Coniasaurus is an extinct genus of Late Cretaceous marine squamates that range in age from Cenomanian to Santonian.

[1] It was first described by Richard Owen in 1850 from lower Cenomanian chalk deposits in South East England (Sussex).

[2][3] Two species have been described from this genus: C. crassidens (Owen, 1850), known from Cenomanian to Santonian deposits from South East England, Germany and North America, and C. gracilodens (Caldwell, 1999) from the Cenomanian of southeast England.

[1] Coniasaurus has only been described from incomplete specimens, but it is known to have had a relatively elongate skull with specialised teeth.

[3][4] Phylogenetic analysis suggests that Coniasaurus is a sister group to the Mosasauroidea within the clade Pythonomorpha.