Redescription, palaeobiogeography and palaeoecology of Coniasaurus crassidens Owen, 1850 (Squamata) from the Lower Chalk (Cretaceous; Cenomanian) of SE England

A New Species of the Pythonomorph Carentonosaurus from the Cenomanian of Algora (Guadalajara, Central Spain)

The Cenomanian (lowermost Upper Cretaceous) faunal assemblages are of high interest in understanding the turnovers that took place between the Early and the Late Cretaceous, resulting in significant differences. In this context, the analysis of the association of reptiles found in the Algora fossil site (Guadalajara Province, Central Spain) is of great interest since it represents the first European Cenomanian site with a high concentration of macrovertebrate remains. A new pythonomorph ‘lizard’ from Algora, Carentonosaurus algorensis sp. nov., is described here. It is the second representative of this European genus. Its microanatomical study reveals that an extreme pachyosteosclerosis affected at least its dorsal vertebrae, suggesting adaptations for slow-swimming habits in shallow-water environments. Consequently, this new taxon is interpreted as a slow swimmer, hovering near the bottom of near-shore marine environments of the Late Cretaceous European Archipelago and, more specifically, along the shores of the larger Iberian Island for that period. This is in concordance with the high diversification of ‘pachyostotic’ pythonomorphs recorded during the Cenomanian, allowing the subsequent adaptation of this lineage to open marine environments.

Inferring 'weak spots' in phylogenetic trees: application to mosasauroid nomenclature

Mosasauroid squamates represented the apex predators within the Late Cretaceous marine and occasionally also freshwater ecosystems. Proper understanding of the origin of their ecological adaptations or paleobiogeographic dispersals requires adequate knowledge of their phylogeny. The studies assessing the position of mosasauroids on the squamate evolutionary tree and their origins have long given conflicting results. The phylogenetic relationships within Mosasauroidea, however, have experienced only little changes throughout the last decades. Considering the substantial improvements in the development of phylogenetic methodology that have undergone in recent years, resulting, among others, in numerous alterations in the phylogenetic hypotheses of other fossil amniotes, we test the robustness in our understanding of mosasauroid beginnings and their evolutionary history. We re-examined a data set that results from modifications assembled in the course of the last 20 years and performed multiple parsimony analyses and Bayesian tip-dating analysis. Following the inferred topologies and the 'weak spots' in the phylogeny of mosasauroids, we revise the nomenclature of the 'traditionally' recognized mosasauroid clades, to acknowledge the overall weakness among branches and the alternative topologies suggested previously, and discuss several factors that might have an impact on the differing phylogenetic hypotheses and their statistical support.

The Cenomanian-Turonian (late Cretaceous) radiation of marine squamates (Reptilia): the role of the Mediterranean Tethys

During the Cenomanian-Turonian interval, marine squamates display a spectacular radiation in particular on the margins of the Mediterranean Tethys and, to a lesser extent, in the Interior Seaway of North America. In this span of time, three major groups diversified: the “hind-limbed” snakes (“pachyophiids”), the “dolichosaurids”, and the mosasauroids. “Hind-limbed” snakes, exhibiting all a pachyostotic bony structure, were small tropical inhabitants, known exclusively from the Cenomanian of the Mediterranean Tethys. “Dolichosaurids” and mosasauroids were rather mid latitude distributed groups, found in a wide range of palaeoenvironments of both the Mediterranean Tethys and the Western Interior Seaway. Whereas “dolichosaurids” remain of small size and become rare after the Cenomanian/Turonian (C/T) boundary, mosasauroids exhibit a notable size-increase and develop since the mid Turonian to become highly diversified and cosmopolitan large predators of the end of the Cretaceous. This important radiation of marine squamates is thus, except for derived mosasauroids (mosasaurids), restricted in time (Cenomanian-Turonian) and space (mostly the northern and southern margins of the Mediterranean Tethys). It is probable that: 1) the Mediterranean Tethys played an important role in both the radiation and the dispersion of these marine squamates during the Cenomanian-Turonian interval; 2) certain major geological and biological events that characterize this pivotal period (i.e., global high sea-level stand and warm sea-surface temperatures allowing the development of large carbonated platforms) could have permitted this radiation; and 3) conversely, other factors occurring at or just after the C/T boundary (OAE2, sea-level and sea-surface temperature drops, marine extinctions including the demise of carbonated platforms) as well as factors inherent to each of the groups (mainly the size and bone microstructure) could have had an effect on and insured the success of the mosasaurids with respect to the other groups, whereas thereafter the radiation of snakes succeeded only in continental environments.