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Evolution: Placing Darwin’s “strangest animals” in the tree of life

Nature Communications

June 28, 2017

The nearly complete mitochondrial genome of the extinct South American native ungulate Macrauchenia patachonica is reported in Nature Communications this week. The ancient DNA provides new insights into the evolutionary relationships of an animal group that has puzzled biologists since their fossils were first discovered by Charles Darwin.

The South American native ungulates have no surviving descendants and their unusual combinations of traits - such as the camel-like body and tapir-like snout of Macrauchenia - defy classic methods of taxonomic classification. Previously, protein sequences from ancient collagen have provided the best idea of how these perplexing species are related to living mammals. Attempts to use ancient DNA to understand more about the evolutionary history of these unusual animals have been hampered by DNA degradation and a lack of reference genome from close relatives.

Michael Hofreiter and colleagues overcome these issues by using new sequencing and mapping techniques to assemble the mitochondrial genome from ancient DNA collected from Macrauchenia fossil samples. They then used the DNA sequences in phylogenetic analyses to assess the evolutionary relationships of these animals, which strengthen previous proteomic evidence that Litopterna (including Macrauchenia) is the sister group to Perissodactyla (horses, tapirs, and rhinoceroses) and reveal that these groups diverged approximately 66 million years ago.

The study demonstrates how ancient genomes can be reconstructed even without reference genomes from living relatives. However, additional studies will be needed to elucidate the evolutionary relationships of other South American native ungulate groups.

doi: 10.1038/ncomms15951

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