A large, anatomically primitive tristichopterid (Sarcopterygii: Tetrapodomorpha) from the Late Devonian (Frasnian) Alves Beds, Upper Old Red Sandstone, Moray, Scotland

摘要

A nearly complete mandible of a large tetrapodomorph sarcopterygian from the Frasnian Alves Beds is studied with the aid of computed tomography. The absence of cosmine, a small parasymphysial dental plate bearing dentition that is discontinuous with that of the coronoids, and the presence of an elongated posterior coronoid that bears two fang pairs restrict placement of the tetrapodomorph from the Alves Beds to Tristichopteridae, and suggest that is a member of the clade that is sister to the anatomically primitive Givetian genus Tristichopterus. Taxa from this segment of tristichopterid phylogeny include the Givetian-Frasnian Eusthenopteron and Frasnian Jarvikina, but the tristichopterid from the Alves Beds is distinguished from both by the presence of an organized row of well-developed teeth on the posterior coronoid. This character has been proposed as a synapomorphy of taxa crownward of Trischopteridae, but is widely distributed among tetrapodomorph fishes. Our reinterpretation of lower jaw material of Tinirau clackae suggests this species is a member of the Tristichopteridae rather than the 'Elpistostegalia', and likely includes material assigned to a second species and genus of tetrapodomorph from the Red Hill site, Bruehnopteron murphyi. Proposal of a formal taxonomic name for the tristichopterid from the Alves Beds is withheld pending the discovery or analysis of further material from these deposits.