Publications by authors named "Marc R Meyer"

11 Publications

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Is ulna curvature in the StW 573 ('Little Foot') Australopithecus natural or pathological?

J Hum Evol 2021 Feb 25;151:102927. Epub 2020 Dec 25.

Center for the Study of Human Origins, Department of Anthropology, New York University, 25 Waverly Place, New York, NY, 10003, USA; New York Consortium in Evolutionary Primatology, New York, NY, 10024, USA.

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http://dx.doi.org/10.1016/j.jhevol.2020.102927DOI Listing
February 2021

Late subadult ontogeny and adult aging of the human thorax reveals divergent growth trajectories between sexes.

Sci Rep 2020 07 1;10(1):10737. Epub 2020 Jul 1.

CNRS, MCC, PACEA, UMR5199, University of Bordeaux, Allée Geoffroy Saint Hilaire Bat. B8, CS 50023, 33615, Pessac Cedex, France.

Sexual dimorphism is an important feature of adult thorax morphology, but when and how sex-related differences in the ribcage arise during ontogeny is poorly known. Previous research proposed that sex-related size differences in the nasal region arise during puberty. Therefore, we explore whether ribcage sexual dimorphism also arises at that time and whether this sexual dimorphism is maintained until old age. We measured 526 (semi)landmarks on 80 CT-based human ribcage reconstructions, on individuals ranging from 7 to 65 year-old. The 3D coordinates were submitted to the Procrustes superimposition and analyzed. Our results show that the trajectories of thorax size and shape between sexes diverge at around 12 years of age, and continue slightly diverging until old age. The differential ontogenetic trends cause adult male ribcages to become deeper, shorter, and wider than female. Our results are consistent with the evidence from the cranial respiratory system, with the development of sexual dimorphism probably related to changes in body composition during puberty combined with changes in the reproductive system.
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http://dx.doi.org/10.1038/s41598-020-67664-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7329879PMC
July 2020

Earliest axial fossils from the genus Australopithecus.

J Hum Evol 2019 07 30;132:189-214. Epub 2019 May 30.

Center for the Study of Human Origins, Department of Anthropology, New York University, 25 Waverly Place, New York, NY, 10003, USA; New York Consortium in Evolutionary Primatology, New York, NY, 10024, USA.

Australopitheus anamensis fossils demonstrate that craniodentally and postcranially the taxon was more primitive than its evolutionary successor Australopithecus afarensis. Postcranial evidence suggests habitual bipedality combined with primitive upper limbs and an inferred significant arboreal adaptation. Here we report on A. anamensis fossils from the Assa Issie locality in Ethiopia's Middle Awash area dated to ∼4.2 Ma, constituting the oldest known Australopithecus axial remains. Because the spine is the interface between major body segments, these fossils can be informative on the adaptation, behavior and our evolutionary understanding of A. anamensis. The atlas, or first cervical vertebra (C1), is similar in size to Homo sapiens, with synapomorphies in the articular facets and transverse processes. Absence of a retroglenoid tubercle suggests that, like humans, A. anamensis lacked the atlantoclavicularis muscle, resulting in reduced capacity for climbing relative to the great apes. The retroflexed C2 odontoid process and long C6 spinous process are reciprocates of facial prognathism, a long clivus and retroflexed foramen magnum, rather than indications of locomotor or postural behaviors. The T1 is derived in shape and size as in Homo with an enlarged vertebral body epiphyseal surfaces for mitigating the high-magnitude compressive loads of full-time bipedality. The full costal facet is unlike the extant great ape demifacet pattern and represents the oldest evidence for the derived univertebral pattern in hominins. These fossils augment other lines of evidence in A. anamensis indicating habitual bipedality despite some plesiomorphic vertebral traits related to craniofacial morphology independent of locomotor or postural behaviors (i.e., a long clivus and a retroflexed foramen magnum). Yet in contrast to craniodental lines of evidence, some aspects of vertebral morphology in A. anamensis appear more derived than its descendant A. afarensis.
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http://dx.doi.org/10.1016/j.jhevol.2019.05.004DOI Listing
July 2019

Neck function in early hominins and suspensory primates: Insights from the uncinate process.

Am J Phys Anthropol 2018 07 28;166(3):613-637. Epub 2018 Feb 28.

Paleoanthropology Group, Museo Nacional de Ciencias Naturales (MNCN-CSIC), Madrid 28006, Spain.

Objectives: Uncinate processes are protuberances on the cranial surface of subaxial cervical vertebrae that assist in stabilizing and guiding spinal motion. Shallow uncinate processes reduce cervical stability but confer an increased range of motion in clinical studies. Here we assess uncinate processes among extant primates and model cervical kinematics in early fossil hominins.

Materials And Methods: We compare six fossil hominin vertebrae with 48 Homo sapiens and 99 nonhuman primates across 20 genera. We quantify uncinate morphology via geometric morphometric methods to understand how uncinate process shape relates to allometry, taxonomy, and mode of locomotion.

Results: Across primates, allometry explains roughly 50% of shape variation, as small, narrow vertebrae feature the relatively tallest, most pronounced uncinate processes, whereas larger, wider vertebrae typically feature reduced uncinates. Taxonomy only weakly explains the residual variation, however, the association between Uncinate Shape and mode of locomotion is robust, as bipeds and suspensory primates occupy opposite extremes of the morphological continuum and are distinguished from arboreal generalists. Like humans, Australopithecus afarensis and Homo erectus exhibit shallow uncinate processes, whereas A. sediba resembles more arboreal taxa, but not fully suspensory primates.

Discussion: Suspensory primates exhibit the most pronounced uncinates, likely to maintain visual field stabilization. East African hominins exhibit reduced uncinate processes compared with African apes and A. sediba, likely signaling different degrees of neck motility and modes of locomotion. Although soft tissues constrain neck flexibility beyond limits suggested by osteology alone, this study may assist in modeling cervical kinematics and positional behaviors in extinct taxa.
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http://dx.doi.org/10.1002/ajpa.23448DOI Listing
July 2018

New fossil remains of from the Lesedi Chamber, South Africa.

Elife 2017 05 9;6. Epub 2017 May 9.

Evolutionary Studies Institute, University of the Witwatersrand, Wits, South Africa.

The Rising Star cave system has produced abundant fossil hominin remains within the Dinaledi Chamber, representing a minimum of 15 individuals attributed to . Further exploration led to the discovery of hominin material, now comprising 131 hominin specimens, within a second chamber, the Lesedi Chamber. The Lesedi Chamber is far separated from the Dinaledi Chamber within the Rising Star cave system, and represents a second depositional context for hominin remains. In each of three collection areas within the Lesedi Chamber, diagnostic skeletal material allows a clear attribution to . Both adult and immature material is present. The hominin remains represent at least three individuals based upon duplication of elements, but more individuals are likely present based upon the spatial context. The most significant specimen is the near-complete cranium of a large individual, designated LES1, with an endocranial volume of approximately 610 ml and associated postcranial remains. The Lesedi Chamber skeletal sample extends our knowledge of the morphology and variation of , and evidence of from both recovery localities shows a consistent pattern of differentiation from other hominin species.
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http://dx.doi.org/10.7554/eLife.24232DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5423776PMC
May 2017

The cervical spine of Australopithecus sediba.

J Hum Evol 2017 03 9;104:32-49. Epub 2017 Feb 9.

Evolutionary Studies Institute, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa.

Cervical vertebrae are rare in the early hominin fossil record, presenting a challenge for understanding the evolution of the neck and head carriage in hominin evolution. Here, we examine the cervical vertebrae of Australopithecus sediba, which unlike other South African taxa is known from associated cervical vertebrae. The A. sediba cervical vertebrae exhibit human-like values for wedging, pedicle cross-sectional areas, and articular facet heights, indicating reduced ventral loading relative to African apes. These features combine with a pattern of vertebral body bone distribution and caudally progressive size expansion suggesting a mode of cervical lordosis, load mitigation, and head carriage similar to humans and distinct from the cantilevered mode of head carriage of the extant African great apes. Yet these derived features in A. sediba are accompanied by ape-like vertebral body and dorsal pillar sizes, articular facet orientation, and uncinate process morphology signaling reduced lateral and rotational coupled movements between vertebral elements and indicate a considerably stiffer neck than in humans. A primitively long and horizontally-oriented C7 spinous process is likely related to a prognathic viscerocranium, although the complimentary C3 spinous process is short, implying large moments emanating from scapular and shoulder elevators rather than large muscles of head stabilization. Cross-sectional spinous process shape and robust anterior tubercles similarly signal increased arm elevation consistent with climbing behavior in corroboration with arboreal signatures previously observed in the shoulder, arms, and hand of A. sediba. Spinal canal shape and size suggests that A. sediba lacked the cervical spinal cord enlargement of Homo that confers humans with enhanced motor control to the upper limbs. The cervical spine of A. sediba thus presents a mosaic of primitive and derived characters, with anatomical features relating to neck posture and head carriage mirroring humans juxtaposed with most other aspects of functional anatomy that resemble chimpanzees.
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http://dx.doi.org/10.1016/j.jhevol.2017.01.001DOI Listing
March 2017

The vertebrae and ribs of Homo naledi.

J Hum Evol 2017 03 13;104:136-154. Epub 2017 Jan 13.

Evolutionary Studies Institute and Centre for Excellence in PalaeoSciences, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa.

Hominin evolution featured shifts from a trunk shape suitable for climbing and housing a large gut to a trunk adapted to bipedalism and higher quality diets. Our knowledge regarding the tempo, mode, and context in which these derived traits evolved has been limited, based largely on a small-bodied Australopithecus partial skeleton (A.L. 288-1; "Lucy") and a juvenile Homo erectus skeleton (KNM-WT 15000; "Turkana Boy"). Two recent discoveries, of a large-bodied Australopithecus afarensis (KSD-VP-1/1) and two Australopithecus sediba partial skeletons (MH1 and MH2), have added to our understanding of thorax evolution; however, little is known about thorax morphology in early Homo. Here we describe hominin vertebrae, ribs, and sternal remains from the Dinaledi chamber of the Rising Star cave system attributed to Homo naledi. Although the remains are highly fragmented, the best-preserved specimens-two lower thoracic vertebrae and a lower rib-were found in association and belong to a small-bodied individual. A second lower rib may belong to this individual as well. All four of these individual elements are amongst the smallest known in the hominin fossil record. H. naledi is characterized by robust, relatively uncurved lower ribs and a relatively large spinal canal. We expect that the recovery of additional material from Rising Star Cave will clarify the nature of these traits and shed light on H. naledi functional morphology and phylogeny.
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http://dx.doi.org/10.1016/j.jhevol.2016.11.003DOI Listing
March 2017

Spinal cord evolution in early Homo.

J Hum Evol 2015 Nov 22;88:43-53. Epub 2015 Oct 22.

Institute of Evolutionary Medicine, Universität Zürich, 8057 Zürich, Switzerland; Institute of Anatomy, Universität Zürich, 8057 Zürich, Switzerland.

The discovery at Nariokotome of the Homo erectus skeleton KNM-WT 15000, with a narrow spinal canal, seemed to show that this relatively large-brained hominin retained the primitive spinal cord size of African apes and that brain size expansion preceded postcranial neurological evolution. Here we compare the size and shape of the KNM-WT 15000 spinal canal with modern and fossil taxa including H. erectus from Dmanisi, Homo antecessor, the European middle Pleistocene hominins from Sima de los Huesos, and Pan troglodytes. In terms of shape and absolute and relative size of the spinal canal, we find all of the Dmanisi and most of the vertebrae of KNM-WT 15000 are within the human range of variation except for the C7, T2, and T3 of KNM-WT 15000, which are constricted, suggesting spinal stenosis. While additional fossils might definitively indicate whether H. erectus had evolved a human-like enlarged spinal canal, the evidence from the Dmanisi spinal canal and the unaffected levels of KNM-WT 15000 show that unlike Australopithecus, H. erectus had a spinal canal size and shape equivalent to that of modern humans. Subadult status is unlikely to affect our results, as spinal canal growth is complete in both individuals. We contest the notion that vertebrae yield information about respiratory control or language evolution, but suggest that, like H. antecessor and European middle Pleistocene hominins from Sima de los Huesos, early Homo possessed a postcranial neurological endowment roughly commensurate to modern humans, with implications for neurological, structural, and vascular improvements over Pan and Australopithecus.
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http://dx.doi.org/10.1016/j.jhevol.2015.09.001DOI Listing
November 2015

Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa.

Elife 2015 Sep 10;4. Epub 2015 Sep 10.

Evolutionary Studies Institute and Centre of Excellence in PalaeoSciences, University of the Witwatersrand, Johannesburg, South Africa.

Homo naledi is a previously-unknown species of extinct hominin discovered within the Dinaledi Chamber of the Rising Star cave system, Cradle of Humankind, South Africa. This species is characterized by body mass and stature similar to small-bodied human populations but a small endocranial volume similar to australopiths. Cranial morphology of H. naledi is unique, but most similar to early Homo species including Homo erectus, Homo habilis or Homo rudolfensis. While primitive, the dentition is generally small and simple in occlusal morphology. H. naledi has humanlike manipulatory adaptations of the hand and wrist. It also exhibits a humanlike foot and lower limb. These humanlike aspects are contrasted in the postcrania with a more primitive or australopith-like trunk, shoulder, pelvis and proximal femur. Representing at least 15 individuals with most skeletal elements repeated multiple times, this is the largest assemblage of a single species of hominins yet discovered in Africa.
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http://dx.doi.org/10.7554/eLife.09560DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4559886PMC
September 2015

Lucy's back: Reassessment of fossils associated with the A.L. 288-1 vertebral column.

J Hum Evol 2015 Aug 6;85:174-80. Epub 2015 Jun 6.

Division of Anthropology, American Museum of Natural History, New York, NY 10024, USA.

The Australopithecus afarensis partial skeleton A.L. 288-1, popularly known as "Lucy" is associated with nine vertebrae. The vertebrae were given provisional level assignments to locations within the vertebral column by their discoverers and later workers. The continuity of the thoracic series differs in these assessments, which has implications for functional interpretations and comparative studies with other fossil hominins. Johanson and colleagues described one vertebral element (A.L. 288-1am) as uniquely worn amongst the A.L. 288-1 fossil assemblage, a condition unobservable on casts of the fossils. Here, we reassess the species attribution and serial position of this vertebral fragment and other vertebrae in the A.L. 288-1 series. When compared to the other vertebrae, A.L. 288-1am falls well below the expected size within a given spinal column. Furthermore, we demonstrate this vertebra exhibits non-metric characters absent in hominoids but common in large-bodied papionins. Quantitative analyses situate this vertebra within the genus Theropithecus, which today is solely represented by the gelada baboon but was the most abundant cercopithecoid in the KH-1s deposit at Hadar where Lucy was discovered. Our additional analyses confirm that the remainder of the A.L. 288-1 vertebral material belongs to A. afarensis, and we provide new level assignments for some of the other vertebrae, resulting in a continuous articular series of thoracic vertebrae, from T6 to T11. This work does not refute previous work on Lucy or its importance for human evolution, but rather highlights the importance of studying original fossils, as well as the efficacy of the scientific method.
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http://dx.doi.org/10.1016/j.jhevol.2015.05.007DOI Listing
August 2015

The mismeasure of science: Stephen Jay Gould versus Samuel George Morton on skulls and bias.

PLoS Biol 2011 Jun 7;9(6):e1001071. Epub 2011 Jun 7.

Department of Anthropology, Stanford University, Stanford, California, United States of America.

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http://dx.doi.org/10.1371/journal.pbio.1001071DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3110184PMC
June 2011