Ontogeny of hallucal metatarsal rigidity and shape in the rhesus monkey (Macaca mulatta) and chimpanzee (Pan troglodytes)

Life history variables including the timing of locomotor independence, along with changes in preferred locomotor behaviors and substrate use during development, influence how primates use their feet throughout ontogeny. Changes in foot function during development, in particular the nature of how the hallux is used in grasping, can lead to different structural changes in foot bones. To test this hypothesis, metatarsal midshaft rigidity [estimated from the polar second moment of area (J) scaled to bone length] and cross-sectional shape (calculated from the ratio of maximum and minimum second moments of area, Imax /Imin ) were examined in a cross-sectional ontogenetic sample of rhesus macaques (Macaca mulatta; n = 73) and common chimpanzees (Pan troglodytes; n = 79). Results show the hallucal metatarsal (Mt1) is relatively more rigid (with higher scaled J-values) in younger chimpanzees and macaques, with significant decreases in relative rigidity in both taxa until the age of achieving locomotor independence. Within each age group, Mt1 rigidity is always significantly higher in chimpanzees than macaques. When compared with the lateral metatarsals (Mt2-5), the Mt1 is relatively more rigid in both taxa and across all ages; however, this difference is significantly greater in chimpanzees. Length and J scale with negative allometry in all metatarsals and in both species (except the Mt2 of chimpanzees, which scales with positive allometry). Only in macaques does Mt1 midshaft shape significantly change across ontogeny, with older individuals having more elliptical cross-sections. Different patterns of development in metatarsal diaphyseal rigidity and shape likely reflect the different ways in which the foot, and in particular the hallux, functions across ontogeny in apes and monkeys

The atlas of StW 573 and the late emergence of human-like head mobility and brain metabolism

Functional morphology of the atlas reflects multiple aspects of an organism’s biology. More specifically, its shape indicates patterns of head mobility, while the size of its vascular foramina reflects blood flow to the brain. Anatomy and function of the early hominin atlas, and thus, its evolutionary history, are poorly documented because of a paucity of fossilized material. Meticulous excavation, cleaning and high-resolution micro-CT scanning of the StW 573 (‘Little Foot’) skull has revealed the most complete early hominin atlas yet found, having been cemented by breccia in its displaced and flipped over position on the cranial base anterolateral to the foramen magnum. Description and landmark-free morphometric analyses of the StW 573 atlas, along with other less complete hominin atlases from Sterkfontein (StW 679) and Hadar (AL 333-83), confirm the presence of an arboreal component in the positional repertoire of Australopithecus. Finally, assessment of the cross-sectional areas of the transverse foramina of the atlas and the left carotid canal in StW 573 further suggests there may have been lower metabolic costs for cerebral tissues in this hominin than have been attributed to extant humans and may support the idea that blood perfusion of these tissues increased over the course of hominin evolution.The DST-NRF for sponsoring the Micro-XCT facility at Necsa, and the DST-NRF and Wits University for funding the microfocus X-ray CT facility in the ESI. The Ghent University Special Research Fund (BOF-UGent) for the financial support of the Centre of Expertise UGCT (BOF.EXP.2017.0007), the Sterkfontein excavations and MicroCT scanning work have been provided by National Research Foundation and by PAST.http://www.nature.com/srepam2021Anatom

Bipedalism or bipedalisms: The os coxae of StW 573

There has been a long debate about the possibility of multiple contemporaneous species of Australopithecus in both eastern and southern Africa, potentially exhibiting different forms of bipedal locomotion. Here, we describe the previously unreported morphology of the os coxae in the 3.67 Ma Australopithecus prometheus StW 573 from Sterkfontein Member 2, comparing it with variation in ossa coxae in living humans and apes as well as other Plio‐Pleistocene hominins. Statistical comparisons indicate that StW 573 and 431 resemble humans in their anteroposteriorly great iliac crest breadth compared with many other early australopiths, whereas Homo ergaster KNM WT 15000 surprisingly also has a relatively anterioposteriorly short iliac crest. StW 573 and StW 431 appear to resemble humans in having a long ischium compared with Sts 14 and KNM WT 15000. A Quadratic Discriminant Function Analysis of morphology compared with other Plio‐Pleistocene hominins and a dataset of modern humans and hominoids shows that, while Lovejoy's heuristic model of the Ardipithecus ramidus os coxae falls with Pongo or in an indeterminate group, StW 573 and StW 431 from Sterkfontein Member 4 are consistently classified together with modern humans. Although clearly exhibiting the classic “basin shaped” bipedal pelvis, Sts 14 (also from Sterkfontein), AL 288‐1 Australopithecus afarensis, MH2 Australopithecus sediba and KNM‐WT 15000 occupy a position more peripheral to modern humans, and in some analyses are assigned to an indeterminate outlying group. Our findings strongly support the existence of two species of Australopithecus at Sterkfontein and the variation we observe in os coxae morphology in early hominins is also likely to reflect multiple forms of bipedality

Cortical Structure of Hallucal Metatarsals and Locomotor Adaptations in Hominoids

International audienceDiaphyseal morphology of long bones, in part, reflects in vivo loads experienced during the lifetime of an individual. The first metatarsal, as a cornerstone structure of the foot, presumably expresses diaphyseal morphology that reflects loading history of the foot during stance phase of gait. Human feet differ substantially from those of other apes in terms of loading histories when comparing the path of the center of pressure during stance phase, which reflects different weight transfer mechanisms. Here we use a novel approach for quantifying continuous thickness and cross-sectional geometric properties of long bones in order to test explicit hypotheses about loading histories and diaphyseal structure of adult chimpanzee, gorilla, and human first metatarsals. For each hallucal metatarsal, 17 cross sections were extracted at regularly-spaced intervals (2.5% length) between 25% and 65% length. Cortical thickness in cross sections was measured in one degree radially-arranged increments, while second moments of area were measured about neutral axes also in one degree radially-arranged increments. Standardized thicknesses and second moments of area were visualized using false color maps, while penalized discriminant analyses were used to evaluate quantitative species differences. Humans systematically exhibit the thinnest diaphyseal cortices, yet the greatest diaphyseal rigidities, particularly in dorsoplantar regions. Shifts in orientation of maximum second moments of area along the diaphysis also distinguish human hallucal metatarsals from those of chimpanzees and gorillas. Diaphyseal structure reflects different loading regimes, often in predictable ways, with human versus non-human differences probably resulting both from the use of arboreal substrates by non-human apes and by differing spatial relationships between hallux position and orientation of the substrate reaction resultant during stance. The novel morphological approach employed in this study offers the potential for transformative insights into form-function relationships in additional long bones, including those of extinct organisms (e.g., fossils)

The antiquity of bow-and-arrow technology: evidence from Middle Stone Age layers at Sibudu Cave

The bowand arrowis thought to be a unique development of our species, signalling higherlevel cognitive functioning. How this technology originated and how we identify archaeological evidence for it are subjects of ongoing debate. Recent analysis of the putative bone arrow point from Sibudu Cave in South Africa, dated to 61.7±1.5kya, has provided important new insights. High-resolution CT scanning revealed heat and impactdamage in both the Sibudu point and in experimentally produced arrow points. Thesefeatures suggest that the Sibudu point was first used as an arrowhead for hunting, andafterwards was deposited in a hearth. Our results support the claim that bone weapon tips were used in South African hunting long before the Eurasian Upper Palaeolithic.Fil: Backwell, Lucinda Ruth. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Estudios Sociales. Universidad Nacional de Tucumán. Instituto Superior de Estudios Sociales; ArgentinaFil: Bradfield, Justin. University of the Witwatersrand; SudáfricaFil: Carlson, Kristian J.. University of Southern California; Estados UnidosFil: Jashashvili, Tea. University of Southern California; Estados UnidosFil: Wadley, Lyn. University of the Witwatersrand; SudáfricaFil: D'Errico, Francesco. Universite de Bordeaux; Franci

Penalized discriminant analysis (PDA) of standardized cortical bone thicknesses (CBTs).

<p>Due to differences in configurations resulting from hallucal abduction in chimpanzees and gorillas (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117905#pone.0117905.g001" target="_blank">Fig. 1</a>), functionally equivalent cortices (columns in the color map) differ in anatomical correspondence (i.e., dorsal cortices of chimpanzee and gorilla hallucal metatarsals are comparable with medial cortices of human hallucal metatarsals, etc.). Rows of color maps along the top (PDF1 and PDF2) visualize the distribution of mean scaled CBT for interspecific comparisons. In the uppermost row (PDF1), boundaries (dashed yellow lines) superimposed on consensus maps (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117905#pone.0117905.g003" target="_blank">Fig. 3A</a>) differentiate pixels with positive loading (red) from those with negative loading (blue) on PDF1. A positive loading for a given pixel indicates that a larger CBT value at that pixel increases the relative score on that discriminant axis. Similarly, a negative loading for a given pixel indicates that a larger CBT value at that pixel decreases the relative score on that discriminant axis. In the middle row (PDF2), boundaries (dashed black lines) superimposed on the same consensus maps differentiate pixels with positive loading (red) from those with negative loading (blue) for PDF2. Along the bottom, color maps (far left and far right in a red-blue colour scale) visualize pixel-wise loadings of 1^st and 2^nd penalized discriminant functions (PDF1 on the right and plotted on the horizontal axis of the centre scatter plot; PDF2 on the left and plotted on the vertical axis of the centre scatter plot). Note that white indicates the transition between positive and negative loadings (i.e., 0 loading by default). The bivariate scatter plot (bottom centre) presents the projection of each individual in the sample (<i>n</i> = 43; open symbols) into discriminant space via PDF1 and PDF2. Circles in the scatter plot indicate species means in discriminant space, effectively indicating group separation. Squares indicate subjects used in the training sample. Stars indicate test subjects. See the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117905#sec002" target="_blank">methods</a> for an explanation of training versus test subjects. M—medial, D—dorsal, L—lateral, P—plantar.</p

Non-scaled values for cortical bone thickness (CBT) and second moments of area (SMA).

<p>Non-scaled values for cortical bone thickness (CBT) and second moments of area (SMA).</p

Comparisons of cortical bone thicknesses (CBTs).

<p>Due to differences in configurations resulting from hallucal abduction in chimpanzees and gorillas (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117905#pone.0117905.g001" target="_blank">Fig. 1</a>), functionally equivalent cortices (columns in the color map) differ in anatomical correspondence (i.e., dorsal cortices of chimpanzee and gorilla hallucal metatarsals are comparable with medial cortices of human hallucal metatarsals, etc.). <b>A</b>: Distribution of standardized cortical thickness visualized for interspecific comparisons. The color scheme is mapped to cortical thickness measurements standardized by length, thus creating dimensionless values. Amongst all pixels in the species consensus maps, global minimum (0.02) and maximum (0.08) values were used to establish the same range against which each species map was illustrated. Color maps demonstrate variation between species (e.g., gorillas exhibit the highest standardized cortical thickness, while humans exhibit the lowest). <b>B</b>: Distribution of standardized cortical thickness visualized for intraspecific comparisons. The color scheme is mapped to cortical thickness measurements standardized by length, thus creating dimensionless values. Amongst all pixels in respective species consensus maps, global minimum and maximum values were used to establish species-specific ranges for visualizing each map. <b>C</b>: Distribution of coefficients of variation (CVs) of standardized cortical thickness for interspecific comparisons. Minimum and maximum CVs from the three species were used to establish the same range with which each individual species color map was illustrated. Each CV color map visualizes the range of variation expressed within the diaphysis of a species. M—medial, D—dorsal, L—lateral, P—plantar.</p

Sample composition.

<p>Sample composition.</p

Adaptation to bipedal gait and fifth metatarsal structural properties in Australopithecus , Paranthropus , and Homo

International audienc