'Although the bones of these animals had been studied for over 180 years, no clear picture of their origins had been reached.'
Prof Ian Barnes, molecular evolutionary biologist
Toxodon platensis was the last survivor of a huge group of South American ungulates, or hooved animals. Toxodon were a puzzling group of mammals that lived from 50 million to just ten thousand years ago. Charles Darwin collected the first known specimen of Toxodon on the Beagle voyage, and it was studied by the Museum's founder, Richard Owen, who described its odd combination of rodent-, hippo- and whale-like features. Darwin called them the ‘strangest animals ever discovered’, and until recently the origins of Toxodon and the other South American ungulates have remained a mystery.
Museum scientists were part of an international team who analysed 48 fossils of Toxodon platensis and Macrauchenia patachonica, another species whose remains Darwin collected 180 years ago when he visited Uruguay and Argentina on the Beagle voyage. The team began by looking for ancient DNA but this had not survived in the fossils. They instead studied collagen, a structural protein found in all animal bones that can survive for millions of years. Chemical structures inside the proteins can be compared between different species, revealing clues about how closely the species are related.
Although Toxodon most closely resembles a large hippo and the Macrauchenia a fat, long-legged camel with a trunk, the scientists determined that the closest living relatives of South America’s ungulates were the perissodactyls - the group that includes horses, rhinos and tapirs. This makes them part of Laurasiatheria, one of the major groups of mammals that have placentas.