fibrous tooth attachment via periodontal ligament that's usually found in mammals and archosaurs. The marginal tooth rows in mosasauroids like Clidastes are found on the premaxilla, maxilla and the dentary. On the dorsal surface of the dentary there is an interdental ridge that separates successive teeth labially. These interdental ridges serve to separate succeeding teeth that grow upward between existing teeth. Occurrences Clidastes is currently found in marine deposits in the US. In past, however, specimens were referred to this genus from Sweden, Germany, Russia, Mexico, and the Maastrichtian of Jordan. However, Lively (2019) questioned the referral of these remains to Clidastes due to their fragmentary nature and lack of apomorphies placing them in the genus to the exclusion of other mosasaurs. Discovery E. D. Cope discovered the first specimens of Clidastes propython in 1869 from the Mooreville Chalk in Lowndes County, Alabama. The remains unearthed were that of a juvenile but are one of the best preserved and most complete mosasaurs collected from the state and is regarded as the generic holotype of Clidastes. In 1918, Charles H. Sternberg and his son found additional remains of Clidastes in Kansas. They were surprised to see that it had humeri and femora with round heads, similar to that of mammals. Due to good preservation of the caudals, Sternberg noted that the chevrons along the vertebrae were ankylosed to the center, which is not observed in other mosasaurs. This synapamorphy was believed to aid in fitting the proximal heads snugly into the basins that hew out from the vertebrae almost locking them in place. Classification and species The dental and vertebral morphology of Clidastes is closer to that of Mosasaurus than to any other mosasaur, firmly placing it within the subfamily Mosasaurinae. Besides being different in size, the teeth of Campanian species of Mosasaurus (namely M. missouriensis and M. conodon) differ from those of Clidastes in having a large number of facets that are also more distinct than those in Clidastes. The cervical vertebrae of Clidastes are also different from those in Mosasaurus by being more elongated. Clidastes is most frequently recovered as one of the most basal mosasaurines, and the most basal hydropedal mosasaurine genus, being more derived than the plesiopedal Dallasaurus but less derived than later genera like Prognathodon or Globidens. The cladogram below is modified from Aaron R. H. Leblanc, Michael W. Caldwell and Nathalie Bardet, 2012: There is