Actinopterygians from the Namurian of Bearsden, Scotland, with comments on early actinopterygian neurocrania

Abstract

Two new stem-actinopterans,Melanecta anneaegen.etsp. nov.andWoodichthys bearsdenigen.etsp. nov., are described from the Manse Burn Formation (basal Namurian) of Bearsden, Glasgow.Melanectaresembles Devonian taxa such asHowqualepisandMimia. Significant features include a large head, long gape, well preserved otoliths, micromeric squamation, broad-based fins, and fringing fulcra restricted to the extended leading pectoral edge. New data onErpetoichthysotoliths are presented for comparison with those ofMelanectaand other early actinopterygians. The primitive actinopterygian condition probably includes partly vateritic otoliths, with a small sagitta and large asteriscus contained within a single chamber. The small scales ofMelanectamay be a primitive characteristic, but the apparent independence of factors such as size, histology, and scale row to somite ratios, obscures clear evolutionary trends.WoodichthysresemblesMoythomasiaandKentuckia, and includes a flattened but detailed neurocranium. A new neurocranial specimen ofPteronisculus magnusexamined for comparison reveals new data on the otic labyrinth, lateral cranial canals, and postorbital wall. Haemopoietic organ accommodation is considered insufficient explanation for lateral cranial canal elaboration. Several new basisphenoidal and postorbital wall characters are identified which are associated with early stages in posterior myodome evolution. Most of these characters are present inMoythomasia durgaringa.