. What is immediately striking about the fossil is how complete it is.

Most Triassic remains are fragmentary. This specimen, now named Diandongosuchus fuyuanensis, is almost complete with just a portion of the tale missing. As a result, constructing its lifestyle was relatively straight forward for the researchers. Its streamlined shape combined with the limestone and clay matrix showed that it was marine in nature. While the tail vertebra were missing, resulting in a preserved length of 97 centimeters, its nature as an ancient crocodile relative means that the tail occupied around 53% of the body.

The skull of Diandongosuchus fuyuanensis, showing
its distinctive patterns of grooves, ridges and pits
It is likely that the creature was 177 centimetres long. The final question was where, exactly, did it fit in the reptile family tree? Its overall shape and age narrowed down the field, but in the end, it was the ornamentation on its skull which pinned down its true nature. The pattern of pits, grooves and ridges showed that it was, in fact, more closely related to modern day crocodiles rather than other groups of ancient, extinct marine reptiles.

'These skull features suggest that Diandongosuchus might have had a lifestyle similar to phytosaurs or recent saltwater crocodiles, living near the water and adapted for an amphibious way of life. In addition, such a way of life for Diandongosuchus may be further inferred from its stomach contents which include fish remains,' added Dr. Xiao-Chun Wu from the Canadian Museum of Nature in Ottawa.

The ancient marine reptiles flourished for many more millions of years, but they would suffer a fall during the extinction event which marked the boundary between the Triassic and Jurassic periods. All groups were decimated except for the ancestors of the modern marine reptiles and the now extinct plesiosaurs. These would go on to create a new marine empire which would dominate the seas of the Jurassic and Cretaceous for over 150 million years.