New finds of vertebrates in the Chotěvice Formation (Asselian) of the Krkonoše Piedmont Basin

Abstract

© 2019 Czech Geological Survey. All rights reserved. The Chotěvice Formation has been considered to be free of vertebrates until recently (Prouza - Tásler 2001). Later, only Čech et al. (2013) recorded rarely occurring fish scales, unlike the older Prosečné and Vrchlabí formations which in contrary contain several horizons with rich vertebrate fauna (Štamberg - Zajíc 2008). Stárková and Čáp (2017), however, have recently described isolated scales of actinopterygians and coprolites from limestones of a promising locality in a new road cut in the village Tatobity (Fig. 1). New collections of fossils at the Tatobity site delivered numerous fragments of vertebrates, which are described here. The finds come from a light grey laminated limestone in the road cut which overlay red brown siltstones. Some of the isolated vertebrate fragments were obtained from the limestone using 10% acetic acid. Sharks of the family Xenacanthidae Fritsch, 1889 are represented by isolated teeth of Triodus cf. sessilis (Figs 2A, B). Numerous finds of teeth exhibit their typical morphology with slender-conical lateral cusps and a middle cusp longer than half of the lateral cusps length. Actinopterygii Cope, 1877 are represented by isolated scales or isolated bones of the skull. Smooth scales (Figs 2D, G) of rhombic shape have two or three denticles on their posterior margin or they are without denticles. Outer surfaces of the scales show microtubercles (Fig. 2C), similar to microtubercles described in Aeduellidae by Štamberg (2018). Futhermore, actinopterygian skull bones, as operculum (Fig. 2E), suboperculum (Fig. 2F) and maxilla, occur in the light grey limestone. All three bone types evidently belong to the family Aeduellidae. The suboperculum (Fig. 2F) has an unusual sculpture in the ventral area of the bone made up of distinct tubercles and ridges diverging on the bone surface radially from the ossification center. Another bone, a significantly sculptured cleithrum, which was found in the underlying red brown siltstones, belongs also to the Aeduellidae. Numerous fragments of the bones, which probably belong to small amphibians, are preserved in the light grey limestone, but they are not clearly identifiable yet. It is obvious that the bed of limestone of the Chotěvice Formation in Tatobity with the vertebrates represented by Triodus cf. sessilis and actinopterygians of the family Aeduellidae clearly differs from the faunistic content of limestones of the Prosečné Formation occurring in the vicinity of the Tatobity site (Čáp 2010, Štamberg - Zajíc 2008). The faunal content of the limestones at Tatobity together with the radioisotope dating obtained from the ignimbrite of the Chotěvice Formation in the vicinity of Tatobity (Opluštil et al. 2016) proved the age of the local limestone to be the latest Asselian.