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1. A three‐dimensional musculoskeletal model of the pelvis and lower limb of Australopithecus afarensis

   https://doi.org/10.1002/ajpa.24845  

   O'Neill, Matthew C. ; Nagano, Akinori ; Umberger, Brian R. ( September 2023 , American Journal of Biological Anthropology)

   Musculoskeletal modeling is a powerful approach for studying the biomechanics and energetics of locomotion.Australopithecus (A.) afarensisis among the best represented fossil hominins and provides critical information about the evolution of musculoskeletal design and locomotion in the hominin lineage. Here, we develop and evaluate a three‐dimensional (3‐D) musculoskeletal model of the pelvis and lower limb ofA. afarensisfor predicting muscle‐tendon moment arms and moment‐generating capacities across lower limb joint positions encompassing a range of locomotor behaviors.

   A 3‐D musculoskeletal model of an adultA. afarensispelvis and lower limb was developed based primarily on the A.L. 288‐1 partial skeleton. The model includes geometric representations of bones, joints and 35 muscle‐tendon units represented using 43 Hill‐type muscle models. Two muscle parameter datasets were created from human and chimpanzee sources. 3‐D muscle‐tendon moment arms and isometric joint moments were predicted over a wide range of joint positions.

   Predicted muscle‐tendon moment arms generally agreed with skeletal metrics, and corresponded with human and chimpanzee models. Human and chimpanzee‐based muscle parameterizations were similar, with some differences in maximum isometric force‐producing capabilities. The model is amenable to size scaling from A.L. 288‐1 to the larger KSD‐VP‐1/1, which subsumes a wide range of size variation inA. afarensis.

   This model represents an important tool for studying the integrated function of the neuromusculoskeletal systems inA. afarensis. It is similar to current human and chimpanzee models in musculoskeletal detail, and will permit direct, comparative 3‐D simulation studies.

    

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2. Relative tooth size, Bayesian inference, and Homo naledi

   https://doi.org/10.1002/ajpa.24353  

   Irish, Joel D. ; Grabowski, Mark ( June 2021 , American Journal of Physical Anthropology)

   Size‐corrected tooth crown measurements were used to estimate phenetic affinities amongHomo naledi(~335–236 ka) and 11 other Plio‐Pleistocene and recent species. To assess further their efficacy, and identify dental evolutionary trends, the data were then quantitatively coded for phylogenetic analyses. Results from both methods contribute additional characterization ofH. naledirelative to other hominins.

   After division by their geometric mean, scaled mesiodistal and buccolingual dimensions were used in tooth size apportionment analysis to compareH. nalediwithAustralopithecus africanus,A. afarensis,Paranthropus robustus,P. boisei,H. habilis,H. ergaster,H. erectus,H. heidelbergensis,H. neanderthalensis,H. sapiens, andPan troglodytes. These data produce equivalently scaled samples unaffected by interspecific size differences. The data were then gap‐weighted for Bayesian inference.

   Congruence in interspecific relationships is evident between methods, and with many inferred from earlier systematic studies. However, the present results placeH. naledias a sister taxon toH. habilis,based on a symplesiomorphic pattern of relative tooth size. In the preferred Bayesian phylogram,H. nalediis nested within a clade comprising allHomospecies, but it shares some characteristics with australopiths and, particularly, earlyHomo.

   Phylogenetic analyses of relative tooth size yield information about evolutionary dental trends not previously reported inH. nalediand the other hominins. Moreover, with an appropriate model these data recovered plausible evolutionary relationships. Together, the findings support recent study suggestingH. naledioriginated long before the geological date of the Dinaledi Chamber, from which the specimens under study were recovered.

    

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3. Myological reconstruction of the pelvic girdle and hind limb of the giant titanosaurian sauropod dinosaur Dreadnoughtus schrani

   https://doi.org/10.1111/joa.13334  

   Voegele, Kristyn K. ; Ullmann, Paul V. ; Lamanna, Matthew C. ; Lacovara, Kenneth J. ( October 2020 , Journal of Anatomy)

   Osteological correlates preserve more readily than their soft tissue counterparts in the fossil record; therefore, they can more often provide insight into the soft tissue anatomy of the organism. These insights can in turn elucidate the biology of these extinct organisms. In this study, we reconstruct the pelvic girdle and hind limb musculature of the giant titanosaurian sauropodDreadnoughtus schranibased on observations of osteological correlates and Extant Phylogenetic Bracket comparisons. Recovered fossils ofDreadnoughtusexhibit remarkably well‐preserved, well‐developed, and extensive muscle scars. Furthermore, this taxon is significantly larger bodied than any titanosaurian for which a myological reconstruction has previously been performed, rendering this contribution highly informative for the group. All 20 of the muscles investigated in this study are sufficiently well supported to enable reconstruction of at least one division, including reconstruction of the M. ischiocaudalis for the first time in a sauropod dinosaur. In total, 34 osteological correlates were identified on the pelvic girdle and hind limb remains ofDreadnoughtus, allowing the reconstruction of 14 muscles on the basis of Level I or Level II inferences (i.e., not Level I' or Level II' inferences). Comparisons among titanosaurians suggest widespread myological variation, yet potential phylogenetic and other paleobiologic patterns are often obscured by fragmentary preservation, infrequent myological studies, and lack of consensus on the phylogenetic placement of many taxa. However, a ventrolateral accessory process is present on the preacetabular lobe of the ilium in all of the largest titanosauriforms that preserve this skeletal element, suggesting that the presence of this process (representing the origin of the M. puboischiofemoralis internus part II) may be associated with extreme body size. By identifying such myological patterns among titanosauriforms, we can begin to address specific evolutionary and biomechanical questions related to their skeletal anatomy, how they were capable of leaving wide‐gauge trackways, and resulting locomotor attributes unique to this clade.

    

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4. A Geometric Morphometric Examination of Hominoid Third Metacarpal Shape and Its Implications for Inferring the Precursor to Terrestrial Bipedalism

   https://doi.org/10.1002/ar.23985  

   Rein, Thomas R. ( November 2018 , The Anatomical Record)

   The third metacarpal has been a focus of study when examining questions surrounding early hominin locomotion since this bone is adapted to the diverse range of positional behaviors performed by extant hominoids. The shape of this bone is potentially under strong selective pressure related to the biomechanical demands of terrestrial knuckle‐walking, arboreal clambering, and brachiation performed by extant hominoids since the hand directly interacts with the substrate during the performance of these movements. The objective of the present study was to explore shape variation of the third metacarpal and examine how different parts of the bone discriminated between hominoid genera that perform these different locomotor behaviors. In addition to examining general interspecies variation, shape analysis was applied to testing the knuckle‐walking hypothesis for human evolution. Fourteen 3D landmark coordinates were collected on hominoid third metacarpals, and principal component analysis and Procrustes distances were used to examine metacarpal shape. Comparable measurements were collected on fossilized third metacarpals ofAustralopithecus afarensisas an early hominin test case for examining the knuckle‐walking hypothesis. Analyses that included landmarks collected on both ends of the bone distinguished humans from great apes and presented a strong functional signal related to suspensory locomotion among nonhuman hominoids, whereas the distal articular surface provided the strongest knuckle‐walking signal. The shapes ofAustralopithecus afarensismetacarpals examined in the current study did not provide evidence for a trajectory of shape change in early hominin evolution that started from a metacarpal adapted for terrestrial knuckle‐walking. Anat Rec, 302:983–998, 2019. © 2018 Wiley Periodicals, Inc.

    

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5. Hundreds of Colobus (Cercopithecidae: Primates) fossils from the later Pleistocene of Ethiopia's Middle Awash study area

   https://doi.org/10.1002/ajpa.24639  

   Brasil, Marianne F. ; Monson, Tesla A. ; Taylor, Catherine E. ; Yohler, Ryan M. ; Hlusko, Leslea J. ( November 2022 , American Journal of Biological Anthropology)

   The aim of this study is to introduce and systematically assess a new assemblage of colobine fossils (n = 360) recovered from Late Pleistocene (ca. 100,000 years ago) sediments in the Middle Awash research area, Afar Rift, Ethiopia.

   We describe the colobine fossils relative to extant colobine taxa and Middle Pleistocene fossil samples from “Andalee” and Asbole, Ethiopia using linear dental, cranial, and postcranial metrics, as well as qualitative features. We also document the ontogenetic and sex profiles of this sample.

   Based on morphological affinities to extant and fossilColobus, we refer these 360 individuals toColobuscf.guereza. The majority of the individuals (76%) fall into young‐ and middle‐adult age categories. Females are slightly better represented than males, although the majority of individuals (84%) could not be assigned to sex.

   Details of the last half million years ofColobusmorphological evolution have remained obscured by a sparse fossil record. The newly recovered, prepared, and curated fossils described herein add significantly to the record of this group. Several morphologies seen in these new fossils fall between the AsboleColobussample and extantColobus guereza, suggesting an ancestral‐descendant phyletic relationship among the three time‐successive samples. The populational variation documented among these samples indicates that the distinctive pattern of sexual dimorphism observed inC. guerezahad evolved by 100 ka.

    

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