Locomotor ontogeny and the evolution of primate quadrupedalism

The form of quadrupedal walking used by primates is unusual among mammals, and is thought to have arisen as an evolutionary innovation when the earliest primates diverged from their mammalian ancestor. My current research focuses on exploring the biomechanics of

primate quadrupedalism as well as the broader issue of why this distinctive gait evolved in primates. I am particularly interested in exploring how aspects of body shape and mass distribution have influenced primates’ distinctive form of quadrupedalism. My current research focuses on a consideration of locomotor ontogeny as a key to understanding the evolution of primate quadrupedal gait. Infant primates are not shaped like, nor do they walk like adults, and they undergo striking changes in both gait and body shapeduring the first year of development. Therefore, infant primates provide an excellent "natural experiment" with which to test the influence of body structure on the kinematics and evolution of quadrupedalism.

Current project in this area (funded by NSF) Collaborators: Chris Kirk, Jesse Young
Locomotor Ontogeny in Microcebus murinus, Petaurus breviceps and Monodelphis domestica: The Influence of very small body size on the evolution of primate quadrupedal locomotion

One important issue often overlooked in research on the evolution of primate quadrupedalism is the interaction of body size with substrate (e.g., branch) size. Clearly, the locomotor challenges presented by the "fine branch niche" cannot be assumed to be the same for small and large primates. Recent debate on primate ancestral size includes the view that ancestral primates may have been much smaller than the smallest living primates (mouse lemurs), perhaps as small as 10-15g, yet few studies have considered the effects of body sizes of 100g or less on primate quadrupedalism. For this project, I am using locomotor growth and development as a means to investigate the influence of very small body size on primate locomotor evolution. The project takes a broad comparative perspective, comparing locomotion in the smallest living primates (mouse lemurs) to similarly sized non-primate mammals (two marsupials- sugar gliders and the gray short-tailed opossum). The comparative approach will provide new insight on the evolution of primate quadrupedalism by directly addressing the unique means by which small primates and other mammals navigate arboreal substrates.