Recent work in the Upper Cretaceous of northeastern Mexico has produced a diversity of vertebrate remains. For specimens referable to Squamata, both old and new, an annotated catalogue is here provided, wherein are summarised the geological context and morphological features of each specimen. All specimens appear to represent marine squamates, including an aigialosaur-like reptile preserving integumentary structures, several vertebrae possibly representing mosasauroids, the first Mexican mosasaur known from significant cranial material, an isolated mosasaur mandibular fragment, and the holotype of Amphekepubis johnsoni (considered to belong to Mosasaurus). These discoveries are auspicious and should deepen our understanding of palaeobiogeographic and evolutionary patterns

A new genus and species of primitive-limbed mosasauroid, Dallasaurus turneri, from the Middle Turonian (∼92 Ma) of north-central Texas, is described on the basis of two incomplete skeletons. The new taxon retains plesiomorphic characters such as facultatively terrestrial limbs (plesiopedal) but also exhibits certain characters shared with derived mosasaurs of the subfamily Mosasaurinae. In phylogenetic analysis, the new taxon reconstructs as the basal member of that clade. Other plesiopedal taxa previously included in the family Aigialosauridae reconstruct in basal positions within three different, major clades that include members that achieved the derived (hydropedal) fin-like limb condition. In addition, Opetiosaurus and Aigialosaurus reconstruct as successive outgroup taxa to all other mosasauroids, thereby demonstrating the paraphyletic nature of the current concept of Aigialosauridae. Interpretation of our phylogenetic analysis suggests that three different lineages of mosasauroids independently achieved the derived mosasaur body plan, including fully marine limb modifications culminating in the development of flippers or paddle-like appendages. The inclusion of plesiopedal forms within lineages of well-established hydropedal clades requires a reorganisation of our concepts of Mosasauridae to include these basal forms. In order to avoid continued use of the paraphyletic taxon ‘Aigialosauridae’ as currently defined, we recommend ‘Aigialosauridae’ as a formal taxonomic name be used only for inclusion of Aigialosaurus dalmaticus and potential members of its own independent lineage. This also avoids the implicit polyphyletic use of ‘Mosasauridae’. Additionally, the diagnosis of Mosasauridae should be modified to exclude limb characters that discriminate between more terrestrial versus more aquatic adaptations.