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A brief review of Agenian rhinocerotids in Western Europe Pierre-Olivier Antoine • Damien Becker

Received: 18 December 2012 / Accepted: 22 March 2013 / Published online: 16 November 2013 Ó Swiss Geological Society 2013

Abstract The Agenian is the earliest Neogene European Land Mammal Age. It encompasses the mammalian zones MN1 (23.03–22.7 Ma) and MN2 (22.7–20.0 Ma) and roughly coincides with the Aquitanian standard age. Agenian mammalian assemblages from Western Europe encompass a mixture of rhinocerotid taxa of Oligocene affinities and of Miocene newcomers, mostly recorded in France, Germany, Switzerland, and to a lesser extent, Spain. Rhinocerotidae are documented by seven species referred to five genera (Pleuroceros pleuroceros, Protaceratherium minutum, Plesiaceratherium aquitanicum, Mesaceratherium paulhiacense, Diaceratherium lemanense, D. asphaltense, and D. aginense), further attesting to a low suprageneric diversity. Their systematics, morphology, ecology, stratigraphical and geographical ranges are detailed in the present article. Occurrences and geographical ranges of all seven rhinocerotid species are illustrated on palaeogeographical maps of the circum-Mediterranean region at 23 Ma (MN1) and 21 Ma (MN2). The richest Agenian localities (Paulhiac, MN1; Laugnac, MN2) record a specific diversity similar to that of Orleanian rhinocerotid assemblages, with up to five/six associated species. All Agenian rhinocerotid species from Western Europe are

Editorial Handling: D. Marty. P.-O. Antoine (&) Institut des Sciences de l’Evolution, Universite´ Montpellier 2, Place Euge`ne Bataillon, 34095 Montpellier, France e-mail: [email protected] D. Becker Muse´e Jurassien des Sciences Naturelles, Route de Fontenais 21, 2900 Porrentruy, Switzerland e-mail: [email protected]

endemic to the concerned region, which is consistent with the complete geographic isolation of Western Europe by earliest Miocene times. However, all five genera are documented by twin species in coeval localities of South and Central Asia, which implies (1) vicariant speciation events by latest Oligocene times and (2) the existence of intermittent pathways for terrestrial megamammals such as rhinocerotids during the concerned interval. Keywords Perissodactyla
Systematics
Biochronology
Palaeogeographical maps
Fossil record
Early Miocene

1 Introduction The Agenian is the earliest Neogene European Land Mammal Age (ELMA). It encompasses the mammalian zones MN1 [23.03–22.7 Ma] and MN2 [22.7–20.0 Ma] (Mein 1975, 1999; Bruijn et al. 1992; Ro¨gl 1999; Gradstein et al. 2004) and roughly coincides with the Aquitanian standard age (23.03–20.43 Ma; Ro¨gl 1999; Steininger and Wessely 2000; Gradstein et al. 2004). Agenian land mammal assemblages contrast with the Late Oligocene assemblages (Arvernian ELMA) at Western European scale, primarily because many faunal elements became extinct at the Oligocene–Miocene transition or earlier, such as theridomyid rodents, hyracodontid and amynodontid rhinocerotoids, lophiomerycid ruminants