The cranial osteology of the large ichthyosaur Guizhouichthyosaurus tangae from the Wayao Member of the Falang Formation (Lower Carnian, Upper Triassic) of Guizhou, southwest China, is described, based on a well preserved skull and mandible and additional specimens. It can be diagnosed by a suite of cranial characters that include premaxilla without well-developed processus subnarialis, maxilla reaches far anteriorly and has a very long processus postnarialis, orbit of characteristic shape with concave dorsal and straight posterior and ventral margins, small prefrontal that forms only the anterior third of the dorsal orbital margin, postfrontal meets the supratemporal externally, postorbital forms a large part of the lateral margin of the temporal fenestra internally, deep triangular incisura postjugalis, jugal fails to meet quadratojugal externally, short postorbital skull segment; frontals and parietals form sharp ridges lateral to the area of the foramen parietale; parietals form a low and narrow sagittal crest; teeth thecodontously implanted, blunt, conical and without carinae. New data on the postcranial skeleton are also provided. The available evidence indicates that Guizhouichthyosaurus is an advanced member of the Merriamosauria, but more plesiomorphic than the parvipelvians. The taxonomy of the large ichthyosaurs from the Falang Formation remains largely problematic. It appears probable that only two taxa are valid, Guizhouichthyosaurus tangae and Guanlingsaurus liangae. They differ in the length of the snout, the number of the presacral vertebrae, vertebral proportions, the shape of the humerus and fibula, among other features.
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Vol. 26 • No. 3