The massive size of some sauropod dinosaurs imposed many biomechanical constraints on their locomotion and behaviour. Postural transitions within Sauropoda reflect these constraints including the development of a quadrupedal stance from the bipedal stance of more basal sauropodomorphs, as well as the transition to a wide-gauge stance in titanosaurs from the narrow-gauge stance of other sauropods. In this thesis muscle moment arms and bone mechanical performance in the forelimb and hind limb of sauropods have been analysed using three-dimensional musculoskeletal modelling and finite element analysis. Taxa chosen for study represented a diversity of postures and gaits. Plateosaurus engelhardti from the Late Triassic is a basal and bipedal sauropodomorph. Diplodocus carnegii from the Late Jurassic is a narrow-gauge sauropod with a gracile bone morphology and posteriorly located centre of mass. Giraffatitan brancai, also from the Late Jurassic, is a titanosauriform sauropod with an intermediate stance and more centrally located centre of mass. It had gracile a bone morphology and greatly elongated forelimbs. Finally, the Australian Late Cretaceous titanosaur Diamantinasaurus matildae displayed a fully wide-gauge stance and robust bone morphology. It is also thought to have a more anteriorly located centre of mass, as has been previously suggested for titanosaurs.

By examining changes in the shift from a bipedal to a quadrupedal posture, I found that the bipedal sauropodomorph Plateosaurus had higher knee extension moment arms compared with the sauropod taxa analysed. I proposed this was indicative of leverage for maintaining a more flexed hind limb stance and more variable locomotor behaviours in contrast to the development of a columnar stance in sauropods and the resulting reduction in locomotor capabilities. More derived sauropods in this analysis (Giraffatitan and Diamantinasaurus) displayed a reduction in hip extensor leverage, possibly associated with an anterior shift in centre of mass. This shift, combined with higher bone stress magnitudes observed in the humeri and femora of these taxa, indicated they were not well-adapted to maintain a bipedal pose for long periods of time; however, the much more posteriorly located centre of mass and the low stress magnitudes in the proximal limb bones of Diplodocus suggested that this taxon was well-adapted for more habitual bipedal rearing. This was partially supported by hind limb moment arm results for Diplodocus which showed high leverage in hip mediolateral rotation and knee flexion and extension. There were also some interesting results uncovered in the forelimb of Giraffatitan and Plateosaurus during the course of this project. The elongated forelimb of Giraffatitan increased moment arm magnitudes in shoulder flexion thought to reduce peak forces acting on the forelimb during locomotion. This was supported by finite element analysis results which showed high relative stress in the humerus of Giraffatitan compared with the other sauropod taxa. This suggested that an increase in mechanical advantage of the muscles in the forelimb would have been advantageous for protecting the limb against peak stresses. Low stress magnitudes in the humerus of Plateosaurus suggested its bone morphology was still well-adapted for a weight-bearing role even though it is considered to be bipedal. This indicated that it might have used its forelimbs during locomotion as hatchlings or when traversing unstable substrates as adults, or in other non-locomotor behaviours like feeding or defence.

In assessing the biomechanical impact of the transition to a wide-gauge stance in titanosaurs, I found moment arm results for Diamantinasaurus showed increased action in both shoulder adduction and hip adduction, presumably for stabilising limbs less well-aligned with ground reaction force. Bone stress magnitudes were also lower when counteracting adductor rather than abductor loads in Diamantinasaurus, indicating an adaptation for resisting these forces. In the forelimb of Diamatinasaurus, high leverage in elbow flexion and extension was found when compared with the other taxa studied. This result, combined with an increased role for the forelimb in forward propulsion indicated by an anteriorly shifted centre of mass, suggested that the forelimb in titanosaurs was adapted for increased manoeuvrability. I proposed this would have allowed titanosaurs to adopt a broader range of behaviours. In the hind limb however, results were a little different. Knee moment arm results showed low leverage about the knee in Diamantinasaurus, possibly indicating a preference for high velocity movements for improved stabilisation rather than manoeuvrability in the hind limb. In addition to this, the lateral shift of the limbs from the body with the development of a wide-gauge stance was also observed to have increased bone stress in both the humerus and femur of Diamantinasaurus. This increase in stress magnitude suggested that improved manoeuvrability in titanosaurs compared with other sauropods might have been less likely than previously thought. I therefore suggested that the transition to a wide-gauge stance in titanosaurs might not be related to the development of a broader range of behaviours, but might instead be related to an increased need for stability (and manoeuvrability in the forelimb) for inhabiting different palaeoenvironments.

Recently the hopping capability of Sthenurinae, extinct short-faced kangaroos, has become heavily debated. While much of the research has centred on skeletal morphology, there has been little work on the biomechanics of Sthenurinae. This thesis investigates whether one of the larger macropodoids, Simosthenurus occidentalis, would be capable of withstanding the forces that would be required for an animal of such size to hop.

This thesis is innovative to the topic of sthenurine locomotion and to a broader extent macropodoid locomotion, as it is the first to specifically incorporate finite element analysis to the hind limbs of S. occidentalis and many other macropodoids. This research is broken into three parts. First, a comparison of peak ground reaction force in the femur of S. occidentalis and thirteen other macropodoids, comparing the stresses generated during hopping at equal moment arm and equal internal loads relative to body mass. Secondly, I investigated muscle moment arms by reconstructing the muscular of Macropus giganteus, Dengrolagus lumholtzi and a possible muscular system for S. occidentalis based off of the musculature of the two extant species (M. giganteus and D. lumholtzi). These models were then compared to determine at what joint angle muscle moment arms would be the largest, and at what joint angle the greatest percentage of muscles would produce their largest moment arm in order to determine a probable limp posture for optimal body support in S. occidentalis. Finally, I conducted a second FEA on muscle forces which investigated if the forces required by the muscles during hopping would generate reasonable stress for S. occidentalis.

By comparing ground reaction force, results indicated that despite the relatively gigantic size (compared to many extant species of Macropodoidea today) S. occidentalis would generate stress equivalent to a species roughly 25 times smaller in body mass, In addition analysis of muscle moment arms indicated that S. occidentalis would produce its largest moment arms at joint angles closer in similarity to D. lumholtzi than to M. giganteus and would do so at limb postures relatively more up right than the two extant species. Finally in comparing muscle forces, results again indicated lower than predicted stress for S. occidentalis. Based on my results, I suggest that S. occidentalis might be capable of hopping but might also use striding for lower speed travel.

In recent years there have been an increasing number of studies investigating the relationship between diet preference, skull shape and biomechanics of primates. Understanding the relationship between morphological and mechanical variations and extrinsic factors, such as diet and feeding behaviour, provides insights into the evolution of our own species. However, most diet-related morphological studies have focused on the mandibles and dentition, while most biomechanical studies have concentrated on species that either feed on mechanically challenging foods (hard-object feeders) or are mechanically challenged during food acquiring (e.g., tree-gouging exudate feeders). These mechanical studies are usually small scale with only a few species and there is a lack more comprehensive comparisons. Studies on the relationship between cranial shape and biomechanical performances in primates are also limited. In the present study, whether cranial morphology and/or mechanical performance reflect dietary preferences were examined in Anthropoidea, which is a clade of primates that includes all the New World and Old World monkeys. It was hypothesised that cranial shape and its mechanical behaviour reflect diet regardless of phylogeny and cranial size.

Three-dimensional geometric morphometrics was used to investigate the relationship between cranial shape and diet. Finite element analysis was used to assess the mechanical performance in the anthropoid crania during premolar, molar, and incisor loadings. Von Mises strain magnitudes and distributions were used to determine the ability to withstand high bite forces. Mechanical advantages were calculated as the ratio of bite force per muscle force. Results showed that diet had very limited influence on cranial morphology. New World monkeys generally exhibited a stronger correlation between diet and cranial shape than Old World monkeys. This suggested that cranial morphology in primates was not the sole result of dietary selection. Variations of strain magnitudes were also found to be mostly insignificant with diet. However, results showed that mechanical advantages were a better predictor of diet preference, especially for species that require higher bite forces during feeding. Hard food feeders were more mechanically efficient at producing high premolar and molar bites compared to other dietary groups. Exudate feeders were also relatively efficient at producing high bite forces at the incisors. While cranial morphology was found to have limited correlation with diet, there was a strong relationship between cranial shape and mechanical advantage. This result indicated that mechanical advantage can be achieved by different combinations of craniofacial features.