On the aquatic squamate Dolichosaurus longicollis Owen, 1850 (Cenomanian, Upper Cretaceous), and the evolution of elongate necks in Squamates

The marine squamate, Dolichosaurus longicollis, from the Upper Cretaceous ( Cenomanian) Chalk deposits of southeast England is redescribed. The elongat e neck of D. longicollis is produced by an increased number of cervical ver tebrae. Cervical peduncles are elongate, curved and are nor fused to the hy papophyses. There is no scapulocoracoid fenestra, the coracoid is not emarg inated, and the scapula and coracoid are not fused. The splenial and angula r articulate in a ball-and-socket joint similar to that of mosasaurs and Co niasaurus crassidens. The forelimb and pectoral girdle elements show eviden ce of reduction as compared to the pelvic girdle and rearlimb. Cladistic an alysis of six mosasaur taxa, three 'aigialosaur' taxa. Coniasaurus crasside ns. Coniasaurus gracilodens. and D. longicollis. using 66 characters, found 27 most parsimonious cladograms (MPCs): 122 steps: C.I. 0.648: H.I. 0.352: R.I. 0.669. A Strict Consensus Tree found support for the monophyly of the Mosasauridae and Aigialosauridae; sister-group relationships between conia saurs. Dolichosaurus. Aigialosauridae and Mosasauridae are an unresolved po lytomy. A Majority Rule Consensus Tree finds Dolichosaurus as sistergroup t o (C. crassidens, C. gracilodens (Aigialosauridae (Mosasauridae))) in nine (33%) of the MPCs. Lack of support for a more inclusive Dolichosauridae com posed of Dolichosaurus + (C. crassidens, C. gracilodens) is attributed to t he incompleteness of the fossil remains of these three taxa. Presence/absen ce of a pectoral girdle currently defines the presence/absence of a neck. T his definition is insufficient and hypapophyses are found more informative regarding taxic differences and transformational scenarios. The paleobiolog y of Dolichosaurus is reconstructed as similar to coniasaurs. nothosaurs, a nd modern sea snakes.