Friday, 29 August 2014

Teeth and osteoderms of a Sebecosuchian Crocodylomorph from the Middle Eocene of France.

The Sebecosuchians were the only group of Crocodylomorphs other than the modern Crocodyliforms to survive the end Cretaceous extinction, radiating in South America and Europe during the Palaeogene, then going extinct later in the Tertiary. A variety of South American forms have been described, and the group is reasonably well understood there, but the European forms are less well understood, and known largely from fragmentary material. These European forms are not thought to have been as abundant as the South American members of the group, and to have become extinct sooner. It has been suggested that Sebecosuchians were more terrestrial than modern Crocodyliforms, and as a result were in more direct competition with Mammalian predators, hence persisting later in South America (where predatory Placental Mammals were absent for much of the Tertiary) than in Europe.

In a paper published in the journal Acta Palaeontologica Polonica on 10 July 2014, Jeremy Martin of the Laboratoire de Géologie de Lyon: Terre, Planète, Environnement describes a series of Crocodylomorph teeth and osteoderms (bony plates within the skin of a Crocodylomorph) from the Middle Eocene karst limestone deposits at Lissieu in Rhône, France, which he assigns to an unknown Sebecosuchian on the basis of the osteoderm morphology, which is fairly distinctive.

Isolated ziphodont teeth from the middle Eocene of Lissieu, France. A. Isolated apex in labial (A1), mesial or distal (A2) views, detail of the denticles (A3). B. Isolated crown corresponding to a maxillary or midposition in the dentary distal (B1), labial or lingual (B2) views, detail of the denticles (B3). C. Isolated crown nearly circular in cross section corresponding to a premaxillary or anterior position in the dentary tooth row in labial (C1), mesial or distal (C2), lingual (C3) views, detail of the denticles (C4). A3, B3, and C4 are enlargements of the boxes in A1, B2, and C3. Martin (2014).

Selected sebecosuchian osteoderms (MNHL 341) from the middle Eocene of Lissieu, France in dorsal (A, D, G, J, M), lateral (B, E, H, K, N), and ventral (C, F, I, L, O) views. Martin (2014).

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