Misconceptions, potential problems and methodological advances in cladistics analyses: relevance for the study of fossil plants

ESCAPA, IGNACIO; TAYLOR, THOMAS N.; TAYLOR, EDITH L.

Mar del Plata

Simposio; XIV Simposio Argentino de Paleobotánica y Palinología; 2009

Universidad Nacional de Mar del Plata

Cladistics is a widespread method used to reconstruct the phylogenetic history of organisms. Empirical studies have shown that extensive taxon sampling, including fossil taxa, improves the performance and increases the empirical content of phylogenetic analyses. Several analyses have demonstrated that fossils are among the most influential taxa in tree resolution. In spite of this, most phylogenetic studies normally exclude fossils from the matrices, even in those that include morphological data. A frequently cited explanation for this bias is related to the lack of information (e.g., incomplete taxa) and difficulties in the assessment of homology for particular structures. In addition, misinterpretation of concepts such as character polarity and missing entries are also used as arguments to exclude fossil taxa as terminals. Recent methodological advances and empirical studies, however, indicate possible ways to avoid the difficulties associated with the inclusion of fossil plants in cladistic analyses. For example, the implementation of the concept “dynamic homology” for morphological characters offers a method that can be used to evaluate different hypotheses of homology for the same structures. Reduced Positional Congruence (PCR) is a recently developed method that can be used for the identification of unstable taxa, so as to determine the characters responsible for the instability. In the present contribution we use these and other methodological advances in a morphological matrix of the conifer family Araucariaceae. These new methodological techniques indicate that some of the generalized assumptions and misinterpretations attributed to fossil plants in phylogenetic analyses needs to be reevaluated.