|The 100 million year old fossils of Cronopio dentiacutus.|
At the bottom an image of the sabre tooth attached to the jaw
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|
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.'