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Chelonioid sea turtles (Order Testudinata; Superfamily Chelonioidea) first appear in the early Cretaceous (Aptian-Albian). Their long fossil record is excellent compared to most marine tetrapods. Nonetheless, there has been no inclusive attempt to provide an analysis of cladistic relationships among this group. In this paper, the following chelonioid classification is proposed, based on 76 characters among 20 fossil and six living well-represented genera:(1) Family Cheloniidae (Coniacian to Recent)

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Among living turtles, highly terrestrial or highly aquatic modes of life are likely to have developed from a plesiomorphic semi-aquatic one. A taxonomically comprehensive data set of turtle humeri was examined to ascertain if adaptation to an aquatic or a terrestrial lifestyle affects the general internal bone structure. Three-dimensional and virtual cross-sections were obtained from computed microtomography to compare humeral changes among the various lifestyles -terrestrial, semi-aquatic and aquatic -focusing on the degree of resorption of periosteal bone. Regardless of lifestyle, the humeri of the 52 turtles examined lacked a large open medullary cavity, and only one or a few small cavity(ies) or intertrabecular spaces were found near the growth centre. Semi-aquatic and aquatic turtles display the highest and lowest median values of humeral compactness, respectively, suggesting that limb-bone lightening is acquired both in highly terrestrial and in highly aquatic turtles. The broad overlap in compactness values between the lifestyles and the lack of tubular structure in all turtles, however, suggest that selection pressure of skeletal lightening in terrestrial turtles is not high enough to cause a tubular structure, possibly because of the rather passive mode of locomotion in terrestrial turtles. This overlap also suggests that the humeral compactness could not be used alone to provide an indication of lifestyle in turtles.

Abstract:Monophyly of the batagurid subfamily Geoemydinae was evaluated, and phylogenetic relationships within the subfamily were inferred on the basis of 35 morphological characters. Two approaches, parsimony analysis using the branch and bound algorithm, and neighbor joining clustering of an absolute distance matrix, were used. The results of these analyses yielded phylograms that were almost identical in branching topology, and poorly supported the monophyly of Geoemydinae. This subfamily thus seems to be a metataxon, most likely consisting of the sister group of Batagurinae (Geoemyda group) and a more primitive stock of Bataguridae (Mauremys group).

Phylogenetic relationships of the genus Cuora sensu lato (Cuora sensu stricto and Cistoclemmys) and other testudinoid genera were inferred from variations in 882 base positions of mitochondrial 12S and 16S rRNA genes. Results yielded a robust support to the monophyly of a group (Cuora group) consisting of Cuora sensu lato and the monotypic Pyxidea. Within the Cuora group, the continental Cuora (sensu stricto) and the two subspecies of Ci. flavomarginata constituted two well-supported monophyletic groups. Distinctly small interspecific genetic distances in the former groups suggested that in the continent speciations in Cuora took place much later than the primary divergences in the Cuora group, or speciations in other related genera, such as Mauremys. Our analyses failed to provide a substantial support to the monophyly of any other combinations of taxa within the Cuora group, including Cuora in broad and strict senses, and Cistoclemmys as consisting of Ci. galbinifrons and Ci. flavomarginata. Besides these, our results also suggested the non-monophyly for the Batagurinae and the Geoemydinae, and sister relationships of the Bataguridae with Testudinidae rather than with the Emydidae.

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