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

Abstract

ABSTRACT A new species of Coniasaurus, from the Lower Chalk Formation (Upper Cretaceous; Lower to Middle Cenomanian) of southeast England, is described. The type and only specimen preserves the right and left maxilla, frontal,? squamosal?, parietal, partial right and left pterygoids, right septomaxilla, partial right and left vomeropalatines, four articulated dorsal vertebrae, several fragmentary ribs, and the left scapula and coracoid. The maxilla and vertebrae of the new species are similar in form to equvialent elements from the genotype, Coniasaurus crassidens Owen, 1850. However, significant differences are found in maxillary tooth morphology, the number of maxillary teeth, and the length of the maxilla. In Coniasaurus, sp. nov., in contrast to the genotype, the maxilla is shorter and slightly more robust, the ascending process of the maxilla is taller (but lower as compared to other squamates), the crowns of the maxillary teeth are swollen and blunt-tipped, not bulbous, 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 to be monophyletic in all cladograms; the six mosasaur taxa also formed a monophyletic group nested higher in the cladogram. However, basal relationships 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 composed of mosasaurs and aigialosaurs. Previous suggestions of aigialosaur paraphyly cannot be verified or refuted by this analysis, however, coniasaurs are a basal clade within the larger clade containing mosasaurs and aigialosaurs.