Importance for Phylogeny of Single and Multiple Stem-group Fossil Species with Examples from Freshwater Fishes

Abstract

The phylogenetic significance of fossils is limited in many groups, such as freshwater fishes, by the sparse fossil record that is available. Nevertheless, even these fossils have a role in phylogenetic analysis. Fossils can be a source of new species, characters, and character states. Fossils can also suggest different character polarities. They often clarify the order in which synapomorphies were acquired and demonstrate convergence in the apparent synapomorphies of living species. In extreme cases, they can change estimated phylogenies based only on living species. Species that diverged early in the history of their group usually have more primitive features than younger species, but these early forms tend to be removed from the fauna by extinction