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The turtle locomotor system is heavily modified owing to the severe impact of development of the shell on the body plan of these reptiles. Although limb and girdle osteology of the earliest, Triassic turtles is relatively well understood in general, the exact impacts of variability, ontogeny and preservation (e.g. deformation) on the observed morphologies have rarely been considered in detail. Here, we describe in detail and document the osteology and intraspecific variability of the limbs and girdles of Proterochersis spp. the basalmost true turtles (Testudinata). We also provide a synthesis of currently available data and detailed comparisons with other Triassic stem turtles to gain a better understanding of the diagnostic value of the early turtle appendicular skeleton and to pave the way for future biomechanical and functional studies. Our data suggest that Proterochersis spp. could be at least partly aquatic and could change their preferred habitat during ontogeny, with larger (and, presumably, older) specimens presenting more characters suggestive of a more terrestrial environment. [ABSTRACT FROM AUTHOR]

The material historically referred to Chelytherium obscurum is exceptional for a number of reasons. It is the first described Triassic turtle, the oldest testudinate among the British palaeontological collections, and it is one of the oldest testudinates in the world. Nevertheless, after its establishment in 1863, the taxon remained in a taxonomic limbo and was eventually almost forgotten. However, the recent reconsideration of proterochersid turtles, with improved understanding of their anatomy, allows reassessment of Chelytherium obscurum as a member of the Proterochersidae, subjectively synonymous with Proterochersis robusta. Despite nomenclatural priority, in accordance with the suggestions of previous authors, the name Proterochersis robusta is endorsed to be upheld. [ABSTRACT FROM AUTHOR]

A recently discovered Norian outcrop in Poręba, Poland, has yielded numerous well-preserved turtle remains. These, together with historical materials from Germany, enabled the identification of two new proterochersid taxa: Proterochersis porebensis sp. nov. from Poland and Keuperotesta limendorsa gen. et sp. nov. from Germany. Moreover, two problematic taxa, Proterochersis intermedia Fraas, 1913; and Murrhardtia staeschei Karl & Tichy, 2000; are shown to be conspecific with Proterochersis robusta Fraas, 1913. New diagnoses for the family Proterochersidae Nopcsa, 1923 and all included taxa are provided. Proterochersids are of great importance to turtle phylogeny because of their age (they comprise the oldest fully shelled turtle species known to date) and their still-debated phylogenetic position (classically they are considered the basalmost Pleurodira, but in some analyses they are placed on the stem of Testudinata). Newly discovered plesiomorphic aspects of the anatomy of these three species included in the phylogenetic analysis demonstrate that they are not only the oldest, but are also the most basal fully shelled turtles. The unique features of their shell (e.g. the first thoracic rib unreduced and costal-bearing, and the osseous contact between the carapace and sacral vertebra) are of special significance for future research of the earliest stages of turtle shell evolution. This is the first contribution focused solely on the new, phylogenetically informative, and important characters of this group since the initial description of P. robusta more than 100 years ago. [ABSTRACT FROM AUTHOR]