While the Galápagos finches are the most well-known part of Charles Darwin's voyage on the Beagle in the 1830s, the soon-to-be scientific icon was able to delight in other natural wonders during his trip around South America.
It was in Argentina and Uruguay where he would meet his match: the fossils of "neoungulates" that were such a morphological hodge-podge that they didn't have a home on the evolutionary tree until recently.
During his travels in Uruguay, Darwin was able to meet up with a person who had a fossilized Toxodon skeleton and purchased the skull for 18 pence (roughly 9 bucks today). This is how he described the complete skeleton:
Toxodon [is] perhaps one of the strangest animals ever discovered. In size it equalled an elephant or megatherium; but the structure of the teeth, as Mr. Owen states, provides indisputably that it was intimately related to the Gnawers, the order which at the present day includes most of the smaller quadrupeds. In many details it is allied to the Pachydermata. Judging from the position of its eyes, ears, and nostrils, it was probably aquatic, like the dugong and manatee, to which it is also allied. How wonderfully are the different orders, at the present time so well separated, blended together in different points of the structure of the toxodon!
Darwin had a similar reaction in the Patagonian region of Argentina when he found fossils of Macrauchenia, a tall quadruped with the body structure of a humpless camel and the face of a tapir.
Evolutionary biologists were stuck trying to place these chimeric animals on the tree of life since they share so many traits with other groups, but a collaboration between natural history museums in the U.S. and U.K. was able to give them a rough home using protein analysis. DNA degrades very quickly, especially in warmer climates like that of South America, but proteins, which are coded by the genetic material, last much longer, allowing researchers to work with older specimens.
In the end, Darwin's strangest animal, Toxodon, and its neighbor Macrauchenia are most closely related to horses and rhinos, but more research needs to be done before they get a permanent address on the evolutionary tree.
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