Carlomonnius quasigobius gen. et sp nov.: the first gobioid fish from the Eocene of Monte Bolca, Italy

The first gobioid fish from the Eocene of Monte Bolca, Italy, dagger Carlomonnius quasigobius gen. et sp. nov., is described based on a single well-preserved diminutive specimen. This taxon is the oldest member of the Gobioidei known to date based on articulated skeletal remains. dagger Carlomonnius gen. nov. exhibits a suite of features that unquestionably support its alignment with gobioids, including the absence of parietals and basisphenoid, possession of a large and subquadrangular saccular otolith, infraorbital series exclusively represented by the lachrymal, presence of suspensorial interspace, caudal skeleton with reduced parhypural and fused hypurals 1+2 and 3+4 (the latter fused to the urostyle), absence of uroneurals, absence of supraneurals, presence of cleithral notch, and absence of lateral line. Within the Gobioidei, dagger Carlomonnius gen. nov. has a unique combination of derived (five branchiostegal rays, dorsal postcleithrum absent, 13 principal caudal-fin rays, four pelvic-fin rays) and plesiomorphic (dorsal fin continuous, 24 vertebrae, autogenous haemal spine of the second preural centrum, first two abdominal centra shortened, first dorsal-fin pterygiophore inserting in the second interneural space) features found in none of the extant gobioid lineages. Because of this unique combination of features, dagger Carlomonnius gen. nov. cannot be confidently accommodated within any familial category and it is therefore interpreted herein as incertae sedis within the Gobioidei. Palaeoecological considerations suggest that dagger Carlomonnius quasigobius gen. et sp. nov. was a benthic generalist carnivore.