Darwin's strangest animals have now been placed in the biological family tree, after more than 180 years of disagreement over their relationships to other species.
One of the creatures, in the genus Toxodon, has the body of a rhinoceros and the head of a hippopotamus. Macrauchenia, the other of Darwin's strangest animals, was similar to a horse, with an exceptionally long snout similar to that of anteaters. This new study concluded that these species are descended from condylarths, and ancient group of mammals related to perissodactyls, including horses, rhinoceros and tapirs.
The Toxodon fossil was purchased by pioneering naturalist Charles Darwin during his famous voyage aboard the H.M.S. Beagle. These artifacts were previously owned by a rancher living in Uruguay. Macrauchenia was first unearthed by Darwin in southern Patagonia.
Darwin "soon recognized that these gigantic mammals might provide clues to his understanding of species formation. As he looked at other living mammals, he felt that they were related to those, but they were much smaller. And he wondered how that could have happened," Duncan Porter of Virginia Tech said.
The co-founder of the theory of evolution had little idea how to classify the animals. He thought Toxodons were related to rhinos or hippos, or even armadillos. Since that time, biologists have debated how to place the ungulates (hoofed animals) into the family tree of life. Theories have placed the species into groups that include elephants, aardvarks, manatees and a wide range of other creatures.
The 48 fossil samples examined in the study were estimated to be around 12,000 years old, using radio carbon dating.
Collagen within the fossils was examined in an effort to identify information about protein sequences from the animals. The protein fragments were precisely weighed, in order to measure the composition of amino acids in the sample. This data was then compared to known amino acid patterns in other animals in order to identify related species. These two unusual species likely branched off from horses about 55 million years ago, researchers concluded.
Typically, DNA is destroyed over a period of time, preventing investigators from extracting genetic information from fossils. However, collagen is better able to preserve genetic information than most other components of bodies, and data was collected from five of the 45 samples tested in the study. This technique is able to extract genetic records from fossils up to four million years old. Future development could extent that limit up to 10 million years.
Analysis of the genetic structure of Darwin's strangest animals and their placement on the tree of life was detailed in the journal Nature.
Photo: Ashley Basil | Flickr
