New fossil scombrid (Pelagia: Scombridae) fishes preserved as predator and prey from the Eocene of Senegal

Lower Eocene fossil fish material from the Thies Formation in the region of Bargny near the Cap-Vert peninsula, Senegal, reveals predator-prey interaction between two scombrid fishes, the first ever described in the fossil record for the clade. The material is a part and counterpart concretion preserving nearly complete skulls of both predator and prey in 3-dimensions. The larger, predator-fish is here proposed as the second specimen of † Auxides huberti , the only non-Tethyan representative of † Auxides . The smaller, prey-fish is a new genus and species, † Eoscomber senegalicus , closely resembling Scomber . Evidence that † E. senegalicus gen. et sp. nov. was swallowed includes the presence of several of its caudal vertebrae obscured near the area of the opercle of † A. huberti and continuing into its pharynx. Additionally, the skull of † E. senegalicus . is partially enclosed within the abdominal ribs of † A. huberti . † Auxides huberti is the only species of † Auxides recovered with serrated pelvic fin spines, which are normally smooth. † Auxides huberti has 28–30 vertebral centra (16–17 caudal) including the urostyle. The new specimen of † A. huberti has small, pointed teeth and a thickened, sickle-shaped first haemal spine. The first dorsal fin has 6–7 interneurals and associated dorsal fin spines. The bony dorsal and anal finlets begin immediately behind the second dorsal and anal fins respectively. Ventral corselet-like scales are present, a condition similar to that of the genera Auxis , and Thunnus , but unlike the type species of † Auxides . The caudal fin has gracile hemitrichia that proximally surround the entire hypural plate and the two posteriormost epineurals. † Eoscomber senegalicus . differs from Scomber in possessing frontal bones that approach the midline anteriorly and long sigmoid shaped nasal bones that project further anteriorly past the frontal bone than the length of the nasalarticulating surface. The exceptional preservation of † E. senegalicus and the second ever recorded occurrence of † A. huberti , is the first direct evidence of scombrid feeding behavior and demonstrates that smaller ‘mackerel-like’ scombrids have been prey for larger tuna-like scombrids since at least the middle Eocene as they are today.