Does footprint depth correlate with foot motion and pressure?

Abstract

Footprints are the most direct source of evidence about locomotor biomechanics in extinct vertebrates. One of the principal suppositions underpinning biomechanical inferences is that footprint geometry correlates with dynamic foot pressure, which, in turn, is linked with overall limb motion of the trackmaker. In this study, we perform the first quantitative test of this longstanding assumption, using topological statistical analysis of plantar pressures and experimental and computer-simulated footprints. In computer-simulated footprints, the relative distribution of depth differed from the distribution of both peak and pressure impulse in all simulations. Analysis of footprint samples with common loading inputs and similar depths reveals that only shallow footprints lack significant topological differences between depth and pressure distributions. Topological comparison of plantar pressures and experimental beach footprints demonstrates that geometry is highly dependent on overall print depth; deeper footprints are characterized by greater relative forefoot, and particularly toe, depth than shallow footprints. The highlighted difference between 'shallow' and 'deep' footprints clearly emphasizes the need to understand variation in foot mechanics across different degrees of substrate compliance. Overall, our results indicate that extreme caution is required when applying the 'depth equals pressure' paradigm to hominin footprints, and by extension, those of other extant and extinct tetrapods.

Laetoli footprints reveal bipedal gait biomechanics different from those of modern humans and chimpanzees

“…Yet the conclusions of this study are limited by the small sample sizes. One study [15] compared plantar pressure records from non-human apes with the Laetoli footprints, although it has since been demonstrated by those same researchers [18] and others [19,20] that pressure distributions are only weakly related to footprint shapes, calling into question the extent to which non-human ape pressure distributions may reflect their footprint topographies. Even more important than the absence of relevant comparative footprint samples though has been the limited knowledge of how specific biomechanical variables are expressed in, and can be inferred from, footprint morphologies.…”

Corroborating trackmaker identification through footprint functional analysis: the case study of Ichniotherium and Dimetropus

“…abduction) during the stroke, transmitting its movement and constraining positions and actions of the adjacent elements. This complex anatomical and physiological arrangement is virtually mirrored in any footprint but can be accurately reconstructed only in those where these types of information are better recorded (in most cases they are elite tracks sensu Lockley & Meyer 2000 or natural casts but see also Bates et al 2013). Defining the timing of the registration process then means determining, to the best of our ability, different paths of activation and deactivation of single elements enabling locomotion and thus, from another standpoint, means going back to the mode of loading, transfer and unloading of the body weight to the ground.…”

Interpreting ecology and behaviour from the vertebrate fossil track record

“…the manus or pes) is directly linked to the motion of more proximal limb elements, and ultimately of the animal itself. As such, changes in contact area, centre of pressure, and ground reaction force orientation and magnitude occur throughout the step cycle (Panagiotopoulou et al, 2012;Bates et al, 2013). As the pressure exerted by the foot increases (e.g.…”

“…Accelerations and decelerations result in differences between relative forces exerted by the foot at either foot strike or kick-off (Thulborn, 1990;Manning, 2004), with deceleration increasing force at the rear of the foot during initial contact and acceleration increasing that force anteriorly at kick-off. These forces may in turn directly affect the relative depths of the front and rear of a track, observable as variations in pitch or depth profile that may correlate with other speed-related features such as stride length (Mossman, Brüning & Powell, 2003;Bates et al, 2013;Pataky et al, 2013).…”