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AbstractFour new fossil feathertail possum species (Marsupialia, Diprotodontia, Phalangerida, Petauroidea, Acrobatidae) are described from late Oligocene to middle Miocene fossil deposits in the Riversleigh World Heritage Area, northwestern Queensland. They are the first pre-Pleistocene fossil representatives of this family to be described. Two species are referred to the modern genus Acrobatesand two to the modern genus Distoechurus. These species are distinguished from each other and from the living Distoechurus pennatusand Acrobates pygmaeuson the basis of qualitative and quantitative characters of the first lower molar (m1), which is the only tooth known for all four fossil species. Fortunately, m1 is morphologically the most variable tooth in the cheektooth row of acrobatids, and it exhibits numerous genus- and species-specific features. Phylogenetic analyses based on dental characters strongly support monophyly of Acrobatidae relative to other petauroids, as well as providing relatively strong support for reciprocal monophyly of Acrobatesand Distoechurus, including the newly described fossil members of these genera. Recognition of species of Acrobatesand Distoechurusin these fossil deposits is broadly congruent with recent estimates for the time of divergence of the two modern genera based on molecular data, and also provides an additional fossil calibration point for future studies of marsupial divergence times. These fossil species provide new insights into the biogeographical and ecological history of this enigmatic family of small possums, specifically that the oldest known species of Acrobatesoccurred in closed forest environments (in contrast to the living species, A. pygmaeusand Acrobates frontalis, which today inhabit open sclerophyll forests and woodlands) and that Distoechurusappears to have originated in Australia, only subsequently dispersing to New Guinea before becoming extinct in its Australian homeland.Prudence R. Fabian [pruefabian@gmail.com], Michael Archer [m.archer@unsw.edu.au], Suzanne J. Hand [s.hand@unsw.edu.au], Earth and Sustainability Science Research Centre, School of Biological, Earth and Environmental Sciences, UNSW Sydney, NSW 2052, Australia; Robin M.D. Beck [r.m.d.beck@salford.ac.uk], School of Science, Engineering and Environment, University of Salford, Manchester M5 4WT, UK.

AbstractLarge-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.Matthew J. Phillips [m9.phillips@qut.edu.au]; Mélina A. Celik [melina.celik@gmail.com] School of Biology and Environmental Science, Queensland University of Technology, 2 George Street, Brisbane, Qld, 4000, Australia; Robin M.D Beck [r.m.d.beck@salford.ac.uk] Ecosystems and Environment Research Centre, School of Science, Engineering and Environment, University of Salford, Manchester, UK.