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Morphofunctional analysis of the postcranium of Amphicyon major (Mammalia, Carnivora, Amphicyonidae) from the Miocene of Sansan (Gers, France) compared to three extant carnivores: Ursus arctos, Panthera leo, and Canis lupus

Christine ARGOT

en Geodiversitas 32 (1) - Pages 65-106

Published on 30 March 2010

The postcranial skeleton of the amphicyonid Amphicyon major from the middle Helvetian of Sansan (Gers, France) is described and compared to extant taxa belonging to the families Ursidae (Ursus arctos), Felidae (Panthera leo), and Canidae (Canis lupus). From the perspective of the forelimb, the scapula is very similar to that of a bear, as well as the elbow joint suggesting habitually abducted postures of the arm and the ability to supinate the forefoot. The mobile shoulder joint and massive triceps are features shared by both extant ursids and felids. A powerful hand musculature, short and divergent metacarpals, and an important range of dorsifl exion of the wrist recall the forefoot of an ursid and indicate good grasping ability. On the axial skeleton, the complex atlas/axis, the shape of the lumbar vertebrae, and a long, heavy tail are more similar to the same anatomical regions in felids than to any other extant carnivore. The pelvis and femur, as well as the knee and tibio-astragalar joints, are also more similar to those of a felid than an ursid, although the ischium and femur of Amphicyon allowed more abducted and erected postures. The size and shape of the tibia, calcaneum, and metatarsals are more similar to those of a bear. The short metatarsals, with a divergent Mt I and a powerful hind foot musculature also suggest potential grasping ability. Therefore, the skeleton of Amphicyon major that displays a series of bear-like and cat-like morphological similarities would deserve the term of "bear-lion" instead of "bear-dog".

Keywords :

Mammalia, Carnivora, Amphicyonidae, Miocene, functional adaptations, Western Europe

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