Reconstructing skull evolution of fossil crown birds

What processes shape vertebrate diversity over large time scales? Previous approaches to this question have focused on many different factors, from life history, ecology, and biogeography to large-scale environmental change and extinction, and can use many different metrics to quantify diversity. To date, the majority of studies on the evolution of vertebrate diversity have focused on relatively simple metrics, specifically taxon counts or univariate measures, such as body size. However, an approach based on either of those measures would be unable to distinguish between an elephant and a whale, similarly-sized mammals that otherwise differ in most attributes of consequence for understanding and reconstructing organismal evolution. Multivariate morphological data requires more extensive time and effort to collect but ultimately provides a more complete picture of evolutionary and palaeoecological change. Moreover, morphological traits provide a bridge between studies of palaeoecological and palaeobiological change and studies of the genetic and developmental factors that intrinsically shape organismal morphology, and must also influence large-scale patterns of evolutionary change. Thus, a complete understanding of the patterns and processes underlying evolution requires an approach that can fully represent an organism's phenome, the sum total of their observable traits. Fortunately, recent advances in imaging and morphometric data analysis now allow for study of phenomic evolution across large clades.

Huge improvements in data collection and data analysis in recent years have produced a step change in accuracy of evolutionary rates and identification of factors shaping diversity, in particular through quantifying the complex morphology of organisms. In my lab, we use high-density 3D surface morphometrics from surface and CT scans to reconstruct the evolution of organismal shape through development and across deep time, bridging datasets from embryos to fossils. Many studies have demonstrated that fossil data significantly improve the accuracy of evolutionary reconstructions; however, several hyperdiverse modern clades, such as birds, lack fossils that are well-preserved in 3-D, hindering their inclusion in these analyses. In this study, the student will use cutting-edge retrodeformation techniques to reconstruct the cranial morphology from micro-CT scans of early crown fossil birds housed in international collections, conduct high-density 3D morphometric analyses of those fossils, and combine them with existing data from Prof. Goswami's lab for over 400 extant birds to reconstruct the early evolution of birds and identify the ecological and environmental factors that shaped this highly successful radiation. Using our recent analyses identifying seven cranial modules in birds, s/he will test several hypotheses relating to ecological and developmental drivers of morphological diversity in living and extinct birds, analysing tempo and mode of evolution, and ecomorphology. The reconstructions of early birds alone will be of immense value to the broader community, but the project will ultimately provide a much more accurate understanding of the evolution of birds and what drove their immense diversification.