|The 32.5 million year old jaw of Eoviscaccia frassnettii|
Yet a team of palaeontologists composed of scientists from the American Museum of Natural History, University of California, Santa Barbara and Case Western Reserve University have found the remains of two new species of rodents from 32.5 million year old rocks in the Tinguiririca River Valley in the Chilean Andes. One of the two (named Eoviscaccia frassinettii), after examination, is now believed to be the oldest chinchilla (a mouse-like creature) on Earth.
The second, named Andemys termasi which translates as 'the mouse of the Andes,' is the creature which hints at the ecological past of the region. The tiny rodent is the second oldest on the continent, the first being 41 million year old close relative from Peru. What is interesting is that the ancient relative had small crowns on its back teeth, indicating that it fed on soft food such as fruits. The younger Andemys had much larger crowns.
|The 32.5 million year old jaw of Andemys termasi|
This indicates that it fed on tougher foods. The specific pattern on the teeth showed that the staple of Andemys's diet was grass. What the change, coupled with the time difference, indicates is that the entire region experienced a massive ecological change from something (possibly forest or jungle based on fossils older than 32 million years) to open grass plains. 'The Tinguiririca chinchilla replicates a dental pattern appearing in many other South American herbivores such as Notoungulates—hooved animals that are now extinct—at that time.'
'The island continent of South America represented a land of evolutionary opportunity for the ancestors of chinchillas and other caviomorph rodents,' said co-author Darin Croft of Case Western Reserve University in Cleveland. 'These remarkable rodents came to fill an amazing variety of ecological niches and today are among the most characteristic Neotropical mammals.' This would all change 30 million years later when North and South America collided.