Stenokranio

''Stenokranio'' (from the Greek στενός tenosfor narrow and κρανίο raniofor skull) is a genus of eryopid temnospondyl from the Permo-Carboniferous Remigiusberg Formation of Germany. It is represented by the type species, ''Stenokranio boldi'', which was named for two specimens collected from the Remigiusberg quarry near Kusel, Saar–Nahe Basin, southwest Germany.

Description

The type and only species, ''S. boldi'', is diagnosed by three autapomorphic features of the skull that differentiate it from all other eryopids: (1) the relatively narrow posterior skull table, therefore nearly parallel lateral margins of the skull; (2) the short postparietals and tabulars; and (3) the wide ectopterygoid. The two known skulls measure (holotype) and (paratype) and are thought to represent adult, though not fully mature, individuals. The holotype is represented by a nearly complete skull and mandibles, while the paratype is represented by a partial skull, mandible, and anterior postcrania. The holotype also preserves a few isolated bones associated with diadectomorphs and ' microsaurs,' although it is not clear that these represent consumed items. In general, the skulls preserve many of the features observed in other eryopids, such as a coarsely pitted ornamentation on the surface of the skull; prominent longitudinal ridges and some transverse ridges that frame depressions on the skull; and relatively thick cranial bones. The most distinctive feature of ''S. boldi'' is a proportionately narrow skull; rather than continually broadening posteriorly, the "cheek" (temporal) region of the skull in ''S. boldi'' is squared-off such that the margins run parallel to each other. It is differentiated from an isolated eryopid mandible previously reported from the site on the basis of tooth positions (48–50 in ''Stenokranio'' vs. 35–40 in the isolated mandible). The postcrania differ little from those previously described in the North American '' Eryops'', which is the sister taxon of ''Stenokranio'' based upon phylogenetic analysis.

Discovery and species

''Stenokranio boldi'' is based on two specimens discovered in 2013 and 2018 from the Remigiusberg quarry in Rhineland-Palatinate. The quarry is a large open-cast mine that is mined for subvolcanic rock that is used in road and railroad gravel; this rock was formed from Permian-aged volcanic intrusions into rocks dated to between the latest Carboniferous and the earliest Permian (Gzhelian/Asselian) Remigiusberg Formation.

The taxon was named by paleontologists Ralf Werneburg (Naturhistorisches Museum Schloss Bertholdsburg Schleusingen), Florian Witzmann (Museum für Naturkunde Berlin), Larry Rinehart (New Mexico Museum of Natural History and Science), Jan Fischer (Urweltmuseum GEOSKOP/Burg Licthenberg), and Sebastian Voigt (Urweltmuseum GEOSKOP/Burg Licthenberg) in the Journal of Paleontology. The species epithet honors Rudolf Bold who discovered the holotype of ''Cryptovenator hirschbergeri''.

Paleobiology

As with other eryopids, the exact paleobiology of ''Stenokranio'' is disputed; Werneburg ''et al.'' (2024) propose that it was semi-aquatic, capable of moving around on land in order to migrate between habitats while also being capable of catching, and primarily feeding on, aquatic prey items such as fish, similar to modern crocodilians. As with some eryopids such as ''Eryops'', ''Stenokranio'' lacks lateral line grooves on the skull, which is typically regarded as evidence of relative terrestriality. Of interest is that the similarly large and semi-aquatic stereospondylomorph '' Sclerocephalus,'' which is abundantly known from Germany, is unknown from Remigiusberg. This indicates that these taxa may have had sufficient ecological overlap such that only one could be present in a given locality.

Palaeoecology

Remigiusberg Formation has produced a diverse record of vertebrates, including a variety of fish, 'lepospondyls', a trimerorhachid dvinosaur ('' Trypanognathus remiguisbergensis''), diadectomorphs, an edaphosaurid 'pelycosaur' ('' Remigiomontanus robustus''), and a sphenacodontid 'pelycosaur' ('' Cryptovenator hirschbergeri''). The jaw of another eryopid distinct from ''S. boldi'' was also recovered from the site, indicating the presence of at least two eryopids at the locality. The two specimens of ''S. boldi'' were recovered from different horizons at the locality and are thought to represent decomposed skeletons that were transported into the marginal lacustrine environment.

References

{{Taxonbar, from=Q124305526

Eryopidae
Carboniferous temnospondyls of Europe
Permian temnospondyls of Europe
Fossil taxa described in 2024