Abstract
A newly discovered, well-preserved skull and associated fragment of a juvenile mandible from the Early Oligocene locality of Poillat (Canton Jura, NW Switzerland), bearing close affinities with the rhinocerotid Protaceratherium albigense (Roman, 1912), are attributed to a new small-sized representative of early diverging Rhinocerotinae, Molassitherium delemontense gen. et sp. nov. Other specimens from Western Europe, formerly questionably referred to Epiaceratherium Abel, 1910, are assigned to this new genus. Comparison with the previously described Protaceratherium Abel, 1910 (including type material) and a phylogenetic analysis highlight the mismatch of Protaceratherium minutum (Cuvier, 1822) and Protaceratherium albigense (Roman, 1912). Given the topology of the most parsimonious tree, a basal split within Rhinocerotidae coincides with the well-supported divergence of the Elasmotheriinae and Rhinocerotinae clades. Relationships within Rhinocerotinae are [Epiaceratherium bolcense Abel, 1910 [Epiaceratherium magnum Uhlig, 1999 [Molassitherium gen. nov. [Mesaceratherium Heissig, 1969 [Pleuroceros Roger, 1898 [Protaceratherium minutum (Cuvier, 1822) [Plesiaceratherium mirallesi (Crusafont, Villalta and Truyols, 1955) [Aceratheriini, Rhinocerotini]]]]]]]]. The only paraphyletic genus in the analysis is Epiaceratherium, with the earliest Oligocene Epiaceratherium bolcense Abel, 1910 being sister taxon to an [Epiaceratherium magnum Uhlig, 1999, Rhinocerotinae] clade. In the single most parsimonious tree, Molassitherium gen. nov., included within the early diverging Rhinocerotinae, forms a clade encompassing Molassitherium delemontense gen. et sp. nov. and the type species Molassitherium albigense comb. nov. The range of Molassitherium delemontense gen. et sp. nov. is so far restricted to the late Early–early Late Oligocene interval in Western Europe (Germany, Switzerland, France; ‘late MP22’–MP25).
Highlights
Abel (1910) established the genus Protaceratherium for the small slender rhinoceros P. minutum (Cuvier, 1822) from the Early Miocene of Europe, previously assigned to Diceratheriinae Dollo, 1885 under the name Diceratherium minutum by Osborn (1900). Roman (1912) described the species Acerotherium albigense, reassessed as P. albigense by von Breuning (1924), on the basis of an anterior part of an adult skull, with preserved left and right P1–M3, discovered in the molassic deposits of the early Late Oligocene of La Sauziere Saint-Jean (MP25–26; SW France)
We report here a recently discovered, well-preserved skull and associated fragment of a juvenile mandible attributed to a new small-sized representative of Rhinocerotinae very close to P. albigense, Molassitherium delemontense gen. et sp. nov., from Poillat, a new Early Oligocene vertebrate locality within the Delemont valley (Canton Jura, NW Switzerland; Fig. 1)
The small hornless rhinocerotid from the ‘middle’ Oligocene of Europe forms a well-supported clade with the Delemont rhinocerotid, described here, which leads us to propose a new monophyletic genus, Molassitherium gen. nov., encompassing the two taxa under the names M. albigense (Roman, 1912) comb. nov. and M. delemontense sp. nov
Summary
Abel (1910) established the genus Protaceratherium for the small slender rhinoceros P. minutum (Cuvier, 1822) from the Early Miocene of Europe, previously assigned to Diceratheriinae Dollo, 1885 under the name Diceratherium minutum by Osborn (1900). Roman (1912) described the species Acerotherium albigense, reassessed as P. albigense by von Breuning (1924), on the basis of an anterior part of an adult skull, with preserved left and right P1–M3, discovered in the molassic deposits of the early Late Oligocene of La Sauziere Saint-Jean (MP25–26; SW France). Many authors have regularly attributed the genus Protaceratherium to the subfamily Aceratheriinae (e.g. von Breuning 1924; Hugueney & Guerin 1981; Menouret & Guerin 2009), as opposed to Antoine et al (2003b) who assigned P. minutum to the tribe Rhinocerotini (Rhinocerotinae). Nov., from Poillat, a new Early Oligocene vertebrate locality within the Delemont valley (Canton Jura, NW Switzerland; Fig. 1). We include this sample as a terminal taxon in a cladistic analysis in order to establish its phylogenetic relationships, notably with other European Oligocene and Miocene rhinocerotids
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