An extraordinary larval-like teleost fish from the Eocene of Bolca

Abstract

"Pegasus" volans is a highly unusual fossil teleost fish from the celebrated Eocene Bolca Lagerstatte. The fossil, known on the basis of two specimens, has been historically assigned to seamoths (Pegasidae), then to oarfish and relatives (Lampriformes). We describe its enigmatic skeletal anatomy in detail, and provide a new genus name. "Pegasus" volans is an extremely elongate and slender animal, with long anal and dorsal fins and a very well-developed first dorsal-fin ray reminiscent to the vexillum of some modern teleost larvae. Most striking is its extreme ventral projection of the pelvic girdle (basipterygium), associated with an element of the pectoral girdle (a long process of the coracoid) and developed pelvic-fin rays. The strongly reduced abdominal region suggests that "Pegasus" volans had an external gut, once again reminiscent of those of certain larval teleosts. The unique character state combination displayed by "Pegasus" volans make it impossible to assign it to a specific subclade within perch-like spiny-rayed fishes (Percomorpha). Nevertheless, it offers a valuable perspective on the diversity of morphologies and ecological niches occupied by teleost fishes of the early Eocene Bolca fauna.