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Midfoot Flexibility, Fossil Footprints, and Sasquatch Steps: New Perspectives on the Evolution of Bipedalism
Abstract
The chimpanzee foot is flexible near its middle, it can bend about the axis of the transverse tarsal joint, whereas the human foot is a comparatively rigid arched platform. Flexion at the transverse tarsal joint—the ''midtarsal break''—uncouples the functions of a grasping, or prehensile, forefoot and a propulsive hindfoot during grasp-climbing on vertical or inclined supports. At some point after the transition to habitual bipedalism, these grasp-climbing adaptations were compromised by the evolution of the longitudinal arch, which permits increased mechanical advantage of the flexors of the ankle and im- proved endurance for long-distance walking and running. Ape, human, and Plio-Pleistocene hominid footprints were examined for the effects of a midtarsal break. The human footprint reflects arched-foot architecture, combined with a stiff-legged striding gait. Pressure releases occur at particular locations behind the ball and the great toe, or hallux. Early (ca. 3.5 million years ago) hominid footprints from the Laetoli excavation confirm midfoot flexibility, including repeated suggestion of an associated pressure ridge. The Terra Amata footprint (ca. 400,000 years ago), yet to be fully pub- lished, exhibits evidence of midfoot flexibility. Several footprints attributed to an alleged North American ape, commonly known as sasquatch, exhibit a distinctive midtarsal pressure ridge and other indications of midfoot flexibility. In the Patterson-Gimlin film, the feet of the film subject correlate with the kinematics inferred from the footprints, in that a midtarsal break is present. Additional independent examples corroborate the consistent presence of this feature, including examples of half-tracks that record contact beneath the foot only anterior to the midtarsus. These data provide a fresh perspective from which to consider the pattern and timing of the emer- gence of the distinctive features of modern human bipedalism and bear on the credibility of the possible existence of sasquatch. The observed and inferred sas- quatch locomotor anatomy parallels the stable adaptations that marked the greater span of early hominid bipedalism.
... Several of these footprints exhibited evidence of midfoot flexibility, producing either distinct pressure ridges bearing remarkable resemblance to the Titmus cast from the P-G film site, or in one instance of very wet mud, an extrusion feature at the midfoot. The implications of this correlation, corroborated through numerous additional documented footprint examples, provided insight into the functional morphology of the sasquatch foot (Meldrum 2004a(Meldrum , 2010. ...
... The Mill Creek cast was documented in 1991. To these could be added the tracks I cast near Walla Walla in February 1996 (Meldrum 2004a). How could these independent examples, separated by nearly three decades and half-a-world apart coincidently share these sound and significant subtleties of anatomy and functional morphology? ...
First off, I would like to express my appreciation to Patrick Huyghe and the members of the Tim Dinsdale Award Search Committee for this honor and privilege of addressing the members of SSE. I accept this Award, not so much in recognition of my modest accomplishments, but as acknowledgment of the import of the fundamental question -- Are there biological species, i.e. relict hominoids, behind the legends of man-made monsters? -- as a legitimate and timely question.
... For decades, researchers have argued over whether the Laetoli hominins walked with a modern human-like extended limb gait [3,[5][6][7][8][9][10], or a more ape-like form of bipedalism [11][12][13][14]. Most recently, the discovery of 1.5 Ma footprints from Kenya provides new evidence that the Laetoli prints were not completely modern in weight transfer and morphology [15]. ...
... The larger impulse when the body is supported by the forefoot explains the increased toe-depth in BKBH footprints. Since most researchers agree that the Laetoli prints exhibit evidence of a longitudinal arch [5,6,8,10,[23][24][25][26] (but see [13][14][15] and supplementary materials Text S1; Figs. S1, S2), an analysis of relative toe depths should provide unequivocal evidence of limb posture in these early hominins. ...
... Although the navicular has several ape-like features [4,6], indicating possible midfoot flexion, inferred insertions of ligaments on both the talus and the navicular imply there may have been a stiff mid-foot region [2,5,7]. Some suggest that the Laetoli prints also do not show evidence of an arch [8,9,10]. Meldrum [9,10] drew attention to two features of the Laetoli prints that could suggest the lack of a longitudinal arch. ...
... Some suggest that the Laetoli prints also do not show evidence of an arch [8,9,10]. Meldrum [9,10] drew attention to two features of the Laetoli prints that could suggest the lack of a longitudinal arch. First, he found three prints out of 14 (21% of the prints in the trail) in the G-1 series that had a ridge proximal to the mid-foot (two other prints were described as having possible ridges; [10]). ...
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... An interesting note is that a degree of idiosyncrasy was evident in hallucal position among the extant apes studied. One chimp and one gorilla in particular tended to adduct the hallux preferentially and orient it to the line of travel consistently (Meldrum, 2004b). A pair of female gorilla tracks cast in snow displays some notable similarities to the Laetoli tracks in the position of the hallux (Fig. 8). ...
... It has been hypothesized that midfoot flexion associated with the midtarsal break under the appropriate substrate conditions, produces a distinct pressure release as weight is transferred distal to the midtarsus (Meldrum, 2004b). This pressure release artifact in a footprint is a characteristic deformation of the compressed substrate as a result of the action of the foot during the terminal stance phase of the step. ...
At 3.6 Ma, the Laetoli Pliocene hominin trackways are the earliest direct evidence of hominin bipedalism. Three decades since their discovery, not only is the question of their attribution still discussed, but marked differences in interpretation concerning the footprints’ qualitative features and the inferred nature of the early hominin foot morphology remain. Here, we establish a novel ichnotaxon, Praehominipes laetoliensis, for these tracks and clarify the distinctions of these footprints from those of later hominins, especially modern humans. We also contrast hominin, human, and ape footprints to establish morphological features of these footprints correlated with a midtarsal break versus a stiff longitudinal arch. Original photos, including stereo photographs, and casts of footprints from the 1978 Laetoli excavation, confirm midtarsal flexibility, and repeatedly indicate an associated midfoot pressure ridge. In contrast, the modern human footprint reflects the derived arched-foot architecture, combined with a stiff-legged striding gait. Fossilized footprints of unshod modern human pedestrians in Hawaii and Nicaragua unambiguously illustrate these contrasts. Some points of comparisons with ape footprints are complicated by a variable hallucal position and the distinct manner of ape facultative bipedalism.
... This is surprising because hominid footprints, even those that have proved to be artifacts or fakes (Schoolcraft, 1822;Benton, 1822;Sarjeant, 1987;Bird, 1985) or the tracks of other animals (Harkness, 1882;Marsh, 1883Marsh, , 1894Marché, 1984) attract public interest, even if only as novelties. Likewise, the purported footprints of Bigfoot, otherwise known as the Sasquatch, Yeti or by other names, have attracted extraordinary attention among believers and nonbelievers alike, and have generated a substantial literature which has allowed various researchers to employ forensic and tracking methodologies in attempts to either verify or debunk the footprints (Meldrum, 2004b(Meldrum, , 2006. Given that these footprints have (Rector, 1999), M: Cuatro Cienegas, Mexico (Gonzalez et al., in press) N: Nicaragua (Brown, 1947; in press), W: 5: Severn Estuary, Wales (Aldhouse-Green et al., 1992;Roberts et al., 1996), F: Cave of Niaux, France (Clottes and Simonet, 1972), I: Southern Italy (Mietto et al., 2003), K: Koobi Fora, Kenya (Behrensmeyer and Laporte, 1981), T: Laetoli, Tanzania (Leakey and Hay, 1979), J: Jeju Island, Korea (Kim et al., 2004(Kim et al., , 2005, E: Formby Point, England (Roberts, in press), and A: Willandra Lakes Australia (Webb et al., 2005). ...
... Since there would be no obstacle to naming the fossil footprints of any ancient primate, there is no logical reason to make an exception for advanced (derived) hominids. In reference to Bigfoot tracks, Meldrum (2004bMeldrum ( , 2006 first noted that the application of serious ichnological studies to these controversial footprints can help determine their true nature. As noted above, he subsequently named them Anthropoidipes ameriborealis, selecting the best documented trackway as the type. ...
Although more than 60 ancient hominid track sites ranging in age from 3.7 million to less than 500 B. P. are recorded from all continents except Antarctica, no ichnotaxonomic names have ever been formally proposed for hominid tracks. There is no prohibition to the naming of fossil footprints of species that created tracks and trackways similar to those of living species. On the contrary, there is precedent for the naming of ichnotaxa corresponding to the dominant extant vertebrates classes: mammals = Mammalipedia and birds = Avipeda. The hominid track site sample includes only about a dozen sites where footprint preservation is good enough to show details of diagnostic foot morphology and typical trackway morphology. We infer that the Acahualinca Footprint Museum site in Nicaragua represents the most important ancient hominid track site that combines accessibility, a large sample of well-preserved trackways and reliable dating. For this reason, we select the Nicaraguan tracks as the type sample for the new ichnotaxon Hominipes modernus ichnogen., and ichnsp. et ichnosp. nov., which we infer to represent fully modern Homo sapiens. Our preliminary investigations of other track sites suggest that the majority also yield H. modernus. However, at many sites preservation is insufficient to make an ichnotaxonomic designation at the species level or to infer that the trackmaker was H. sapiens. Thus, at many sites including the famous Laetoli site, we apply the more general label of Hominipes isp. indet.
... These prints represent the earliest direct evidence of bipedalism in the fossil record, yet no study to date has demonstrated exactly how these hominins walked. For decades, researchers have argued over whether the Laetoli hominins walked with a modern human-like extended limb gait [3,5678910, or a more ape-like form of bipedalism11121314. Most recently, the discovery of 1.5 Ma footprints from Kenya provides new evidence that the Laetoli prints were not completely modern in weight transfer and morphology [15]. ...
... The larger impulse when the body is supported by the forefoot explains the increased toe-depth in BKBH footprints. Since most researchers agree that the Laetoli prints exhibit evidence of a longitudinal arch [5,6,8,10,23–26] (but see131415 and supplementary materials Text S1; Figs. S1, S2), an analysis of relative toe depths should provide unequivocal evidence of limb posture in these early hominins. ...
Debates over the evolution of hominin bipedalism, a defining human characteristic, revolve around whether early bipeds walked more like humans, with energetically efficient extended hind limbs, or more like apes with flexed hind limbs. The 3.6 million year old hominin footprints at Laetoli, Tanzania represent the earliest direct evidence of hominin bipedalism. Determining the kinematics of Laetoli hominins will allow us to understand whether selection acted to decrease energy costs of bipedalism by 3.6 Ma.
Using an experimental design, we show that the Laetoli hominins walked with weight transfer most similar to the economical extended limb bipedalism of humans. Humans walked through a sand trackway using both extended limb bipedalism, and more flexed limb bipedalism. Footprint morphology from extended limb trials matches weight distribution patterns found in the Laetoli footprints.
These results provide us with the earliest direct evidence of kinematically human-like bipedalism currently known, and show that extended limb bipedalism evolved long before the appearance of the genus Homo. Since extended-limb bipedalism is more energetically economical than ape-like bipedalism, energy expenditure was likely an important selection pressure on hominin bipeds by 3.6 Ma.
... Another form of evidence presented (albeit unconvincingly) by cryptozoologists is tracks and prints (e.g., Meldrum (2004Meldrum ( , 2007). Trace fossils studied in the palaeoscience of ichnotaxonomy parallel with, but are not exactly equivalent to, putative cryptid tracks (note: the International Code of Zoological Nomenclature actually excludes traces from animals that are extant, and evolutionary biologist Leigh Van Valen (1983: 155) has said that the comparison between cryptozoological tracks and ichnotaxonomy "perhaps should not be pushed very far"). ...
Cryptozoology seeks to study ‘hidden animals’ by separating ‘metaphors and similes’ from possible underlying insight. Variously described as a science, pseudoscience, or fringe field, cryptozoology may be viewed under the lenses of both heterodox science and orthodox science. Cryptozoology is heterodox in its unconventional methods and strategy; its ‘fuzzy’ data in the form of circumstantial and testimonial evidence; and its mostly amateur investigators. Cryptozoology also borrows from orthodox science, and in recent years may have influenced orthodox science: traditional ecological knowledge, pioneered in cryptozoology, is beginning to enter ‘mainstream’ scientific research, and these data have facilitated recent zoological (re)discoveries. Some contemporary cryptozoological studies have also applied more orthodox and rigorous statistical methodology. Controversial photographic taxonomy has been applied in both crypto- and conventional zoology, and cryptozoology has been investigated by qualified scientists at reputable institutions and in reputable academic journals. Cryptozoological methods, when applied more scrupulously, may have some unrealised scientific potential.
... However, before these data can better inform us of the detailed nature of early hominin bipedalism, we must understand how footprints actually record evidence of locomotor patterns. Beginning with the earliest analysis of the Laetoli footprints (Day and Wickens, 1980), many researchers compared the shapes of fossil hominin footprints to those produced by modern humans and drew conclusions about foot function or locomotion based on differences in footprint morphology (e.g., Tuttle et al., 1990;Meldrum, 2004;Berge et al., 2006;Bennett et al., 2009;Crompton et al., 2012). These studies have required the assumption that footprint morphologies directly represent particular functional signals, yet this has never been validated experimentally. ...
... This pattern applies equally to human and non-human primate feet. These data appear to support the more recent interpretations (D'Août et al., 2002;Vereecke et al., 2003;Ball, 2008a,b, 2010;DeSilva, 2010;Bates, 2013) and may serve to contradict the long standing supposition that a unique reduction of calcaneocuboid joint motion is the key to lateral longitudinal arch stability in the human foot (Elftman, 1960;Bojsen-Mïller, 1979;Ouzounian and Shereff, 1989;Gebo, 1992;Meldrum, 2004). These results also provide kinematic evidence that demonstrate comparable levels of midfoot flexibility in both human and nonhuman primate feet, which was suspected by several authors (Crompton et al., , 2012DeSilva and Gill, 2013). ...
This study describes a unique assessment of primate intrinsic foot joint kinematics based upon bone pin rigid cluster tracking. It challenges the assumption that human evolution resulted in a reduction of midfoot flexibility, which has been identified in other primates as the “midtarsal break.” Rigid cluster pins were inserted into the foot bones of human, chimpanzee, baboon, and macaque cadavers. The positions of these bone pins were monitored during a plantarflexion-dorsiflexion movement cycle. Analysis resolved flexion-extension movement patterns and the associated orientation of rotational axes for the talonavicular, calcaneocuboid, and lateral cubometatarsal joints. Results show that midfoot flexibility occurs primarily at the talonavicular and cubometatarsal joints. The rotational magnitudes are roughly similar between humans and chimps. There is also a similarity among evaluated primates in the observed rotations of the lateral cubometatarsal joint, but there was much greater rotation observed for the talonavicular joint, which may serve to differentiate monkeys from the hominines. It appears that the capability for a midtarsal break is present within the human foot. A consideration of the joint axes shows that the medial and lateral joints have opposing orientations, which has been associated with a rigid locking mechanism in the human foot. However, the potential for this same mechanism also appears in the chimpanzee foot. These findings demonstrate a functional similarity within the midfoot of the hominines. Therefore, the kinematic capabilities and restrictions for the skeletal linkages of the human foot may not be as unique as has been previously suggested. Am J Phys Anthropol, 2014. © 2014 Wiley Periodicals, Inc.
... Analyses of the Laetoli footprints have often included comparisons with actual footprints produced by modern humans or other great apes. Some have argued that modern human footprints are indistinguishable from those at Laetoli (e.g., Day and Wickens, 1980;White and Suwa, 1987;Tuttle et al.,1990), yet others have concluded that the Laetoli prints could not have been produced by a modern humanlike foot anatomy and gait (e.g., Stern and Susman, 1983;Susman et al., 1984;Deloison, 1991;Meldrum, 2004). ...
The sophistication and quality of field data obtained from human tracksites has increased dramatically during the last decade from the largely descriptive papers of Holocene tracksites common before the late 1990s to the more sophisticated data-rich papers of recent years. There are exceptions of course to this generalisation largely around the tracks at Laetoli which drove early innovation in methods. In this chapter we review the methods and approaches that can be adopted at human tracksites and equip the interested researcher with the knowledge necessary to execute such investigations themselves given suitable excavation permits and permissions. We recognise four broad stages to the process each of which is considered in turn: (1) geo-prospection and excavation; (2) recognition of human tracks and their dating; (3) methods of digital data capture; and (4) methods of analysis.
What can, and perhaps more importantly cannot, be inferred from a series of human tracks? In this chapter we explore this question by first looking at the relationships that exist between various foot dimensions and such things as stature and body mass. We explore the population specific nature of these empirical relationships and demonstrate their limitations with respect to the interpretation of tracks in the geological record. In the latter part of the chapter we explore what can deduced about the speed of a track-maker and the way in which variations in that speed may be reflected in the topology of the tracks themselves.
Human tracks have now been recorded at a number of sites across the globe. Lockley et al. (Ichnos 15:106–125, 2008) provides a definitive review of many of these sites and our aim here is to focus on a few important examples which are either in the authors’ judgement particularly significant or feature within this book. Sites can be grouped on many different criteria such as by: (1) geographical regions; (2) geological facies in which they are preserved; (3) their age and therefore potential species of track-maker; or (4) by their archaeological or palaeoanthropological significance. While there is a natural tendency to focus on the unusual, biggest, or oldest, in reality footprint sites tend to separate into those which pre-date Homo sapiens and those that don’t. Those that do are limited in number but have the potential to offer information about the evolution of gait between hominin species and as such they accord a level of significance far greater than other footprint sites. Such sites are few in number however and while Holocene sites may not have the glamour of older localities, they have the potential to offer important laboratories in which to explore the interaction of a track-maker’s gait with such things as substrate. For ease we have chosen to divide this chapter into those examples that potentially pre-date Homo sapiens (Pliocene to Early/Middle Pleistocene) and those that don’t (Late Pleistocene to Holocene).
The hominin footprint record spans ~3.6 Ma, from Late Pliocene to Holocene, and thus also spans a temporal duration corresponding to many of the major events in hominin evolution. While the oldest (~3.6 Ma) tracks from Laetoli (Tanzania) have been attributed, provisionally, to genus Australopithecus, all others are attributed to various species of the genus Homo, including H. erectus (H. ergaster), H. neanderthalensis, and H. sapiens.
Recent reviews of the previously neglected hominin track record have demonstrated that more than 60 sites are documented in the literature, and that these are found on all continents (excepting Antarctica). Based on age, geographic location, and to a lesser degree footprint morphology, it is possible to infer which post-Laetoli sites and footprint assemblages represent H. erectus (H. ergaster), and which are attributable to later Homo species. However, distinguishing between H. sapiens and H. neanderthalensis on the basis of footprint morphology is not demonstrated conclusively. All the older sites (~3.6- Ma to ~117,000 yBP), from Africa and Europe, including those that represent pre-H. sapiens species, are “open-air” sites, whereas a number of younger, pre-Holocene sites (~62,000 to ~10,000 yBP), especially in Europe, are cave sites. With the exception of a very controversial site in Mexico dated at ~40,000 yBP, no other New World footprint sites are more than ~12,500 years old, and the oldest Australian sites are ~19,000–23,000 yBP.
The extent to which significant modifications in the morphology of the hominin foot and corresponding footprints between 3.6 million and ~50,000 yBP has occurred continues to be debated, but there are two distinct polar morphologies (Praehominipes and Hominipes) now documented in the ichnologic literature. The question of whether transitions in such morphologic features as midfoot flexibility vs. a fully modern arch, and separation of the big toe from traces of lateral digits, and their inferred lengths, constitute evidence of major evolutionary changes may not be resolved to consensus without additions to pedal fossil remains and trace fossil record.
In most cases, sites reveal associated tracks and traces of other tetrapods, mostly mammals and birds, as well as, in some instances, other hominin-manufactured artifacts. Such contextual trace fossil evidence is important for understanding the ecology of early hominin habitats. As recent studies have noted, there is no well-defined line between the hominin track record, narrowly defined as footprints, and the broader ichnologic record, which includes cut marks on bone, handprints, paintings in caves, and even various artifacts. Paleolithic cave paintings that depict tracks and associated track makers could be considered as the earliest examples of vertebrate ichnology field guides, although the significance to the artists themselves likely differed from our modern notion of a guidebook. Although not normally thought of as part of the track record, footprints on the Moon, as well as the tracks of lunar vehicles, and robotic vehicles employed on Mars, represent the ichnologic signatures of recent major events in hominin evolution.
Only two vertebrate groups, humans and sauropod dinosaurs, have a well-developed entaxonic foot (with the big toe, or digit I, the largest), and both have vertical limbs. Thus, convergence applies not only to the feet but also to the limbs. When viewed in relation to their closest relatives among the hominoids and saurischian dinosaurs, and in the context of known developmental growth patterns in higher vertebrates, both humans and sauropod dinosaurs appear to be excellent examples of peramorphosis (specifically hypermorphosis). Thus, it is essential to understand morphodynamics as a field that is inseparable from the study of heterochrony.The morphodynamic developmental perspective, while recognized as important in genetics and embryology, has for many generations been overlooked in studies of feet, footprints and limbs (i.e., the marco-morphology of organs). Investigating these dynamics reveals striking recursive (or fractal) patterns of anterior-posterior and proximal distal development, which in turn demonstrate that vertebrate growth proceeds in an organized or “formal” manner. Thus, convergence is not merely, or only, a by-product of functional adaptation to the external environment but also a manifestation of the complex but intelligible internal organization of dynamic organic systems.
Functional-morphological analyses related to fossil and contemporary hominin locomotion are the focus of this volume. As locomotion is considered a key element in the overall behavior of living primates, allowing them to fulfill such basic needs as avoiding predators, foraging for food, and finding mates, biological anthropologists have generally agreed that it most likely served similar functions in earlier hominins as well. In primates, differing locomotor behaviors and their impact on other biological complexes have produced a diverse range of behavioral and anatomical configurations. In turn, primate locomotion studies are diverse in their scope. Anthropologists interested in hominin locomotion frequently draw on primate and other animal locomotor studies in efforts to understand the complexities associated with the evolution of hominin locomotion. Through comparative analyses on musculo-skeletal structures, positional behavior, and the kinematic and kinetic components of body motion in settings ranging from dissection rooms, laboratories, and in the field, researchers have developed a wide variety of approaches and techniques for investigating the intricacies of locomotor movement in living contemporary hominins and their closest relatives.
The fossil foot remains of the Neandertals (immediate predecessors of anatomically modern humans in Europe and western Asia between about 100,000 and 35,000 to 40,000 years ago) indicate an overall pedal configuration for these prehistoric humans that was largely indistinguishable from that of modern humans. They had fully adducted halluces, longitudinal and transverse pedal arches, compact posterior tarsal regions, slight valgus deviation of the hallux, and abbreviation of the lateral toes. Their pedal remains differed from those of modern humans only in their tendency to be more robust and their relatively short proximal hallucial phalanges and associated elongated distal hallucial phalanges. The former is related to their habitual levels of physical activity, which were greater than those of modern humans, and the latter is a pleiotropic effect of a biomechanical adaptation in the pollex for strength during manipulation.
The ratio of fore- to hindlimb size plays an important role in our understanding of human evolution. Although Homo habilis was relatively modern craniodentally, its body proportions are commonly believed to have been more apelike than in the earlier Australopithecus afarensis. The evidence for this, however, rests, on two fragmentary skeletons, OH 62 and KNM-ER 3735. The upper limb of the better-preserved OH 62 from Olduvai Gorge is long and slender, but its hindlimb is represented mainly by the proximal portion of a thin femur of uncertain length. The present analysis shows that upper-to-lower limb shaft proportions of both OH 62 and AL 288-1 (A. afarensis) fall in the modern human range of variation, although OH 62 also falls inside that of chimpanzees due to their overlap in small individuals. Despite being more fragmentary, the larger-bodied KNM-ER 3735 lies outside the chimpanzee range and close to the human mean. Because the differences between any of the three individuals are compatible with the range of variation seen in extant hominoid groups, it is not legitimate to infer more primitive upper-to-lower limb shaft proportions for either H. habilis or A. afarensis. Femur length of OH 62 can only be estimated by comparison. Its closest match in size and morphology is with the gracile OH 34 specimen, which therefore provides a better analogue for the reconstruction of OH 62 than the stocky AL 288-1 femur that is traditionally used. OH 34's slender proportions are hardly due to abrasion, but match those of a modern human of that body-size, suggesting that the relative length of OH 62's leg may have been human-like. Brachial proportions, however, remained primitive. Long legs may imply long distance terrestrial travel. Perhaps this adaptation evolved early in the genus Homo, with H. habilis providing an early representative of this important change.