Mammals are known for their great range of locomotor behaviors, including unique asymmetric gaits such as galloping and bounding. Asymmetric gaits are made possible by the subdivision of the dorsal vertebral column (the area between the pectoral and pelvic girdles) into two morphologically and functionally distinct regions. Anteriorly, the thoracic region bears ribs and is specialized for respiration, whereas posteriorly the dorsoventrally mobile lumbar region functions in locomotion. Combined, the regionalized dorsal vertebrae allow mammals to breathe and move simultaneously, permitting the use of high speed gaits for prolonged periods of time. But, how did this key mammalian trait evolve? Modern species provide little information for examining this fundamental evolutionary question, as they all possess distinct thoracic and lumbar regions. However, the clade to which mammals belong, Synapsida, has a rich fossil record that provides a detailed view of the origin and evolution of mammals. Using cutting-edge morphometric, biomechanical, and 3D digital modeling techniques, this project takes a deep-time approach to examine function of the vertebral column in fossil synapsids, and to trace the origin and evolution of the thoracolumbar region and dorsoventral mobility.
This research is funded by the National Science Foundation Grant 1524523: Collaborative Research: Functional Evolution of the Mammalian Backbone: Insights from the Forerunners of Mammals
Flesh reconstruction of the therapsid (cynodont) Thrinaxodon showing evolution of the "pectoral region". See Jones et al. 2018. Image copyright April Neander.