The oldest rodent fossils yet found in South America have been unearthed along the Ucayali River near Contamana, Peru.
The specimens comprise the tiny teeth of mouse-sized and rat-sized animals that lived at least 41 million years ago.
This makes the fossils some 10 million years older than all previous rodent discoveries made on the continent.
An international team of scientists reports the remains in the Royal Society journal Proceedings B.
The researchers describe how the shape of the teeth and other factors point to the ancient animals being most closely related to African rodents.
"As palaeontologists, we're interested in how animals are related to each other, and we do what are called 'phylogenetic analyses'," explained co-author Darin Croft, an anatomy professor at Case Western Reserve University School of Medicine, Cleveland, US.
"We did those analyses for our animals and they are very close in the evolutionary tree to African rodents, which suggests that that's where their ancestors came from - from Africa," he told BBC News.
Tiny teeth
Dr Croft and colleagues had to use microscopes to study the teeth, so small were some of them.
Features seen in the dentition suggest the animals probably ate soft seeds and plant parts, just like many small rodents do today.
Read on...
By Jonathan Amos Science correspondent, BBC News
http://www.bbc.co.uk/news/science-environment-15268643
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