Marc Meyer | Chaffey College (original) (raw)

Papers by Marc Meyer

Journal of Human Evolution, 2023

Because the ulna supports and transmits forces during movement, its morphology can signal aspects... more Because the ulna supports and transmits forces during movement, its morphology can signal aspects of functional adaptation. To test whether, like extant apes, some hominins habitually recruit the forelimb in locomotion, we separate the ulna shaft and ulna proximal complex for independent shape analyses via elliptical Fourier methods to identify functional signals. We examine the relative influence of locomotion, taxonomy, and body mass on ulna contours in Homo sapiens (n ¼ 22), five species of extant apes (n ¼ 33), two Miocene apes (Hispanopithecus and Danuvius), and 17 fossil hominin specimens including Sahelanthropus, Ardipithecus, Australopithecus, Paranthropus, and early Homo. Ulna proximal complex contours correlate with body mass but not locomotor patterns, while ulna shafts significantly correlate with locomotion. African apes' ulna shafts are more robust and curved than Asian apes and are unlike other terrestrial mammals (including other primates), curving ventrally rather than dorsally. Because this distinctive curvature is absent in orangutans and hylobatids, it is likely a function of powerful flexors engaged in wrist and hand stabilization during knuckle-walking, and not an adaptation to climbing or suspensory behavior. The OH 36 (purported Paranthropus boisei) and TM 266 (assigned to Sahelanthropus tchadensis) fossils differ from other hominins by falling within the knuckle-walking morphospace, and thus appear to show forelimb morphology consistent with terrestrial locomotion. Discriminant function analysis classifies both OH 36 and TM 266 with Pan and Gorilla with high posterior probability. Along with its associated femur, the TM 266 ulna shaft contours and its deep, keeled trochlear notch comprise a suite of traits signaling African ape-like quadrupedalism. While implications for the phylogenetic position and hominin status of S. tchadensis remain equivocal, this study supports the growing body of evidence indicating that S. tchadensis was not an obligate biped, but instead represents a late Miocene hominid with knuckle-walking adaptations.

OSFPreprints, 2023

In their recent article, "The atlas of StW 573 and the late emergence of human-like head mobility... more In their recent article, "The atlas of StW 573 and the late emergence of human-like head mobility and brain metabolism" Beaudet and colleagues (Scientific Reports, March 2020) contend that StW 573 had lower metabolic costs for cerebral tissues and that blood perfusion of these tissues increased recently over the course of hominin evolution. This conclusion is in large part based on the assumption of a correlation between the size of the fossil vertebra's transverse foramen and arterial canal diameters, and by extension, they use the foramen's cross-sectional area in conjunction with the size of the cranium's carotid canal to reconstruct blood flow volume to the brain as a proxy of the brain's metabolic demands. As I show here, these assumptions are unsupported because the C1 cervical vertebra cannot help indicate hemodynamics or investment in brain metabolism.

eLS, 2016

Spinal cord dimensions increased in both relative and absolute terms during the course of hominin... more Spinal cord dimensions increased in both relative and absolute terms during the course of hominin evolution. Recent discoveries demonstrate the presence of a fully developed human-sized cervical spinal cord in Australopithecus afarensis at 3.6 million years before present (Ma) and in the cervical and thoracic regions of Homo erectus at 1.8 Ma. The fossil evidence suggests that these hominins possessed a fully human-like postcranial neurological substrate for precision coordination of the arm and hand, corroborated by corresponding skeletal anatomy of the hand and shoulder, as well as discoveries of penecontemporaneous lithic use and putative throwing manuports in the archaeological record. These new fossils provide insight into the neurobiological underpinnings of sophisticated manual behaviours, and overturn prior thinking on the evolution of the central nervous system in the human lineage, indicating that the evolution of the hominin spinal cord was completed well in advance of advances in brain size. Key Concepts The brain and spinal cord are both larger in humans than those of the African great apes. New Australopithecus afarensis fossils from Woranso-Mille, Ethiopia, demonstrate that hominin cervical spinal cord enlargement was completed by at least 3.6 million years ago. Evidence from Homo erectus now shows that hominin thoracic spinal cord enlargement was completed by at least 1.8 million years ago. These new discoveries reveal the neurological capability for fine-motor coordination of the arm, hand, and thoracic muscles in our smaller brained ancestors. It is now apparent that spinal cord expansion was completed prior to brain size expansion in the human lineage. Keywords: spinal cord; human evolution; brachial plexus; Australopithecus; Homo erectus

Vertebrate Paleobiology and Paleoanthropology, 2015

A series of six partial cervical vertebrae were recovered in association with the KSD-VP-1/1 post... more A series of six partial cervical vertebrae were recovered in association with the KSD-VP-1/1 postcranial remains from the C2 axis to the C7 vertebral level, representing the oldest adult cervical column known in the hominin fossil record. The vertebrae of this large male australopith are more derived than those of its smaller female counterparts, and as a whole, present a biomechanical and enthesopathological signature typical of the dynamic vertical loading regime of orthograde humans. Differences between KSD-VP-1/1 and humans observed in the most cranial cervical levels appear to have insignificant functional implications, and are likely developmental reciprocates of australopith cranial morphogenesis. Despite their antiquity, the KSD-VP-1/1 vertebrae produce a surprisingly human-like kinematic signal, with a highly mobile neck, a head carriage consistent with habitual upright posture and bipedalism, and spinal cord dimensions most similar to that of modern humans.

Journal of human evolution, 2015

The discovery at Nariokotome of the Homo erectus skeleton KNM-WT 15000, with a narrow spinal cana... more 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-...

Journal of Cerebral Blood Flow & Metabolism, 2009

Although crucial in regulating intracranial hydrodynamics, the cerebral venous system has been ra... more Although crucial in regulating intracranial hydrodynamics, the cerebral venous system has been rarely studied because of its structural complexity and individual variations. The purpose of our study was to evaluate the organization of cerebral venous system in healthy adults. Phase-contrast magnetic resonance imaging (PC-MRI) was performed in 18 healthy volunteers, in the supine position. Venous, arterial, and cerebrospinal fluid (CSF) flows were calculated. We found heterogeneous individual venous flows and variable side dominance in paired veins and sinuses. In some participants, the accessory epidural drainage preponderated over the habitually dominant jugular outflow. The PC-MRI enabled measurements of venous flows in superior sagittal (SSS), SRS (straight), and TS (transverse) sinuses with excellent detection rates. Pulsatility index for both intracranial (SSS) and cervical (mainly jugular) levels showed a significant increase in pulsatile blood flow in jugular veins as compared with that in SSS. Mean cervical and cerebral arterial blood flows were 714 ± 124 and 649 ± 178 mL/min, respectively. Cerebrospinal fluid aqueductal and cervical stroke volumes were 41±22 and 460±149 lL, respectively. Our results emphasize the variability of venous drainage for side dominance and jugular/epidural organization. The pulsatility of venous outflow and the role it plays in the regulation of intracranial pressure require further investigation.

Paleoanthropology, 2016

Homo naledi is a previously unknown species of extinct hominin discovered within the Dinaledi Cha... more Homo naledi is a previously unknown species of extinct hominin discovered within the Dinaledi Chamber of the Rising Star cave system, Gauteng, South Africa. This species is characterized by body mass and stature similar to small-bodied human populations, with a small endocranial volume similar to australopiths. Cranial morphology of H. naledi is unique, but most similar to early Homo species including H. erectus, H. habilis, or H. 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 leg and foot. These humanlike aspects are contrasted in the postcrania with a more primitive or australopith-like trunk, shoulder, fingers, pelvis, and proximal femur. Nonetheless, the shared derived features that connect H. naledi with other members of Homo occupy most regions of the H. naledi skeleton and represent distinct functional systems, including locom...

American Journal of Biological Anthropology

PNAS Nexus, 2022

Lumbar lordosis is a key adaptation to bipedal locomotion in the human lineage. Dorsoventral spin... more Lumbar lordosis is a key adaptation to bipedal locomotion in the human lineage. Dorsoventral spinal curvatures enable the body's center of mass to be positioned above the hip, knee, and ankle joints, and minimize the muscular effort required for postural control and locomotion. Previous studies have suggested that Neandertals had less lordotic (ventrally convex) lumbar columns than modern humans, which contributed to historical perceptions of postural and locomotor differences between the two groups. Quantifying lower back curvature in extinct hominins is entirely reliant upon bony correlates of overall lordosis, since the latter is significantly influenced by soft tissue structures (e.g. intervertebral discs). Here, we investigate sexual dimorphism, ancestry, and lifestyle effects on lumbar vertebral body wedging and inferior articular facet angulation, two features previously shown to be significantly correlated with overall lordosis in living individuals, in a large sample of...

These data were taken on a global sample of skulls from the Samuel George Morton Cranial Collecti... more These data were taken on a global sample of skulls from the Samuel George Morton Cranial Collection dated to the middle 19th century. We report craniofacial measurements from individuals belonging to 97 geographic and ethnic populations. We also report age, sex, craniofacial measurements, provenience, elevation and climatic information for each specimen. In addition to endocranial volumes, 23 linear measurements for each cranium are reported, as well as indices for several features (i.e., cranial, orbital, nasal). Age at death and the sex of each specimen are also reported. Climate data for each skull's place of origin comprise a suite of 13 surface variables taken between 1901-1990. These data may be useful in the study of brain size, sexual dimorphism, human variation, and human adaptation.

Differences in thorax shape between humans and the great apes are well documented, with the narro... more Differences in thorax shape between humans and the great apes are well documented, with the narrow upper thorax and wide lower thorax of apes contrasting with the opposite pattern in fossil Homo and extant humans. Interestingly, current reconstructions of thoraces in small-bodied hominins, such as the Australopithecus afarensis A.L. 288-1, may feature a smaller, more apelike pulmonary thorax (upper thorax), while its larger-bodied conspecific KSD-VP-1/1 is suggested to be more human with a relatively expanded upper thorax. Toward understanding this dichotomy, we examine the relationship between body size and thorax shape, and model trajectories of the upper limb relative to differently shaped thoraces. We show that variation in thorax shapes facilitate or constrain certain locomotor patterns, as a small upper with an expanded lower thorax facilitates knuckle-walking, orienting the upper limb close to the sagittal midline and center of gravity during locomotion, and confers efficient scapular movement around the ribcage. Conversely, an expanded upper and small lower thorax better facilitates bipedality, facilitating more efficient arm swing and energy return from upper limb momentum, while lower thoracic expansion constrains arm swing in bipedal locomotion. Since lung volume and body mass scale isometrically, increases in lung capacity (and concomitant expansion of the thorax) would be best apportioned to the lower thorax in knuckle-walkers. By contrast, increases in lung capacity and thorax expansion in bipeds are best apportioned superiorly. Thus, locomotor constraints, in concert with the isometric relationship between body size and lung size, may explain thoracic shape variation in early hominins.

tionary biologist and science historian, argued that ‘‘unconscious manipulation of data may be a ... more tionary biologist and science historian, argued that ‘‘unconscious manipulation of data may be a scientific norm’ ’ because ‘‘scientists are human beings rooted in cultural contexts, not automatons directed toward external truth’’ [1], a view now popular in social studies of science [2–4]. In support of his argument Gould presented the case of Samuel George Morton, a 19th-century physician and phys-ical anthropologist famous for his measure-ments of human skulls. Morton was consid-ered the objectivist of his era, but Gould reanalyzed Morton’s data and in his prize-winning book The Mismeasure of Man [5] argued that Morton skewed his data to fit his preconceptions about human variation.Mor-ton is now viewed as a canonical example of scientific misconduct. But did Morton really fudge his data? Are studies of human variation inevitably biased, as per Gould, or are objective accounts attainable, as Morton attempted? We investigated these questions by remeasuring Morton’s skulls and reexa...

Spinal Evolution, 2019

In this chapter, we summarize vertebral remains from early Pleistocene Homo, including H. erectus... more In this chapter, we summarize vertebral remains from early Pleistocene Homo, including H. erectus, as well as H. naledi and H. floresiensis fossils from the Middle and Late Pleistocene, respectively. Two partial immature H. erectus skeletons where vertebrae are well represented are KNM-WT 15000 (“Turkana boy”) and the D2700 individual from Dmanisi. Vertebrae from H. naledi are also considered here, including those from the LES1 partial skeleton (“Neo”), despite their younger date to the Middle Pleistocene. We review the fossil record of presacral vertebrae in early Homo, and summarize work on the functional morphology, metameric patterning, and postcranial neuroanatomy of early Homo, comparing and contrasting the presacral spine with their putative australopith forbears and extant apes and humans. Based on the current evidence, the vertebral column of H. erectus possessed a modal number of twelve thoracic and five lumbar segments, as is the case in australopiths, as well as modern humans. The spine of H. erectus reveals key changes relative to earlier hominins, with an expanded thoracolumbar spinal canal offering increased neurovascular capacities, and a ventral pillar (formed by the vertebral bodies) better equipped to mitigate compressive loads and provide energy return. These biological developments are germane to understanding the advent of derived human behaviors, including efficient long-range locomotion and the first hominin expansion out of Africa.

Considered individually, many aspects of early hominin cervical anatomy appear more similar to th... more Considered individually, many aspects of early hominin cervical anatomy appear more similar to the African great apes than to humans, suggesting an ape-like pattern of load transfer, and by extension points to significant differences with human head carriage. However, when the australopith cervical spine is examined as a whole, rather than as separate isolated elements, a more human-like pattern emerges. In this context anatomical differences appear to have only insignificant functional implications and may be explained as developmental reciprocates of cranial base morphogenesis. Corroborating this observation is a nearly complete series of new cervical vertebrae from Australopithecus afarensis (KSD-VP-1/1) from Woranso-Mille, Ethiopia, dated to ~3.6 million years before present, which we compare to a sample of Homo sapiens (N=57), Pan troglodytes (20), Gorilla gorilla (20) Au afarensis (2) Au. sediba (2), Homo erectus (2), Pleistocene hominins from Sima de los Huesos (3), and Neandertals (7). The new Au. afarensis fossils from Woranso-Mille reveal an aggregate biomechanical and enthesopathological signature typical of Homo sapiens and present a surprisingly human-like kinematic signal. These lines of evidence evince a mode of head posture in early hominins very similar to modern humans as early as 3.6 million years ago.

H. naledi shows a mosaic morphological pattern with several derived (Homo-like) features of the s... more H. naledi shows a mosaic morphological pattern with several derived (Homo-like) features of the skull, hands and feet, and primitive (australopith- like) features in the ribcage, shoulder, and pelvis. This pattern reflects a morphology that might be expected of a hominin at the evolutionary transition between Australopithecus and Homo. Two thoracic vertebrae from levels 10 and 11 and the proximal aspect of an 11th rib were found in near anatomical connection in the Dinaledi Chamber of Rising Star cave, therefore likely belonging to the same individual. In this study we explore this association and report our ongoing work towards a quantitative 3D reconstruction of the H. naledi thorax. We measured 512 3D-(semi)landmarks on human and other hominoid ribcages (hylobatids, Pongo, Gorilla, Pan; N=33) for geometric morphometric analyses. Covariation between the 11th rib and remaining thorax shape was analyzed by partial least squares analysis (PLS) and overall thorax variation by principal components analysis (PCA). PCA results show wide ranges of complex thoracic variation. Gorilla and Pan are characterized by highly constricted upper thoraces when compared to their wide lower ribcages. Pongo and hylobatids have less narrow upper but also wide lower thoraces. Those of humans are expanded superiorly, narrow inferiorly, and with declined ribs. PLS analyses suggest that the morphology of the articulated rib-vertebra complex at the 11th level of H. naledi is compatible with a ribcage with declined ribs and inferiorly wider than observed in humans. This corresponds with evidence for laterally flared iliac blades of the H. naledi pelvis.

South African Journal of Science, 2016

We describe the earliest evidence for neoplastic disease in the hominin lineage. This is reported... more We describe the earliest evidence for neoplastic disease in the hominin lineage. This is reported from the type specimen of the extinct hominin Australopithecus sediba from Malapa, South Africa, dated to 1.98 million years ago. The affected individual was male and developmentally equivalent to a human child of 12 to 13 years of age. A penetrating lytic lesion affected the sixth thoracic vertebra. The lesion was macroscopically evaluated and internally imaged through phase-contrast X-ray synchrotron microtomography. A comprehensive differential diagnosis was undertaken based on gross- and micro-morphology of the lesion, leading to a probable diagnosis of osteoid osteoma. These neoplasms are solitary, benign, osteoid and bone-forming tumours, formed from well-vascularised connective tissue within which there is active production of osteoid and woven bone. Tumours of any kind are rare in archaeological populations, and are all but unknown in the hominin record, highlighting the importance of this discovery. The presence of this disease at Malapa predates the earliest evidence of malignant neoplasia in the hominin fossil record by perhaps 200 000 years.

Journal of Human Evolution, 2023

OSFPreprints, 2023

eLS, 2016

Vertebrate Paleobiology and Paleoanthropology, 2015

Journal of human evolution, 2015

Journal of Cerebral Blood Flow & Metabolism, 2009

Paleoanthropology, 2016

American Journal of Biological Anthropology

PNAS Nexus, 2022

Spinal Evolution, 2019

South African Journal of Science, 2016

We show that variation in thorax shapes facilitate or constrain certain locomotor patterns, as a small upper with an expanded lower thorax facilitates knuckle-walking, orienting the upper limb close to the sagittal midline and center of gravity during locomotion, and confers efficient scapular movement around the ribcage. Conversely, an expanded upper and small lower thorax better facilitates bipedality, facilitating more efficient arm swing and energy return from upper limb momentum, while lower thoracic expansion constrains arm swing in bipedal locomotion.
Since lung volume and body mass scale isometrically, increases in lung capacity (and concomitant expansion of the thorax) would be best apportioned to the lower thorax in knuckle-walkers. By contrast, increases in lung capacity and thorax expansion in bipeds are best apportioned superiorly. Thus, locomotor constraints, in concert with the isometric relationship between body size and lung size, may explain thoracic shape variation in early hominins.

Considered individually, many aspects of early hominin cervical anatomy appear more similar to th... more Considered individually, many aspects of early
hominin cervical anatomy appear more similar
to the African great apes than to humans,
suggesting an ape-like pattern of load transfer,
and by extension points to significant differences
with human head carriage.
However, when the australopith cervical spine
is examined as a whole, rather than as separate
isolated elements, a more human-like pattern
emerges. In this context anatomical differences
appear to have only insignificant functional implications
and may be explained as developmental
reciprocates of cranial base morphogenesis.
Corroborating this observation is a nearly
complete series of new cervical vertebrae from
Australopithecus afarensis (KSD-VP-1/1) from
Woranso-Mille, Ethiopia, dated to ~3.6 million
years before present, which we compare to a
sample of Homo sapiens (N=57), Pan troglodytes
(20), Gorilla gorilla (20) Au afarensis (2) Au. sediba (2), Homo erectus (2), Pleistocene hominins from
Sima de los Huesos (3), and Neandertals (7).
The new Au. afarensis fossils from Woranso-Mille
reveal an aggregate biomechanical and enthesopathological
signature typical of Homo sapiens
and present a surprisingly human-like kinematic
signal. These lines of evidence evince a mode
of head posture in early hominins very similar to
modern humans as early as 3.6 million years ago.

Spinal Evolution, 2019

The early hominin (Ardipithecus and Australopithecus) fossil record contains over 100 preserved v... more The early hominin (Ardipithecus and Australopithecus) fossil record contains over 100 preserved vertebral elements (n = 107; approximately half of which are well-preserved), ~65% of which have not been described since the turn of the millennium. Many are fragments, some for which detailed descriptions are pending (e.g., those of Australopithecus anamensis). Australopithecus afarensis and Australopithecus sediba are known from cervical, thoracic, and lumbar vertebrae, whereas Australopithecus africanus is known from thoracic and lumbar vertebrae but not cervical vertebrae. A partial skeleton from Member 4 of Sterkfontein, StW 573, preserves vertebrae from all presacral regions, but its species designation is debated and not yet formalized in the literature. Other early hominin species, such as Sahelanthropus tchadensis, Orrorin tugenensis, Ardipithecus kadabba, Australopithecus deyiremeda, Australopithecus bahrelghazali, and Australopithecus garhi, do not preserve vertebrae. Vertebrae from Swartkrans and Cooper’s Cave are thought to belong to either Paranthropus or Homo and are discussed in Meyer and Williams (this volume). The vertebrae discussed in this chapter are from five sites in East and South Africa: Aramis, Asa Issie, and Hadar from the Afar Depression of Ethiopia and Sterkfontein and Malapa in the Cradle of Humankind, South Africa.

Spinal Evolution, 2019

The Postcranial Anatomy of Australopithecus afarensis, 2016

Spinal Evolution: Morphology, Function, and Pathology of the Spine in Hominoid Evolution, 2019

The early hominin (Ardipithecus and Australopithecus) fossil record contains over 100 preserved v... more The early hominin (Ardipithecus and Australopithecus) fossil record contains over 100 preserved vertebral elements (n = 107; approximately half of which are well-preserved), ~65% of which haven’t been described since the turn of the millennium (Table 1). Many are fragments, some for which detailed descriptions are pending (e.g., those of Australopithecus anamensis; Meyer and Williams, in review). Australopithecus afarensis and Australopithecus sediba are known from cervical, thoracic, and lumbar vertebrae, whereas Australopithecus africanus is known from thoracic and lumbar vertebrae but not cervical vertebrae. A partial skeleton from Member 4 of Sterkfontein, StW 573, preserves vertebrae from all presacral regions, but its species designation is debated and not yet announced in the literature. Other early hominin species, such as Sahelanthropus tchadensis, Orrorin tugenensis, Ardipithecus kadabba, Australopithecus deyiremeda, Australopithecus barelghazali, and Australopithecus garhi do not preserve vertebrae. Vertebrae from Swartkrans and Cooper’s Cave are thought to belong to either Paranthropus or Homo and are discussed in Meyer and Williams (this volume). The vertebrae discussed in this chapter are from five sites in East and South Africa: Aramis, Asa Issie, and Hadar from the Afar Depression of Ethiopia, and Sterkfontein and Malapa in the Cradle of Humankind, South Africa.

Spinal Evolution: Morphology, Function, and Pathology of the Spine in Hominoid Evolution, 2019