Exploring the relationship between Litopterns and Perissodactyls
[sciencythoughts.blogspot.com]
The Mammalian group Litopterna was coined by Florentino Ameghino in 1889, as a Suborder of the Perissodactyla, with the aim to include the aberrant Macrauchenia and its kin. Ameghino recognized affinities with the Laurasian clade Perissodactyla, a hypothesis sustained by some old workers. This idea was posteriorly criticised and refuted, and it was proposed that the similarities between Litopterns and Perissodactyls were acquired by convergence. In the same line of thought, together with Xenarthrans and Marsupials, South American native Ungulates were considered by George Gaylord Simpson. as comprising the 'Ancient Immigrants' Faunistic Stratum, coming from North America through a intercontinental bridge. Since then, the Litopterna weas regarded as an endemic clade exclusive of South America, with uncertain affinities to other Mammalian lineages. In line with Simpson proposal, most authors indicate that Litopterns were the descendants of 'ancient Ungulates' arriving at South America from North America by a land connection at the Latest Cretaceous–Early Paleocene. However eecent phylogenetic analysis based on protein spectrometry and DNA analyses resulted in the referral of Litopterna to Perissodactyla, in agreement with nineteenth century authors.