Zverkov NG, Fischer V, Madzia D & Benson RBJB. 2018 Increased pliosaurid dental disparity across the Jurassic–Cretaceous transition. Palaeontology doi: 10.1111/pala.12367.
Pliosaurid marine reptiles played important roles in marine food chains from the Middle Jurassic to the ‘middle’ Cretaceous, frequently as apex predators. The evolution of pliosaurids during the later parts of the Early Cretaceous has recently been illuminated by discoveries from Russia (Hauterivian) and Colombia (Barremian). However, knowledge of pliosaurids representing the Jurassic–Cretaceous transition (late Tithonian–Valanginian), is still largely incomplete, especially during the earliest Cretaceous. As such, the effect on pliosaurids of hypothesized faunal turnover during the Jurassic–Cretaceous boundary interval is poorly understood. We report pliosaurid teeth from theupper Volgian (Tithonian, Upper Jurassic) of the Kheta river basin (Eastern Siberia, Russia), to the Berriasian and Valanginian (Lower Cretaceous) of the Volga region (European Russia). These assemblages yielded a series of distinct tooth morphotypes, including the first reports of conical-toothed pliosaurids from the latest Jurassic–earliest Cretaceous.This challenges the hypothesis that only one lineage of pliosaurids crossed the Jurassic–Cretaceous boundary. It appears that conical-toothed pliosaurids co-existed with their trihedral-toothed relatives for at least 25 million years during the latest Jurassic and earliest Cretaceous. In fact, our quantitative analyses indicate that pliosaurids reached their maximal dental disparity during this interval, showing little evidence of turnover associated with the Jurassic–Cretaceous transition. Instead, disparity decreased later in the Early Cretaceous, with the disappearance of trihedral-toothed forms in the Barremian.
The very first paper of Isaure!
Rhinochelys amaberti Moret (1935), a protostegid turtle from the Early Cretaceous of France
Scavezzoni I & Fischer V. PeerJ 6:e4594; DOI 10.7717/peerj.4594 Freely available here
Modern marine turtles (chelonioids) are the remnants of an ancient radiation that roots in the Cretaceous. The oldest members of that radiation are first recorded from the Early Cretaceous and a series of species are known from the Albian- Cenomanian interval, many of which have been allocated to the widespread but poorly defined genus Rhinochelys, possibly concealing the diversity and the evolution of early marine turtles. In order to better understand the radiation of chelonioids, we redescribe the holotype and assess the taxonomy of Rhinochelys amaberti Moret (1935)(UJF-ID.11167) from the Late Albian (Stoliczkaia dispar Zone) of the Vallon de la Fauge (Isère, France). We also make preliminary assessments of the phylogenetic relationships of Chelonioidea using two updated datasets that widely sample Cretaceous taxa, especially Rhinochelys. Rhinochelys amaberti is a valid taxon that is supported by eight autapomorphies; an emended diagnosisis proposed. Our phylogenetic analyses suggest that Rhinochelys could be polyphyletic, but constraining it as a monophyletic entity does not produce trees that are significantly less parsimonious. Moreover, support values and stratigraphic congruence indexes are fairly low for the recovered typologies, suggesting that missing data still strongly affect our understanding of the Cretaceous diversification of sea turtles.
Isaure's drawing on Rhinochelys amaberti
The evolutionary history of polycotylid plesiosaurians
Fischer V., Benson R.B.J., Druckenmiller P.S., Ketchum H.F.& Bardet N.
VF and RBJB are co-first authors
Royal Society Open Science 5: 172177. http://dx.doi.org/10.1098/rsos.172177. Freely available here
Polycotylidae is a clade of plesiosaurians that appeared during the Early Cretaceous and became speciose and abundant early in the Late Cretaceous. However, this radiation is poorly understood. Thililua longicollisfrom the Middle Turonian of Morocco is an enigmatic taxon possessing an atypically long-neck and, as originally reported, a series of unusual cranial features that cause unstable phylogenetic relationships for polycotylids. We reinterpret the holotype specimen of Thililua longicollisand clarify its cranial anatomy. Thililua longicollispossesses an extensive, foramina-bearing jugal, a premaxilla-parietal contact, and carinated teeth. Phylogenetic analyses of a new cladistic dataset based on first hand observation of most polycotylids, recovers Thililua and Mauriciosaurusas successive lineages at the base of the earliest Late Cretaceous polycotyline radiation. A new dataset summarizing the Bauplan of polycotylids reveal that their radiation produced an early burst of disparity during the Cenomanian-Turonian interval, with marked plasticity in relative neck length, but this did not arise as an ecological release following the extinction of ichthyosaurs and pliosaurids. This disparity vanished during and after the Turonian, which is consistent with a model of ‘early experimentation/late constraint’. Two polycotylid clades, Occultonectia clade nov. and Polycotylinae, survived up to the Maastrichtian, but with low diversity.
Our interpretation of the skull of Thililua longicollis, an early Late Cretaceous polycotylid from Morocco