DEWEL, R.A.*; SOLOMON, S.; BENEDICT, D.; DEWEL, W.C.; Appalachian State University, Boone, NC; Cornell University, Ithaca; The TSR Group, Denver; Appalachian State University, Boone, NC: New perspectives on arthropod characters: bridging gaps between the living and the dead

The relationships of higher arthropod taxa remain obscure in part because of a paucity of both molecular and morphological characters. In an attempt to increase the number of useful morphological characters, we have undertaken a phylogenetic analysis of ecdysozoans, primarily arthropods, with several objectives. First, the number of characters that can be identified in both extinct and living organisms needs to be improved. Fossil characters are critical for bridging morphological gaps between living taxa, and yet few of them are considered to be suitable for this task. Second, the homology of many characters has been uncritically accepted and should be reevaluated. An example is the antenniform appendage of myriapods and hexapods and perhaps basal chelicerates that is widely assumed to be homologous to the A1 appendage or antennule of crustaceans. The purported homology of arthropod antennae is based on structural and positional similarity, yet one would expect this similarity to develop readily in any anterior sensory appendage that evolved from a leg. Few attempts have been made to analyze the primary homology of antenniform appendages, particularly those in the fossils that are likely to constitute the stem groups of living arthropods. Finally, many characters are defined so narrowly, often restricted to a single well-defined taxon, that they are useless for relating more disparate taxa. The concepts of many characters can be broadened to encompass previously unrecognized states. The results of the analysis were surprising and included a lack of support for such widely accepted taxa as Mandibulata and Myriapoda.