First fossil records of the tholichthys larval stage of butterfly fishes (Perciformes, Chaetodontidae), from the Oligocene of Europe

The first fossils of the tholichthys larval stage of a chaetodontid from the lower Oligocene (Rupelian, Fish Shales; about 30.1 MYA) of Frauenweiler (Baden-Württemberg, S Germany) are described, along with two less well-preserved probable tholichthys from the lower Oligocene Menilite-Formation (IPM3, 30–29 MYA and IPM4A, 29–28 MYA) of Przemyśl (Outer Carpathians, SE Poland). The fossils are compared with tholichthys larvae of the extant genus of Chaetodontidae to which they are most similar, namely Chaetodon. The German specimens are identified as tholichthys larvae by the plate-like expansions of the supracleithrum and posttemporal that extend posteriorly well behind the head and by an expanded preopercle with a large posterior spine; these bones, and the frontals and supraoccipital, are distinctively rugose. The Polish specimen from IPM3 has similar features so it is safe to assume that it also is a chaetodontid tholichthys, whereas the specimen from IPM4A is so poorly preserved that it can only very tentatively be referred to the Chaetodontidae. The occurrence of tholichthys larvae prompts reconsideration of the paleoenvironmental situation at their respective fossil sites.