AN ARCHOSAUR-LIKE LATEROSPHENOID IN EARLY TURTLES(REPTILIA: PANTESTUDINES)

摘要

Turtles are placed with increasing consistency by molecular phylogenetic studies within Diapsida assister to Archosauria, but published gross morphology—based phylogenetic analyses do not recover this position.Here, we present a previously unrecognized unique morphological character offering support for this hypothesis: thepresence in stem turtles of a laterosphenoid ossification identical to that in Archosauriformes. The laterosphenoid is atripartite chondrocranial ossification, consisting of an ossified pila antotica, pila metoptica, and taenia medialis +planum supraseptale. It forms the anterior border of the exit for the trigeminal nerve (V) and partially encloses theexits for cranial nerves III, IV, and II. This ossification is unique to turtles and Archosauriformes within Vertebrata.It has been mistakenly dismissed as anatomically dissimilar in these two groups in the past, so we provide a completedescription and detailed analysis of correspondence between turtles and Archosauriformes in each of itsembryologically distinct components. A preliminary phylogenetic.analysis suggests other potential synapomorphiesof turtles and archosaurs, including a row or rows of mid-dorsal dermal ossifications.