Underfoot Pressure Equalisation as an Explanation for Extreme Heteropody

Heteropody is the phenomenon in which the manus and pes of quadrupedal animals differ substantially in size and shape. The term is most often used in reference to the extreme foot size differences present in fossils and trackways of some non-avian dinosaurs, particularly sauropods. Previous studies have asserted the possibility that extreme heteropody developed in these animals as a mechanism to equalise underfoot pressure, compensating for unusually anterior/posterior centre of mass positions. This thesis sets out to test this hypothesis by answering the following questions: 1. Can skeletal surface area predict soft tissue foot surface area? 2. Is antero-posterior centre of mass position correlated with heteropody in extant taxa? 3. Do underfoot forces and pressures in extant taxa indicate the presence of a pressure equalisation mechanism? 4. Is there evidence in the fossil record for a link between centre of mass and extreme heteropody in dinosaurs? These questions were answered using the corresponding methods: 1. Using CT scans of the feet of extant animals and a custom Matlab script to derive underfoot surface area for skeletal and soft tissue and if they correlate. 2. Using digitized skeletons and convex hulls of quadrupedal extant animals to gather centre of mass and heteropody data for a range of extant animals, and seeing how they correspond with CoM positions. 3. Combining new pressure mat recordings with recordings in the literature for quadrupedal animals and seeing how they correspond with CoM positions. 4. Gathering heteropody data from sauropodomorph fossil trackways and some quadrupedal dinosaur body fossils, and testing how they correspond with previously established CoM position estimates. From these lines of enquiry, no link between CoM position and heteropody was definitively established. Results for live animal studies showed more signal for a correlation than in skeleton-only studies, and dinosaur trackway analysis showed potential for a link in sauropodomorphs, but neither of these studies provided enough evidence to establish a correlation between CoM and heteropody in tetrapods. This thesis does not support the hypothesis that heteropody is used as a pressure equalisation mechanism in tetrapods, especially as a universal rule. This thesis also found that soft tissue underfoot surface area is highly predictable from skeletal underfoot surface area. In addition, it found that underfoot surface area based on soft tissue is larger in forefeet compared to hindfeet that would be expected from skeletal surface area alone