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Evolution of anatomical plasticity in squamate reptiles

Brain evolution in vertebrates

Supervisors: Dr Jason Head

Project summary:

Squamata (“lizards” including snakes) is one of the three major vertebrate radiations over the last 100 million years, and demonstrates considerable variation in body form including repeated histories of: loss (and possible reacquisition) of limbs; changes in number of vertebrae, ribs, and associated muscles; evolution of extreme body sizes; and reduction of visual and auditory sensory systems. Ecological correlates to anatomical specializations in squamates are well documented for only a limited number of taxa and individual anatomical systems, and no study has comprehensively examined anatomical variation, such as relative plasticity of cranial versus post-cranial characters, across squamate phylogeny.

We will reconstruct evolutionary patterns of anatomical change and innovation, represented by the skeletal system, in all major modern and fossil squamate clades. Focusing on anatomical specialisations associated with the repeated evolution of arboreal, aquatic, and burrowing habits, we will use phylogenetic comparative methods and quantified morphology to determine if particular skeletal regions are under greater or lesser functional and/or evolutionary constraint, and if regions of the skeletal system are integrated or dissociated across squamate phylogeny and ecology. We will use fossil data to place results in the contexts of radiation, extinction, and environmental change through deep time. 

 

What the student will be doing:

The student will formulate hypotheses on the history and mechanisms underlying the evolution of squamate anatomical
plasticity by collecting data on skeletal morphology in modern and fossil reptiles through examination of museum collections, including Computed-Tomographic (C-T) scanning techniques. The student will use geometric morphometric analysis of anatomical shape to quantify skeletal changes between taxa, and will use phylogenetic comparative methods to reconstruct ancestral states for morphometric and discrete characters, calculate rates of change, and to examine historical patterns of anatomical change

 

References:

 

Head, J. J., and P. D. Polly. 2015. Evolution of the snake body form reveals homoplasy in amniote Hox gene function. Nature, 520:86-89. doi: 10.1038/nature14042.

Müller, J., T. Scheyer, J. J. Head, P.M. Barrett, P. Ericson, D. Pol, and M. R. Sanchéz-Villagra. 2010. The evolution of vertebral numbers in recent and fossil amniotes: The roles of homeotic effects and somitogenesis. Proceedings of the National Academy of Sciences of the United States of America (PNAS), 107:2118-2123

Brandley, M.C., J.P. Huelsenbeck, and J.J. Wiens. 2008. Rates and patterns in the evolution of snakelike body form in squamate reptiles: evidence for repeated reevolution of lost digits and longterm persistence of intermediate body forms. Evolution62:2042-2064.