Proterochersis intermedia, Fraas, 1913

Szczygielski, Tomasz & Sulej, Tomasz, 2016, Revision of the Triassic European turtles Proterochersis and Murrhardtia (Reptilia, Testudinata, Proterochersidae), with the description of new taxa from Poland and Germany, Zoological Journal of the Linnean Society (Zool. J. Linn. Soc.) 177 (2), pp. 395-427 : 406

PROTEROCHERSIS INTERMEDIA

Both Proterochersis robusta and Proterochersis intermedia were named in the same paper by Fraas (1913) on the basis of turtle material from the same strata (Norian, Lowenstein Formation) and region (area around Stuttgart) of Germany. According to Fraas (1913), Proterochersis intermedia differs from Proterochersis robusta in shell curvature and plastron thickness. Such discrimination is problematic for two reasons. Firstly, Fraas (1913) had only two specimens at his disposal, thus having no insight into ontogenetic and intraspecific variability. Secondly, the holotype of Proterochersis intermedia is fragmentary, possibly compacted, and its overall shape most likely changed during restoration (see description of SMNS 11396 in Material and methods). Additionally, our studies on turtle material from the lower Lowenstein Formation demonstrate that the height and curvature of the shells may vary, possibly ontogenetically, taphonomically, or diagenetically, not only between several otherwise morphologically identical specimens, but also between two sides of the same specimen (SMNS 17757). The putative fontanelles between rib endings of Proterochersis intermedia were considered by Fraas to be juvenile characteristics and specific at the same time, whereas we consider them to be artefacts of preservation. The rib tips, which seem to protrude from the distal ends of the first two preserved costal plates (thus bordering ‘fontanelles’) are in fact painted plaster, as shown by the fracture in one of them. No actual bone material indicates their existence. Even if any real bone fragments are embedded in this part, the interpretation of their nature is impossible, but most likely they originated from breakage or weathering. Although the internal mould might have been informative in that case, the condition cannot be inferred from it because the corresponding part is also entirely reconstructed. The only comparable diagnostic part, the fragment of plastron, is structurally identical, with the exception of thickness. Changes in thickness of plastron may be attributed to intraspecific diversity, age of the specimens, or sexual dimorphism. Bearing this in mind, the validity of Proterochersis intermedia is doubtful. Therefore, there is no basis to distinguish between Proterochersis robusta and Proterochersis intermedia , and the latter should be synonymized with the former.