Amphicotylus is an extinct genus of goniopholidid mesoeucrocodylian from the Tithonian of Colorado, Wyoming, and Oklahoma. It was described in 1878.<ref name=Cope78>E. D. Cope. 1878. Descriptions of new extinct Vertebrata from the Upper Tertiary and Dakota Formations. 'Bulletin of the United States Geological and Geographical Survey of the Territories, 4(2):379-396</ref> Discovery and speciesAmphicotylus was first described by Edward Drinker Cope in 1878 based on dorsal and lumbar vertebrae, ribs and osteoderms. Based on these remains, found in the same locality as Camarasaurus supremus, Cope determined the animal to have been smaller in size than the extant American Alligator and named the species A. lucasii after Superintendent Lucas who initially made the discovery. Cope also collected skull material from the same locality and level, however did not refer it to Amphicotylus. The cranial material was examined by Charles C. Mook in 1942 who referred it to the type species not only on the basis of its locality, but also its matching size, general morphological characters and the absence of any other crocodilian remains from the area. Mook furthermore uses this skull to establish a provisional neotype to account for the fragmentary nature of the original material described by Cope. In the 1930s the Works Progress Administration discovered further remains in Oklahoma which were initially investigated by J. W. Stovall, noting similarities to Amphicotylus gilmorei. The remains were officially described by Mook in 1964 as a species of Goniopholis, Goniopholis stovalli. In 2012 Eric Randall Allen argued that the goniopholidids found in the Morrison Formation differ significantly from their European counterparts in the anatomy of the palate, with the choanae fully splitting the palatines unlike in the taxa from the UK and mainland Europe. Consequently, Allen reasons that Goniopholis should exclusively refer to European forms while Amphicotylus should serve as a constituent for Morrison goniopholidids previously referred to Goniopholis, such as "Goniopholis" felix. Furthermore, it is noted that there are no significant differences between A. lucasii and the only known material of A. gilmorei, with the only notable morphological character being artificially created by breakage, rendering it a junior synonym of the genus' type species. Excavations in the East Camarasaurus Quarry, Wyoming, in 1993 yielded the largest and most complete goniopholidid skeleton found to date. Since 1996 the fossil has been exhibited and stored in the Gunma Museum of Natural History in Japan before it was described by Yoshida et al. in