DOI: 10.15468/jstjh8
title: Cranial morphology and phylogenetic relationships of Amynodontidae Scott & Osborn, 1883 (Perissodactyla, Rhinocerotoidea)

description: This dataset contains the digitized treatments in Plazi based on the original journal article Veine-Tonizzo, Léa, Tissier, Jérémy, Bukhsianidze, Maia, Vasilyan, Davit, Becker, Damien (2023): Cranial morphology and phylogenetic relationships of Amynodontidae Scott & Osborn, 1883 (Perissodactyla, Rhinocerotoidea). Comptes Rendus Palevol 22 (8): 109-142, DOI: 10.5852/cr-palevol2023v22a8, URL: http://dx.doi.org/10.5852/cr-palevol2023v22a8ABSTRACTAmynodontidae Scott & Osborn, 1883 are an extinct family of Rhinocerotoidea Owen, 1845 known from the middle Eocene to the latest Oligocene of Asia, North America, and Europe. We report here two unpublished specimens of Amynodontidae, a skull and a mandible of Zaisanamynodon borisovi Belyaeva, 1971 from the late Eocene of the Zaysan Basin (Kazakhstan) and a skull of Metamynodon planifrons Scott & Osborn, 1887, from the early Oligocene of the Big Badlands (United States). This new material has been incorporated into a morpho-anatomical character matrix. It was completed with the coding of the recently described species of Amynodontopsis jiyuanensis Wang X. -Y., Wang Y.-Q., Zhang R., Zhang Z.-H., Liu & Ren, 2020 and the revised coding of Cadurcotherium cayluxi Gervais, 1873 and Cadurcotherium minum Filhol, 1880. We computed a cladistic analysis based on this matrix, including 31 Rhinocerotoidea terminal taxa. The new phylogenetic hypothesis proposed allows to discuss the relationships of the referred specimens within Amynodontidae and those of Amynodontidae within Rhinocerotoidea. Our cladistic analysis clarifies the generic and spe- cific composition of the tribes Metamynodontini Kretzoi, 1942 and Cadurcodontini Wall, 1982 and supports the monophyly of the genus Zaisanamynodon Belyaeva, 1971. The dichotomy between the two tribes is notably expressed by the presence of several cranial features such as “the deep nasal notch” or “the well-developed preorbital fossa” in Cadurcodontini. These cranial specializations attest to an adaptation of the peri-nasal region to the presence of a proboscis with a feeding function. Our study also opens a discussion on the biogeography of Amynodontidae, their emergence and dispersal in Asia and their subsequent migration to North America, and Eastern Europe. Their presence in Western Europe remains restricted to the Oligocene, after a dispersal related to the “Grande Coupure” event.KEY WORDSAmynodontidae,Zaisanamynodon,Metamynodon,phylogeny,skull,Zaysan Basin,Big Badlands,Eocene,Oligocene,Rhinocerotoidea.RÉSUMÉMorphologie crânienne et relations phylogénétiques des Amynodontidae Scott & Osborn, 1883 (Perissodactyla, Rhinocerotoidea). Les Amynodontidae Scott & Osborn, 1883 sont une famille éteinte de Rhinocerotoidea Owen, 1845 connue depuis l’Éocène moyen jusqu’à la fin de l’Oligocène en Asie, en Amérique du Nord et en Europe. Nous présentons ici deux spécimens inédits d’Amynodontidae, un crâne et une mandibule, de Zaisanamynodon borisovi Belyaeva, 1971, datés de la fin de l’Éocène du bassin de Zaïssan (Kazakhstan) et un crâne de Metamynodon planifrons Scott & Osborn, 1887, daté du début de l’Oligocène des Big Badlands (États-Unis). Ce nouveau matériel a été inclus dans une matrice de caractères morpho-anatomiques. Elle a été complétée par le codage de l’espèce récemment décrite Amynodontopsis jiyuanensis Wang X. -Y., Wang Y.-Q., Zhang R., Zhang Z.-H., Liu & Ren, 2020 et les codages révisés de Cadurcotherium cayluxi Gervais, 1873 et Cadurcotherium minum Filhol, 1880. Nous avons réalisé une analyse cladistique basée sur cette matrice, incluant 31 taxons terminaux de Rhinocerotoidea. La nouvelle hypothèse phylogénétique proposée permet de discuter des positions phylogénétiques des spécimens étudiés au sein des Amynodontidae et de la position des Amynodontidae au sein des Rhinocerotoidea. Notre analyse cladistique clarifie la composition générique et spécifique des tribus Metamynodontini Kretzoi, 1942 et Cadurcodontini Wall, 1982 et soutient la monophylie de Zaisa-namynodon Belyaeva, 1971. La dichotomie des deux tribus s’exprime notamment par la présence de plusieurs caractéristiques crâniennes telles que “l’allongement de l’incisure nasale” ou “la fosse préorbitaire bien développée” chez les Cadurcodontini. Ces spécialisations témoignent d’une adaptation de la région péri-nasale à la présence d’un proboscis. Notre étude ouvre également une discussion sur la biogéographie des Amynodontidae, leur émergence et dispersion en Asie à l’Éocène moyen puis leur colonisation de l’Amérique du Nord et de l’Europe de l’Est. Leur présence en Europe occidentale est, quant à elle, restreinte à l’Oligocène et liée à l’événement de la Grande Coupure.MOTS CLÉSAmynodontidae,Zaisanamynodon,Metamynodon,phylogénie,crâne,Bassin Zaïssan,Big Badlands,Éocène,Oligocène,Rhinocerotoidea. INTRODUCTION Amynodontidae Scott & Osborn, 1883 are an extinct family of hornless perissodactyls, which are included within Rhinocerotoidea Owen, 1845. They are assumed to be terrestrial herbivores but some of them were probably semi-aquatic (e.g. Wall 1982b, 1989, 1998; Wall & Heinbaugh 1999). They had a noticeable diversification during the middle and late Eocene in Asia and North America (e.g. Wall 1998; Averianov et al. 2016; Tissier et al. 2018). Amynodontidae were also present in Eastern Europe since the middle Eocene, and later during the Oligocene they are documented in Western Europe (e.g. Averianov et al. 2016; Tissier et al. 2018). This late dispersal would have been the consequence of establishment of land connections between Asia and Europe at the beginning of the Oligocene (i.e., the “Grande Coupure” event; Stehlin 1909; Legendre 1989; Hooker et al. 2004). The monophyly of Amynodontidae is defined by wellsupported synapomorphies such as the presence of a preorbital fossa, the loss of upper and lower P1, enlarged canines and the quadratic shape of the M3 (Wall 1980; Tissier et al. 2018). Relationships within Amynodontidae have been well studied since the 1940s (e.g. Wood 1941; Kretzoi 1942; Gromova 1954; Wall 1980). The first handmade phylogenetic analyses were performed by Wall (1982a, 1989, 1998) and, more recently, Averianov et al. (2016) and Tissier et al. (2018) published comprehensive phylogenies of the family based on computed cladistic analyses. Their new phylogenetic results led to a better understanding of the evolutionary history and the generic composition of the two major clades of the family: the Cadurcodontini Wall, 1982 and the Metamynodontini Scott & Osborn, 1887. Tissier et al. (2018) also underlined that suprageneric relationships within Rhinocerotoidea appear to be unclear, especially concerning the “ Hyracodontidae ” Cope, 1879 and basal taxa of Amynodontidae. Indeed, the position of Amynodontidae within the Rhinocerotoidea is conflictual according to the most recent phylogenies. According to Wang et al. (2016, 2018) and Tissier et al. (2018), Amynodontidae would be the sister-group of the Paraceratheriidae Osborn, 1923, whereas according to Bai et al. (2020), they would be either sister-group of the clade formed by Eggysodon Roman, 1910, Paraceratheriidae and Rhinocerotidae Gray, 1821 based on a parsimony analysis, or sister-group of the Hyracodontidae, Eggysodontidae Breuning, 1923, Paraceratheriidae and Rhinocerotidae based on a Bayesian tip-dating analysis. Therefore, more data is necessary to better understand the early diversification of the main families of Rhinocerotoidea, which can be done by documenting their taxonomical and morphological diversity. A Ma RUSSIA C 29 CHINA 10 m 30 31 32 33 34 35 36 37 CHINA N 50 km Aksyir Svita D 10 m Conglomerate Sandstone Siltstone Mudstone FIG. 1. — Biochronology, geography and stratigraphy information on cited localities: A, correlations between considered localities and temporal distributions of species described in the present paper; B, map of the area of the Lake Zaysan, Kazakhstan with locality of collect of ZSN-KKS-28-IPB; C, outcrop of the Aksyir Svita at Kiin Kerish (adapted from Lucas et al. 2012); D, map of Big Badlands,South Dakota,United States with supposed area of collect of UNISTRA.2015.0.1106; E, outcrop of the Scenic Member (Oreodon zone) of the Brule Formation of the White River Group (adapted from Benton et al. 2015). Numbers: 1, Kiin Kerish, locality of collect of ZSN-KKS-28-IPB (48°07’52.2”N, 84°28’52.3”E); 2, supposed area of collect of UNISTRA.2015.0.11.06 (see Gillet 1960). Here, we describe an unpublished skull and mandible (ZSN-KKS-28- IPB) of Amynodontidae from the late Eocene of the Zaysan Basin (Kazakhstan) and another amynodontid skull (UNISTRA.2015.0.1106) from the early Oligocene of the Big Badlands (United States). These specimens have been included in a parsimony analysis of a morphological characters matrix. It includes a large sample of Rhinocerotoidea and a comprehensive amynodontid sampling. Our sampling aims to infer the phylogenetic positions of the referred specimens within Amynodontidae and the position of Amynodontidae within Rhinocerotoidea. The results are also discussed within the scope of the peculiar cranio-dental anatomy of the Amynodontidae and their biogeographical distribution.Amynodontidae Scott & Osborn, 1883 are an extinct family of hornless perissodactyls, which are included within Rhinocerotoidea Owen, 1845. They are assumed to be terrestrial herbivores but some of them were probably semi-aquatic (e.g. Wall 1982b, 1989, 1998; Wall & Heinbaugh 1999). They had a noticeable diversification during the middle and late Eocene in Asia and North America (e.g. Wall 1998; Averianov et al. 2016; Tissier et al. 2018). Amynodontidae were also present in Eastern Europe since the middle Eocene, and later during the Oligocene they are documented in Western Europe (e.g. Averianov et al. 2016; Tissier et al. 2018). This late dispersal would have been the consequence of establishment of land connections between Asia and Europe at the beginning of the Oligocene (i.e., the “Grande Coupure” event; Stehlin 1909; Legendre 1989; Hooker et al. 2004).The monophyly of Amynodontidae is defined by wellsupported synapomorphies such as the presence of a preorbital fossa, the loss of upper and lower P1, enlarged canines and the quadratic shape of the M3 (Wall 1980; Tissier et al. 2018). Relationships within Amynodontidae have been well studied since the 1940s (e.g. Wood 1941; Kretzoi 1942; Gromova 1954; Wall 1980). The first handmade phylogenetic analyses were performed by Wall (1982a, 1989, 1998) and, more recently, Averianov et al. (2016) and Tissier et al. (2018) published comprehensive phylogenies of the family based on computed cladistic analyses. Their new phylogenetic results led to a better understanding of the evolutionary history and the generic composition of the two major clades of the family: the Cadurcodontini Wall, 1982 and the Metamynodontini Scott & Osborn, 1887. Tissier et al. (2018) also underlined that suprageneric relationships within Rhinocerotoidea appear to be unclear, especially concerning the “ Hyracodontidae ” Cope, 1879 and basal taxa of Amynodontidae. Indeed, the position of Amynodontidae within the Rhinocerotoidea is conflictual according to the most recent phylogenies. According to Wang et al. (2016, 2018) and Tissier et al. (2018), Amynodontidae would be the sister-group of the Paraceratheriidae Osborn, 1923, whereas according to Bai et al. (2020), they would be either sister-group of the clade formed by Eggysodon Roman, 1910, Paraceratheriidae and Rhinocerotidae Gray, 1821 based on a parsimony analysis, or sister-group of the Hyracodontidae, Eggysodontidae Breuning, 1923, Paraceratheriidae and Rhinocerotidae based on a Bayesian tip-dating analysis. Therefore, more data is necessary to better understand the early diversification of the main families of Rhinocerotoidea, which can be done by documenting their taxonomical and morphological diversity.A Ma RUSSIA C 29 CHINA 10 m 30 31 32 33 34 35 36 37 CHINA N 50 km Aksyir Svita D 10 m Conglomerate Sandstone Siltstone MudstoneFIG. 1. — Biochronology, geography and stratigraphy information on cited localities: A, correlations between considered localities and temporal distributions of species described in the present paper; B, map of the area of the Lake Zaysan, Kazakhstan with locality of collect of ZSN-KKS-28-IPB; C, outcrop of the Aksyir Svita at Kiin Kerish (adapted from Lucas et al. 2012); D, map of Big Badlands,South Dakota,United States with supposed area of collect of UNISTRA.2015.0.1106; E, outcrop of the Scenic Member (Oreodon zone) of the Brule Formation of the White River Group (adapted from Benton et al. 2015). Numbers: 1, Kiin Kerish, locality of collect of ZSN-KKS-28-IPB (48°07’52.2”N, 84°28’52.3”E); 2, supposed area of collect of UNISTRA.2015.0.11.06 (see Gillet 1960).Here, we describe an unpublished skull and mandible (ZSN-KKS-28- IPB) of Amynodontidae from the late Eocene of the Zaysan Basin (Kazakhstan) and another amynodontid skull (UNISTRA.2015.0.1106) from the early Oligocene of the Big Badlands (United States). These specimens have been included in a parsimony analysis of a morphological characters matrix. It includes a large sample of Rhinocerotoidea and a comprehensive amynodontid sampling. Our sampling aims to infer the phylogenetic positions of the referred specimens within Amynodontidae and the position of Amynodontidae within Rhinocerotoidea. The results are also discussed within the scope of the peculiar cranio-dental anatomy of the Amynodontidae and their biogeographical distribution.