Early Hominin Foot Morphology Based on 1.5-Million-Year-Old Footprints from Ileret, Kenya

Abstract

Downloaded fromwhen approaching the HOMO or LUMO resonance of the molecular wire (28). The increased conductance at higher bias voltages then compensates for the molecular wire length increase in Fig. 4B (a factor of 40 is not sufficient for the achieved current increase). Thus, such a setup allows the determination of the small conductance (8.6 × 10 -13 S) of a single and the same molecular wire with 20 nm length (the conductance at small bias voltages cannot be measured over such a large distance, due to the extremely low current-below the detection limit-passing through the polymer in this case). In this regard, it would be interesting to prepare and study conjugated polymers with smaller HOMO-LUMO gaps. Such molecular wires should exhibit higher conductances and allow charge transport to be determined over even larger distances. Hominin footprints offer evidence about gait and foot shape, but their scarcity, combined with an inadequate hominin fossil record, hampers research on the evolution of the human gait. Here, we report hominin footprints in two sedimentary layers dated at 1.51 to 1.53 million years ago (Ma) at Ileret, Kenya, providing the oldest evidence of an essentially modern human-like foot anatomy, with a relatively adducted hallux, medial longitudinal arch, and medial weight transfer before push-off. The size of the Ileret footprints is consistent with stature and body mass estimates for Homo ergaster/erectus, and these prints are also morphologically distinct from the 3.75-millionyear-old footprints at Laetoli, Tanzania. The Ileret prints show that by 1.5 Ma, hominins had evolved an essentially modern human foot function and style of bipedal locomotion. Bipedalism is a key human adaptation that appears in the fossil record by 6 million years ago (Ma) (1). Considerable debate continues over when and in what context a modern human-like form of bipedalism evolved, because of a fragmentary record and disagreements over the functional interpretations of existing fossils and footprints (2-7). Modern human footprints reflect the specialized anatomy and function of the human foot, which is characterized by a fully adducted hallux, a large and robust calcaneus and tarsal region, a pronounced medial longitudinal arch, and short toes (2). Footprints reflect the pressure distribution as the foot makes contact with the substrate, but also the sediment's geomechanical properties (8). During normal walking, the weight-bearing foot undergoes a highly stereotypical movement and pressure distribution pattern in which the heel contacts the ground first, making a relatively deep impression on the substrate. This is followed by contact with the lateral side of the foot and metatarsal heads, after which weight transfers to the ball of the foot with peak pressure under the medial metatarsal heads, and finally ending with toe-off pressure under the hallux (9, 10). As a consequence, the deepest part of a footprint often occurs beneath the first and second metatarsal heads, that along with a deep hallucal impression cor...

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

“…Briefly, each subject produced footprints in at least 12 trials by walking and running at various speeds across a trackway containing a patch of hydrated sediment that was taken directly from a layer containing 1.5 Ma fossil hominin footprints. Although this sediment differs typologically from the natrocarbonatite ash that preserves the Laetoli hominin prints, there is no evidence to suggest that the slight difference in their grain sizes (the Laetoli ash was closest in size to fine-grained sand [23] while the experimental sediment was a mixture of clayey silt and sand [13]) would influence gross footprint morphology. Furthermore, the experimentally produced and fossil footprints were of similar depths and preserved similar levels of anatomical detail, suggesting that the strength of the two substrates and their cohesive properties are comparable.…”

Possible hominin footprints from the late Miocene (c. 5.7 Ma) of Crete?

“…Similar landmarks were placed on comparative track populations. The comparative populations consist of: (1) 31 3D scans of habitually unshod tracks made by members of the Daasanach people from Ileret (Kenya; Bennett et al, 2016a); (2) four 3D scans of baboons from Amboseli (Kenya); (3) 11 3D tracks from the G1 trails at Laetoli taken from first generation casts held at the National Museum of Kenya (Bennett et al, 2009);and (4) due to the lack of 3D primate data, 15 mixed species 2D primate images (baboons, gorilla, green monkeys, and chimpanzees) were also included. Although 3D scans were available, only 2D landmarks were extracted using DigTrace, because of the inclusion of 2D primate images in the analysis.…”

“…The Trachilos tracks resemble hominin prints (Leakey and Hay, 1979;Harcourt-Smith and Aiello, 2004;Bennett et al, 2009Bennett et al, , 2016aLockley et al, 2016) due to their plantigrade and entaxonic nature. By contrast, the morphology of the sole print is not especially hominin-like: compared to a modern human sole print it is proportionately shorter, with a narrow tapering heel, and lacks a permanent arch.…”

“…Late Miocene (ValesianTurolian) faunas from Crete contain large non-endemic mammals such as hyaenids, proboscideans (gomphotheres and deinotheres), a hipparionine horse, pigs, a cervid, a bovid and tragulids (Benda et al, 1970;de Bruijn et al, 1971;Kuss, 1976;Leinders and Meulenkamp, 1978; van der Made, 1996; Athanassiou, 2004; Bennett et al (2009). In hominins, the hallux is large and morphologically distinctive but positioned close to digit 2; there is also a distinct ball.…”

From four hands to two feet: human evolution in the context of primate evolution

“…The international team (Bennett et al 2009) used a special apparatus, using the reflection of laser beams, to precisely measure the depth of the footprint. Fossilized footprints can tell us not only about the shape of hominid feet, but also about the way in which they walked.…”