Article: Capitosauroid labyrinthodonts from the Trias of England

Amphibian remains from several 'Lower Keuper' Sandstone localities in England, including the holo-type of Cyclotosaurus stantonensis (Woodward), are examined. Differences in patterns of skull ornamentation in mastodonsaurs and parotosaur/cyclotosaurs are discussed and it is suggested that these are of taxonomic value. The specimens fall into three groups, two of which are species of Cyclotosaurus, the other group representing a primitive mastodonsaur. Basic differences between mastodonsaurs and parotosaur/cyclotosaurs are discussed.The complicated nomenclature of the English fossils is investigated and the valid names of the cyclotosaurs are shown to be Cyclolosaurus leptognathus (Owen), of which C. stantonensis (Woodward) is a subjective junior synonym, and C. pachygnathus (Owen). The valid name of the mastodonsaur is demonstrated to be Mastodonsaurus lavisi (Seeley). The phylogeny of the superfamily Capitosauroidea is discussed.The significance of the vertebrate remains in the stratigraphic correlation of the 'Lower Keuper' Sandstone is considered; the degree of specialization of the labyrinthodonts suggests an early Ladinian (Middle Trias, Upper Muschelkalk) age for their horizon.