The anatomy of Askeptosaurus italicus from the Middle Triassic of Monte San Giorgio and the interrelationships of thalattosaurs (Reptilia, Diapsida)

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Abstract:

The anatomy of the thalattosauriform reptile Askeptosaurus italicus from the Middle Triassic of Monte San Giorgio is redescribed. Important anatomical features are the plesiomorphic braincase, the unique fronto-lacrimal contact, the absence of a previously described thyroid fenestra, and significant intraspecific variation in the carpus. An analysis of thalattosaur ingroup relationships reveals that Endennasaurus and the monophyletic Askeptosaurus and Anshunsaurus are the sister group to all other thalattosaurs, whereas the Monte San Giorgio taxa Clarazia and Hescheleria form the sister clade of Thalattosaurus, and the Chinese Xinpusaurus and the Californian Nectosaurus form a monophyletic group. The analysis supports the biogeographic interpretation of trans-Pacific relationships and a re-invasion of Tethyan areas.

L'anatomie du reptile thalattosauriforme Askeptosaurus italicus du Trias de la région de Monte San Giorgio est redécrite. Le crâne plésiomorphe, la nature particulière du contact fronto-lacrymal, l'absence d'une fenêtre thyroïde décrite antérieurement et la variabilité intraspécifique considérable du carpus constituent d'importants caractères anatomiques. Une analyse des liens entre les différents thalattosaures révèle qu'Endennasaurus et les genres monophylétiques Askeptosaurus et Anshunsaurus forment le groupe-frère de tous les autres thalattosaures, alors que les taxons Clarazia et Hescheleria de la région de Monte San Giorgio constituent le clade-frère de Thalattosaurus et que Xinpusaurus, de Chine, et Nectosaurus, de Californie, forment un groupe monophylétique distinct. Cette analyse vient appuyer l'interprétation biogéographique de l'existence de liens transpacifiques et d'une réinvasion des régions téthysiennes.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: July 1, 2005

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