CONICET | Buscador de Institutos y Recursos Humanos

Little is known about the large-scale evolutionary patterns of skull sizerelative to body size, and the possible drivers behind these patterns, in Archosauromorpha.For example, the large skulls of erythrosuchids, a group of non-archosaurianarchosauromorphs from the Early and Middle Triassic, and of theropod dinosaursare regarded as convergent adaptations for hypercarnivory. However, fewinvestigations have explicitly tested whether erythrosuchid and theropod skullsare indeed disproportionately large for their body size, and whether this trendis driven by hypercarnivory. Here, we investigate relative skull sizesof Mesozoic archosauromorphs using a robust phylogenetic framework to assessthe influence of potential drivers on relative skull size (taxonomy, diet,locomotory mode and inhabited biotope), to investigate scaling relationshipsbetween skull and body size according to these drivers and to reconstructarchosauromorph relative skull size evolution. Our analyses find that archosauromorphrelative skull sizes are largely determined by phylogeny and that the otherdrivers have much weaker levels of influence. Skull size scales with negativeallometry for all studied archosauromorphs, scales with positive allometry innon-archosaurian archosauromorphs and interestingly, scales isometrically intheropods. Ancestral skull:body size ratio reconstructions reveal that theancestral erythrosuchid had a disproportionately large skull and the ancestraltheropod had a proportionately sized skull. Relative skull sizes oferythrosuchids and theropods are therefore distinct from each other, indicatingthat disproportionately large skulls are not a prerequisite for hypercarnivory inarchosauromorphs, and that erythrosuchids exhibit a bauplan unique among terrestrialMesozoic carnivores.

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