A new species of Osteoglossomorpha (Actinopterygii: Teleostei) from the Upper Cretaceous Nemegt Formation of Mongolia: Paleobiological and paleobiogeographic implications

Compared to abundant dinosaur faunas, fish materials are scarce in the Nemegt Formation (Maastrichtian) of Mongolia except for isolated centra assigned to the Hiodontidae (Osteoglossomopha). Here we report new additional fish materials collected from the Nemegt Formation. They include skull parts (quadrate, premaxilla, and dentary), isolated and articulated centra, and a caudal fin. New specimens appear to be the same taxon as the previously reported samples from the Nemegt Formation based on morphological similarities in the abdominal centra. However, all specimens represent a new genus and species of osteoglossomorph fish, Harenaichthys lui gen. et sp. nov. Phylogenetic analysis reveals that Harenaichthys is a basal member of the osteoglossomorphs instead of being included in the hiodontids. The comparison of Harenaichthys with Chinese osteoglossomorph Xixiaichthys tongxinensis and a fish centrum found along with the theropod dinosaur Raptorex kriegsteini supports a previous conclusion that R. kriegsteini comes from the Nemegt Formation. Unusual monospecific occurrences of Harenaichthys in many localities allow us to understand their paleoecology and paleobiogeography better. In addition, the pathologic features seen on some centra of Harenaicthys indicate that they suffered from various diseases in life. • All Nemegt specimens represent a new genus and species of osteoglossomorph fish, Harenaichthys lui gen. et sp. nov. • A fish centrum found with Raptorex kriegsteini is assigned to Harenaichthys . • The monospecific assemblages of Harenaichthys were affected by the high altitude of their habitat.