Meeting Abstract
Though evolutionary rates of living organisms can be estimated using molecular data, paleontological studies of morphology can be hindered by a reliance on parsimony, which fails to account for saturation and homoplasy. One such parsimony-based study used the Aetosauria, a clade of armored, crocodylian-line archosaurs, whose osteoderms are debated to evolve faster than the rest of the skeleton, and may be too homoplastic for reconstructing deeper clade relationships. One previous attempt to resolve the debate was limited to sub-setting data by the parsimony framework used. We use this same dataset (26 taxa, 83 characters) and implement partitioning, then a phylogenetic reconstruction in a ML framework to better address the debate. Using PartionFinder 2.0 we found osteoderms (= 33 characters) evolve at a different rate than the endoskeleton (= 50 characters). When we used this dataset to reconstruct the phylogeny of aetosaurs, with variable gamma distributed rates, we found osteoderm characters had a lower global evolutionary rate than endoskeletal characters. We conclude that though osteoderms evolve slower on average, the different gamma shapes show osteoderms are more variable in their evolutionary rates than endoskeletal features. Although the phylogeny we generated is identical in topology to the parsimony hypothesis, when using the same collapse rules, only by phylogenetic comparative methods (PCMs) can we address the debate in evolutionary rates. By accounting for rate heterogeneity across characters, we can resolve phylogenetic hypotheses with better estimates of support. With these refined hypotheses and PCMs to trace evolutionary rate shifts for these extinct clades, we inform our understanding of the macroevolutionary processes surrounding faunal turnovers, mass extinctions, and radiations.
