Abstract

Ontogeny is rarely included in phylogenetic analyses of morphological data. When used, the ontogenetic information is reduced to one character for two or three different ontogenetic stages. Several examples show that current methods miss a major part of the information. We here propose a new method for including the ontogenetic dimension in coding schemes of phylogenetic analyses. Our goal was to maximize the phylogenetic information extracted from ontogenetic trajectories. For discrete features, we recommend including precise timings of transformation(s) from one state to another in the ontogenetic trajectories. For continuously varying features, growth laws are modeled on raw data using least-square regressions. Then, parameters of models are included in the coding scheme as continuous characters. This method is employed to reconstruct phylogenetic relationships using the ammonite family Amaltheidae as a test subject. Based on the same data set, a second analysis has been performed only for characters of the adult stage. Comparisons of retention index, bootstrap support, and stratigraphic congruence between the two analyses show that the inclusion of ontogeny yields better phylogenetic reconstruction. Morphological traits in ammonites which are usually the most homoplastic show a better fit to most parsimonious trees by including the ontogenetic dimension. In several cases, growth rates and patterns of growth have better fit to phylogeny than adult shapes, implying that paths of ontogeny can be more relevant than its products.