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William H. Kimbel - One of the best experts on this subject based on the ideXlab platform.
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Australopithecus Afarensis endocasts suggest ape-like brain organization and prolonged brain growth.
Science advances, 2020Co-Authors: Philipp Gunz, William H. Kimbel, Dean Falk, Simon Neubauer, Paul Tafforeau, Adeline Le Cabec, Tanya M. Smith, Fred Spoor, Zeresenay AlemsegedAbstract:Human brains are three times larger, are organized differently, and mature for a longer period of time than those of our closest living relatives, the chimpanzees. Together, these characteristics are important for human cognition and social behavior, but their evolutionary origins remain unclear. To study brain growth and organization in the hominin species Australopithecus Afarensis more than 3 million years ago, we scanned eight fossil crania using conventional and synchrotron computed tomography. We inferred key features of brain organization from endocranial imprints and explored the pattern of brain growth by combining new endocranial volume estimates with narrow age at death estimates for two infants. Contrary to previous claims, sulcal imprints reveal an ape-like brain organization and no features derived toward humans. A comparison of infant to adult endocranial volumes indicates protracted brain growth in A. Afarensis, likely critical for the evolution of a long period of childhood learning in hominins.
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Aspects of mandibular ontogeny in Australopithecus Afarensis
Vertebrate Paleobiology and Paleoanthropology, 2017Co-Authors: Halszka Glowacka, William H. Kimbel, Donald C. JohansonAbstract:Human and ape mandibles differ in the proportion of adult size attained at equivalent dental emergence stages; for most dimensions human mandibles are more advanced. These dissimilarities in pattern of growth underlie the vastly different adult mandibular morphologies of these taxa. Australopithecus mandibles represent a third distinctive mandibular morphology, but the pattern of its mandibular growth remains underexplored. The Australopithecus Afarensis sample from the Hadar site, Ethiopia, ca. 3.4–3.0 Ma, is represented by three infant (pre-M1 emergence) and two juvenile (pre-M3 emergence) mandibles. A recently recovered mandible, A.L. 1920-1, though edentulous, appears to capture an A. Afarensis individual during M2 emergence, thus bridging these developmental stages. In this chapter, we (1) describe three new infant/juvenile A. Afarensis mandibles and confirm that the suite of features used to distinguish A. Afarensis from other taxa is present early in ontogeny, and (2) investigate how the A. Afarensis mandible changes in size and shape throughout growth in comparison to humans and chimpanzees . Our results indicate that A. Afarensis resembles humans more than chimpanzees in its percentage of adult corpus breadth attained at successive stages of dental emergence. A. Afarensis is also more similar to humans in corpus cross-sectional shape changes throughout ontogeny. We suggest that canine reduction may have had an important influence on the growth trajectory of the A. Afarensis mandibular corpus such that, as in humans, it achieved adult values relatively early. Our results underscore the importance of considering the influence of the developing dentition on both juvenile and adult mandibular morphology.
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Dietary flexibility of Australopithecus Afarensis in the face of paleoecological change during the middle Pliocene: Faunal evidence from Hadar, Ethiopia.
Journal of human evolution, 2016Co-Authors: Jonathan G. Wynn, Zelalem K. Bedaso, Zeresenay Alemseged, William H. Kimbel, Matt Sponheimer, Kaye E. Reed, Christopher J. CampisanoAbstract:One approach to understanding the context of changes in hominin paleodiets is to examine the paleodiets and paleohabitats of contemporaneous mammalian taxa. Recent carbon isotopic studies suggest that the middle Pliocene was marked by a major shift in hominin diets, characterized by a significant increase in C4 foods in Australopithecus-grade species, including Australopithecus Afarensis. To contextualize previous isotopic studies of A. Afarensis, we employed stable isotopes to examine paleodiets of the mammalian fauna contemporaneous with A. Afarensis at Hadar, Ethiopia. We used these data to inform our understanding of paleoenvironmental change through the deposition of the Hadar Formation. While the majority of the taxa in the Hadar fauna were C4 grazers, most show little change in the intensity of C4 food consumption over the 0.5 million-year interval sampled. Two taxa (equids and bovins) do show increases in C4 consumption through the Hadar Formation and into the younger, overlying Busidima Formation. Changes in the distributions of C4-feeders, C3-feeders and mixed-C3/C4-feeders in the sampled intervals are consistent with evidence of dietary reconstructions based on ecomorphology, and with habitats reconstructed using community structure analyses. Meanwhile, A. Afarensis is one of many mammalian taxa whose C4 consumption does not show directional change over the intervals sampled. In combination with a wide range of carbon and oxygen isotopic composition for A. Afarensis as compared to the other large mammal taxa, these results suggest that the C3/C4 dietary flexibility of A. Afarensis was relatively unusual among most of its mammalian cohort.
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Postnatal temporal bone ontogeny in Pan, Gorilla, and Homo, and the implications for temporal bone ontogeny in Australopithecus Afarensis
American Journal of Physical Anthropology, 2013Co-Authors: Claire E Terhune, William H. Kimbel, Charles A. LockwoodAbstract:Assessments of temporal bone morphology have played an important role in taxonomic and phylogenetic evaluations of fossil taxa, and recent three-dimensional analyses of this region have supported the utility of the temporal bone for testing taxonomic and phylogenetic hypotheses. But while clinical analyses have examined aspects of temporal bone ontogeny in humans, the ontogeny of the temporal bone in non-human taxa is less well documented. This study examines ontogenetic allometry of the temporal bone in order to address several research questions related to the pattern and trajectory of temporal bone shape change during ontogeny in the African apes and humans. We further apply these data to a preliminary analysis of temporal bone ontogeny in Australopithecus Afarensis. Three-dimensional landmarks were digitized on an ontogenetic series of specimens of Homo sapiens, Pan troglodytes, Pan paniscus, and Gorilla gorilla. Data were analyzed using geometric morphometric methods, and shape changes throughout ontogeny in relation to size were compared. Results of these analyses indicate that, despite broadly similar patterns, African apes and humans show marked differences in development of the mandibular fossa and tympanic portions of the temporal bone. These findings indicate divergent, rather than parallel, postnatal ontogenetic allometric trajectories for temporal bone shape in these taxa. The pattern of temporal bone shape change with size exhibited by A. Afarensis showed some affinities to that of humans, but was most similar to extant African apes, particularly Gorilla. Am J Phys Anthropol 151:630–642, 2013. © 2013 Wiley Periodicals, Inc.
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Premolar microwear and tooth use in Australopithecus Afarensis.
Journal of human evolution, 2013Co-Authors: Lucas K. Delezene, William H. Kimbel, Frederick E. Grine, Mark F. Teaford, Melissa S. Zolnierz, Peter S. UngarAbstract:The mandibular third premolar (P3) of Australopithecus Afarensis is notable for extensive morphological variability (e.g., metaconid presence/absence, closure of the anterior fovea, root number) and temporal trends in crown length and shape change over its 700 Ka time range. Hominins preceding A. Afarensis have unicuspid, mesiodistally elongated P3s with smaller talonids, and subsequent australopiths have bicuspid, more symmetrically-shaped P3 crowns with expanded talonids. For these features, A. Afarensis is intermediate and, thus, evinces the incipient stages of P3 molarization. Here, we examine A. Afarensis P3 Phase II microwear and compare it with that of Australopithecus africanus and Cercocebus atys, an extant hard-object specialist, to assess whether the role of the P3 in food processing changed over time in A. Afarensis. Premolar Phase II microwear textures are also compared with those of the molars to look for evidence of functional differentiation along the tooth row (i.e., that foods with different mechanical properties were processed by separate regions of the postcanine battery). Microwear textures were also examined along the mesial protoconid crest, the site of occlusion with the maxillary canine, of the A. Afarensis P3 and compared with the same region in Pan troglodytes to determine whether microwear can be useful for identifying changes in the occlusal relationship between the P3 and maxillary canine in early Australopithecus. Finally, temporal trends in P3 Phase II and mesial microwear are considered. Results indicate that 1) both the P3 and molar Phase II facets of A. Afarensis have less complex microwear textures than in A. africanus or C. atys; 2) A. Afarensis P3 and molar Phase II textures differ, though not to the extent seen in taxa that eat hard and tough items; 3) microwear along the A. Afarensis mesial protoconid crest is clearly distinct from that of the P. troglodytes, indicating that there is no honing equivalent in A. Afarensis; and 4) there is little evidence of change over time in A. Afarensis P3 microwear on either the mesial or Phase II facet. In sum, these results provide no evidence that A. Afarensis routinely loaded either its premolars or molars to process hard objects or that A. Afarensis P3 function changed over time.
C. Owen Lovejoy - One of the best experts on this subject based on the ideXlab platform.
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Conclusion: Implications of KSD-VP-1/1 for Early Hominin Paleobiology and Insights into the Chimpanzee/Human Last Common Ancestor
Vertebrate Paleobiology and Paleoanthropology, 2015Co-Authors: Yohannes Haile-selassie, Bruce Latimer, C. Owen Lovejoy, Stephanie M. Melillo, Marc R MeyerAbstract:KSD-VP-1/1 is a 3.6 million years old (Ma) partial skeleton of Australopithecus Afarensis recently discovered from the Woranso-Mille study area in the Afar region of Ethiopia. The recovered elements of this specimen, which include cervical vertebrae, a complete scapula, clavicle, numerous ribs, pelvis, and elements of the fore- and hindlimbs, greatly enhance our understanding of the paleobiology of early Australopithecus Afarensis. Detailed analyses of the cervical vertebrae indicate that Australopithecus Afarensis had a highly mobile neck, signaling human-like kinematics consistent with habitual upright posture and bipedalism. Elements of the shoulder girdle exhibit some primitive morphology but are overall more similar to humans than has been previously understood. This similarity is inconsistent with the notion that the Australopithecus Afarensis shoulder retained primitive morphology from an African ape-like chimpanzee/human last common ancestor. Morphology of the thorax also indicates that while some individual traits may appear to superficially suggest arboreality, Australopithecus Afarensis did not have an abundance of functionally significant morphological traits that would suggest high canopy arboreality as found today in large-bodied apes. Most of the inconsistencies in interpretations of early hominin paleobiology appear to stem from methodological differences, incorrect a priori assumptions, or incomplete information derived from fragmentary specimens.
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From Lucy to Kadanuumuu: Balanced Analyses of Australopithecus Afarensis Assemblages Confirm Only Moderate Skeletal Dimorphism
PeerJ, 2015Co-Authors: Philip L. Reno, C. Owen LovejoyAbstract:Sexual dimorphism in body size is often used as a correlate of social and reproductive behavior in Australopithecus Afarensis. In addition to a number of isolated specimens, the sample for this species includes two small associated skeletons (A.L. 288-1 or "Lucy" and A.L. 128/129) and a geologically contemporaneous death assemblage of several larger individuals (A.L. 333). These have driven both perceptions and quantitative analyses concluding that Au. Afarensis was markedly dimorphic. The Template Method enables simultaneous evaluation of multiple skeletal sites, thereby greatly expanding sample size, and reveals that A. Afarensis dimorphism was similar to that of modern humans. A new very large partial skeleton (KSD-VP-1/1 or "Kadanuumuu") can now also be used, like Lucy, as a template specimen. In addition, the recently developed Geometric Mean Method has been used to argue that Au. Afarensis was equally or even more dimorphic than gorillas. However, in its previous application Lucy and A.L. 128/129 accounted for 10 of 11 estimates of female size. Here we directly compare the two methods and demonstrate that including multiple measurements from the same partial skeleton that falls at the margin of the species size range dramatically inflates dimorphism estimates. Prevention of the dominance of a single specimen's contribution to calculations of multiple dimorphism estimates confirms that Au. Afarensis was only moderately dimorphic.
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An enlarged postcranial sample confirms Australopithecus Afarensis dimorphism was similar to modern humans
Philosophical transactions of the Royal Society of London. Series B Biological sciences, 2010Co-Authors: Philip L. Reno, Melanie A. Mccollum, Richard S. Meindl, C. Owen LovejoyAbstract:In a previous study, we introduced the template method as a means of enlarging the Australopithecus Afarensis postcranial sample to more accurately estimate its skeletal dimorphism. Results indicated dimorphism to be largely comparable to that of Homo sapiens. Some have since argued that our results were biased by artificial homogeneity in our Au. Afarensis sample. Here we report the results from inclusion of 12 additional, newly reported, specimens. The results are consistent with those of our original study and with the hypothesis that early hominid demographic success derived from a reproductive strategy involving male provisioning of pair-bonded females.
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An early Australopithecus Afarensis postcranium from Woranso-Mille, Ethiopia
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Yohannes Haile-selassie, Bruce Latimer, Stephanie M. Melillo, Mulugeta Alene, Alan L. Deino, Luis Gibert, Beverly Z. Saylor, Gary R. Scott, C. Owen LovejoyAbstract:Only one partial skeleton that includes both forelimb and hindlimb elements has been reported for Australopithecus Afarensis. The diminutive size of this specimen (A.L. 288-1 ["Lucy"]) has hampered our understanding of the paleobiology of this species absent the potential impact of allometry. Here we describe a large-bodied (i.e., well within the range of living Homo) specimen that, at 3.58 Ma, also substantially antedates A.L. 288–1. It provides fundamental evidence of limb proportions, thoracic form, and locomotor heritage in Australopithecus Afarensis. Together, these characteristics further establish that bipedality in Australopithecus was highly evolved and that thoracic form differed substantially from that of either extant African ape.
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Sexual dimorphism in Australopithecus Afarensis was similar to that of modern humans
Proceedings of the National Academy of Sciences of the United States of America, 2003Co-Authors: Philip L. Reno, Melanie A. Mccollum, Richard S. Meindl, C. Owen LovejoyAbstract:The substantial fossil record for Australopithecus Afarensis includes both an adult partial skeleton [Afar Locality (A.L.) 288-1, “Lucy”] and a large simultaneous death assemblage (A.L. 333). Here we optimize data derived from both to more accurately estimate skeletal size dimorphism. Postcranial ratios derived from A.L. 288-1 enable a significant increase in sample size compared with previous studies. Extensive simulations using modern humans, chimpanzees, and gorillas confirm that this technique is accurate and that skeletal size dimorphism in A. Afarensis was most similar to that of contemporary Homo sapiens. These data eliminate some apparent discrepancies between the canine and skeletal size dimorphism in hominoids, imply that the species was not characterized by substantial sexual bimaturation, and greatly increase the probability that the reproductive strategy of A. Afarensis was principally monogamy.
Donald C. Johanson - One of the best experts on this subject based on the ideXlab platform.
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Aspects of mandibular ontogeny in Australopithecus Afarensis
Vertebrate Paleobiology and Paleoanthropology, 2017Co-Authors: Halszka Glowacka, William H. Kimbel, Donald C. JohansonAbstract:Human and ape mandibles differ in the proportion of adult size attained at equivalent dental emergence stages; for most dimensions human mandibles are more advanced. These dissimilarities in pattern of growth underlie the vastly different adult mandibular morphologies of these taxa. Australopithecus mandibles represent a third distinctive mandibular morphology, but the pattern of its mandibular growth remains underexplored. The Australopithecus Afarensis sample from the Hadar site, Ethiopia, ca. 3.4–3.0 Ma, is represented by three infant (pre-M1 emergence) and two juvenile (pre-M3 emergence) mandibles. A recently recovered mandible, A.L. 1920-1, though edentulous, appears to capture an A. Afarensis individual during M2 emergence, thus bridging these developmental stages. In this chapter, we (1) describe three new infant/juvenile A. Afarensis mandibles and confirm that the suite of features used to distinguish A. Afarensis from other taxa is present early in ontogeny, and (2) investigate how the A. Afarensis mandible changes in size and shape throughout growth in comparison to humans and chimpanzees . Our results indicate that A. Afarensis resembles humans more than chimpanzees in its percentage of adult corpus breadth attained at successive stages of dental emergence. A. Afarensis is also more similar to humans in corpus cross-sectional shape changes throughout ontogeny. We suggest that canine reduction may have had an important influence on the growth trajectory of the A. Afarensis mandibular corpus such that, as in humans, it achieved adult values relatively early. Our results underscore the importance of considering the influence of the developing dentition on both juvenile and adult mandibular morphology.
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New postcranial fossils of Australopithecus Afarensis from Hadar, Ethiopia (1990-2007).
Journal of human evolution, 2012Co-Authors: Carol V. Ward, William H. Kimbel, Elizabeth H. Harmon, Donald C. JohansonAbstract:Renewed fieldwork at Hadar, Ethiopia, from 1990 to 2007, by a team based at the Institute of Human Origins, Arizona State University, resulted in the recovery of 49 new postcranial fossils attributed to Australopithecus Afarensis. These fossils include elements from both the upper and lower limbs as well as the axial skeleton, and increase the sample size of previously known elements for A. Afarensis. The expanded Hadar sample provides evidence of multiple new individuals that are intermediate in size between the smallest and largest individuals previously documented, and so support the hypothesis that a single dimorphic species is represented. Consideration of the functional anatomy of the new fossils supports the hypothesis that no functional or behavioral differences need to be invoked to explain the morphological variation between large and small A. Afarensis individuals. Several specimens provide important new data about this species, including new vertebrae supporting the hypothesis that A. Afarensis may have had a more human-like thoracic form than previously appreciated, with an invaginated thoracic vertebral column. A distal pollical phalanx confirms the presence of a human-like flexor pollicis longus muscle in A. Afarensis. The new fossils include the first complete fourth metatarsal known for A. Afarensis. This specimen exhibits the dorsoplantarly expanded base, axial torsion and domed head typical of humans, revealing the presence of human-like permanent longitudinal and transverse arches and extension of the metatarsophalangeal joints as in human-like heel-off during gait. The new Hadar postcranial fossils provide a more complete picture of postcranial functional anatomy, and individual and temporal variation within this sample. They provide the basis for further in-depth analyses of the behavioral and evolutionary significance of A. Afarensis anatomy, and greater insight into the biology and evolution of these early hominins.
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Associated cranial and forelimb remains attributed to Australopithecus Afarensis from Hadar, Ethiopia
Journal of human evolution, 2005Co-Authors: Michelle S.m. Drapeau, Donald C. Johanson, William H. Kimbel, Carol V. Ward, Yoel RakAbstract:A partial skeleton from Hadar, Ethiopia (A.L. 438-1) attributed to Australopithecus Afarensis is comprised of part of the mandible, a frontal bone fragment, a complete left ulna, two second metacarpals, one third metacarpal, plus parts of the clavicle, humerus, radius, and right ulna. It is one of only a few early hominin specimens to preserve both cranial and postcranial elements. It also includes the first complete ulna from a large A. Afarensis individual, and the first associated metacarpal and forelimb remains. This specimen, dated to approximately 3 Ma, is among the geologically youngest A. Afarensis fossils and is also one of the largest individuals known. Its ulnar to mandibular proportions are similar to those of the geologically older and much smaller A.L. 288-1, suggesting that body size increased without disproportional enlargement of the mandible. Overall, however, analysis of this large specimen and of the diminutive A.L. 288-1 demonstrates that the functional morphology of the A. Afarensis upper limb was similar at all body sizes; there is no evidence to support the hypothesis that more than one hominin species is present at Hadar. Morphologically, all apparent apomorphic traits of the elbow, forearm, wrist, and hand of A.L. 438-1 are shared uniquely with humans. Compared to humans, A.L. 438-1 does have a more curved ulna, although A.L. 288-1 does not, and it appears to have had slightly less well-developed manipulatory capabilities of its hands, although still more derived than in apes. We conclude that selection for effective arboreality in the upper limb of Australopithecus Afarensis was weaker than in nonhominins, and that manipulative ability was of greater selective advantage than in extant great apes. 2005 Elsevier Ltd. All rights reserved.
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The Skull of Australopithecus Afarensis
2004Co-Authors: William H. Kimbel, Donald C. Johanson, Yoel Rak, Ralph L Holloway, Michael S YuanAbstract:The book is the most in-depth account of the fossil skull anatomy and evolutionary significance of the 3.6-3.0 million year old early human species Australopithecus Afarensis. Knowledge of this species is pivotal to understanding early human evolution, because 1) the sample of fossil remains of A. Afarensis is among the most extensive for any early human species, and the majority of remains are of taxonomically inormative skulls and teeth; 2) the wealth of material makes A. Afarensis an indispensable point of reference for the interpretation of other fossil discoveries; 3) the species occupies a time period that is the focus of current research to determine when, where, and why the human lineage first diversified into separate contemporaneous lines of descent. Upon publication of this book, this species will be among the most thoroughly documented extinct ancestors of humankind. The main focus of the book - its organizing principle - is the first complete skull of A. Afarensis (specimen number A.L. 444-2) at the Hadar site, Ethiopia, the home of the remarkably complete 3.18 million year old skeleton known as "Lucy," found at Hadar by third author D. Johanson in 1974. Lucy and other fossils from Hadar, together with those from the site of Laetoli in Tanzania, were controversially attributed to the then brand new species A. Afarensis by Johanson, T. White and Y. Coppens in 1978. However, a complete skull, which would have quickly resolved much of the early debate over the species, proved elusive until second author Y. Rak's discovery of the 444 skull in 1992. The book details the comparative anatomy of the new skull (and the cast of its brain, analyzed by R. Holloway and M. Huan) , as well as of other skull and dental finds recovered during the latest, ongoing field work at Hadar, and analyzes the evolutionary significance of A. Afarensis in the context of other critically important discoveries of earliest humans made in recent years. In essence, it summarizes the state of knowledge about one of the central subjects of current paleoanthropological investigation.
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the skull of Australopithecus Afarensis
2004Co-Authors: William H. Kimbel, Donald C. Johanson, Yoel Rak, Ralph L Holloway, Michael S YuanAbstract:1. Background to This Study 2. Recovery and Reconstruction of A.L.444-2 3. A.L. 444-2: The Reconstructed Skull as a Whole 4. Endocranial Morphology of A.L. 444-2 5. Elements of the Disarticulated Skull 6. Implications of A.L. 444-2 for the Taxonomic and Phylogenetic Status of Australopithecus Afarensis Notes References
Charles A. Lockwood - One of the best experts on this subject based on the ideXlab platform.
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Postnatal temporal bone ontogeny in Pan, Gorilla, and Homo, and the implications for temporal bone ontogeny in Australopithecus Afarensis
American Journal of Physical Anthropology, 2013Co-Authors: Claire E Terhune, William H. Kimbel, Charles A. LockwoodAbstract:Assessments of temporal bone morphology have played an important role in taxonomic and phylogenetic evaluations of fossil taxa, and recent three-dimensional analyses of this region have supported the utility of the temporal bone for testing taxonomic and phylogenetic hypotheses. But while clinical analyses have examined aspects of temporal bone ontogeny in humans, the ontogeny of the temporal bone in non-human taxa is less well documented. This study examines ontogenetic allometry of the temporal bone in order to address several research questions related to the pattern and trajectory of temporal bone shape change during ontogeny in the African apes and humans. We further apply these data to a preliminary analysis of temporal bone ontogeny in Australopithecus Afarensis. Three-dimensional landmarks were digitized on an ontogenetic series of specimens of Homo sapiens, Pan troglodytes, Pan paniscus, and Gorilla gorilla. Data were analyzed using geometric morphometric methods, and shape changes throughout ontogeny in relation to size were compared. Results of these analyses indicate that, despite broadly similar patterns, African apes and humans show marked differences in development of the mandibular fossa and tympanic portions of the temporal bone. These findings indicate divergent, rather than parallel, postnatal ontogenetic allometric trajectories for temporal bone shape in these taxa. The pattern of temporal bone shape change with size exhibited by A. Afarensis showed some affinities to that of humans, but was most similar to extant African apes, particularly Gorilla. Am J Phys Anthropol 151:630–642, 2013. © 2013 Wiley Periodicals, Inc.
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Temporal trends and metric variation in the mandibles and dentition of Australopithecus Afarensis
Journal of human evolution, 2000Co-Authors: Charles A. Lockwood, William H. Kimbel, Donald C. JohansonAbstract:The Pliocene hominin samples from Hadar and Laetoli are thought to represent one species, Australopithecus Afarensis, that exhibits stasis throughout its temporal range and has high levels of skeletal sexual dimorphism. In this paper, we test the hypothesis of stasis in dental and mandibular dimensions using nonparametric rank correlation methods to detect temporal trends and randomization tests to evaluate their statistical significance. We then use two methods (CV resampling; Fligner-Killeen test) to compare overall levels of variation in the fossil sample to those of extant hominoid species. Together, these analyses allow us to gauge the effects of changes through time on variation in mandibles and teeth of A. Afarensis.P(3)mesiodistal length, M(3)size, and canine shape change through time but do not appear unusually variable in the sample as a whole. These temporal trends possibly reflect differences between the Laetoli and Hadar site-samples. For mandibles, a pronounced trend towards greater corpus size occurs late in the temporal sequence and contributes to high levels of variation compared to African apes. These results show that significant directional changes do occur in the A. Afarensis mandibles and teeth, and in these elements, at least, the species is not static. Temporal variation is clearly an important component of overall variation in the A. Afarensis lineage, even though other factors, such as sexual dimorphism, may also play a part.
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Randomization procedures and sexual dimorphism in Australopithecus Afarensis
Journal of Human Evolution, 1996Co-Authors: Charles A. Lockwood, Brian G. Richmond, William L. Jungers, William H. KimbelAbstract:Etude du dimorphisme sexuel des Australopithecus Afarensis sur la base de procedures par randomisation a partir d'echantillons de mandibule, de proximal de femurs et d'humerus. Il apparait que Afarensis represente le plus ancien hominide pour lequel le dimorphisme sexuel peut etre examine en detail
Weijie Wang - One of the best experts on this subject based on the ideXlab platform.
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Stride lengths, speed and energy costs in walking of Australopithecus Afarensis: using evolutionary robotics to predict locomotion of early human ancestors
Journal of the Royal Society Interface, 2005Co-Authors: William I. Sellers, Weijie Wang, Gemma M Cain, Robin H. CromptonAbstract:This paper uses techniques from evolutionary robotics to predict the most energy-efficient upright walking gait for the early human relative Australopithecus Afarensis , based on the proportions of the 3.2 million year old AL 288-1 ‘Lucy’ skeleton, and matches predictions against the nearly contemporaneous (3.5–3.6 million year old) Laetoli fossil footprint trails. The technique creates gaits de novo and uses genetic algorithm optimization to search for the most efficient patterns of simulated muscular contraction at a variety of speeds. The model was first verified by predicting gaits for living human subjects, and comparing costs, stride lengths and speeds to experimentally determined values for the same subjects. Subsequent simulations for A. Afarensis yield estimates of the range of walking speeds from 0.6 to 1.3 m s −1 at a cost of 7.0 J kg −1 m −1 for the lowest speeds, falling to 5.8 J kg −1 m −1 at 1.0 m s −1 , and rising to 6.2 J kg −1 m −1 at the maximum speed achieved. Speeds previously estimated for the makers of the Laetoli footprint trails (0.56 or 0.64 m s −1 for Trail 1, 0.72 or 0.75 m s −1 for Trail 2/3) may have been underestimated, substantially so for Trail 2/3, with true values in excess of 0.7 and 1.0 m s −1 , respectively. The predictions conflict with suggestions that A. Afarensis used a ‘shuffling’ gait, indicating rather that the species was a fully competent biped.
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comparison of inverse dynamics musculo skeletal models of al 288 1 Australopithecus Afarensis and knm wt 15000 homo ergaster to modern humans with implications for the evolution of bipedalism
Journal of Human Evolution, 2004Co-Authors: Weijie Wang, Robin H. Crompton, Tanya S. Carey, Michael Günther, Russell Savage, Williams I. SellersAbstract:Size and proportions of the postcranial skeleton differ markedly between Australopithecus Afarensis and Homo ergaster, and between the latter and modern Homo sapiens. This study uses computer simulations of gait in models derived from the best-known skeletons of these species (AL 288-1, Australopithecus Afarensis, 3.18 million year ago) and KNM-WT 15000 (Homo ergaster, 1.5-1.8 million year ago) compared to models of adult human males and females, to estimate the required muscle power during bipedal walking, and to compare this with those in modern humans. Skeletal measurements were carried out on a cast of KNM-WT 15000, but for AL 288-1 were taken from the literature. Muscle attachments were applied to the models based on their position relative to the bone in modern humans. Joint motions and moments from experiments on human walking were input into the models to calculate muscle stress and power. The models were tested in erect walking and 'bent-hip bent-knee' gait. Calculated muscle forces were verified against EMG activity phases from experimental data, with reference to reasonable activation/force delays. Calculated muscle powers are reasonably comparable to experimentally derived metabolic values from the literature, given likely values for muscle efficiency. The results show that: 1) if evaluated by the power expenditure per unit of mass (W/kg) in walking, AL 288-1 and KNM-WT 15000 would need similar power to modern humans; however, 2) with distance-specific parameters as the criteria, AL 288-1 would require to expend relatively more muscle power (W/kg.m(-1)) in comparison to modern humans. The results imply that in the evolution of bipedalism, body proportions, for example those of KNM-WT 15000, may have evolved to obtain an effective application of muscle power to bipedal walking over a long distance, or at high speed.
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Comparison of inverse-dynamics musculo-skeletal models of AL 288-1 Australopithecus Afarensis and KNM-WT 15000 Homo ergaster to modern humans, with implications for the evolution of bipedalism.
Journal of human evolution, 2004Co-Authors: Weijie Wang, Robin H. Crompton, Tanya S. Carey, Michael Günther, Russell Savage, Williams I. SellersAbstract:Size and proportions of the postcranial skeleton differ markedly between Australopithecus Afarensis and Homo ergaster, and between the latter and modern Homo sapiens. This study uses computer simulations of gait in models derived from the best-known skeletons of these species (AL 288-1, Australopithecus Afarensis, 3.18 million year ago) and KNM-WT 15000 (Homo ergaster, 1.5-1.8 million year ago) compared to models of adult human males and females, to estimate the required muscle power during bipedal walking, and to compare this with those in modern humans. Skeletal measurements were carried out on a cast of KNM-WT 15000, but for AL 288-1 were taken from the literature. Muscle attachments were applied to the models based on their position relative to the bone in modern humans. Joint motions and moments from experiments on human walking were input into the models to calculate muscle stress and power. The models were tested in erect walking and ‘bent-hip bent-knee’ gait. Calculated muscle forces were verified against EMG activity phases from experimental data, with reference to reasonable activation/force delays. Calculated muscle
