1 INTRODUCTION Extant mammals can dorsoventrally flex and extend the spine, which facilitates breathing and increases stride length during locomotion (Carrier, 1987; Gambaryan, 1974; Hildebrand, 1959; Schilling & Hackert, 2006). The extent to which the spine bends varies across extant mammals, corresponding to locomotor style and gait, but the evolution of this function has not been explored in the fossil record (Boszczyk et al., 2001; Gambaryan, 1974; Slijper, 1946).
