Thursday, 3 November 2011

The Sabre Toothed Squirrels Of South America

The 100 million year old fossils of Cronopio dentiacutus.
At the bottom an image of the sabre tooth attached to the jaw
The sabre toothed cats are, of course, most famous for their  long, sharp canine teeth. However there were once many other sabre toothed beasts which roamed our planet. Palaeontologists discovered the remains of a sabre toothed bandicoot in 2010. There have even been finds of sabre toothed carps. Now a new creature has joined the ranks of the long toothed predators. Anyone who has seen the film Ice Age will remember the sabre toothed and acorn-obsessed squirrel 'Scrat.'

Yet no such creature has been found in the fossil record....until now. In 2006, a team led by Dr Guillermo Rougier from the University of Louisville discovered a series of very fragile mammal skulls in a remote exposure of rock in the Patagonian desert, 100 miles north of the city of Allen in the Argentinian province of Rio Negro. As  mammal skulls are very fragile, they are very rare finds indeed and the team immediately knew that they had found something important.

An artist's impression of Cronopio dentiacutus
Once rock was removed from the incredibly delicate bones over several years, proper analysis could begin. It became clear that this creature, with its incredibly long canine teeth, was a completely new species. The team named it Cronopio dentiacutus. Besides being a completely new species, its age makes it very important. Radioactive dating gave it an age of around 100 million years old. This breaks a 60 million year gap in the mammalian fossil record of South America.

The two fossils, apart from shedding light upon the geneology of early Cretaceous, South American mammals and their relationship to the North American and European lineages, gave palaeontologists insight into the morphology of the dryolestids, the group of mammals which Cronopio is part of. The dryolestids are a group of rodent-like creatures that lived during the Jurassic, Cretaceous and Palaeogene periods and are closely related to the marsupials and placental mammals.

Previously, the only known evidence about these creatures was from tiny fragments of bone or the teeth covered in hard-wearing enamel. The skulls have provided a very complete picture of the cranial structure of Cronopio mammals, and subsequently, its lifestyle. The team believes that it was an insectivore, 4 to 5 inches in length, living on the lush floodplains of prehistoric South America alongside the dinosaurs over 100 million years ago.

The prospects for further investigation are exciting. 'In recent years it has become clear that southern continents hosted their own endemic groups of mammals during the Age of Dinosaurs. But until now, all we have had are isolated teeth and a few jaw fragments…which don't really help much in deciphering broader relationships,' said Rich Cifelli, Professor of Zoology at the University of Oklahoma, expert on the remains of ancient mammals.

'For this reason, the new fossils provide a sort of Rosetta Stone for understanding the genealogy of early South American mammals, and how they fit in with those known from northern landmasses. Now the burden is on the rest of us to find similarly well preserved fossils from elsewhere, so that the broader significance of Rougier's finds can be fully placed in a context. Cronopio lived in a completely different world than ours, dominated by dinosaurs and with a different geography; these new fossils give us information on how transient and ever-evolving our world is.'