The mystery of the strangest animals ever discovered solved
When Darwin first visited South America in the 1830, he collected some fossils of what he called the strangest animal ever discovered. The animals were classified as Macrauchenia that looked like a humpless camel with a long snout and Toxodon, with a rhino’s body, hippo’s head and rodent-like teeth. It is not clear if these animals have one origin or several, appeared before or after the Cretaceous/Palaeogene transition (66.2 millions years ago); or, as previous researches suggested, are more likely to belong to the supraorder Afrotheria (along with elephants and aardvarks). No one has been able to find out where the bizarre animals fit in the mammalian phylogenetic tree.
The confusion of their ancestry and origin is in part due to the fragmentary fossil record, and also because researchers have not been able to isolate DNA from the South America ungulates fossils; the DNA degrades quickly due to the warm and humid climate of that continent.
Recently scientists from the UK have published a paper in Nature solving the mystery. First, the researchers have extracted and sequenced the collagen from the bones from tapirs and hippos to build up a collagen family tree. This protein survives ten times longer than DNA and is a main component of the bones. Then, the team have analysed the ancient collagen protein from the 12 000 years old fossils: from Toxodon platensis and Macracuehnia patachonia.The analyses have revealed that Toxodon and Macrauchenia form a monophyletic group closely related to Perissodactyla, a group that includes horses, tapirs and rhinos.
The research findings support a theory that the ancestors of these South American ungulates came from North America more than 60 millions years ago, probably just after the mass extinction that killed off non avian dinosaurs and many other vertebrates.
Left picture: Macrauchenia patachonica
Right picture: Toxodon
Welker, F., et al. 2015. Ancient proteins resolve the evolutionary history of Darwin’s South American ungulates. Nature, http://dx.doi.org/10.1038/nature14249.
Cover photo: nature
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