CLADOGRAM VERSATILITY - EVOLUTION AND BIOGEOGRAPHY OF ACANTHUROID FISHES

A highly corroborated cladogram of acanthuroid fishes is used to explo re several aspects of the biogeographic and microevolutionary events d uring the evolution of the group. Five events in acanthuroid evolution are documented here, which demonstrate not only the power of cladogra ms to provide adaptational hypotheses, but also how they can be used t o frame significant questions for further research. Biogeographic anal ysis indicates that basal cladogenesis of the acanthuroids must have o ccurred prior to the Eocene (50-55 mya), because at least the basal li neages of the Acanthuridae, one of the last acanthuroid families to ha ve evolved, were present at that time. In addition, optimization of cu rrent distributions suggests that the ancestors of the Acanthurinae, o f the Acanthuridae, and of the Acanthuroidei each had an Indo-West Pac ific distribution, Subsequent dispersion and/or speciation in one or m ore of these lineages may have been related either to the closure of t he Tethys (ca 20 mya), or to colonization from the Pacific of the Cari bbean/Atlantic prior to the formation of the Panamanian isthmus. Hypot heses about adaptation in acanthuroids begin with a discussion of seve ral cases of dietary plasticity. The importance of information from fo ssils is illustrated in an investigation of predorsal bone evolution. Morphologically divergent and convergent tendencies in the modificatio n of the pelvic fins concludes the examples. The morphologically most derived genus, Ctenochaetus, seems the least active taxon evolutionari ly in the characters investigated.