New material of Ikechosaurus sunailinae (Reptilia: Choristodira) from the Early Cretaceous Laohongdong Formation, Ordos Basin, Inner Mongolia, and the interrelationships of the genus

Abstract

New material of Ikechosaurus sunailinae from the Early Cretaceous Laohongdong Formation of the Ordos Basin, Inner Mongolia, People's Republic of China, is described. This material, which includes well-preserved articulated skeletons and a series of isolated elements, demonstrates that Ikechosaurus is more closely related to Champsosaurus than to Simoedosaurus, sharing with Champsosaurus the presence of an elongate snout, anteriorly constricted parasphenoid with the foramen canalis caroticus internus located in or near the suture between the parasphenoid and the pterygoid, an anterior extension of the anterior end of the jugal, and an elongate symphysis including the splenial. Ikechosaurus is primitive relative to Champsosaurus in the anterior position of the internal narial openings, in the less strongly flared temporal region with the temporal openings placed largely above one another, in the absence of fenestra in the occiput between the parietal and squamosal, and in the interpterygoid vacuity bordered posteriorly by the basisphenoid. Ikechosaurus and Tchoiria are at a similar grade of evolution, but can be separated by details in the arrangement of bone forming the skull roof.