A Cretaceous Cusk-Eel (Teleostei, Ophidiiformes) from Italy and the Mesozoic Diversification of Percomorph Fishes

Cusk-eels of the order Ophidiiformes are a morphologically diverse assemblage of eel-like, elongate, posteriorly tapering percomorph fishes that occur worldwide in marine waters, from tropical reef areas to the deep sea. The about 400 extant and fossil species included in the ophidiiform clade are arranged into two main lineages, Bythitoidei and Ophidioidei, based on reproductive biology and the position of the anterior nostrils. The anatomy and phylogenetic relationships of these fishes are largely unknown, and the fossil record has not provided substantial information about the earliest phases of their evolutionary history. dagger Pastorius methenyi, new genus and species, the oldest member of the Ophidiiformes based on articulated skeletal remains, is described herein based on a single specimen collected from the Campanian-Maastrichtian organic-rich laminated limestone of the Liburnica Formation outcropping near the village of Trebiciano, north-eastern Italy. The comparative analysis of osteological and meristic features indicates that dagger Pastorius methenyi is characterized by at least one of the probable ophidiiform synapomorphies (exclusion of the supraoccipital from the posterior cranial margin by substantial posterodorsal extension of the exoccipitals) and exhibits a unique combination of characters, including a posteriorly broadly expanded maxilla; supramaxilla present; eight branchiostegals; 39 vertebrae; first neural spine shorter than those following; neural arch of first vertebra feebly connected to the first vertebral centrum though a narrow pedestal of bone; anterior abdominal vertebrae ostensibly lacking expanded ribs; caudal skeleton with ostensibly fused first preural, first ural centrum, first uroneural, and ventral hypural plate, and ostensibly fused second ural centrum and dorsal hypural plate, autogenous parhypural, and two epurals; caudal fin free, with 13 rays; a single ossified supraneural located in front of the second neural spine; and notably reduced number of dorsal-and anal-fin rays. dagger Pastorius is placed as the sister-group of all recent bythitoids, even if some features might indicate that it represents the sister-group of all ophidiiforms. dagger Pastorius provides the first unequivocal evidence that percomorphs with very elongate and compressed bodies were in existence in the Cretaceous, indicating that this group was characterized by a very high disparity and a vast diversification of bodyplans well before the Cretaceous-Paleogene extinction.