Out of Africa: A New Afrotheria Lineage Rises From Extinct South American Mammals

Leonardo S Avilla,Dimila Mothé

doi:10.3389/fevo.2021.654302

Abstract

The South American native ungulates (SANUs) are usually overlooked in Eutherian phylogenetic studies. In the rare studies where they were included, the diversity of SANUs was underrated, keeping their evolutionary history poorly known. Some authors recognized the SANUs as a monophyletic lineage and formally named it Meridiungulata. Here, we recognized and defined a new supraordinal lineage of Eutheria, the Sudamericungulata, after performing morphological phylogenetic analyses including all lineages of SANUs and Eutheria. The SANUs resulted as non-monophyletic; thus, Meridiungulata is not a natural group; Litopterna and “Didolodontidae” are Panameriungulata and closer to Laurasiatheria than to other “Meridiungulata” (Astrapotheria, Notoungulata, Pyrotheria, and Xenungulata). The other “Meridiungulata” is grouped in the Sudamericungulata, as a new monophyletic lineage of Afrotheria Paenungulata, and shared a common ancestor with Hyracoidea. The divergence between the African and South American lineages is estimated to Early Paleocene, and their interrelationships support the Atlantogea biogeographic model. Shortly afterward, the Sudamericungulata explosively diversified in its four lineages. Confronting the Sudamericungulata evolutionary patterns and the Cenozoic natural events (such as tectonics and climatic and environmental changes, among others) helps to unveil a new chapter in the evolution of Gondwanan Eutheria, as well as the natural history of South America during the Cenozoic.

Highlights

Several molecular phylogenies shook up the Eutheria tree in the last decades, dismissing traditional groups recognized by morphological studies, such as Ungulata, Insectivora, and Anagalida (Murphy et al, 2001; Springer et al, 2003; Gheerbrant et al, 2016)
The other “Meridiungulata” assembles Astrapotheria, Notoungulata, Pyrotheria, and Xenungulata (Figures 1, 2), and it is positioned among paenungulate afrotherians, closer to Hyracoidea, being supported by seven synapomorphies (Supplementary Material Section 4)
The South American native ungulates (SANUs) have been overlooked in traditional morphological phylogenies of Eutheria, and when mentioned, they were informally included in the Ungulata (McKenna, 1975)

Summary

Introduction

Several molecular phylogenies shook up the Eutheria tree in the last decades, dismissing traditional groups recognized by morphological studies, such as Ungulata, Insectivora, and Anagalida (Murphy et al, 2001; Springer et al, 2003; Gheerbrant et al, 2016). Molecular studies mostly include living mammals and classified extant eutherians into three lineages, each with distinct geographical origins: the Boreoeutheria (Northern Hemisphere), the Xenarthra (South America), and the Afrotheria (Africa). Every eutherian lineage spread its geographical boundaries after its origin. New South American Afrotheria Lineage still challenges scientists, and their divergence sequence remains unsettled, it possibly occurred rapidly around 120 Mya (Nishihara et al, 2009). All paired combinations among Xenarthra, Boreoeutheria, and Afrotheria were and statistically recovered, including Atlantogenata, a Gondwanan clade comprising South American and African lineages. The extinct South American native ungulates (SANUs: Astrapotheria, Didolodontidae, Litopterna, Notoungulata, Pyrotheria, and Xenungulata) received enthusiastic attention from great naturalists in the past (Darwin, 1845; Owen, 1846, 1853; Ameghino, 1889, 1897; Simpson, 1945, 1948), their phylogenetic relationships—among each other and within Eutheria—as well as their evolutionary history remain insufficiently explored

Methods

Results

Conclusion