CLADOGRAM VERSATILITY: EVOLUTION AND BIOGEOGRAPHY OF ACANTHUROID FISHES.

A highly corroborated cladogram of acanthuroid fishes is used to explore several aspects of the biogeographic and microevolutionary events during the evolution of the group. Five events in acanthuroid evolution are documented here, which demonstrate not only the power of cladograms to provide adaptational hypotheses, but also how they can be used to frame significant questions for further research. Biogeographic analysis indicates that basal cladogenesis of the acanthuroids must have occurred prior to the Eocene (50-55 mya), because at least the basal lineages of the Acanthuridae, one of the last acanthuroid families to have evolved, were present at that time. In addition, optimization of current distributions suggests that the ancestors of the Acanthurinae, of the Acanthuridae, and of the Acanthuroidei each had an Indo-West Pacific distribution. Subsequent dispersion and/or speciation in one or more of these lineages may have been related either to the closure of the Tethys (ca 20 mya), or to colonization from the Pacific of the Caribbean/Atlantic prior to the formation of the Panamanian isthmus. Hypotheses about adaptation in acanthuroids begin with a discussion of several cases of dietary plasticity. The importance of information from fossils is illustrated in an investigation of predorsal bone evolution. Morphologically divergent and convergent tendencies in the modification of the pelvic fins concludes the examples. The morphologically most derived genus, Ctenochaetus, seems the least active taxon evolutionarily in the characters investigated.