ABSTRACT
A great deal has happened in the fi eld of lungfi sh phylogenetics over the two decades that have passed since the publication of Th e Biology and Evolution of Lungfi shes. Th ree major contributory factors can be discerned: the application of cladistic methodology to ever larger data sets, the advent of molecular phylogenetics, and the conceptual impact of the node-based terminology of crown group, stem group and total group introduced by Jeff eries. In this chapter we will review the eff ect of these factors on the development of the subject and present a brief overview of current opinion. We will not, however, be able to outline a neat set of consensus views; despite, or perhaps because of, the richness of the fossil data set, the deep phylogeny of the lungfi shes is still the subject of much debate. Keywords: lungfi shes, Dipnoi, phylogeny, evolution, Sarcopterygii
Th e Biology and Evolution of Lungfi shes, published in 1987, provided the fi rst computer-generated phylogenetic analysis of the lungfi shes, presented by Charles Marshall (1987a). Later, Schultze and Marshall (1993) provided a more comprehensive analysis, including taxa from the Devonian to Recent, with 90 characters coded from the skull, dentition and postcranium. However, even before this, an attempt to apply phylogenetic principles to the question of
lungfi sh relationships had been made by Roger Miles. Miles (1977) presented a revised phylogeny of the Dipnoi, which diff ered from earlier phylogenies in that characters were clearly assessed as being primitive or derived, and principles of parsimony used to evaluate relationships within the group (i.e., with a minimum number of character changes allowed). Although Miles’s resulting cladogram (Miles 1977: Fig. 157) left many taxa unresolved within the larger phylogeny, it was, as he noted, an advance over previous phylogenies because his hypotheses of character evolution and taxon relationships were explicit and could be tested by future researchers. In the years since Miles (1977) and Schultze and Marshall (1993), several new analyses have been performed, most involving computer-based parsimony programs. Interestingly, there has been disagreement among these trees, particularly with regard to the resolution of Devonian taxa. Nevertheless, there appears to be broad agreement regarding the identity of basal taxa as well as relationships among Carboniferous and younger taxa, but less agreement on the resolution of taxa between these nodes. Other researchers have examined relationships of the Dipnoi within the Sarcopterygii, most recently using EST sequences (express sequence tags; Hallström and Janke 2009). Th ere seems to be broad agreement now that lungfi sh represent the extant sister taxon to the Tetrapoda. Th ese agreements and disagreements are reviewed below, with a fi nal word on potential directions for future research.
