Collaborative Research: Ecomorphological Diversification and the Origin of Phenotypic Disparity in Crocodile-line Archosaurs

Species morphology typically evolves to meet the demands of the environment. In the fossil record, and among existing species, large morphological changes are frequently associated with changes in habitat or ecology. However, there remains little understanding of the general rules that govern morphological change associated with ecological change. This project will use skeletal and soft-tissue anatomy as well as detailed 3D shape data to study closely-related, transitional species to investigate the evolution of morphology and ecology in the long-lived and fossil-rich group Crocodylomorpha (crocodiles, alligators, and their extinct relatives). The project will exploit the group's multiple natural experimentation with extreme environments to develop detailed conceptual models for major ecological and morphological transitions that will inform on the rules underlying morphological change. These models will then serve as predictors for how and why transformations occur, which can be tested in other groups with similar narratives. Important examples include the initial emergence of four-limbed vertebrates onto land, how birds took the sky, and the first steps in the reign of mammals. The innovative technologies, techniques, and widely applicable conclusions from this research will promote interdisciplinary work among paleontologists, biomechanists, ecologists, and evolutionary biologists. The researchers will make their data, digital models, analytical tools, and essential supplementary files available for wide access. Furthermore, this project will support associated PhD and Postdoctoral research as well as foster access to higher education for substantially underrepresented groups. This project will use integrative approaches to reveal the complexities of ecomorphological changes across major evolutionary transitions. The study will examine how novel environments put new, often extreme demands on historical phenotypes by addressing how large-scale habitat and ecological transitions drive evolution across multiple integrated anatomical systems. The research will test hypotheses about phenotypic integration on an evolutionary scale to determine whether developmental rates, sequence heterochrony, and/or patterns of modularity determine if consistently applied rules of ecomorphological diversification underlie adaptive radiations. The outcome will be an unprecedented database of crocodylomorph cranial and post-cranial diversity that includes contrast-enhanced neural and skeletal tissues, raw and partitioned CT stacks, and 3D digital models as well as comparative, intra-clade conceptual models for how predatory vertebrates shift to lives on the shoreline, within the sea, and toward herbivory. The microCT and cutting-edge, diffusible iodine-based contrast-enhanced computed tomography imaging, in addition to a robust morphological phylogeny for analysis of evolutionary trends using the latest phylogenetic methods, represent potentially transformative methodologies developed by this research group. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.