The outstanding suction-feeder Marcopoloichthys furreri new species (Actinopterygii) from the Middle Triassic Tethys Realm of Europe and its implications for early evolution of neopterygian fishes

Abstract

Marcopoloichthys furrerisp. nov., a small scaleless fish from the Ladinian of Switzerland, is described based on ten well preserved specimens, which provide outstanding morphological information, allowing the re-study of the family and generic diagnoses that were solely based on a few Eurasian marcopoloichthyids. An exhaustive investigation of morphological features of M. furreri provides evidence of new morphological structures not previously known in Triassic neopterygians (e.g., supraneural carrier; two pairs of nasal bones; mesethmoid; series of three bony postcleithra) that are interpreted as autapomorphies of Marcopoloichthys, which occur together with some primitive features (e.g., lack of supramaxillae; presence of surangular and coronoid; aspondylous vertebral column; clavicle present). The combination of primitive and advanced characters proved to be critical when M. furreri was added to a previous hypothesis of neopterygian relationships, because it provided unquestionable support for Marcopoloichthys as a stem teleost or teleosteomorph. Some characters supporting this interpretation are the presence of a mobile premaxilla; an unpaired vomer; and first and last principal rays forming leading margins of caudal fin. Additionally, Marcopoloichthys furreri, due to a combination of teleostean synapomorphies (e.g., epineural processes; four pectoral radials; propterygium fused with first pectoral ray), stands in a polytomy with aspidorhynchiforms and more advanced teleosteomorphs in another phylogenetic analysis. Consequently, the combination of characters of Marcopoloichthys is relevant for understanding the taxonomy and systematics of crown neopterygians. Marcopoloichthyids were suction-feeding fishes, and the excellent preservation of the new species permits discussion of the anatomical modifications involved in the feeding and resting processes.