Body plan evolution and development in jawed vertebrates
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My research spans a wide range of systems and questions, but all of these center on the evolution and development of the body plan in jawed vertebrates. I use a combination of developmental biology, comparative anatomy, and paleontology to gain a comprehensive understanding of the patterns and processes that contribute to the diversity of vertebrates alive today.
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Vertebral development and segmentation in chondrichthyans
A stage 32 little skate, removed from its egg case.
Until recently, vertebral development in cartilaginous fishes had not been studied in detail for decades. However, as the outgroup to all other jawed vertebrates, data from chondrichthyans help to identify primitive and derived morphological and developmental features of the axial skeleton. I use the little skate (Leucoraja erinacea) as a cartilaginous fish model for vertebral development. To study vertebral development in the skate I perform dye labeling experiments to track cell migration, study gene expression patterns, and use microCT scans to visualize embryonic morphology.
Vertebral column evolution in fossil and living fishes
A time-scaled supertree of jawed vertebrates
I study the skeletons of the axial columns of fossil and living fishes to reconstruct the evolutionary histories of different vertebral components. By compiling separate phylogenetic hypotheses into one supertree and scaling it to time, I have a scaffold on which I can run phylogenetic analyses. Techniques such as ancestral state reconstructions help to show that different parts of the vertebrae, such as centra and vertebral duplications, evolved independently numerous times in vertebrates.
Paleontology and evolution of chondrichthyans
A reconstruction of the fossil shark Dwykaselachus by K. Tietjen.
The early evolution of cartilaginous fishes, and their relationships to other groups of early jawed vertebrates, is still not well understood. To help uncover these relationships, I investigate the morphology of early chondrichthyan fossils through the use of CT scans to determine how this group began. These include fossils like the symmoriid shark Dwykaselachus, which connects well known groups of fossil sharks with the chimaeras, an enigmatic but major division of jawed vertebrates.