SANTINI, F.; University of Toronto: The importance of highly incomplete fossil taxa in reconstructing phylogenetic relationships for various clades of acanthomorph fishes (Zeiformes, Caproiformes and Tetraodontiformes: Teleostei: Pisces)

The use of fossils in phylogenetics has traditionally been a contentious issue. Fossils usually are incomplete, and their use commonly leads to an increase in the number of most equally parsimonious trees and a decrease in the resolution of phylogenies. Fossils alone, however, provide certain kinds of information about the biological history of a clade, and computersimulations have shown that even highly incomplete material can, under certain circumstances, increase the accuracy of a phylogeny, rather than decrease it. Since empirical data on the effects of the inclusion of fossils on phylogeny reconstructions are still scarce, I attempted to use some well known groups of acanthomorph fishes, for which robust phylogenies using extant taxa already exist, and which have well-studied fossil records- the Tetraodontiformes (pufferfishes, triggerfishes and ocean sunfishes), Zeiformes (john dories) and Caproiformes (boarfishes) — to investigate this problem. Adding incomplete fossil taxa usually increases the number of equally most parsimonious trees and often decreases the resolution of consensus trees.However, adding fossil taxa may break long branches for lineages that have experienced high degrees of morphological diversification, increasing, rather than decreasing, the resolution. Furthermore, taxa that were scored for 25% or more of their characters did not cause a significant loss of resolution, while providing unique biological information.