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1.
Am J Biol Anthropol ; 177(3): 581-602, 2022 03.
Article in English | MEDLINE | ID: mdl-35755956

ABSTRACT

Current approaches to quantify phalangeal curvature assume that the long axis of the bone's diaphysis approximates the shape of a portion of a circle (included angle method) or a parabola (second-degree polynomial method). Here we developed, tested, and employed an alternative geometric morphometrics-based approach to quantify diaphysis shape of proximal phalanges in humans, apes and monkeys with diverse locomotor behaviors. 100 landmarks of the central longitudinal axis were extracted from 3D surface models and analyzed using 2DGM methods, including Generalized Procrustes Analyses. Principal components analyses were performed and PC1 scores (>80% of variation) represented the dorsopalmar shape of the bone's central longitudinal axis and separated taxa consistently and in accord with known locomotor behavioral profiles. The most suspensory taxa, including orangutans, hylobatids and spider monkeys, had significantly lower PC1 scores reflecting the greatest amounts of phalangeal curvature. In contrast, bipedal humans and the quadrupedal cercopithecoid monkeys sampled (baboons, proboscis monkeys) exhibited significantly higher PC1 scores reflecting flatter phalanges. African ape (gorillas, chimpanzees and bonobos) phalanges fell between these two extremes and were not significantly different from each other. PC1 scores were significantly correlated with both included angle and the a coefficient of a second-degree polynomial calculated from the same landmark dataset, but had a significantly higher correlation with included angles. Our alternative approach for quantifying diaphysis shape of proximal phalanges to investigate dorsopalmar curvature is replicable and does not assume a priori either a circle or parabola model of shape, making it an attractive alternative compared with existing methodologies.


Subject(s)
Atelinae , Finger Phalanges , Hominidae , Animals , Diaphyses/diagnostic imaging , Finger Phalanges/diagnostic imaging , Gorilla gorilla
2.
J Hum Evol ; 131: 152-175, 2019 06.
Article in English | MEDLINE | ID: mdl-31182200

ABSTRACT

The KNM-ER 64060 dentition derives from a horizon that most likely dates to between 2.02 and 2.03 Ma. A proximate series of postcranial bones (designated KNM-ER 64061) derives from the same siltstone unit and may be associated with the dentition, but their separation on the surface of the site leaves some room for doubt. KNM-ER 64060 is one of fewer than ten hominin specimens from the Early Pleistocene of East Africa that comprises a full or nearly complete mandibular dentition. Its taxonomic attribution is potentially significant, especially if the postcranial elements are related. At least three, and probably four hominin species, including Paranthropus boisei and Homo erectus (= H. ergaster), are known at about this time in East Africa. Other penecontemporaneous fossils have been referred to a single, highly variable species, H. habilis, or two taxa, namely H. habilis and H. rudolfensis. Although the weight of evidence supports the attribution of these specimens to two species, there is notable lack of agreement over the assignation of individual fossils. We take a conservative approach and group all such specimens under the designation "early Homo sp." for comparative purposes. KNM-ER 64060 is clearly attributable to Homo rather than Paranthropus. The preponderance of the evidence suggests that the affinities of KNM-ER 64060 are with fossils assigned to the early Homo sp. category rather than with H. erectus. This is indicated by the overall sizes of the KNM-ER 64060 canine, premolar and molar crowns, the size relationships of the P3 to P4, the relative narrowness of its premolar crowns, the cusp proportions of the M1 and especially those of the M2 and M3, and seemingly the possession of a two-rooted P4. Some of these comparisons suggest further that among the fossils comprising the early Homo sp. sample, the KNM-ER 64060 dentition exhibits greater overall similarity to specimens such as OH 7 and OH 16 that represent Homo habilis sensu stricto.


Subject(s)
Dentition, Permanent , Fossils/anatomy & histology , Hominidae/anatomy & histology , Mandible , Tooth/anatomy & histology , Animals , Kenya
3.
Sci Rep ; 9(1): 7687, 2019 05 22.
Article in English | MEDLINE | ID: mdl-31118467

ABSTRACT

Sexual dimorphism can be one of the most important indicators of social behavior in fossil species, but the effects of time averaging, geographic variation, and differential preservation can complicate attempts to determine this measure from preserved skeletal anatomy. Here we present an alternative, using footprints from near Ileret, Kenya, to assess the sexual dimorphism of presumptive African Homo erectus at 1.5 Ma. Footprint sites have several unique advantages not typically available to fossils: a single surface can sample a population over a very brief time (in this case likely not more than a single day), and the data are geographically constrained. Further, in many cases, the samples can be much larger than those from skeletal fossil assemblages. Our results indicate that East African Homo erectus was more dimorphic than modern Homo sapiens, although less so than highly dimorphic apes, suggesting that the Ileret footprints offer a unique window into an important transitional period in hominin social behavior.


Subject(s)
Fossils , Hominidae/anatomy & histology , Animals , Anthropometry , Biological Evolution , Body Size , Female , Foot/anatomy & histology , Gorilla gorilla/anatomy & histology , Humans , Kenya , Male , Pan paniscus/anatomy & histology , Pan troglodytes/anatomy & histology , Sex Characteristics , Social Behavior , Species Specificity
4.
Proc Natl Acad Sci U S A ; 115(35): 8746-8751, 2018 08 28.
Article in English | MEDLINE | ID: mdl-30104373

ABSTRACT

The primate foot functions as a grasping organ. As such, its bones, soft tissues, and joints evolved to maximize power and stability in a variety of grasping configurations. Humans are the obvious exception to this primate pattern, with feet that evolved to support the unique biomechanical demands of bipedal locomotion. Of key functional importance to bipedalism is the morphology of the joints at the forefoot, known as the metatarsophalangeal joints (MTPJs), but a comprehensive analysis of hominin MTPJ morphology is currently lacking. Here we present the results of a multivariate shape and Bayesian phylogenetic comparative analyses of metatarsals (MTs) from a broad selection of anthropoid primates (including fossil apes and stem catarrhines) and most of the early hominin pedal fossil record, including the oldest hominin for which good pedal remains exist, Ardipithecus ramidus Results corroborate the importance of specific bony morphologies such as dorsal MT head expansion and "doming" to the evolution of terrestrial bipedalism in hominins. Further, our evolutionary models reveal that the MT1 of Ar. ramidus shifts away from the reconstructed optimum of our last common ancestor with apes, but not necessarily in the direction of modern humans. However, the lateral rays of Ar. ramidus are transformed in a more human-like direction, suggesting that they were the digits first recruited by hominins into the primary role of terrestrial propulsion. This pattern of evolutionary change is seen consistently throughout the evolution of the foot, highlighting the mosaic nature of pedal evolution and the emergence of a derived, modern hallux relatively late in human evolution.


Subject(s)
Biological Evolution , Hominidae , Metatarsal Bones , Phylogeny , Animals , Hominidae/anatomy & histology , Hominidae/physiology , Metatarsal Bones/anatomy & histology , Metatarsal Bones/physiology
5.
Int J Paleopathol ; 22: 97-100, 2018 09.
Article in English | MEDLINE | ID: mdl-30025270

ABSTRACT

Here we evaluate Bhattacharya et al.'s (2018) recent paper "Whole-genome sequencing of Atacama skeleton shows novel mutations linked with dysplasia" published in Genome Research. In this short report, we examine the hypothesis that the so-called "Atacama skeleton" has skeletal abnormalities indicative of dysplasia, critique the validity of the interpretations of disease based on genomic analyses, and comment on the ethics of research on this partially mummified human foetus. The current paper acts as a case study of the importance of using an anthropological approach for aDNA research on human remains. A critical evaluation of the ethically controversial paper by Bhattacharya et al. highlights how an understanding of skeletal biological processes, including normal and abnormal growth and development, taphonomic processes, environmental context, and close attention to ethical issues of dealing with human remains, is vital to scientific interpretations. To this end, close collaboration with palaeopathologists and local archaeologists through appropriate peer-reviewed journals will add to the rigour of scientific interpretation and circumvent misinterpretation.


Subject(s)
Anthropology , Research , Ethics, Research , Humans , Infant, Newborn , Mutation , Whole Genome Sequencing
6.
J Hum Evol ; 122: 84-92, 2018 09.
Article in English | MEDLINE | ID: mdl-29910044

ABSTRACT

Many hypotheses regarding the paleobiology of the earliest possible hominins, Orrorin tugenensis and Ardipithecus ramidus, are dependent upon accurate body mass estimates for these taxa. While we have previously published body mass predictions for Orrorin and Ardipithecus, the accuracies of those estimates depend on the assumption that the postcranial skeletal dimensions and body masses of these taxa followed scaling patterns that were similar to those observed in modern humans. This assumption may not be correct because certain aspects of postcranial morphology in Orrorin and Ardipithecus differ from modern humans, and suggest that their overall body plans might be unique but more similar to modern non-human great apes than to modern humans. Here we present individual body mass predictions for O. tugenensis and Ar. ramidus assuming that they followed postcranial scaling patterns similar to those of chimpanzees. All estimates include individual prediction intervals as measures of uncertainty. In addition, we provide equations for predicting body mass from univariate postcranial measurements based on the largest sample (n = 25) yet compiled of common chimpanzee skeletons with known body masses, which is vital for calculating prediction intervals for individual fossils. Our results show that estimated body masses in Orrorin and Ardipithecus are generally larger when derived from a chimpanzee-like scaling pattern compared to estimates that assume a human-like pattern, though the prediction intervals of the two sets of estimates overlap. In addition, the more complete of the two known Orrorin femora has an overall scaling pattern that is more similar to common chimpanzees than to modern humans, supporting the application of a non-human great ape comparative model. Our new estimates fall near the male (Ardipithecus) average and in between the male and female averages (Orrorin) for wild-caught common chimpanzees. If a chimpanzee-like pattern of scaling between postcranial dimensions and body mass did exist in these earliest hominins, our results suggest the large body masses found in some early australopiths were already present in taxa near the origins of our lineage, and perhaps also in the Pan-Homo last common ancestor.


Subject(s)
Biological Evolution , Body Weight , Hominidae/physiology , Animals , Female , Male
7.
Nat Commun ; 8(1): 880, 2017 10 12.
Article in English | MEDLINE | ID: mdl-29026075

ABSTRACT

Body mass directly affects how an animal relates to its environment and has a wide range of biological implications. However, little is known about the mass of the last common ancestor (LCA) of humans and chimpanzees, hominids (great apes and humans), or hominoids (all apes and humans), which is needed to evaluate numerous paleobiological hypotheses at and prior to the root of our lineage. Here we use phylogenetic comparative methods and data from primates including humans, fossil hominins, and a wide sample of fossil primates including Miocene apes from Africa, Europe, and Asia to test alternative hypotheses of body mass evolution. Our results suggest, contrary to previous suggestions, that the LCA of all hominoids lived in an environment that favored a gibbon-like size, but a series of selective regime shifts, possibly due to resource availability, led to a decrease and then increase in body mass in early hominins from a chimpanzee-sized LCA.The pattern of body size evolution in hominids can provide insight into historical human ecology. Here, Grabowski and Jungers use comparative phylogenetic analysis to reconstruct the likely size of the ancestor of humans and chimpanzees and the evolutionary history of selection on body size in primates.


Subject(s)
Biological Evolution , Body Size , Hominidae/anatomy & histology , Phylogeny , Animals , Environment , Fossils , Humans , Musculoskeletal Physiological Phenomena , Pan troglodytes/anatomy & histology
9.
J Hum Evol ; 107: 107-133, 2017 06.
Article in English | MEDLINE | ID: mdl-28438318

ABSTRACT

Although the diminutive Homo floresiensis has been known for a decade, its phylogenetic status remains highly contentious. A broad range of potential explanations for the evolution of this species has been explored. One view is that H. floresiensis is derived from Asian Homo erectus that arrived on Flores and subsequently evolved a smaller body size, perhaps to survive the constrained resources they faced in a new island environment. Fossil remains of H. erectus, well known from Java, have not yet been discovered on Flores. The second hypothesis is that H. floresiensis is directly descended from an early Homo lineage with roots in Africa, such as Homo habilis; the third is that it is Homo sapiens with pathology. We use parsimony and Bayesian phylogenetic methods to test these hypotheses. Our phylogenetic data build upon those characters previously presented in support of these hypotheses by broadening the range of traits to include the crania, mandibles, dentition, and postcrania of Homo and Australopithecus. The new data and analyses support the hypothesis that H. floresiensis is an early Homo lineage: H. floresiensis is sister either to H. habilis alone or to a clade consisting of at least H. habilis, H. erectus, Homo ergaster, and H. sapiens. A close phylogenetic relationship between H. floresiensis and H. erectus or H. sapiens can be rejected; furthermore, most of the traits separating H. floresiensis from H. sapiens are not readily attributable to pathology (e.g., Down syndrome). The results suggest H. floresiensis is a long-surviving relict of an early (>1.75 Ma) hominin lineage and a hitherto unknown migration out of Africa, and not a recent derivative of either H. erectus or H. sapiens.


Subject(s)
Biological Evolution , Fossils/anatomy & histology , Hominidae/anatomy & histology , Skull/anatomy & histology , Africa , Animals , Bayes Theorem , Female , Hominidae/classification , Humans , Islands , Phylogeny
10.
Elife ; 52016 12 14.
Article in English | MEDLINE | ID: mdl-27964779

ABSTRACT

New fossil footprints excavated at the famous Laetoli site in Tanzania suggest that our bipedal ancestors had a wide range of body sizes.


Subject(s)
Hominidae , Animals , Body Size , Fossils , Tanzania , Walking
11.
Sci Rep ; 6: 30532, 2016 07 28.
Article in English | MEDLINE | ID: mdl-27464580

ABSTRACT

During bipedal walking, modern humans dorsiflex their forefoot at the metatarsophalangeal joints (MTPJs) prior to push off, which tightens the plantar soft tissues to convert the foot into a stiff propulsive lever. Particular features of metatarsal head morphology such as "dorsal doming" are thought to facilitate this stiffening mechanism. In contrast, chimpanzees are believed to possess MTPJ morphology that precludes high dorsiflexion excursions during terrestrial locomotion. The morphological affinity of the metatarsal heads has been used to reconstruct locomotor behavior in fossil hominins, but few studies have provided detailed empirical data to validate the assumed link between morphology and function at the MTPJs. Using three-dimensional kinematic and morphometric analyses, we show that humans push off with greater peak dorsiflexion angles at all MTPJs than do chimpanzees during bipedal and quadrupedal walking, with the greatest disparity occurring at MTPJ 1. Among MTPJs 2-5, both species exhibit decreasing peak angles from medial to lateral. This kinematic pattern is mirrored in the morphometric analyses of metatarsal head shape. Analyses of Australopithecus afarensis metatarsals reveal morphology intermediate between humans and chimpanzees, suggesting that this species used different bipedal push-off kinematics than modern humans, perhaps resulting in a less efficient form of bipedalism.


Subject(s)
Foot/anatomy & histology , Foot/physiology , Hominidae , Metatarsophalangeal Joint/physiology , Animals , Biomechanical Phenomena , Fossils , Head/anatomy & histology , Hominidae/anatomy & histology , Hominidae/physiology , Humans , Imaging, Three-Dimensional , Metatarsophalangeal Joint/anatomy & histology , Pan troglodytes/anatomy & histology , Pan troglodytes/physiology , Walking
12.
PLoS One ; 11(6): e0155731, 2016.
Article in English | MEDLINE | ID: mdl-27275928

ABSTRACT

The Liang Bua hominins from Flores, Indonesia, have been the subject of intense scrutiny and debate since their initial description and classification in 2004. These remains have been assigned to a new species, Homo floresiensis, with the partial skeleton LB1 as the type specimen. The Liang Bua hominins are notable for their short stature, small endocranial volume, and many features that appear phylogenetically primitive relative to modern humans, despite their late Pleistocene age. Recently, some workers suggested that the remains represent members of a small-bodied island population of modern Austro-Melanesian humans, with LB1 exhibiting clinical signs of Down syndrome. Many classic Down syndrome signs are soft tissue features that could not be assessed in skeletal remains. Moreover, a definitive diagnosis of Down syndrome can only be made by genetic analysis as the phenotypes associated with Down syndrome are variable. Most features that contribute to the Down syndrome phenotype are not restricted to Down syndrome but are seen in other chromosomal disorders and in the general population. Nevertheless, we re-evaluated the presence of those phenotypic features used to support this classification by comparing LB1 to samples of modern humans diagnosed with Down syndrome and euploid modern humans using comparative morphometric analyses. We present new data regarding neurocranial, brain, and symphyseal shape in Down syndrome, additional estimates of stature for LB1, and analyses of inter- and intralimb proportions. The presence of cranial sinuses is addressed using CT images of LB1. We found minimal congruence between the LB1 phenotype and clinical descriptions of Down syndrome. We present important differences between the phenotypes of LB1 and individuals with Down syndrome, and quantitative data that characterize LB1 as an outlier compared with Down syndrome and non-Down syndrome groups. Homo floresiensis remains a phenotypically unique, valid species with its roots in Plio-Pleistocene Homo taxa.


Subject(s)
Down Syndrome/pathology , Down Syndrome/physiopathology , Hominidae/abnormalities , Phenotype , Animals , Down Syndrome/diagnosis , Hominidae/classification , Indonesia
13.
Article in English | MEDLINE | ID: mdl-27298459

ABSTRACT

Body size is a fundamental biological property of organisms, and documenting body size variation in hominin evolution is an important goal of palaeoanthropology. Estimating body mass appears deceptively simple but is laden with theoretical and pragmatic assumptions about best predictors and the most appropriate reference samples. Modern human training samples with known masses are arguably the 'best' for estimating size in early bipedal hominins such as the australopiths and all members of the genus Homo, but it is not clear if they are the most appropriate priors for reconstructing the size of the earliest putative hominins such as Orrorin and Ardipithecus The trajectory of body size evolution in the early part of the human career is reviewed here and found to be complex and nonlinear. Australopith body size varies enormously across both space and time. The pre-erectus early Homo fossil record from Africa is poor and dominated by relatively small-bodied individuals, implying that the emergence of the genus Homo is probably not linked to an increase in body size or unprecedented increases in size variation. Body size differences alone cannot explain the observed variation in hominin body shape, especially when examined in the context of small fossil hominins and pygmy modern humans.This article is part of the themed issue 'Major transitions in human evolution'.


Subject(s)
Biological Evolution , Body Size , Hominidae/physiology , Africa , Animals , Fossils , Humans
14.
Nature ; 532(7599): 366-9, 2016 Apr 21.
Article in English | MEDLINE | ID: mdl-27027286

ABSTRACT

Homo floresiensis, a primitive hominin species discovered in Late Pleistocene sediments at Liang Bua (Flores, Indonesia), has generated wide interest and scientific debate. A major reason this taxon is controversial is because the H. floresiensis-bearing deposits, which include associated stone artefacts and remains of other extinct endemic fauna, were dated to between about 95 and 12 thousand calendar years (kyr) ago. These ages suggested that H. floresiensis survived until long after modern humans reached Australia by ~50 kyr ago. Here we report new stratigraphic and chronological evidence from Liang Bua that does not support the ages inferred previously for the H. floresiensis holotype (LB1), ~18 thousand calibrated radiocarbon years before present (kyr cal. BP), or the time of last appearance of this species (about 17 or 13-11 kyr cal. BP). Instead, the skeletal remains of H. floresiensis and the deposits containing them are dated to between about 100 and 60 kyr ago, whereas stone artefacts attributable to this species range from about 190 to 50 kyr in age. Whether H. floresiensis survived after 50 kyr ago--potentially encountering modern humans on Flores or other hominins dispersing through southeast Asia, such as Denisovans--is an open question.


Subject(s)
Archaeology , Fossils , Hominidae , Radiometric Dating , Aluminum Silicates , Animals , Australia , Calibration , Caves , Geologic Sediments/analysis , Glass , Humans , Indonesia , Potassium Compounds , Quartz , Time Factors , Uncertainty
15.
Am J Phys Anthropol ; 159(Suppl 61): S4-S18, 2016 Jan.
Article in English | MEDLINE | ID: mdl-26808111

ABSTRACT

Gorillas living in western central Africa (Gorilla gorilla) are morphologically and genetically distinguishable from those living in eastern central Africa (Gorilla beringei). Genomic analyses show eastern gorillas experienced a significant reduction in population size during the Pleistocene subsequent to geographical isolation from their western counterparts. However, how these results relate more specifically to the recent biogeographical and evolutionary history of eastern gorillas remains poorly understood. Here we show that two rare morphological traits are present in the hands and feet of both eastern gorilla subspecies at strikingly high frequencies (>60% in G. b. graueri; ∼28% in G. b. beringei) in comparison with western gorillas (<1%). The intrageneric distribution of these rare traits suggests that they became common among eastern gorillas after diverging from their western relatives during the early to middle Pleistocene. The extremely high frequencies observed among grauer gorillas-which currently occupy a geographic range more than ten times the size of that of mountain gorillas-imply that grauers originated relatively recently from a small founding population of eastern gorillas. Current paleoenvironmental, geological, and biogeographical evidence supports the hypothesis that a small group of eastern gorillas likely dispersed westward from the Virungas into present-day grauer range in the highlands just north of Lake Kivu, either immediately before or directly after the Younger Dryas interval. We propose that as the lowland forests of central Africa expanded rapidly during the early Holocene, they became connected with the expanding highland forests along the Albertine Rift and enabled the descendants of this small group to widely disperse. The descendant populations significantly expanded their geographic range and population numbers relative to the gorillas of the Virunga Mountains and the Bwindi-Impenetrable Forest, ultimately resulting in the grauer gorilla subspecies recognized today. This founder-effect hypothesis offers some optimism for modern conservation efforts to save critically endangered eastern gorillas from extinction.


Subject(s)
Biological Evolution , Gorilla gorilla , Africa, Central , Africa, Eastern , Animals , Environment , Female , Foot Bones/anatomy & histology , Fossils , Gorilla gorilla/anatomy & histology , Gorilla gorilla/classification , Gorilla gorilla/genetics , Gorilla gorilla/physiology , Male , Phylogeny
16.
J Hum Evol ; 86: 136-46, 2015 Sep.
Article in English | MEDLINE | ID: mdl-26276534

ABSTRACT

Modern human metatarsal heads are typically described as "dorsally domed," mediolaterally wide, and dorsally flat. Despite the apparent functional importance of these features in forefoot stability during bipedalism, the distinctiveness of this morphology has not been quantitatively evaluated within a broad comparative framework. In order to use these features to reconstruct fossil hominin locomotor behaviors with any confidence, their connection to human bipedalism should be validated through a comparative analysis of other primates with different locomotor behaviors and foot postures, including species with biomechanical demands potentially similar to those of bipedalism (e.g., terrestrial digitigrady). This study explores shape variation in the distal metatarsus among humans and other extant catarrhines using three-dimensional geometric morphometrics (3 DGM). Shape differences among species in metatarsal head morphology are well captured by the first two principal components of Procrustes shape coordinates, and these two components summarize most of the variance related to "dorsal doming" and "dorsal expansion." Multivariate statistical tests reveal significant differences among clades in overall shape, and humans are reliably distinguishable from other species by aspects of shape related to a greater degree of dorsal doming. Within quadrupeds, terrestrial species also trend toward more domed metatarsal heads, but not to the extent seen in humans. Certain aspects of distal metatarsus shape are likely related to habitual dorsiflexion of the metatarsophalangeal joints, but the total morphological pattern seen in humans is distinct. These comparative results indicate that this geometric morphometric approach is useful to characterize the complexity of metatarsal head morphology and will help clarify its relationship with function in fossil primates, including early hominins.


Subject(s)
Cercopithecidae/anatomy & histology , Cercopithecidae/physiology , Hominidae/anatomy & histology , Hominidae/physiology , Metatarsal Bones/anatomy & histology , Metatarsal Bones/physiology , Walking/physiology , Animals , Biological Evolution , Fossils , Humans
17.
Nat Commun ; 6: 7717, 2015 Jul 14.
Article in English | MEDLINE | ID: mdl-26171589

ABSTRACT

Human hands are distinguished from apes by possessing longer thumbs relative to fingers. However, this simple ape-human dichotomy fails to provide an adequate framework for testing competing hypotheses of human evolution and for reconstructing the morphology of the last common ancestor (LCA) of humans and chimpanzees. We inspect human and ape hand-length proportions using phylogenetically informed morphometric analyses and test alternative models of evolution along the anthropoid tree of life, including fossils like the plesiomorphic ape Proconsul heseloni and the hominins Ardipithecus ramidus and Australopithecus sediba. Our results reveal high levels of hand disparity among modern hominoids, which are explained by different evolutionary processes: autapomorphic evolution in hylobatids (extreme digital and thumb elongation), convergent adaptation between chimpanzees and orangutans (digital elongation) and comparatively little change in gorillas and hominins. The human (and australopith) high thumb-to-digits ratio required little change since the LCA, and was acquired convergently with other highly dexterous anthropoids.


Subject(s)
Biological Evolution , Fingers/anatomy & histology , Fossils , Animals , Gorilla gorilla , Hand/anatomy & histology , Hominidae , Humans , Organ Size , Pan troglodytes , Phylogeny , Pongo
18.
J Hum Evol ; 85: 75-93, 2015 Aug.
Article in English | MEDLINE | ID: mdl-26094042

ABSTRACT

Body size directly influences an animal's place in the natural world, including its energy requirements, home range size, relative brain size, locomotion, diet, life history, and behavior. Thus, an understanding of the biology of extinct organisms, including species in our own lineage, requires accurate estimates of body size. Since the last major review of hominin body size based on postcranial morphology over 20 years ago, new fossils have been discovered, species attributions have been clarified, and methods improved. Here, we present the most comprehensive and thoroughly vetted set of individual fossil hominin body mass predictions to date, and estimation equations based on a large (n = 220) sample of modern humans of known body masses. We also present species averages based exclusively on fossils with reliable taxonomic attributions, estimates of species averages by sex, and a metric for levels of sexual dimorphism. Finally, we identify individual traits that appear to be the most reliable for mass estimation for each fossil species, for use when only one measurement is available for a fossil. Our results show that many early hominins were generally smaller-bodied than previously thought, an outcome likely due to larger estimates in previous studies resulting from the use of large-bodied modern human reference samples. Current evidence indicates that modern human-like large size first appeared by at least 3-3.5 Ma in some Australopithecus afarensis individuals. Our results challenge an evolutionary model arguing that body size increased from Australopithecus to early Homo. Instead, we show that there is no reliable evidence that the body size of non-erectus early Homo differed from that of australopiths, and confirm that Homo erectus evolved larger average body size than earlier hominins.


Subject(s)
Biological Evolution , Body Size/physiology , Fossils , Hominidae/physiology , Animals , Female , Humans , Male , Models, Statistical , Paleontology
19.
Anat Rec (Hoboken) ; 298(1): 212-29, 2015 Jan.
Article in English | MEDLINE | ID: mdl-25529242

ABSTRACT

Three-dimensional geometric morphometrics (3DGM) is a powerful tool for capturing and visualizing the "pure" shape of complex structures. However, these shape differences are sometimes difficult to interpret from a functional viewpoint, unless specific approaches (mostly based on biomechanical modeling) are employed. Here, we use 3DGM to explore the complex shape variation of the hamate, the disto-ulnar wrist bone, in anthropoid primates. Major trends of shape variation are explored using principal components analysis along with analyses of shape and size covariation. We also evaluate the phylogenetic patterning of hamate shape by plotting an anthropoid phylogenetic tree onto the shape space (i.e., phylomorphospace) and test against complete absence of phylogenetic signal using posterior permutation. Finally, the covariation of hamate shape and locomotor categories is explored by means of 2-block partial least squares (PLS) using shape coordinates and a matrix of data on arboreal locomotor behavior. Our results show that 3DGM is a valuable and versatile tool for characterizing the shape of complex structures such as wrist bones in anthropoids. For the hamate, a significant phylogenetic pattern is found in both hamate shape and size, indicating that closely related taxa are typically the most similar in hamate form. Our allometric analyses show that major differences in hamate shape among taxa are not a direct consequence of differences in hamate size. Finally, our PLS indicates a significant covariation of hamate shape and different types of arboreal locomotion, highlighting the relevance of this approach in future 3DGM studies seeking to capture a functional signal from complex biological structures.


Subject(s)
Hamate Bone/anatomy & histology , Hamate Bone/physiology , Haplorhini/anatomy & histology , Haplorhini/physiology , Mathematics , Phylogeny , Animals , Biological Evolution , Biomechanical Phenomena/physiology , Cebidae , Hominidae , Humans , Hylobates , Imaging, Three-Dimensional , Locomotion/physiology , Principal Component Analysis , Wrist/anatomy & histology , Wrist/physiology
20.
J Hum Evol ; 68: 36-46, 2014 Mar.
Article in English | MEDLINE | ID: mdl-24560803

ABSTRACT

The hypodigm of Homo floresiensis from the cave of Liang Bua on Flores Island in the archipelago of Indonesia includes two mandibles (LB1/2 and LB6/1). The morphology of their symphyses and corpora has been described as sharing similarities with both australopiths and early Homo despite their Late Pleistocene age. Although detailed morphological comparisons of these mandibles with those of modern and fossil hominin taxa have been made, a functional analysis in the context of masticatory biomechanics has yet to be performed. Utilizing data on cortical bone geometry from computed tomography scans, we compare the mechanical attributes of the LB1 and LB6 mandibles with samples of modern Homo, Pan, Pongo, and Gorilla, as well as fossil samples of Paranthropus robustus, Australopithecus africanus and South African early Homo. Structural stiffness measures were derived from the geometric data to provide relative measures of mandibular corpus strength under hypothesized masticatory loading regimes. These mechanical variables were evaluated relative to bone area, mandibular length and estimates of body size to assess their functional affinities and to test the hypothesis that the Liang Bua mandibles can be described as scaled-down variants of either early hominins or modern humans. Relative to modern hominoids, the H. floresiensis material appears to be relatively strong in terms of rigidity in torsion and transverse bending, but is relatively weak under parasagittal bending. Thus, they are 'robust' relative to modern humans (and comparable with australopiths) under some loads but not others. Neither LB1 nor LB6 can be described simply as 'miniaturized' versions of modern human jaws since mandible length is more or less equivalent in Homo sapiens and H. floresiensis. The mechanical attributes of the Liang Bua mandibles are consistent with previous inferences that masticatory loads were reduced relative to australopiths but remained elevated relative to modern Homo.


Subject(s)
Biomechanical Phenomena/physiology , Fossils , Hominidae/anatomy & histology , Mandible/anatomy & histology , Mandible/physiology , Animals , Female , Male , Mandible/diagnostic imaging , Tomography, X-Ray Computed
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