Extraordinary occlusion of caniniforms in the Eocene Masillabune martini from Messel

Abstract The skeleton of the small artiodactyl Masillabune martini Tobien 1980 is a typical example of the mammalian skeletons excavated by private collectors in the famous Messel-Fossillagerstätte in 1970 s, long before the locality became a World Heritage Site. Although the skeleton was found during a private excavation by Thomas Martin, the well-preserved skeleton eventually found its way to a public museum, the Hessisches Landesmuseum in Darmstadt (HLMD). Tobien provided the scientific description of the specimen and erected the skeleton as the type for the species Masillabune martini in honour of the finder. Masillabune martini is a small choeropotamid artiodactyl and differs from many mammals in the occlusion pattern of its caniniform teeth. In contrast to the normal “lower canines mesial to upper canines” pattern, the lower canine of M. martini is reduced and incisiform, whereas the first lower premolar is caniniform and acts as an antagonist to the upper canine, albeit located distally. This occlusal pattern is not an isolated pathological modification, because it occurs in a number of independent mammalian groups as the “canine/premolar functional unit”. The convergent development of this specific occlusal pattern of caniniforms characterises a morphological cluster including Merycoidodontidae and Protoceratidae.