Search for: All records

Fossil footprints (i.e., tracks) were believed to document arch anatomical evolution, although our recent work has shown that track arches record foot kinematics instead. Analyses of track arches can thereby inform the evolution of human locomotion, although quantifying this 3‐D aspect of track morphology is difficult. Here, we present a volumetric method for measuring the arches of 3‐D models of human tracks and feet, using both Autodesk Maya and Blender software. The method involves generation of a 3‐D object that represents the space beneath the longitudinal arch, and measurement of that arch object's geometry and spatial orientation. We provide relevant tools and guidance for users to apply this technique to their own data. We present three case studies to demonstrate potential applications. These include, (1) measuring the arches of static and dynamic human feet, (2) comparing the arches of human tracks with the arches of the feet that made them, and (3) direct comparisons of human track and foot arch morphology throughout simulated track formation. The volumetric measurement tool proved robust for measuring 3‐D models of human tracks and feet, in static and dynamic contexts. This tool enables researchers to quantitatively compare arches of fossil hominin tracks, in order to derive biomechanical interpretations from them, and/or offers a different approach for quantifying foot morphology in living humans.

 

The emergence of bipedalism had profound effects on human evolutionary history, but the evolution of locomotor patterns within the hominin clade remains poorly understood. Fossil tracks record in vivo behaviours of extinct hominins, and they offer great potential to reveal locomotor patterns at various times and places across the human fossil record. However, there is no consensus on how to interpret anatomical or biomechanical patterns from tracks due to limited knowledge of the complex foot–substrate interactions through which they are produced. Here, we implement engineering-based methods to understand human track formation with the ultimate goal of unlocking invaluable information on hominin locomotion from fossil tracks. We first developed biplanar X-ray and three-dimensional animation techniques that permit visualization of subsurface foot motion as tracks are produced, and that allow for direct comparisons of foot kinematics to final track morphology. We then applied the discrete element method to accurately simulate the process of human track formation, allowing for direct study of human track ontogeny. This window lets us observe how specific anatomical and/or kinematic variables shape human track morphology, and it offers a new avenue for robust hypothesis testing in order to infer patterns of foot anatomy and motion from fossil hominin tracks. 

The stance phase of walking is when forces are applied to the environment to support, propel, and maneuver the body. Unlike solid surfaces, deformable substrates yield under load, allowing the foot to sink to varying degrees. For bipedal birds and their dinosaurian ancestors, a shared response to walking on these substrates has been identified in the looping path the digits follow underground. Because a volume of substrate preserves a 3-D record of stance phase in the form of footprints or tracks, understanding how the bipedal stride cycle relates to this looping motion is critical for building a track-based framework for the study of walking in extinct taxa. Here, we used biplanar X-ray imaging to record and analyze 161 stance phases from 81 trials of three Helmeted Guineafowl (Numida meleagris) walking on radiolucent substrates of different consistency (solid, dry granular, and firm to semi-liquid muds). Across all substrates, the feet sank to a range of depths up to 78% of hip height. With increasing substrate hydration, the majority of foot motion shifted from above to below ground. Walking kinematics sampled across all stride cycles revealed six sequential gait-based events originating from both feet, conserved throughout the spectrum of substrate consistencies during normal alternating walking. On all substrates that yielded, five sub-phases of stance phase were drawn out in space and formed a loop of varying shape. We describe the two-footed coordination and weight distribution that likely contributed to the observed looping patterns of an individual foot. Given such complex subsurface foot motion during normal alternating walking and some atypical walking behaviors, we discuss the definition of “stance phase” on deformable substrates. We also discuss implications of the gait-based origins of subsurface looping on the interpretation of locomotory information preserved in fossil dinosaur tracks.

 

The dinosaur track record features numerous examples of trackways with elongated metatarsal marks. Such ‘elongate tracks’ are often highly variable and characterized by indistinct outlines and abbreviated or missing digit impressions. Elongate dinosaur tracks are well‐known from the Paluxy River bed of Texas, where some have been interpreted as ‘man tracks’ by creationists due to their superficially human‐like appearance. The horizontal orientation of the metatarsal marks led to the now widely accepted idea of a facultative plantigrade, or ‘flat‐footed’, mode of locomotion in a variety of dinosaurian trackmakers small to large. This hypothesis, however, is at odds with the observation that elongate tracks do not indicate reduced locomotion speeds and increased pace angulation values, but instead are correlated with low anatomical fidelity. We here interpret elongate tracks as deep penetrations of the foot in soft sediment. Sediment may collapse above parts of the descending foot, leaving a shallow surface track that preserves a metatarsal mark. The length of a metatarsal mark is determined by multiple factors and is not necessarily correlated with the length of the metatarsus. Other types of posterior marks in dinosaur footprints, such as drag and slip marks, are reviewed.

 

Whilst bones present a static view of extinct animals, fossil footprints are a direct record of the activity and motion of the track maker. Deep footprints are a particularly good record of foot motion. Such footprints rarely look like the feet that made them; the sediment being heavily disturbed by the foot motion. Because of this, such tracks are often overlooked or dismissed in preference for more foot‐like impressions. However, the deeper the foot penetrates the substrate, the more motion is captured in the sediment volume. We have used deep, penetrative, Jurassic dinosaur tracks which have been naturally split into layers, to reconstruct foot motions of animals living over 200 million years ago. We consider these reconstructions to be hypotheses of motion. To test these hypotheses, we use the Discrete Element Method, in which individual particles of substrate are simulated in response to a penetrating foot model. Simulations that produce virtual tracks morphologically similar to the fossils lend support to the motion being plausible, while simulations that result in very different final tracks serve to reject the hypothesis of motion and help generate a new hypothesis.