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

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. The mammalian group Litopterna was coined by Ameghino 1 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 2,3. This idea was posteriorly criticized and refuted, and it was proposed that the similarities between litopterns and perissodactyls were acquired by convergence 4,5. In the same line of thought, together with xenarthrans and marsupials, South American native ungulates were considered by Simpson 6,7 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 8-10. Recent phylogenetic analysis based on protein spectrometry and DNA analyses resulted in the referral of Litopterna to Perissodactyla 11-13 , in agreement with nineteenth century authors. 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. Results 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 11-13 (Fig. 1). The inclusion of Litopterna among perissodactyls partially returns to the old ideas of Ameghino 14. However, in contrast with the last author, and in agreement with Cifelli 15 , we also consider Didolodontidae as closely related to litopterns.

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

“…Buckley (2015) and Welker et al (2015) found that both Macrauchenia patachonica (Litopterna) and Toxodon platensis (Notoungulata) were part of the Perissodactyla on a proteomics-based analysis and Westbury et al (2017) recovered M. patachonica as sister to Perissodactyla, but on a mitochondrial genome-based study. Later, Chimento and Agnolin (2020) performed a morphologicalbased cladistic analysis and corroborated molecular proposals that litopterns and their kin (didolodontids and kollpaniids) were "successive stem clades of crown Perissodactyla." Very recently, MacPhee et al (2021) performed a morphologicalbased phylogenetic analysis recovering litopterns closer to perissodactyls than to other SANUs, i.e., a non-monophyletic SANUs, contrasting with the molecular proposals (Buckley, 2015;Welker et al, 2015).…”

“…Under this scenario, the SANUs remained blurred until Agnolin and Chimento (2011) suggest that some of them (Astrapotheria and Notoungulata) might be related to Afrotheria. This study shed light on to SANUs, bringing back the debate on their interrelationships within Eutheria (Billet and Martin, 2011;O'Leary et al, 2013;Kramarz and Bond, 2014;Buckley, 2015;Welker et al, 2015;Westbury et al, 2017;Chimento and Agnolin, 2020;MacPhee et al, 2021). Despite the heated debate, none of these studies included all lineages of SANUs (at least Litopterna, Didolodontidae, Astrapotheria, Notoungulata, Pyrotheria, and Xenungulata) and other Eutheria (at least Afrotheria and Laurasiatheria, the traditional "Ungulata") in the same phylogenetic analysis.…”

“…Our study recovered the same Panameriungulata of de Muizon and Cifelli (2000) (Figures 1, 4). However, in the last few years, the Panameriungulata was challenged by results of molecular and morphological phylogenies that found a clade comprising Litopterna and Notoungulata (Buckley, 2015;Welker et al, 2015) or only Litopterna (Westbury et al, 2017) as more closely related to Perissodactyla than to other Eutheria, even to the other SANUs (Chimento and Agnolin, 2020;MacPhee et al, 2021). Despite the particularities of each topology of these contributions, a close relationship between Litopterna and Perissodactyla was proposed as a new rank of Laurasiatheria, the Panperissodactyla.…”

Taxonomic revision of the snakes of the genera Palaeopython and Paleryx (Serpentes, Constrictores) from the Paleogene of Europe

“…South American) lineages that have a fossil record in the Paleogene of Europe, including reptiles (e.g., Augé & Brizuela, 2020;Scanferla & Smith, 2020b), as well as non-volant birds (Angst et al, 2013). In fact, faunal and floral exchanges between the Paleogene South American and African landmasses have been recently inferred for multiple different clades of non-marine animals and plants (e.g., Antoine et al, 2012;Aranciaga Rolando et al, 2019;Bond et al, 2015;Chimento & Agnolin, 2020;Croft, 2016;Katinas et al, 2013). The identification of Eoconstrictor as booid suggests that at least one of the large European constrictors had South American origin (Scanferla & Smith, 2020b), though of course, an African origin with subsequent dispersals to Europe and South America could also be the case (as it has been suggested for several South American mammal clades; see Croft, 2016).…”

A new proterotheriid (Mammalia, Litopterna) from the Salla Beds of Bolivia (upper Oligocene): phylogeny and litoptern patellar pit knee locks

“…Modern proteomic (i.e., collagen) and mitochondrial DNA (mDNA) analyses support something of an intermediate between these two conflicting hypotheses; that is, there is a close Litopterna–Perissodactyla relationship, with the two groups, along with the Notoungulata, forming the monophyletic Panperissodactyla Welker et al, 2015 (see also Buckley, 2015; Westbury et al, 2017, for the mDNA study; and Chimento & Agnolin, 2020, for a phylogeny based upon skeletal data, but see Kramarz et al, 2021, for a critique of the latter study). The mDNA analysis additionally provided a means to infer the timing of the divergence of litopterns and perissodactyls, an event that appears to have occurred at about 66 Ma (range: 56.64–77.83 Ma), close to the Cretaceous–Paleogene (K–Pg) boundary (Westbury et al, 2017).…”