|Macrauchenia - an extinct South American native ungulate|
Drawn by Kobrina Olga (Wikimedia Commons CC BY 3.0)
The authors used MALDI-TOF mass spectrometry to determine the amino acid sequences of the alpha chains of type I collagen extracted from fossil bones. They then performed a phylogenetic analysis. This showed that Macrauchenia and Toxodon form a monophyletic group. Interestingly, this resolved as the sister group to modern Perissodactyla, i.e. horses, tapirs and rhinoceroses. Together they form a taxon named Panperissodactyla.
The modern species have an epitheliochorial placenta so perhaps this type was present in the sister species Macrauchenia and Toxodon.