Snakes form a natural group of squamate reptiles, an evolutionary lineage that also includes lizards and amphisbaenians. The evolutionary origin of snakes within squamate reptiles is a longstanding, unresolved problem, mainly because several lineages of lizards have independently evolved a snake-like body form (extreme body elongation coupled with limb reduction or complete loss) and basic skull structure. This creates difficult problems for the reconstruction of the evolutionary history (phylogeny) of snakes due to independently evolved (convergent) similarity. In contemporary reptile systematics, two main hypotheses are at the heart of current debate on snake origins: a marine origin of snakes from the extinct, aquatic mosasaurs or a burrowing/terrestrial origin of snakes from fossorial or terrestrial lizards such as the burrowing dibamids or amphisbaenians, or the terrestrial monitor lizards. This debate has recently been fueled by the description of fossil (Upper Cretaceous) snakes that combine a skull structure typical of evolutionarily advanced snakes with the presence of well-developed hind limbs (a presumably primitive feature). For this research, the problem of snake origins is broken down into the following questions: What group of squamates is most closely related to snakes? What are the relationships among the major groups of snakes? What do the answers to these questions tell us about the ecology of snake origins (aquatic vs. terrestrial) and about the morphological evolution of the snake body plan? Research addressing these questions will focus on anatomical investigation of all relevant fossil and living taxa, yielding results that will be combined with relevant molecular data. All anatomical characters used to date in the debate about snake origins will be re-evaluated, and new morphological data will be generated through the initiation of anatomical projects focused on understudied and/or controversial character systems. This will involve organ systems that either are at the center of current discussion (such as the development of the snake dentition), or that are essential for understanding the evolution of the snake body plan (such as patterns of change in the axial musculature and vertebral column that are correlated with the elongation of the body and the reduction or loss of limbs). Student training in anatomical investigative techniques and in methods of phylogeny reconstruction will form an integral part of this research project. Mastering anatomical complexity and methods of phylogenetic systematics, as well as the combination of anatomical and molecular data, are prerequisite for a modern approach to the study of biodiversity in all its aspects.
