Redescription, palaeobiogeography and palaeoecology of Coniasaurus crassidens Owen, 1850 (Squamata) from the Lower Chalk (Cretaceous; Cenomanian) of SE England

Type and referred specimens of Coniasaurus crassidens from the Lower Chalk (Upper Cretaceous; Cenomanian) of southeast: England, are re-described. The type is a left maxilla associated with 14 dorsal vertebrae. The maxilla is elongate, bears a low ascending process, and has a long and posteriorly po sitioned external narial margin. The first maxillary tooth is pointed and b ears a groove on the labial face; more posterior maxillary teeth are increa singly rounded and bulbous, and have a single groove on the labial face. Ma ndibles assigned to Coniasaurus cf. C. crassidens possess teeth of similar form; mandibular bones include the dentary, splenial, angular, coronoid, pr earticular, and surangular. A number of features show important similaritie s to later mosasaurs and contemporaneous groups such as dolichosaurs. These new data provide a very different picture of coniasaurs and their mode of life in the early Upper Cretaceous. The functional morphology of coniasaur teeth is unique and shows occlusion between the lingual platforms of the up per teeth with the crowns of the lower teeth. Coniasaurs can be considered as analgous to small sauropterygians in terms of general morphology, habita ts, and trophic structure. Coniasaur distributions in the Cenomanian and Tu ronian of Europe and North America are similar to the palaeobiogeographic p atterns of other organisms living in the Tethys and SuperTethys Seaway. (C) 1999 The Linnean Society of London.