Phylogenetic Methods and Aetosaur Interrelationships: A Rejoinder

Abstract

In a previous paper (Harris et al., 2003), we discussed the treatment of intraorganismal homology in character construction. Our aims were to highlight alternative approaches and to investigate their theoretical foundations and analytical consequences, andweused the phylogeny of aetosaurian reptiles as an example. In a previous study, Heckert and Lucas (1999) employed several characters describing variation in aetosaur osteoderms. Harris et al. (2003) noted that parallel variations (e.g., presence of either radial or random patterning) in the osteoderms of different body regions were represented as separate but covarying characters, implying independent evolutionary changes in different regions. We suggested that osteoderms are intraorganismal homologues and that a single change affecting multiple osteoderm regions, represented by a single composite character, was a plausible alternative to the previousmore reductive interpretation. We demonstrated that alternative reductive and composite approaches to constructing characters from variation in osteoderms impacts inferred relationships and their apparent levels of support.