An evolutionary puzzle has baffled palaeontologists for more than 180 years - the origins of Toxodon platensis and Macrauchenia patachonica, South American ungulates (hooved animals) described by Charles Darwin as the ‘strangest animals ever discovered’.

Previous attempts by scientists to pinpoint the origin of the animals using morphology-based and DNA analysis of fossils had failed but a new study presents evidence that the animals were related to mammals like horses, rather than elephants and other African species as some taxonomists have maintained.

The breakthrough happened when the researchers switched to analyzing collagen samples, a structural protein that can survive around ten times longer than DNA. The team screened 48 fossil bone samples of  Toxodon and Macrauchenia discovered in the 19th century in the same area as those recovered by Darwin. Charles Darwin collected fossils of the animals 180 years ago in Uruguay and Argentina during a stop-over on his famous journey on board The Beagle.

Toxodon and Macrauchenia disappeared around 10,000 years ago. The 1.5 ton rhinoceros-sized Toxodon was the most common large-hoofed mammal to roam South America during the Late Pliocene and Plesistocene period over 16,500 years ago. The more nimble Macrauchenia, or ‘long llama’ resembled a humpless camel – but with a short trunk-like snout. 

Toxodon platensis: illustration by Peter Schouten from the forthcoming book "Biggest, Fiercest, Strangest" W. Norton Publishers (in production).

The researchers produced sequences covering more than 90 percent of the collagen molecule, providing a phylogenetic family ‘tree’ for the two species, the first time the technique has produced molecular information based on protein sequences from the time of the last Ice Age, opening up the potential for further important evolutionary insights.

“People have been successful in retrieving collagen sequences from specimens dating up to four million years old and this is just the start,” said Professor Matthew Collins of BioArCh at University of York, who carried out the sequencing work with Professor Jane Thomas-Oates, director of York’s Centre of Excellence in Mass Spectrometry. “In theory, with material recovered from permafrost conditions, we might be able to reach back ten million years or more.”

Published in Nature. The research team also included York PhD student Frido Welker and Dr Jessica Thomas from the University’s Department of Biology. Source: University of York