The first record of redfieldiiform fish (Actinopterygii) from the Upper Triassic of Korea: Implications for paleobiology and paleobiogeography of Redfieldiiformes

A new genus and species of redfieldiiform fish, Hiascoactinus boryeongensis gen. et sp. nov., is described based on a nearly complete specimen from the Upper Triassic Amisan Formation of South Korea. Hiascoactinus is distinguished from other redfieldiiforms by having a barely ornamented dermal skull surface except for the snout region, two heteromorphic suborbitals arranged vertically behind the postorbital, a pistol-shaped suprascapular, and dorsal and anal fins with divided fin membranes between rays. The morphological features of the snout region and dorsal and anal fins of Hiascoactinus provide important clues to understand its feeding and swimming behavior. All previously proposed Asian redfieldiiform fossils are inaccurately classified, and consequently, Hiascoactinus is regarded as the only valid redfieldiiform taxon in Asia. Hiascoactinus is assigned to the basal group of redfieldiiforms primarily based on the presence of an antopercle. The basal phylogenetic position of Hiascoactinus indicates that basal redfieldiiforms dispersed from the southern Gondwanaland to the easternmost Laurasia through the terrestrial water system, and these two landmasses were connected during the Late Triassic.