PhD: Too big to hop? Vertebral allometry and locomotor biomechanics in kangaroos

One remarkable feature of mammals is the enormous diversity of methods they have evolved to navigate their environment e.g., swimming, flying, running. Kangaroos are a captivating example, pushing the boundaries of terrestrial locomotion using a bipedal hopping gait that allows them to achieve speeds of over 70km/hr. Exploring the principals governing such extreme locomotor adaptations can help us to understand the mechanical limits of locomotion and its impact on the evolution of locomotor diversity in mammals. Kangaroos are particularly interesting because they hop at much larger body sizes than other saltatorial mammals, and have decoupled the cost of locomotion from speed, meaning that large species can hop faster without additional energy input. Extinct Pleistocene kangaroos were even larger, reaching body sizes of up to 250kg, while still retaining a stereotypical hopping body plan. Given that large extant kangaroos appear to operate close to their safety limits for ligaments during hopping, this raises important questions regarding the scaling of hopping locomotion, potential body size limitations of this locomotor mode, and the inferred ecology of extinct giant kangaroos.

This project will investigate the biomechanics of scaling of hopping locomotion in kangaroos. Biomechanical springs (elastic tissues) in the limbs have been pinpointed as a key adaptation for hopping at large size, however little is known about the importance of similar mechanisms in the other critical components of the locomotor system – the axial skeleton. The student will examine the scaling of vertebral structures in hopping mammals to elucidate the anatomical adaptations of the axial system for increasing size. By integrating data from the back and limbs, the student will explore biomechanical size limitations on hopping locomotion using modelling and biorobotics and apply this knowledge to test locomotor hypotheses in extinct giant kangaroos.

This project will provide the student with access to a unique combination of expertise and resources through a research partnership between the University of Manchester and University of Melbourne. At Manchester, the student will develop a diverse skillset through the interdisciplinary supervisory team: vertebral anatomy (Katrina Jones), mathematical modelling of locomotion (Robert Nudds), and biorobotics (Ben Parslew). At Melbourne (one-year research placement, Andrew Pask), the student gain knowledge of kangaroo biology and have access to collections of fossil and extant kangaroo specimens critical to the project. An external advisor (Dr. Christine Janis, University of Bristol), a world-leading expert on extinct giant kangaroos, will provide guidance on the paleontological data collection.