Biomechanical insights into the role of foot pads during locomotion in camelid species.

From the camel's toes to the horse's hooves, the diversity in foot morphology among mammals is striking. One distinguishing feature is the presence of fat pads, which may play a role in reducing foot pressures, or may be related to habitat specialization. The camelid family provides a useful paradigm to explore this as within this phylogenetically constrained group we see prominent (camels) and greatly reduced (alpacas) fat pads. We found similar scaling of vertical ground reaction force with body mass, but camels had larger foot contact areas, which increased with velocity, unlike alpacas, meaning camels had relatively lower foot pressures. Further, variation between specific regions under the foot was greater in alpacas than camels. Together, these results provide strong evidence for the role of fat pads in reducing relative peak locomotor foot pressures, suggesting that the fat pad role in habitat specialization remains difficult to disentangle.

The architecture and contraction time of intrinsic foot muscles.

Although critical for effective human locomotion and posture, little data exists regarding the segmentation, architecture and contraction time of the human intrinsic foot muscles. To address this issue, the Abductor Hallucis (AH), Abductor Digiti Minimi (ADM), Flexor Digitorum Brevis (FDB) and Extensor Digitorum Brevis (EDB) were investigated utilizing a cadaveric dissection and a non-invasive whole muscle mechanomyographic (wMMG) technique. The segmental structure and architecture of formaldehyde-fixed foot specimens were determined in nine cadavers aged 60-80 years. The wMMG technique was used to determine the contraction time (Tc) of individual muscle segments, within each intrinsic foot muscle, in 12 volunteers of both genders aged between 19 and 24 years. While the pattern of segmentation and segmental -architecture (e.g. fibre length) and -Tc of individual muscle segments within the same muscle were similar, they varied between muscles. Also, the average whole muscle Tc of FDB was significantly (p < 0.05) shorter (faster) (Tc = 58 ms) than in all other foot muscles investigated (ADM Tc = 72 ms, EDB Tc = 72 ms and ABH Tc = 69 ms). The results suggest that the architecture and contraction time of the FDB reflect its unique direct contribution, through toe flexion, to postural stability and the rapid development of ground reaction forces during forceful activities such as running and jumping.

Foraging modes of Mesozoic birds and non-avian theropods.

The origin and early evolution of birds has been a major topic in evolutionary biology. In the 20th century, evolutionary scenarios posited either ground-based bird ancestors or tree-dwelling ancestors. This has since been recognised as a false dichotomy [1]. We suggest that part of the problem is the loose categorisation of many extant bird species as either ground or tree locomotors when considering hind-limb function [2-7]. In reality these are not mutually exclusive alternatives. Many extant birds exhibit different degrees of ground- and tree-based behaviours. We thus propose they can be better placed on a spectrum - rather than a dichotomy - according to the extent of ground and/or tree foraging they exhibit. To test this system we analysed the toe claws of 249 species of Holocene birds, revealing that claw curvature increases as tree foraging becomes more predominant. Improved claw morphometrics allow more direct comparisons between extant and extinct birds in order to infer the behaviours of the latter. In contrast to previous studies [2-6], we find that claw curvatures of Mesozoic birds and closely related non-avian theropod dinosaurs, differ significantly from Holocene arboreal birds and more closely resemble those of Holocene 'ground-foraging' birds.