Abstract
Ronzotherium is one of the earliest Rhinocerotidae in Europe, which first appeared just after the Eocene/Oligocene transition (Grande Coupure), and became extinct at the end of the Oligocene. It is a large-sized rhinocerotid, with a special position in the phylogeny of this group, as being one of the earliest-branching true Rhinocerotidae. However, its intra-generic systematics has never been tested through computational phylogenetic methods and it is basically unknown. Its taxonomical history has gone through numerous complications, and thus we aim to provide here a complete revision of this genus, through phylogenetic methods. After a re-examination of all type specimens (five supposed species) as well as of most well-preserved specimens from all over Europe and ranging through the complete Oligocene epoch, we performed a parsimony analysis to test the position of some problematic specimens. According to our results, five species can be distinguished, Ronzotherium velaunum (type species), R. filholi, R. elongatum and R. romani as well as a new species: R. heissigi sp. nov. We also drastically re-interpret its anatomy and show that the ‘short-limbed’ “Diaceratherium” massiliae, described from Southern France, can be considered as a junior synonym of R. romani. Finally, we exclude the Asian species “Ronzotherium” orientale and “Ronzotherium” brevirostre from Ronzotherium and we consider R. kochi as a junior synonym of R. filholi.
Highlights
The genus Ronzotherium Aymard, 1854 is the most typical rhinocerotoid in the Oligocene of Europe
Based on the phylogenetic results, each species can be properly diagnosed and described. This complete revision allows us to discuss the evolution of Ronzotherium altogether, and we suggest that cingulum may have played a central role in the persistence of R. romani until the end of the Oligocene epoch
The specimens from ‘Marseille’ (= St-Henri, St-André and Les Milles), Gaimersheim, and Rickenbach were always found together with the specimens of Ronzotherium romani from the type locality of La Ferté-Alais, after the addition of Trigonias osborni, their topology slightly differed, resulting in an unresolved polytomy in the strict consensus. They still remained together as a clade and were merged in a single terminal, which supports the former identifications of these specimens by other authors (i.e., Heissig 1969 for Gaimersheim; Ménouret & Guérin 2009 for Marseille; Mennecart et al 2012 for Rickenbach). This highlights the synonymy of Ronzotherium romani with Diaceratherium massiliae Ménouret & Guérin, 2009, that we further detail in the Systematic palaeontology section
Summary
The genus Ronzotherium Aymard, 1854 is the most typical rhinocerotoid in the Oligocene of Europe. The genus Ronzotherium was first named after the hill of Ronzon by the French paleontologist Aymard in 1854, from material found in his hometown of Le Puy-en-Velay, which gave its name to R. velaunum (Aymard in Pictet, 1853) This locality of Ronzon is significant for the study of Western European Oligocene faunas because it has been dated from MP21 (earliest Oligocene) and is very rich, preserving numerous vertebrate and invertebrate taxa. This probably explains why no new material was attributed to this genus until Osborn (1900) wrongly referred a lower jaw from Brons (Cantal, France) to Ronzotherium gaudryi Osborn, 1900 This species is attributed to the genus Eggysodon Roman, 1910 (Rhinocerotoidea, Eggysodontidae Breuning, 1923), like several others that have been erroneously attributed to Ronzotherium such as Eggysodon osborni (Schlosser, 1902) or Eggysodon reichenaui (Deninger, 1903), notably because of the presence of upper and lower canines. Because of these complications and the absence of explicit definition of Ronzotherium by Aymard (1854), Roman (1912a) advocated that the name “Ronzotherium” should be forgotten and replaced by Aceratherium, but the name persisted
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