My current research project addresses the anatomical transformation of the shoulder girdle that occurred during the evolutionary transition from synapsid reptiles to mammals. The sternum integrates the head, neck, chest, and limbs, and plays a key role in establishing patterning along the anterior-posterior axis of the body. Specifically, my students and I ask whether the sternum of living mammals is a single element, or the fusion product of multiple ancestral elements, each with a unique developmental history and peripheral articulation. We use CT scans of fetal whales to document sternal structure along the timeline of an individual’s development, and fossil ground sloths and armadillos to document changes over evolutionary history.