Gyrodus sp.

Szabó, Márton, 2017, Fish remains from the Lower Cretaceous (Valanginian-Hauterivian) of Hárskút (Hungary, Bakony Mts), Fragmenta Palaeontologica Hungarica 34, pp. 49-61 : 55-57

Gyrodus sp.

(Figs 18–20)

Referred material – 1 tooth (MBFSZ 2017.247.1.); stratigraphical origin: Valanginian (HK-12/9) .

Description – The tooth remain is embedded in a piece of stone-matrix, exposed in occlusal aspect. The tooth is flattened, and has a pear to trapezoid shape in occlusal view. A well-marked central tubercle (or central papilla) is present, which is surrounded by an apical ring, running all around the central papilla, covered by crenulations. Near the occlusal margin, a second apical ring is present, also bearing roundish crenulations. In profile view, the inner apical ring is apicobasally higher, than the outer, larger one. Following these features, the tooth is unambiguously referred to the genus Gyrodus . Based on the preserved characters it can not be determined whether the tooth belonged to the vomerine or the prearticular dentition.

Remarks – Gyrodus ranges from the Middle Jurassic to the Early Cretaceous. The genus includes 32 species, among them two, G. hexagonus and G. circularis were based on more than isolated remains, including articulated skeletons ( KRIWET & SCHMITZ 2005). The Early Cretaceous reports of the genus are rare and questionable. G. atherfieldensis from the Aptian of England is characterized by smooth teeth (possible result of wear or abrasion). When unworn, teeth of G. minor (Aptian of England), G. contiguidens (Hauterivian of France) and G. sculptus (Neocomian of France) exhibit an ornamentation similar to that of other Gyrodus species ( KRIWET & SCHMITZ 2005 and references therein). The attribution of a dental remain described as G. ellipticus remains arguable, since it displays similarities with Coelodus and Ocloedus (after KRIWET & SCHMITZ 2005). Isolated, sculptured pycnodont teeth from the Valanginian of France were assigned to genus Gyrodus by PICTET et al. (1858 –60).

Since only one Hárskút fish tooth is assigned to Gyrodus , due to the high variancy of the pycnodontiform dentition, I do not attempt to describe it closer than genus rank. A high similarity to the teeth of G. hexagonus is recognized (see KRIWET 2005, fig. 30C, D), however, G. hexagonus is resricted to the Jurassic (KRIWET 2005; POYATO-ARIZA & WENZ 2002).