Rafetus Bohemicus

''Rafetus bohemicus'' is an extinct species of softshell turtle from the Early Miocene (Burdigalian) of the Czech Republic. Specimens have been found at the northeastern margin of the Most Basin at a fossil site called Břešt’any. Fossil carapaces of "'' R. pontanus''", a potential taxonomic synonym (although currently considered a ''nomen dubium''), have been found in slightly younger rocks in Lom and Louka u Litvínova.

Geology

The composition of the Břešt’any Clay is primarily limnic ceramic clay, with the occasional siderite concretion. It has been dated to ~17.5 Ma. It is located between the layers of rock that make up the Holešice and Libkovice Formations.

This fine, kaolinite rich mudstone preserves fossils from an Early Miocene (Burdigalian) lacustrine environment, during a period of global warming known as the Mid-Miocene Climatic Optimum. Here, fossils of ''Rafetus bohemicus'' are preserved in either limnic clays or siderite concretions; those of the former are very fragile, making it impossible to extract such specimens from the surrounding matrix. However, three skulls embedded in limnic clay have been CT-scanned.

Taxonomy

The species was originally described as ''Trionyx bohemicus'' by Adalbert Liebus in 1930.

In 1998, Hans-Volker Karl synonymized ''T. bohemicus'', as well as all other European fossil species then classified under ''Trionyx'', with the extant ''Trionyx triunguis''. In 1999, V. M. Chkhikvadze concluded that all of these species were actually synonyms of ''Trionyx pontanus'' as it had nomenclatural priority, which he further revised as '' Rafetus pontanus''. In 2017, Georgios L. Georgalis and Walter G. Joyce concluded that ''T. pontanus'' was a ''nomen dubium''; both syntypes were composed only of carapace material, making distinction from ''T. bohemicus'' difficult. However, they agreed with ''T. bohemicus''s placement under the genus ''Rafetus''.

In 2023, Chroust ''et al.'' reaffirmed ''T. pontanus''s affinity with the genus ''Rafetus'', but agreed it should remain a ''nomen dubium'', and furthermore provided a redescription of ''Rafetus bohemicus''.

Description

As a species of ''Rafetus'', ''R. bohemicus'' can be distinguished from other European fossil softshell turtle species of the genus ''Trionyx'' by its shorter and broader snout, a larger internal naris, a non-concave medial edge of the maxilla in palatal view (instead of straight), and a shorter intermaxillary suture developed between the intermaxillary foramen and internal naris.

''Rafetus bohemicus'' is smaller than its living congener, the Yangtze giant softshell (''Rafetus swinhoei''). Of the known skull material, the largest skull is that of RMT PA 1310, measuring 19.2 cm from the anterior rim of the orbit to the posterior end of the supraoccipital crest. Larger specimens show a more developed supraoccipital crest and squamosal posterior process. Two carapaces are known, which are similar in size (around 30 cm long) and belonged to subadult individuals.

Evolution

Phylogenetic analyses in 2014 have estimated that the two living ''Rafetus'' species ('' R. swinhoei'' and '' R. euphraticus'') diverged 20 million years ago, in the Early Miocene. ''R. bohemicus'' is just slightly younger than this time of divergence, at 17.5 million years old, coinciding with a period of global warming known as the Mid-Miocene Climatic Optimum.

Gallery

File:The hind limbs of Rafetus bohemicus from Břešt’any.png, Left pubis and ischium (A-B). Right femur (C–D). Left femur (E). Right femur (F–G).
File:The forelimbs of Rafetus bohemicus from Břešt’any.png, Right pectoral girdle (A-B), right coracoid(C) view, right humerus (D–E) view.
File:The plastron (syntype) of Rafetus bohemicus from Břešt’any.png, Plastron elements in ventral view (A), reconstruction of the plastron in ventral view (B)
File:Isolated cervical vertebrae of Rafetus bohemicus from Břešt’any.png, Isolated cervical vertebrae

References

{{Taxonbar, from=Q131308154

bohemicus
Fossil taxa described in 1930
Burdigalian life
Miocene turtles
Miocene reptiles of Europe
Fossils of the Czech Republic