Phylogenetic tree of Litopterna and Perissodactyla indicates a complex early history of hoofed mammals

Nicolás R Chimento,Federico L Agnolin

doi:10.1038/s41598-020-70287-5

Abstract

The Litopterna is an extinct clade of endemic South American ungulates that range from Paleocene up to late Pleistocene times. Because of their unique anatomy, litopterns are of uncertain phylogenetic affinities. However, some nineteenth century authors, considered litopterns as related to perissodactyl ungulates, a hypothesis recently sustained by molecular data. The aim of the present contribution is to include litopterns and other South American related taxa in a comprehensive phylogenetic analysis together with several extant and extinct basal perissodactyl ungulates. The analysis resulted in the nesting of litopterns and kin as successive stem-clades of crown Perissodactyla. Further, litopterns are not phylogenetically grouped with any North American basal ungulate, in agreement with some previous proposals. Presence of pan-perissodactyls in South America and India indicates that southern continents probably played an important role in the early evolution of hoofed mammals.

Highlights

The Litopterna is an extinct clade of endemic South American ungulates that range from Paleocene up to late Pleistocene times
Phylogenetic analysis here performed is congruent with recent claims, based on molecular evidence, in which Litopterna is nested within Pan-Perissodactyla, as the sister group of remaining perissodactyls[11,12,13] (Fig. 1)
All these taxa are united by features commonly regarded as diagnostic of perissodactyls, including metacone on P3 present but smaller than paracone, p3 metaconid present and close to protoconid, p4 entoconid absent, and m2 hypoconulid separate from hypolophid (Figs. 1 and 2)

Summary

Introduction

The Litopterna is an extinct clade of endemic South American ungulates that range from Paleocene up to late Pleistocene times Because of their unique anatomy, litopterns are of uncertain phylogenetic affinities. The aim of the present contribution is to include litopterns and other South American related taxa in a comprehensive phylogenetic analysis together with several extant and extinct basal perissodactyl ungulates. Ameghino recognized affinities with the Laurasian clade Perissodactyla, a hypothesis sustained by some old workers[2,3] This idea was posteriorly criticized and refuted, and it was proposed that the similarities between litopterns and perissodactyls were acquired by c onvergence[4,5]. The aim of the present work is to include representatives of Litopterna within a comprehensive morphological data matrix of basal ungulates and to test, on the basis of morphology, the phylogenetic results obtained by previous authors[12], as well as to discuss the palaeobiogeographical implications of litoptern affinities

Objectives

Methods

Results

Conclusion