Osteological characters of birds and reptiles show greater congruence with molecular phylogenies than soft characters: homoplasy of morphological partitions

Despite increased use of genomic data in phylogenetics, morphological information remains vital for resolving evolutionary relationships, particularly for fossil taxa. The properties and models of evolution of molecular sequence data are well characterized and mature relative to those of morphological data. In particular, heterogeneity, integration and relative homoplasy of empirical morphological data could prove problematic for phylogenetic reconstruction. Here we compare osteological and non-osteological characters of 28 morphological datasets of extant saurians in terms of their homoplasy relative to molecular trees. Analysis of individual avian datasets finds osteological characters to be significantly more consistent with molecular data than soft characters. Significant differences between morphological partitions were also observed in the age at which characters resolved on molecular trees. Osteological character changes occur relatively earlier in deep branches, whilst soft-tissue character transitions are more recent in shallow branches. The combined results demonstrate differences in evolutionary dynamics between morphological partitions. This may reflect evolutionary constraints acting on osteological characters, compared with the relative lability of soft characters. Furthermore, it provides some support to phylogenetic interpretations of fossil data, including dinosaurs, which are predominately osteological. Recent advances in amphibian and mammal phylogenetics may make these patterns possible to test for all tetrapods.