Karethraichnus zaratan Sato et Jenkins, 2020

Diagnosis.—Elliptic to clavate holes with a smooth surface that penetrate a vertebrate hard tissue and extend perpendicular to the apertural surface. Boreholes in its incomplete part due to the diagenesis penetrate through the hard tissue and appear hemispherical-shaped but they seem to be originally clavate-shaped. The aperture of boreholes is rounded, although the neck part of the clavate should be little more extended in original shape since the epidermal scute of the turtle carapace is missing. Several boreholes include calcareous fossils that are probably pholadoid bivalves since large apophysis-like structures are recognized in some cases (Fig. 2), and these bivalves are potential candidates for these trackmakers.

Remarks.—Karethraichnus zaratan can be distinguished from other Karethraichnus ichnospecies (all described by Zonneveld et al. 2015) as follows; K. lakkos are shallow hemispherical pits, K. kulindros have a cylindrical profile, and K. fiale are penetrative traces with an almost cylindrical profile. Gastrochaenolites lapidicus Kelly and Bromley 1984 is close to K. zaratan in shape but differs in the hard substrate they occur in; Gastrochaenolites ichnospecies occur in lithic substrates (Zonneveld et al. 2015).