A tholichthys‐like larva (Teleostei, Percomorpha) from the Eocene of Northern Caucasus, Russia

Abstract

A morphologically bizarre fish larva is described based on a single specimen from Eocene (Bartonian) locality of Gornyi Luch, Krasnodar Region, Northern Caucasus, SW Russia. The fossil larva described here was collected form the Kuma Horizon and inhabited an open marine setting with bottom waters characterized by poorly oxygenated conditions, where it was associated with abundant pelagic fish taxa. This fossil fish larva exhibits a peculiar morphology, being characterized by remarkably expanded and thickened bones that form an armour-like protective covering, a strong and greatly elongate pelvic-fin spine and a unique head spination that comprises a conical and posterodorsally directed supraoccipital spine, a rostral spine formed by the nasals, and enormous spines on the preopercle and opercle. Moreover, this fish larva has an advanced insertion of the dorsal fin and 17 principal rays in the caudal fin thereby revealing its affinity to percomorph fishes. The hypertrophied bony plates encasing the head and forming a bony armour are shared with the so-called tholichthys larval stage of chaetodontid butterflyfishes, as well as with the larval stages of some other percomorphs. Comparison with selected percomorph larval morphotypes (e.g. families Chaetodontidae, Malacanthidae, Ostracoberycidae and Scatophagidae) suggests that the Eocene larva described herein exhibits a unique combination of characters that would support an attribution to a new, previously undescribed taxon.