Specialization for amphibiosis in Brachyodus onoideus (Artiodactyla, Hippopotamoidea) from the Early Miocene of France
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Specialization for amphibiosis in Brachyodus onoideus (Artiodactyla, Hippopotamoidea) from the Early Miocene of France Maeva J. Orliac • Pierre-Olivier Antoine • Anne-Lise Charruault Sophie Hervet • Fre´de´ric Prodeo • Francis Duranthon
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Received: 28 October 2012 / Accepted: 25 February 2013 / Published online: 16 November 2013 Ó Swiss Geological Society 2013
Abstract A partial cranium of a very large anthracothere was unearthed during a palaeontological excavation at Saint-Antoine-de-Ficalba (Lot-et-Garonne, France; Early Miocene, *18–17.0 Ma). The new material, referred to as Brachyodus onoideus (Gervais, 1859), documents the cranial features of this species, so far mainly known by dental and postcranial remains. The preserved part of the skull roughly coincides with the neurocranium and is remarkable for the dorsally-protruding orbits, the importance of the postorbital constriction, the small volume of the braincase, and the gigantic size of the occipital condyle relative to the other elements of the neurocranium. A very careful dissection of the left auditory region allowed extraction of the left petrosal bone and provides the first description of a petrosal for Brachyodus. The morphology of the petrosal is Editorial Handling: D. Becker & D. Marty. M. J. Orliac (&) P.-O. Antoine A.-L. Charruault Institut des Sciences de l’E´volution, UMR-CNRS 5554, CC064, Universite´ Montpellier 2, Place Euge`ne-Bataillon, 34095 Montpellier, France e-mail: [email protected] M. J. Orliac Department of African Zoology, Royal Museum for Central Africa, Leuvensesteenweg 13, 30080 Tervuren, Belgium S. Hervet Association Pale´overgne, 24 avenue de l’Abattoir, 03450 Ebreuil, France F. Prodeo Institut National de Recherches Arche´ologiques Pre´ventives, 156 avenue Jean-Jaure`s, 33600 Pessac, France F. Duranthon Muse´um d’Histoire Naturelle/AMIS-UMR 5288 CNRS, 35 Alle´es Jules-Guesde, 31000 Toulouse, France
strikingly similar to that of extant hippos with: (1) a ventral basicapsular groove, (2) a sharp crista petrosa, (3) a wide prefacial commissure fossa, (4) a reduced mastoid, and (5) an hyperinflated tegmen tympani. Both the disposition of the orifices of the head and the petrosal morphology support a specialization of Brachyodus onoideus to an amphibious lifestyle and to potential underwater directional hearing. Keywords Anthracotheriidae Middle ear Burdigalian Underwater directional hearing
1 Introduction The renovation of the RN21 motorway between Villeneuve-sur-Lot and Agen (SW France) led to the discovery by one of us (FP) of a new rich vertebrate locality west to the Saint-Antoine-de-Ficalba village (0.712°E, 44.336°N; Fig. 1). The fossiliferous exposure is a thin stripe, *2.6 km-long (North–South) and 60/110 m-wide (East–West). Fossil-yielding deposits consist of non-indurated mica-rich sands and siltstones of fluvio-lacustrine origin, known for decades to be late Early Miocene in age (Burdigalian). Fossil remains were found scattered all over the concerned surface; no significant accumulation, anatomic
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