We study a variety of topics related to the evolution of reptiles including comparative morphology, development, and systematics. Both living and extinct species, and both phenotypic and genetic data, are important in this work. Below is a sample of three specific projects currently under investigation:
Evolution of worm lizards (amphisbaenians)
Amphisbaenians are a poorly known group of fossorial squamate reptiles, nearly all of which are limbless, and many of which exhibit dramatic modifications of the cranium related to their highly derived, head-first burrowing behavior. The evolutionary relationships of worm lizards have long been controversial for several reasons: rarity of museum specimens available for study, highly derived morphological conditions that can confound comparative studies, and difficulty of obtaining tissues for molecular phylogenetic studies due to their secretive habits in the wild. A morphology-based phylogenetic study inferred that the only amphisbaenian to retain limbs (Bipes) was the sister-group to all other amphisbaenians, implying that limb loss occurred once during the evolution of the group (Kearney, 2003). This analysis also grouped taxa with similar cranial morphotypes into monophyletic groups. A DNA-based phylogenetic analysis (Kearney and Stuart, 2004), however, indicates widespread morphological convergence within the group, including three independent incidences of limb loss, and substantial convergence in skull shapes. In collaboration with colleagues at The University of Texas at Austin, new comprehensive anatomical studies of the amphisbaenian skull are being pursued using High-Resolution X-ray Computed Tomography (Kearney, Maisano, and Rowe, 2005; Maisano, Kearney, and Rowe, in press). Future phylogenetic studies of the group will integrate the wealth of new anatomical data being generated through the CT-scanning work with more DNA data; incorporate fossil and living taxa; and attempt to achieve denser taxonomic sampling. Results are certain to have interesting implications for the evolution of worm lizards and the homology of major features such as limblessness and cranial modifications.
The evolutionary origin of snakes within squamate reptiles is a longstanding, unresolved problem. 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 surprisingly combine a derived skull structure typical of evolutionarily advanced snakes with the presence of well-developed hind limbs (a presumably primitive feature). For this research project, 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 focuses on understudied and/or controversial character systems (such as the development of the snake dentition and the development of the vertebral column), as well as features 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). My collaborator on this project is Field Museum paleontologist Olivier Rieppel, and postdoctoral researcher Takanobu Tsuijihi is focusing on the homology of the cervical musculature in snakes, limbless lizards, and tetrapodal lizards. (Project funded by NSF DEB-0235628 to M. Kearney and O. Rieppel.)
Deep Scaly Project
Assembling the Tree of Life — Resolving Squamate Phylogeny Using Genomic and Morphological Approaches. I am collaborating with numerous researchers on a project to resolve the higher-level relationships of squamate reptiles (lizards, snakes, and amphisbaenians). Squamates are the subject of many phylogeny-based research programs in ecology and evolution, yet the relationships among major lineages of squamates remain remarkably uncertain. The project is an integrative one, making use of genomics, morphological imaging techniques, comparative anatomy, and intensive sampling of both fossil and extant representatives of all recognized squamate subfamilies. The results of the research will provide a rigorous phylogenetic framework for comparative and systematic studies within and between squamate families. Collaborators on this project include Jacques Gauthier, Mike Lee, Jessie Maisano, Tod Reeder, Olivier Rieppel, Jack Sites, and John Wiens. Undergraduate students Angela Marion and Beth Bastiaans are research assistants on this project. See http://www.fieldmuseum.org/deepscaly for more information. (Project funded by NSF EF-0334961 to M. Kearney, T. Reeder, O. Rieppel, J. Sites, and J. Wiens.)