Papers about turtles:
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Unlike any other tetrapod, turtles form their dorsal bony shell (carapace) not from osteoderms, but by contribution of the ribs and vertebrae that expand into the dermis to form plate-like shell components. Although this was known from embryological studies in extant turtles, important steps in this evolutionary sequence have recently been highlighted by the Triassic taxa Pappochelys, Eorhynchochelys and Odontochelys, and the Permian Eunotosaurus. The discovery of Pappochelys shed light on the origin of the ventral bony shell (plastron), which formed from enlarged gastralia. A major question is whether the turtle shell evolved in the context of a terrestrial or aquatic environment. Whereas Odontochelys was controversially interpreted as aquatic, a terrestrial origin of turtles was proposed based on evidence of fossorial adaptations in Eunotosaurus. We report palaeohistological data for Pappochelys, a taxon that exemplifies earlier evolutionary stages in the formation of the bony shell than Odontochelys. Bone histological evidence reveals (1) evolutionary changes in bone microstructure in ribs and gastralia approaching the turtle condition and (2) evidence for a predominantly amphibious or fossorial mode of life in Pappochelys, which support the hypothesis that crucial steps in the evolution of the shell occurred in a terrestrial rather than fully aquatic environment.
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A. PÃrez-GarcÃa, E. DÃaz-Berenguer, A. Badiola & J.I. Canudo (2019)
An unexpected finding: identification of the first complete shell of the Franco-Belgian middle Eocene littoral pleurodiran turtle Eocenochelus eremberti in Spain.
Historical Biology (advance online publication)
doi: Â
https://doi.org/10.1080/08912963.2019.1644330 Â
https://www.tandfonline.com/doi/full/10.1080/08912963.2019.1644330
Pleurodiran turtles are relatively abundant in the Eocene record of Europe, being mostly represented by Podocnemididae. Two genera have been identified. The most abundant and diverse is the well-known freshwater Neochelys. The other is Eocenochelus. The record of this poorly-known genus is very scarce. It is the only representative of the Upper Cretaceous to extant Erymnochelyini (i.e., a new tribe proposed here for the âErymnochelys group of turtlesâ) interpreted as a littoral form, and the only one known outside Africa. The finding of the only complete shell of Eocenochelus hitherto identified is presented here. It comes from the CastejÃn de Sobrarbe-41 site, in the middle Eocene (Lutetian) of the Sobrarbe Formation of the Ainsa Basin (Huesca, Spain). The sedimentary environment of the site is compatible with its attribution to a littoral form. It is attributed to the type species of the genus, Eocenochelus eremberti, so far exclusively known by two partial shells from the middle Eocene of the Franco-Belgian Basin. Therefore, the paleobiogeographic distribution of this species is markedly increased, from the southern area of the North Sea to the Bay of Biscay. This finding provides new anatomical data on the species Eocenochelus eremberti and on its poorly known genus.