First dercetid fish from the Upper Cretaceous of Antarctica.

Aulopiformes, a clade including lizardfishes and allies, comprise a long-standing marine lineage from the Early Cretaceous to the Recent. We describe Antarctichthys longipectoralis gen. et sp. nov. from the late Campanian marine strata of Antarctica (Snow Hill Island Formation). This species, represented by a single specimen, was recovered during the expedition of PALEOANTAR in Santa Marta Cove (James Ross Island) and it is the most complete vertebrate found in this locality, with a three-dimensional preservation. It was microCT-scanned, providing exclusive details on the anatomy of Aulopiformes unknown for the early history of the clade, i.e., an unexpected otophysic connection in the neurocranium. It has been classified within Dercetidae due to the presence of a longirostrine head, an elongated body, and very reduced neural spines (their unequivocal synapomorphy). It is distinguished from all known dercetids by its elongated pectoral fin and the absence of teeth. Phylogenetic analysis placed it as sister-genus to the late-diverging clade Rhynchodercetis plus Hastichthys. The earliest occurrence of Dercetidae is recorded in the lower Cenomanian, from Komen, Jebel Tselfat and Ein-Yabrud. The pivotal record of this new dercetid fish in Antarctica marks the southernmost occurrence of the group, previously known from the Pelotas Basin, Southern Brazil.