Origin of the 'strangest animals ever discovered' revealed: New protein analysis solves Darwinian mystery of South American mammals
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Charles Darwin himself described them as the 'strangest animals ever discovered' and was baffled as to how they could have evolved.
Now scientists have unraveled a 180 year old mystery of the evolutionary origins of South America's hooved mammals that died out 10,000 years ago.
The continents native ungulates - hooved animals - have baffled palaeontologists as they share traits with rodents, elephants and camels.
The four-legged Macrauchenia patachonica, shown in the artists impression above, has baffled scientists since fossils of the species, which died out around 10,000 years ago, were found by Charles Darwin 180 years ago
But now by analysing the proteins preserved in fossilised bones, scientists have been able to show that the animals are more closely related to modern horses.
The technique they used also promises to reveal new information about other long-extinct fossilised species.
Unlike DNA, proteins can be better preserved within fossilised remains.
The scientists say it could allow them to look back in time 10 times farther than current techniques using ancient DNA.
Dr Ross MacPhee, a curator at the American Museum of Natural History's department of mammalogy and one of the authors of the study, said: 'Fitting South American ungulates to the mammalian family tree has always been a major challenge for palaeontologists, because anatomically they were these weird mosaics, exhibiting features found in a huge variety of quite unrelated species living all over the place
'This is what puzzled Darwin and his collaborator Richard Owen so much in the early 19th century.
'With all of these conflicting signals, they couldn't say whether these ungulates were related to giant rodents, or elephants, or camels—or what have you.'
The researchers, whose work is published in the journal Nature, began their study by attempting to extract DNA from the fossilised bones of ungulate fossils found in South America.
However, DNA breaks down quickly in the warm wet conditions found in tropical areas that cover much of South America.
Instead the researchers began to look at analysing the sequence of a structural protein called collagen that is found in all animal bones.
Collagen can survive more more than a million years in a range of conditions and is made up from amino acids.
The sequence of these amino acids is ultimately determined by the DNA code of the animal and so can be used to draw conclusions about the species origins.
The researchers screened 48 fossils of Toxodon plantensis and Macrauchenia patachonica - the same species that Darwin discovered the remains of in Uraguay and Argentina 180 years ago.
Dr Ian Barnes, a molecular evolutionary biologist at the Natural History Museum in London who led the research, said: 'Although the bones of these animals had been studied for over 180 years, no clear picture of their origins had been reached.'
The photograph above shows the skull of a Toxodon plantensis kept at the Natural History Museum in London
Charles Darwin (right) was baffled by fossils of the Toxodon (shown in the illustration on the right) when he first discovered it and scientists have struggled ever since to work out where it sits in the evolutionary tree
The modern technique, known as proteomics, allowed the researchers to show that the closest living relatives of these species were perissodactyls - the group that includes horses, rhinos and tapirs.
This suggests the strange South American animals migrated into the continent from North America around 60 million years ago just after a mass extinction killed off many of the non-avian dinosaurs.
The researchers now believe their technique could help to revolutionise palaeotological research by allowing scientists to reach far further back in time than they have been able to with DNA analysis.
Frido Welker, the lead author of the study at the Max Planck Institute for Evolutionary Anthropology and the University of York, said: 'By selecting only the very best preserved bone specimens and with various improvements in proteomic analysis, we were able to obtain roughly 90 percent of the collagen sequence for both species.
'This opens the way for various other applications in paleontology and paleoanthropology, which we are currently exploring.'
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