Reconstructing birth in \u3ci\u3eAustralopithecus sediba\u3c/i\u3e

Hominin birth mechanics have been examined and debated from limited and often fragmentary fossil pelvic material. Some have proposed that birth in the early hominin genus Australopithecus was relatively easy and ape-like, while others have argued for a more complex, human-like birth mechanism in australopiths. Still others have hypothesized a unique birth mechanism, with no known modern equivalent. Preliminary work on the pelvis of the recently discovered 1.98 million-year-old hominin Australopithecus sediba found it to possess a unique combination of Homo and Australopithecus-like features. Here, we create a composite pelvis of Australopithecus sediba to reconstruct the birth process in this early hominin. Consistent with other hominin species, including modern humans, the fetus would enter the pelvic inlet in a transverse direction. However, unlike in modern humans, the fetus would not need additional rotations to traverse the birth canal. Further fetal rotation is unnecessary even with a Homo-like pelvic midplane expansion, not seen in earlier hominin species. With a birth canal shape more closely associated with specimens from the genus Homo and a lack of cephalopelvic or shoulder constraints, we therefore find evidence to support the hypothesis that the pelvic morphology of Australopithecus sediba is a result of locomotor, rather than strictly obstetric constraints

Vertical Climbing Adaptations in the Anthropoid Ankle and Midfoot: Implications for Locomotion in Miocene Catarrhines and Plio-Pleistocene Hominins.

Vertical climbing has featured prominently in hypotheses of early hominoid evolution and the origins of hominin bipedalism. The ankle is a critical region for determining how the foot will be positioned against a tree, and the morphology of this joint may be specifically adapted for vertical climbing in species that practice this form of locomotion. This dissertation tests the hypothesis that the skeletal and ligamentous morphology of the non-human hominoid ankle and midfoot is adapted for bouts of vertical climbing. I employ a multifaceted approach using evidence from kinematics of wild and captive primates, radiographs, dissections, EMG studies, biomechanical data on baboon ankle ligaments, and linear, angular, and 3D surface morphology measurements of the distal tibia and tarsals of extant anthropoids. Results are applied to the ankle and midfoot of early Miocene catarrhines and Plio-Pleistocene hominins to assess whether vertical climbing was a significant component of their locomotion. Analysis of video captured of wild chimpanzees vertically climbing reveals that apes orient their foot in positions of extreme dorsiflexion and inversion during vertical climbing bouts. Functional correlates of vertical climbing in the ape ankle include a mediolaterally expanded anterior aspect of the distal tibia, a robust medial malleolus, and a weakly developed posterior tibiotalar ligament. Most tibiae and tali from early Miocene catarrhines are cercopithecoid-like for these features, although Proconsul major and Rangwapithecus seem to have possessed ankles able to adopt positions of dorsiflexion and inversion. None of fossil hominin tibiae or tali from 4.12 million to 1.53 million years ago is adapted for positions of extreme dorsiflexion and inversion and thus early hominins probably did not engage in ape-like vertical climbing. Instead, adaptations for bipedality in the hominin ankle result in a joint maladapted for vertical climbing. Though many of these adaptations for bipedality evolved in the hominin ankle by 4.12 mya, the evolution of the stabilizing anterior talofibular ligament was a relatively recent event, occurring perhaps in Homo erectus. The morphology of the tarsometatarsal joint also reveals that early hominins possessed a stable lateral midfoot and perhaps a longitudinal arch which would have restricted grasping and hindered arboreality.Ph.D.AnthropologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/60675/1/jdesilva_1.pd

The relationship between foot arch measurements and walking parameters in children

BACKGROUND: Walking mechanics are influenced by body morphology. Foot arch height is one aspect of body morphology central to walking. However, generalizations about the relationship between arch height and walking are limited due to previous methodologies used for measuring the arch and the populations that have been studied. To gain the knowledge needed to support healthy gait in children and adults, we need to understand this relationship in unimpaired, typically developing children and adults using dynamic measures. The purpose of the current study was to examine the relationship between arch height and gait in a sample of healthy children and adults using dynamic measures. METHODS: Data were collected from 638 participants (n = 254 children and n = 384 adults) at the Museum of Science, Boston (MOS) and from 18 4- to 8-year-olds at the Motor Development and Motor Control Laboratories. Digital footprints were used to calculate two arch indices: the Chippaux-Smirak (CSI) and the Keimig Indices (KI). The height of the navicular bone was measured. Gait parameters were captured with a mechanized gait carpet at the MOS and three-dimensional motion analyses and in-ground force plates in the Motor Development and Motor Control Laboratories. RESULTS: Linear regression analyses on data from the MOS confirmed that as age increases, step length increases. With a linear mixed effect regression model, we found that individuals who took longer steps had higher arches as measured by the KI. However, this relationship was no longer significant when only adults were included in the model. A model restricted to children found that amongst this sample, those with higher CSI and higher KI values take longer relative step lengths. Data from the Motor Development and Motor Control Laboratories showed that both CSI and KI added to the prediction; children with lower anterior ground reaction forces had higher CSI and higher KI values. Arch height indices were correlated with navicular height. CONCLUSIONS: These results suggest that more than one measure of the arch may be needed elucidate the relationship between arch height and gait.K12 HD055931 - NICHD NIH HHS; K12HD055931 - NICHD NIH HH

Neonatal Shoulder Width Suggests a Semirotational, Oblique Birth Mechanism in \u3ci\u3eAustralopithecus afarensis\u3c/i\u3e

Birth mechanics in early hominins are often reconstructed based on cephalopelvic proportions, with little attention paid to neonatal shoulders. Here, we find that neonatal biacromial breadth can be estimated from adult clavicular length (R2 = 0.80) in primates. Using this relationship and clavicular length from adult Australopithecus afarensis, we estimate biacromial breadth in neonatal australopiths. Combined with neonatal head dimensions, we reconstruct birth in A. afarensis (A.L. 288-1 or Lucy) and find that the most likely mechanism of birth in this early hominin was a semi-rotational oblique birth in which the head engaged and passed through the inlet transversely, but then rotated so that the head and shoulders remained perpendicular and progressed through the midplane and outlet oblique to the main axis of the female pelvis. Any other mechanism of birth, including asynclitic birth, would have resulted in either the head or the shoulders orthogonal to the short anteroposterior dimension of the A.L. 288-1 pelvis, making birth untenable. There is a tight fit between the infant and all planes of the birth canal, perhaps suggesting a difficult labor in australopiths. However, the rotational birth mechanism of large-brained humans today was likely not characteristic of A. afarensis. Thus, the evolution of rotational birth, usually associated with encephalization, may have occurred in two stages: the first appeared with the origin of the australopiths with their platypelloid pelves adapted for bipedalism and their broad-shouldered neonates; the second which resulted in the modern mechanism of rotational birth may be associated with increasing brain size in the genus Homo. Anat Rec, 300:890–899, 2017

Phenotypic Plasticity of Climbing-Related Traits in the Ankle Joint of Great Apes and Rainforest Hunter-Gatherers

The negrito and African pygmy phenotypes are predominately exhibited by hunter-gatherers living in rainforest habitats. Foraging within such habitats is associated with a unique set of locomotor behaviors, most notably habitual vertical climbing during the pursuit of honey, fruit, and game. When performed frequently, this behavior is expected to correlate with developmentally plastic skeletal morphologies that respond to mechanical loading. Using six measurements in the distal tibia and talus that discriminate nonhuman primates by vertical climbing frequency, we tested the prediction that intraspecific variation in this behavior is reflected in the morphology of the ankle joint of habitually climbing human populations. First, to explore the plasticity of climbing-linked morphologies, we made comparisons between chimpanzees, gorillas, and orangutans from wild and captive settings. The analysis revealed significant differences in two climbing-linked traits (anterior expansion of the articular surface of the distal tibia and increased degree of talar wedging), indicating that these traits are sensitive to climbing behavior. However, our analyses did not reveal any signatures of climbing behavior in the ankles of habitually climbing hunter-gatherers. These results suggest that the detection of fine-grained differences in human locomotor behaviors at the ankle joint, particularly those associated with arboreality, may be obscured by the functional demands of terrestrial bipedalism. Accordingly, it may be difficult to use population-level characteristics of ankle morphology to make inferences about the climbing behavior of hominins in the fossil record, even when facultative arborealism is associated with key fitness benefits

When and Why Did Human Brains Decrease in Size? A New Change-Point Analysis and Insights From Brain Evolution in Ants

Human brain size nearly quadrupled in the six million years since Homo last shared a common ancestor with chimpanzees, but human brains are thought to have decreased in volume since the end of the last Ice Age. The timing and reason for this decrease is enigmatic. Here we use change-point analysis to estimate the timing of changes in the rate of hominin brain evolution. We find that hominin brains experienced positive rate changes at 2.1 and 1.5 million years ago, coincident with the early evolution of Homo and technological innovations evident in the archeological record. But we also find that human brain size reduction was surprisingly recent, occurring in the last 3,000 years. Our dating does not support hypotheses concerning brain size reduction as a by-product of body size reduction, a result of a shift to an agricultural diet, or a consequence of self-domestication. We suggest our analysis supports the hypothesis that the recent decrease in brain size may instead result from the externalization of knowledge and advantages of group-level decision-making due in part to the advent of social systems of distributed cognition and the storage and sharing of information. Humans live in social groups in which multiple brains contribute to the emergence of collective intelligence. Although difficult to study in the deep history of Homo, the impacts of group size, social organization, collective intelligence and other potential selective forces on brain evolution can be elucidated using ants as models. The remarkable ecological diversity of ants and their species richness encompasses forms convergent in aspects of human sociality, including large group size, agrarian life histories, division of labor, and collective cognition. Ants provide a wide range of social systems to generate and test hypotheses concerning brain size enlargement or reduction and aid in interpreting patterns of brain evolution identified in humans. Although humans and ants represent very different routes in social and cognitive evolution, the insights ants offer can broadly inform us of the selective forces that influence brain size

A nearly complete foot from dikika, Ethiopia and its implications for the ontogeny and function of australopithecus afarensis

The functional and evolutionary implications of primitive retentions in early hominin feet have been under debate since the discovery of Australopithecus afarensis. Ontogeny can provide insight into adult phenotypes, but juvenile early hominin foot fossils are exceptionally rare. We analyze a nearly complete, 3.32-million-year-old juvenile foot of A. afarensis (DIK-1-1f). We show that juvenile A. afarensis individuals already had many of the bipedal features found in adult specimens. However, they also had medial cuneiform traits associated with increased hallucal mobility and a more gracile calcaneal tuber, which is unexpected on the basis of known adult morphologies. Selection for traits functionally associated with juvenile pedal grasping may provide a new perspective on their retention in the more terrestrial adult A. afarensis

The relationship between foot arch measurements and walking parameters in children

Background: Walking mechanics are influenced by body morphology. Foot arch height is one aspect of body morphology central to walking. However, generalizations about the relationship between arch height and walking are limited due to previous methodologies used for measuring the arch and the populations that have been studied. To gain the knowledge needed to support healthy gait in children and adults, we need to understand this relationship in unimpaired, typically developing children and adults using dynamic measures. The purpose of the current study was to examine the relationship between arch height and gait in a sample of healthy children and adults using dynamic measures. Methods: Data were collected from 638 participants (n = 254 children and n = 384 adults) at the Museum of Science, Boston (MOS) and from 18 4- to 8-year-olds at the Motor Development and Motor Control Laboratories. Digital footprints were used to calculate two arch indices: the Chippaux-Smirak (CSI) and the Keimig Indices (KI). The height of the navicular bone was measured. Gait parameters were captured with a mechanized gait carpet at the MOS and three-dimensional motion analyses and in-ground force plates in the Motor Development and Motor Control Laboratories. Results: Linear regression analyses on data from the MOS confirmed that as age increases, step length increases. With a linear mixed effect regression model, we found that individuals who took longer steps had higher arches as measured by the KI. However, this relationship was no longer significant when only adults were included in the model. A model restricted to children found that amongst this sample, those with higher CSI and higher KI values take longer relative step lengths. Data from the Motor Development and Motor Control Laboratories showed that both CSI and KI added to the prediction; children with lower anterior ground reaction forces had higher CSI and higher KI values. Arch height indices were correlated with navicular height. Conclusions: These results suggest that more than one measure of the arch may be needed elucidate the relationship between arch height and gait

The relationship between foot arch measurements and walking parameters in children

Walking mechanics are influenced by body morphology. Foot arch height is one aspect of body morphology central to walking. However, generalizations about the relationship between arch height and walking are limited due to previous methodologies used for measuring the arch and the populations that have been studied. To gain the knowledge needed to support healthy gait in children and adults, we need to understand this relationship in unimpaired, typically developing children and adults using dynamic measures. The purpose of the current study was to examine the relationship between arch height and gait in a sample of healthy children and adults using dynamic measures

Locomotor variability in Sterkfontein Member 4: Analysis of the external shape and internal bone structure of the StW 562 and StW 595 first metatarsals

Recent fossil discoveries have highlighted the diversity of foot morphology among fossil hominins. However, determining whether such morphological differences can be interpreted as a signal of substantively different gaits and/or contributions of arboreal locomotion to a species’ behavioural repertoire is unclear. Here, we address this question of behavioural diversity in two fossil first metatarsals from Member 4 of Sterkfontein that differ in their external morphology: StW 562 and StW 595. We analyse external shape using landmark based geometric morphometrics and the internal structure using cross sectional geometry and whole-bone analysis of cortical and trabecular bone structure in StW 562, StW 595, and a comparative sample of humans (N=7), chimpanzees (N=14), bonobos (N=9), gorillas (N=7) and orangutans (N=11). Results of the shape analysis support previous descriptions with both fossil metatarsals being intermediate in shape between humans and extant great apes, with StW 562 more similar to the human sample and StW 595 more similar to extant apes. Cross-sectional geometric analysis demonstrates that StW 562 shares a robust shaft with humans and African apes, whereas StW 595 has a low bending rigidity and cross-sectional area, similar to the less robust orangutans. The pattern of distribution of cortical and trabecular bone differs between these fossils, adding further evidence of morphological and perhaps functional diversity. These results suggest two foot morphotypes may be present in specimens from Sterkfontein Member 4. Future work will further explore the potential biomechanical implications of these differing morphologies and the taxonomic affiliation of these two specimens