A New Tarpon-Like Fish (Elopomorpha, Megalopidae) With Exceptional Preservation and Unusual Features From the Paleogene of Pitt Island, Chatham Islands, New Zealand

Abstract

We report on a large and nearly complete elopomorph fish from the Paleogene of Pitt Island, Chatham Islands, New Zealand. The exquisite specimen is three-dimensionally preserved in a volcanic tuff and is the most complete and informative fossil elopomorph reported to date from the Southern Hemisphere. Features indicating elopomorph affinities include the lack of a separate retroarticular ossification on the lower jaw, and a primitively retained median gular. Assignment to the elopiform Family Megalopidae (tarpons) is indicated by the specimen's superior mouth position, large posttemporal fossae, and laterally compressed body covered in large and extensively overlapping cycloid scales. A number of distinctive features, including the elongate body, high and strongly developed coronoid process, enlarged median gular, relatively low-profile head, extra series of anamestic bones in the cheek region, and the continuation of the lateral line scales as a tapering lobe extending onto the base of the caudal fin, indicate that the Pitt Island fish represents a distinctive new taxon within megalopids, herein named Ikawaihere koehleri gen. et sp. nov. The morphology of the specimen as a whole suggests a fish resembling the extant tarpons Megalops atlanticus and M. cyprinoides but with a lower head profile and more attenuated body.