THE CHALLENGE OF INTEGRATING MORPHOLOGICAL DATA AT THE INFRAORDINAL LEVEL IN ASSEMBLING THE DECAPOD TREE OF LIFE

Development of hypotheses for the phylogeny of decapod Crustacea based upon fossil evidence as well as morphological and molecular evidence has presented some unanticipated challenges. The fossil record of the Decapoda has been scrutinized as carefully as possible, a list of all fossil genera and species has been compiled, and geologic and geographic ranges have been determined for each species. These data serve to constrain the timing of events in the evolution of the group. In order to integrate morphological data from fossil and extant genera, a series of phylogenetic analyses have been performed on subsets of the Decapoda. Analyses of the Portunoidea Rafinesque, 1815, and the Xanthoidea sensu lato have yielded excellent results that demonstrate, among other things, that use of proxy characters in classifying fossil taxa permits reliable placement of extinct forms into a classification originally based solely upon extant representatives. Ongoing phylogenetic analysis of the so-called primitive crabs appears to be yielding similar congruent results. However, broader analyses of the Decapoda, based upon a variety of characters commonly preserved in the fossil record do not yield concordant results. Phylogenetic hypotheses for the Decapoda developed by Schram and Dixon (2004) and Amati et al. (2004) resulted in some striking differences. The apparent anomalies arise at least in part from the emphasis on scoring carapace groove patterns by Amati et al. as compared to the scoring of a somewhat different array of characters by Schram and Dixon. The results, thus far, suggest that some characters customarily used to describe fossil decapods are quite reliable within subsets of the order, but that they may be unreliable across broad taxonomic groups. It is likely that some of the structures judged traditionally to be homologous are, in fact, either homoplasic or incorrectly identified. Resolution of these dilemmas will ultimately strengthen integration of fossil data into the assembly of the tree of life of the decapod Crustacea. Research supported by NSF EF 0531670 to Feldmann and Schweitzer.