The evolutionary relationships of Diprotodontia and improving the accuracy of phylogenetic inference from morphological data

Large-scale molecular datasets have generally outperformed morphological data for inferring phylogeny, and sources of error in the latter are poorly understood. The morphologically and ecologically diverse marsupial order Diprotodontia (kangaroos and their relatives, the koala, wombats and possums) is well suited to considering these issues. Recent molecular results provide a phylogenetic benchmark for comparing previous molecular and morphological studies, encompassing all of the major phylogenetic data sources and methods that have been employed over the past 50 years. We show here that most molecular methodologies and ‘informal-comparative’ morphological studies have inferred diprotodontian relationships that closely resemble the recent molecular consensus. However, and perhaps surprisingly, algorithmic morphology, such as maximum parsimony analysis of morphological matrices, has inferred markedly inaccurate phylogenies, and is not improved by re-analysis with more recently developed, model-based (e.g., likelihood and Bayesian) methods. This is particularly concerning because algorithmic morphology is the primary approach for integrating fossils into the tree of life, and hence, for both calibrating molecular timescales and extending phylogenetic inferences of evolutionary processes beyond the snapshot provided by modern species. A novel simulation study presented here suggests that the inaccuracies in the marsupial algorithmic morphology studies partly stem from functional and body-size correlations among taxa that over-ride phylogenetic signals. We use the results to trial a reverse engineered phylogeny approach to correcting for such functional and developmental correlations among morphological data. In addition, we interrogated a newly published, densely taxon-sampled morphological matrix. Deeper level phylogeny reconstruction was improved by including fossils alongside extant taxa and counterintuitively, by increased effort to resolve relationships among shallow taxa. <i>Matthew J. Phillips [[e-mail]]; Mélina A. Celik [[e-mail]] School of Biology and Environmental Science, Queensland University of Technology, 2 George Street, Brisbane, Qld, 4000, Australia; Robin M.D Beck [[e-mail]] Ecosystems and Environment Research Centre, School of Science, Engineering and Environment, University of Salford, Manchester, UK</i>.