Description and phylogenetic relationships of a new species of ConiasaurusOwen, 1850 (Squamata)

A new species of Coniasaurus, from the Lower Chalk Formation (Upper Cretace ous: Lower to Middle Cenomanian) of southeast England, is described. The ty pe and only specimen preserves the right and left maxilla, frontal,? squamo sal?, parietal, partial right and left pterygoids, right septomaxilla, part ial right and left vomeropalatines, four articulated dorsal vertebrae, seve ral fragmentary ribs, and the left scapula and coracoid. The maxilla and ve rtebrae of the new species are similar in form to equvialent elements from the genotype, Coniasaurus crassidens Owen, 1850. However, significant diffe rences are found in maxillary tooth morphology, the number of maxillary tee th, and the length of the maxilla. In Coniasaurus, sp. nov., in contrast to the genotype, the maxilla is shorter and slightly more robust, the ascendi ng process of the maxilla is taller (but lower as compared to other squamat es), the crowns of the maxillary teeth are swollen and blunt-tipped, not bu lbous, and without lateral sulci. Cladistic analysis of six mosasaur taxa, three 'aigialosaur' taxa, Coniasaurus crassidens, and Coniasaurus, sp. nov. (73 characters, 11 taxa in total) found 52 shortest cladograms (137 steps; CI 0.650; HI 0.350). A Strict Consensus Tree found the genus Coniasaurus t o be monophyletic in air cladograms; the six mosasaur taxa also formed a mo nophyletic group nested higher in the cladogram. However, basal relationshi ps between coniasaurs, the three aigialosaur taxa (Aigialosaurus dalmaticus , Aigialosaurus [=Opetiosaurus] buccichi, Carsosaurus marchesetti), and the mosasaur clade were unresolved. A Majority Rule Consensus tree found that in 58% of the cladograms, coniasaurs are the sister-group to a clade compos ed of mosasaurs and aigialosaurs. Previous suggestions of aigialosaur parap hyly cannot be verified or refuted by this analysis, however, coniasaurs ar e a basal clade within the larger clade containing mosasaurs and aigialosau rs.