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

Abstract

Abstract Two new stem-actinopterans, Melanecta anneae gen. et sp. nov. and Woodichthys bearsdeni gen. et sp. nov. , are described from the Manse Burn Formation (basal Namurian) of Bearsden, Glasgow. Melanecta resembles Devonian taxa such as Howqualepis and Mimia . 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 on Erpetoichthys otoliths are presented for comparison with those of Melanecta and 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 of Melanecta may be a primitive characteristic, but the apparent independence of factors such as size, histology, and scale row to somite ratios, obscures clear evolutionary trends. Woodichthys resembles Moythomasia and Kentuckia , and includes a flattened but detailed neurocranium. A new neurocranial specimen of Pteronisculus magnus examined 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 in Moythomasia durgaringa .