DEB Proposal: SG: Collaborative Research: Repeated evolution of limblessness and head-first burrowing in tetrapods: Testing predictions from the fossil record

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Animal species have evolved an incredible diversity of body shapes to reflect their different ecology and functions, e.g., swimming, flying, burrowing. An intriguing pattern is the independent evolutionary repetition of similar body shapes among distantly related groups of animal species; this is known as convergent evolution. How and why convergence of body shape occurs is a fundamental evolutionary puzzle. This research project examines the anatomical, biomechanical, developmental, and natural selection pressures that drive the evolution of limblessness and head-first burrowing. Burrowing behavior and the loss of limbs is a classic case of convergent evolution, and this project will test general hypotheses concerning the selective pressures that gave give rise to similar body shapes in various snakes, lizard and amphibian species. In this project, computer analysis will be applied to images of skull shape created with technologies derived from medical imaging. That data will then be used to test for relationships between form and function in both fossils and living animals. The results of this work will be important to understanding how and why evolution arrived repeatedly at some common biomechanical solutions for burrowing. The proposed research also provides unique mentoring and outreach opportunities. This project will provide research experience for students from underserved communities. It will develop a mobile toolkit of both analog and digital components devoted to science outreach activities, and it will inform the public about evolutionary processes through multiple public outreach events. The research project will test for variation in the causes of head-first burrowing (HFB) which is a prominent example of convergent evolution. Reduction and loss of limbs is associated with the use of the head as a burrowing tool across snakes, amphibians, multiple clades of lizards, and several extinct tetrapod groups. The research will describe and quantify the morphological variability in bony and soft tissues in living HFB species. Micro CT and histological data will be collected to assess biomaterial composition, suture patterns, and developmental trajectories across distantly-related taxa. Those results will be placed in a phylogenetic and developmental context using phylogenetic comparative methods. The work will thus infer form, function, and evolutionary history from the patterns of variability. The investigative framework devised for extant taxa will then be applied to extinct, putative HFB taxa to provide independent tests of prior observational hypotheses made for fossils. The reach of this work will be extended through data sharing of the 3D anatomical models, phylogenetic matrices, and specimen data via NSF-supported databases such as Morphobank and Dryad.