Authors: Rieppel, Olivier; Müller, Johannes; Liu, Jun

Source: Canadian Journal of Earth Sciences, Volume 42, Number 12, December 2005 , pp. 2081-2086(6)

Publisher: NRC Research Press

Abstract:

The rostral structure of thalattosaurs is reviewed on the basis of a re-investigation of the holotype of Nectosaurus halius and Thalattosaurus alexandrae. The askeptosaurid genera Askeptosaurus and Anshunsaurus share an elongated, parallel-sided rostrum that terminates in a blunt tip. A diastema separating the premaxillary from the maxillary teeth is absent. The claraziid genera Clarazia and Thalattosaurus share a relatively shorter rostrum that has convergent lateral margins and that terminates in a pointed tip. A diastema separating the premaxillary from the maxillary teeth is present. The well-preserved holotype of Nectosaurus halius shows a highly derived rostral structure. The maxilla is short with an anteriorly truncated (vertical) margin, a narrow but high ascending process, and a dorsally curving medial flange that is in natural articulation with the ventrally deflected vomer. These findings corroborate Peyer's original reconstruction of Hescheleria with a nearly vertically placed premaxilla.

La structure rostrale des thalattosaures est revue à la lumière d'un nouvel examen des holotypes de Nectosaurus halius et de Thalattosaurus alexandrae. Les genres d'askeptosauridés Askeptosaurus et Anshunsaurus partagent un rostre allongé aux parois parallèles se terminant en une extrémité arrondie. Les genres claraziidés Clarazia et Thalatto saurus partagent quant à eux un rostre plus court dont les bordures latérales sont convergentes et qui se termine en une pointe fine. Un diastème séparant les dents prémaxillaires des dents maxillaires est également présent. L'holotype de Nectosaurus halius, qui est bien préservé, présente une structure rostrale hautement dérivée. La maxille est courte et montre une bordure tronquée antérieurement (verticale), un processus ascendant étroit mais haut et une bordure médiale inclinée dorsalement qui forme une articulation naturelle avec le vomer dévié ventralement. Ces observations viennent appuyer la reconstitution initiale d'Hescheleria par Peyer qui présentait une prémaxille quasi verticale.

Document Type: Research article

Publication date: 2005-12-01

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