Devonian actinopterygian phylogeny and evolution based on a redescription of Stegotrachelus finlayi

Basal actinopterygian phylogeny is in a state of flux. Discoveries of new Devonian and Carboniferous taxa have not only contributed to our knowledge of these animals, but have also complicated our understanding of their interrelationships. Over the preceding 50 years, there have been several new discoveries and redescriptions of early actinopterygians; however, Tegeolepis clarki, Kentuckia hlavini, and Stegotrachelus finlayi have never been fully redescribed. Although previous authors have re-examined the skull of S. finlayi, new material has recently been collected, in 1973 and 2002. This study synthesizes information from original and new material to fully redescribe S. finlayi, and incorporates these data into a cladistic analysis that examines the interrelationships of early actinopterygians. Phylogenetic systematic data returned support for a monophyletic Stegotrachelidae - an evolutionary systematic hypothesis generated over 40 years ago. Previous palaeoenvironmental and biogeographic hypotheses were tested, with results supporting the independent freshwater origins of several Devonian actinopts, although a regional endemic grade of Gondwanan taxa is not confirmed. (C) 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009.