Gwyneddosaurus is a possibly invalid genus of extinct aquatic tanystropheid reptile. The type species, G. erici was described in 1945 by Wilhelm Bock, who identified it as a coelurosaurian dinosaur related to Podokesaurus (at the time, "podokesaurids" were thought to be coelurosaurians). Its remains were found in the Upper Triassic Lockatong Formation of Montgomery County, eastern Pennsylvania, and include skull fragments, several vertebra, ribs, gastralia, partial shoulder and hip bones, and several forelimb and hindlimb elements found in soft shale. The type specimen is ANSP 15072. It was discovered by Bock's four-year-old son. It was not a large animal; the type skeleton was estimated by Bock as 18 centimetres (7.1 in) long, and its thigh bone was only 23 millimeters long (0.91 in).