Osteología comparada de las familias Nothosauridae y Simosauridae (Reptilia. Sauropterygia)

Abstract

The alleged homodont condition of Simosaurus is not exact, symphisiary and postsymphisiary pieces can be differenciated, based on morphological and size criteria. The dental morphology of Simosaurus is unique within the Sauropterygia, with teeth whose basal diameter has a great relative developpment. The morphology of vertebral centrum between Nothosauridae and Simosauridae is compared. The first ones have a morphotype called "Kreuzform" (dorsal region of centrum) facing that of Simosauridae, here called "Fosetado" (pitted), A typical characteristic of Simosaurus is the occurrence (in the neural arch) of additional articulatin,g structures (infrazygapophyses, Huene, 1952). From the consideration of morphometric variationof centrum in N. raabi SCHROEDER, 1914, it can be concluded that the cervical vertebrae of Nothosaurus are relatively longer and deeper than the thoracic ones, The topographic variation of diameter and Ienght of centrum in Simosaurus is more accused than in Nothosaurus, while depth is more constant. Based on morphometric criteria the vertebral centra no pachyostotic of Pachypleurosaurs (generally smaller in size) can not be discriminated from those of Nothosauridae. The rib morphology of Simosaurus is similar to that of other Notbosaurs. The coracoid of Simosaurus is stronger and unlike Nothosaurus the glenoid notch has a typically anterior position. Simosaurus has a more slender humerus than the rest of Nothosaurs. The analysis of the different genera proposed as Simosauridae up to date, leads towards the conclusion that it is a monogeneric family. Dentary and postcraneal diagnosis of this taxon is proposed.