Archaeopteryx, paravian phylogenetic analyses, and the use of probability-based methods for palaeontological datasets

Archaeopteryx, which has often been considered the earliest avialan, is an iconic species, central to our understanding of bird origins. However, a recent parsimony-based phylogenetic study shifted its position from within Avialae, the group that contains modern birds, to Deinonychosauria, the sister-taxon to Avialae. Subsequently, probability-based methods were applied to the same dataset, restoring Archaeopteryx to basal Avialae, suggesting these methods should be used more often in palaeontological studies. Here we review two key issues: arguments recently advocated for the usefulness of probability-based methodologies in the phylogenetic reconstruction of basal birds and their close relatives, and support for different phylogenetic hypotheses. Our analysis demonstrates that Archaeopteryx represents a challenging taxon to place in the phylogenetic tree, but recent discoveries of derived theropods including basal avialans provide increased support for the deinonychosaurian affinities of Archaeopteryx. Most importantly, we underscore that methodological choices should be based on the adequacy of the assumptions for particular kinds of data rather than on the recovery of preferred or generally accepted topologies, and that certain probability methods should be interpreted with caution as they can grossly overestimate character support.