ArticleLiterature Review

Vertebral numbers and human evolution

January 2016
American Journal of Physical Anthropology 159(S61):S19-S36

DOI:10.1002/ajpa.22901

Authors:

Scott Alan Williams

New York University

Emily R. Middleton

University of Wisconsin - Milwaukee

Catalina I. Villamil

Universidad Central del Caribe

Milena R. Shattuck

New York University

Ever since Tyson (1699), anatomists have noted and compared differences in the regional numbers of vertebrae among humans and other hominoids. Subsequent workers interpreted these differences in phylogenetic, functional, and behavioral frameworks and speculated on the history of vertebral numbers during human evolution. Even in a modern phylogenetic framework and with greatly expanded sample sizes of hominoid species, researchers' conclusions vary drastically, positing that hominins evolved from either a "long-backed" (numerically long lumbar column) or a "short-backed" (numerically short lumbar column) ancestor. We show that these disparate interpretations are due in part to the use of different criteria for what defines a lumbar vertebra, but argue that, regardless of which lumbar definition is used, hominins are similar to their great ape relatives in possessing a short trunk, a rare occurrence in mammals and one that defines the clade Hominoidea. Furthermore, we address the recent claim that the early hominin thoracolumbar configuration is not distinct from that of modern humans and conclude that early hominins show evidence of "cranial shifting," which might explain the anomalous morphology of several early hominin fossils. Finally, we evaluate the competing hypotheses on numbers of vertebrae and argue that the current data support a hominin ancestor with an African ape-like short trunk and lower back. Am J Phys Anthropol 159:S19-S36, 2016. © 2016 Wiley Periodicals, Inc.

Acquired Spinal Conditions in Evolutionary Perspective: Updating a Classic Hypothesis

Article

Jul 2022

In 1923, Sir Arthur Keith proposed that many common back problems are due to the stresses caused by our evolutionarily novel form of locomotion, bipedalism. In this article, we introduce an updated version of Keith’s hypothesis with a focus on acquired spinal conditions. We begin by outlining the main ways in which the human spine differs from those of our closest living relatives, the great apes. We then review evidence suggesting there is a link between spinal and vertebral shape on the one hand and acquired spinal conditions on the other. Next, we discuss recent studies that not only indicate that two common acquired spinal conditions—intervertebral disc herniation and spondylolysis—are associated with vertebral shape, but also suggest that the pathology-prone vertebral shapes can be understood in terms of the shift from quadrupedalism to bipedalism in the course of human evolution. Subsequently, we place the aforementioned findings under an umbrella hypothesis, which we call the “Evolutionary Shape Hypothesis.” This hypothesis contends that individuals differ in their propensity to develop different acquired spinal conditions because of differences in vertebral shape that relate to the evolutionary history of our species. We end the article with some possible directions for future research.

Assessing thoraco‐pelvic covariation in Homo sapiens and Pan troglodytes : A 3D geometric morphometric approach

Article

Aug 2020

Objectives Understanding thoraco‐pelvic integration in Homo sapiens and their closest living relatives (genus Pan) is of great importance within the context of human body shape evolution. However, studies assessing thoraco‐pelvic covariation across Hominoidea species are scarce, although recent research would suggest shared covariation patterns in humans and chimpanzees but also species‐specific features, with sexual dimorphism and allometry influencing thoraco‐pelvic covariation in these taxa differently. Material and Methods N = 30 adult H. sapiens and N = 10 adult Pan troglodytes torso 3D models were analyzed using 3D geometric morphometrics and linear measurements. Effects of sexual dimorphism and allometry on thoraco‐pelvic covariation were assessed via regression analyses, and patterns of thoraco‐pelvic covariation in humans and chimpanzees were computed via Two‐Block Partial Least Squares analyses. Results Results confirm the existence of common aspects of thoraco‐pelvic covariation in humans and chimpanzees, and also species‐specific covariation in H. sapiens that is strongly influenced by sexual dimorphism and allometry. Species‐specific covariation patterns in chimpanzees could not be confirmed because of the small sample size, but metrics point to a correspondence between the most caudal ribs and iliac crest morphology that would be irrespective of sex. Conclusions This study suggests that humans and chimpanzees share common aspects of thoraco‐pelvic covariation but might differ in others. In humans, torso integration is strongly influenced by sexual dimorphism and allometry, whilst in chimpanzees it may not be. This study also highlights the importance not only of torso widths but also of torso depths when describing patterns of thoraco‐pelvic covariation in primates. Larger samples are necessary to support these interpretations.

Great apes and humans evolved from a long-backed ancestor

Article

Jul 2020

There is current debate whether the Homo/Pan last common ancestor (LCA) had a short, stiff lumbar column like great apes or a longer, flexible column observed in generalized Miocene hominoids. Beyond having only four segments, three additional features contribute to lumbar stiffening: the position of the transitional vertebra (TV), orientation of the lumbar spinous processes, and entrapment of lumbar vertebrae between the iliac blades. For great apes, these features would be homologous if inherited from a short-backed LCA but likely functionally convergent through dissimilar phenotypes if evolved from a long-backed LCA. We quantitatively and qualitatively analyzed human, ape, and monkey thoracic and lumbar vertebrae using 3D surface scanning and osteological measurements to compare spinous process morphology and sacral depth. We also used a large sample of hominoid vertebral counts to assess variation in the position of the TV and lumbosacral boundary. All extant hominoids modally place the TV at the ultimate thoracic. However, humans and orangutans place the TV at the 19th postcranial vertebral segment, whereas other apes place the TV at the 20th. Furthermore, chimpanzees, gorillas, and orangutans each have distinct patterns of spinous process angulation and morphology associated with lumbar stiffening, while human spinous process morphology is similar to that of longer backed gibbons, monkeys, and Miocene hominoids Morotopithecus and Pierolapithecus. Finally, chimpanzees are unique compared with other hominoids with a greater sacral depth facilitating lumbar entrapment, and there are differences among African apes with respect to the mechanisms governing variation in the lumbosacral boundary. These differences suggest that lumbar stiffening is convergent among great apes and that human bipedalism evolved from a more generalized long-backed ancestor. Such a model is more consistent with evidence of TV placement in Australopithecus.

Insights into the lower torso in late Miocene hominoid Oreopithecus bambolii

Article

Full-text available

Dec 2019

Oreopithecus bambolii (8.3–6.7 million years old) is the latest known hominoid from Europe, dating to approximately the divergence time of the Pan -hominin lineages. Despite being the most complete nonhominin hominoid in the fossil record, the O. bambolii skeleton IGF 11778 has been, for decades, at the center of intense debate regarding the species’ locomotor behavior, phylogenetic position, insular paleoenvironment, and utility as a model for early hominin anatomy. Here we investigate features of the IGF 11778 pelvis and lumbar region based on torso preparations and supplemented by other O. bambolii material. We correct several crucial interpretations relating to the IGF 11778 anterior inferior iliac spine and lumbar vertebrae structure and identifications. We find that features of the early hominin Ardipithecus ramidus torso that are argued to have permitted both lordosis and pelvic stabilization during upright walking are not present in O. bambolii . However, O. bambolii also lacks the complete reorganization for torso stiffness seen in extant great apes (i.e., living members of the Hominidae), and is more similar to large hylobatids in certain aspects of torso form. We discuss the major implications of the O. bambolii lower torso anatomy and how O. bambolii informs scenarios of hominoid evolution.

Böhme etal 2019_Suppl_Danuvius guggenmosi.pdf

Data

Full-text available

Nov 2019

Modern Medical Consequences of the Ancient Evolution of a Long, Flexible Lumbar Spine

Article

Full-text available

Sep 2019

Modern human bipedality is unique and requires lumbar lordosis, whereas chimpanzees, our closest relatives, have short lumbar spines rendering them incapable of lordosis. To facilitate lordosis, humans have longer lumbar spines, greater lumbosacral angle, dorsally wedged lumbar vertebral bodies, and lumbar zygapophyseal joints with both increasingly coronal orientation and further caudal interfacet distances. These features limit modern lower lumbar spine and lumbosacral joint ailments, albeit imperfectly. The more coronal zygapophyseal orientation limits spondylolisthesis, while increasing interfacet distance may limit spondylolysis. Common back pain, particularly in people who are obese or pregnant, may result from increased lumbar lordosis, causing additional mass transfer through the zygapophyseal joints rather than vertebral bodies. Reduction in lumbar lordosis, such as in flatback syndrome from decreased lumbosacral angle, can also cause back pain. Human lumbar lordosis is necessary for placing the trunk atop the pelvis and presents a balancing act not required of our closest primate relatives.

Comparative morphology and ontogeny of the thoracolumbar transition in great apes, humans, and fossil hominins

Article

Full-text available

Sep 2019
J HUM EVOL

Variation among extant hominoid taxa in the anatomy of the thoracolumbar vertebral transition is well-established and constitutes an important framework for making inferences about posture and locomotion in fossil hominins. However, little is known about the developmental bases of these differences, posing a challenge when interpreting the morphology of juvenile hominins. In this study, we investigated ontogenetic variation in the thoracolumbar transition of juvenile and adult great apes, humans, and fossils attributed to Australopithecus and early Pleistocene Homo erectus. For each vertebra involved in the transition, we quantified functionally relevant aspects of zygapophyseal form: facet curvature in the transverse plane, facet orientation relative to midline, and the shift in these variables across the thoracolumbar transition, from the antepenultimate rib-bearing thoracic to the first lumbar vertebra (L1). Among extant hominids, adult individuals of Pan and Homo exhibit a greater shift in facet morphology across the thoracolumbar transition in comparison to Gorilla and Pongo. This pattern is driven by 2 interspecific differences in the L1 facets, with those of chimpanzees and humans being more curved and more sagittally oriented. Chimpanzees and humans also experience more change in facet morphology during development relative to gorillas and orangutans. Humans differ from chimpanzees in achieving their adultlike configuration much earlier in development. The fossil specimens indicate that early hominins had adult morphologies that were similar to those of extant Homo and Pan, and that they achieved their adult morphologies early in development, like extant humans. Although it is unclear why adult chimpanzees and hominins share an adult morphology, we speculate that the early acquisition of adultlike L1 zygapophyseal morphology in hominins is an evolutionary novelty related to conferring stability to a relatively long lumbar spine as young individuals are learning to walk bipedally.

Vertebral Morphology in Hominoids II: The Lumbar Spine

Chapter

Aug 2019

The evolution of hominoids was accompanied by a transformation of the primate body plan from a monkey-like ancestral condition to one characterized by a derived suite of postcranial features. While diagnostic hominoid features are found throughout the postcranial skeleton, the trunk, and especially the lumbar region, is one of the most functionally important and immediately noticeable aspects of hominoid anatomy. Hominoids have a reduced number of lumbar vertebrae that are generally distinguished from those of their cercopithecoid close relatives with respect to dimensions of lumbar vertebral bodies and pedicles, position and orientation of transverse processes, shape and orientation of spinous processes, and orientation of zygapophyses at the thoracolumbar transition. Traditional functional interpretations emphasize that these features stiffen the lower body and limit sagittal mobility during orthogrady and/or forelimb-dominated behaviors. More recent comparative research on nonhominoid primates and other mammals support that hominoid lumbar features confer axial stability in a variety of positional behaviors, while studies of experimental biomechanics have revealed more rotational capabilities in the hominoid trunk than previously thought, and analyses of back musculature offer new information about fiber-type differences between hominoids and other primates. Multiple models concerning reconstruction of the trunk morphology and behavior of the crown hominoid ancestor, and the sequence in which aspects of the hominoid trunk evolved, have surfaced over the last decade. Given the numerous chapters in this volume devoted to human spinal morphology and adaptations to bipedalism, our discussion is focused primarily on lumbar anatomy shared by all hominoids.

Contributions to the study of the morphological, functional and evolutionary variability of the human thoracic skeleton.

Thesis

Full-text available

May 2017

Daniel García-Martínez

Esta es una tesis sobre Antropología Física, con interés especial en el área de la Paleoantropología. En ella, se estudia la variabilidad morfológica torácica en diferentes vertientes de la biología humana, como la ontogenia, el dimorfismo sexual, la anatomía funcional, la anatomía comparada y la anatomía evolutiva. Aunque diferentes trabajos habían explorado previamente estos aspectos desde un punto de vista bidimensional, gran parte de los aspectos detallados de la morfología tridimensional aún no se conocían. Parte de esta limitación, se debía a que la metodología empleada para la cuantificación de la morfología torácica y costal (básicamente compuesta de curvas) no recogía la realidad tridimensional asociada a la biología de los organismos. Por lo tanto, al no cuantificar las tres dimensiones del tórax, las conclusiones obtenidas eran parcialmente sesgadas. Aunque este hecho es evidente observando la variabilidad humana reciente, se hace más evidente cuando se trata del estudio del registro fósil, ya que, en el caso del esqueleto torácico, este suele aparecer muy fragmentado. Para resolver el problema de la cuantificación metodológica, en esta tesis se ha desarrollado todo un protocolo que va desde la obtención de modelos tridimensionales hasta su medición detallada en un entorno virtual a través de la morfometría geométrica (MG) 3D de sliding semilandmarks. Para la obtención de datos, se han usado técnicas de imagen médica para la obtención de muestra de cajas torácicas de Homo sapiens y de otros primates hominoideos no humanos, así como técnicas de escaneo de superficie a fin de obtener modelos 3D de elementos torácicos aislados (costillas y vértebras) tanto de especies actuales como de especies extintas. Para su cuantificación, se han desarrollado protocolos de landmarks y semilandmarks, tanto para la caja torácica en su conjunto, como para sus elementos (costillas y vértebras) y se ha utilizado el método de sliding semilandmarks a través de la bending energy para convertir los semilandmarks en puntos matemáticamente homólogos, ya que, sin este proceso, los semilandmarks no cumplirían el principio de homología. Los resultados obtenidos han mostrado que la variabilidad torácica (tanto actual como fósil) es bastante más complicada de lo propuesto hasta la fecha. De este modo, las diferencias observadas en la ontogenia y el dimorfismo sexual, podrían estar relacionadas con los patrones de respiración, la postura corporal o incluso con el tamaño del aparato digestivo y reproductivo. En cuanto a la anatomía comparada, se observa que la realidad morfológica 3D torácica de Hominoidea, no responde a las clasificaciones de tórax en forma de barril (Homo e Hylobates) y tórax en forma de embudo (Pongo, Pan, Gorilla) propuestas clásicamente en la literatura, sino que Pongo está morfológicamente más próximo a Homo e Hylobates que al resto de grandes simios. Respecto a la anatomía evolutiva de la caja torácica, los resultados aquí presentados apuntan a que la morfología del tórax superior expandido (característica de Homo sapiens) probablemente apareció antes que la morfología moderna del tórax inferior (proporcionalmente más estrecha). De este modo, la caja torácica de Australopithecus y de los primeros Homo, podría estar caracterizada por una parte inferior amplia (hipotéticamente arcaica), posiblemente heredada de homínidos del Mioceno como Pierolapithecus, y por una parte superior expandida (hipotéticamente derivada), similar a Homo sapiens. Este patrón de cajas torácicas inferiormente amplias podría estar presente incluso en Neandertales, aunque debido al mayor tamaño torácico de estos con respecto a especies previas, algunas ligeras diferencias debidas a factores alométricos o isométricos también serían esperables. Futuros trabajos deberían de ir encaminados a la cuantificación detallada no solo de los elementos aislados de la caja torácica de especies fósiles, sino también al estudio de como la interacción entre las partes (costillas y vértebras), tienen relevancia para entender los cambios del todo al que pertenecen (tórax). Adicionalmente, otros campos que no son recogidos en la presente tesis, como la ontogenia torácica de especie fósiles, la variabilidad o la anatomía comparada de primates con la inclusión de fósiles de primeros Hominoideos (como Pierolapithecus) también deberán ser estudiados en el futuro.

Thoracic vertebral count and thoracolumbar transition in Australopithecus afarensis

Article

May 2017
P NATL ACAD SCI USA

Significance The discovery of a 3.3 million-year-old partial skeleton of Australopithecus afarensis , from Dikika, Ethiopia, preserved all seven cervical (neck) vertebrae and provided the only known evidence for the presence of 12 thoracic (rib-bearing) vertebrae in hominins prior to 60,000 years ago. This skeleton has seven cervical and only 12 thoracic vertebrae like humans, rather than 13 like African apes. However, the anatomical transition from thoracic to lumbar (lower back) vertebral form occurs at the 11th thoracic segment. This distinctive pattern of vertebral segmentation, rare in modern apes and humans, is also seen in the three other early hominins for which this area is known, with the Dikika skeleton providing the earliest and most complete example.

Morphological modularity in the anthropoid axial skeleton

Article

Sep 2022

Previous research has found that hominoids have stronger modularity between limb elements than other anthropoids, suggesting that there is less constraint on morphological diversification (e.g., limb proportions) in hominoids in terms of evolutionary independence. However, degrees of modularity in the axial skeleton have not been investigated across a broad range of anthropoid taxa. Thus, it is unknown whether hominoids also have stronger modularity in the axial skeleton than other anthropoids, which has implications for the evolution of diverse torso morphologies in Miocene apes as well as the evolution of novel characteristics in the skull and vertebrae of fossil hominins. In this study, 12 anthropoid genera were sampled to examine degrees of modularity between axial skeletal elements (i.e., cranium, mandible, vertebrae, and sacrum). Covariance ratio coefficients were calculated using variance/covari-ance matrices of interlandmark distances for each axial skeletal element to evaluate degrees of modu-larity. The results showed that Alouatta, Hylobates, Gorilla, Pan, and Homo showed generally stronger modularity than other anthropoid taxa when considering all axial skeletal elements. When only considering the vertebral elements (i.e., vertebrae and sacrum), Alouatta, Hylobates, Gorilla, and Pan showed generally stronger modularity than other anthropoid taxa. Humans showed stronger modularity between the skull and vertebrae than other hominoids. Thus, the evolution of novel characteristics in the skull and vertebral column may have been less constrained in fossil hominins due to the dissociation of trait covariation between axial skeletal elements in hominoid ancestors, thus fostering more evolutionary independence between the skull and vertebral column.

Phylogenetic and functional signal in prezygapophyseal articular facet shape of the first post‐transitional vertebra in anthropoids

Article

Aug 2022

Previous studies of the prezygapophyseal articular facet (PAF) of the thoracolumbar vertebrae in primates have suggested that the morphology of this feature reflects relative mobility of the lower back, and therefore corresponds to locomotor behavior. Specifically, these studies suggest that the PAF morphology found in cercopithecoids reflects greater mobility of the lower back compared to a stiffer lower back adapted for forelimb‐dominated suspensory behaviors in hominoids. In this study, we sought to re‐examine this question in terms of both locomotor behavior and phylogenetic signal in a broad sample of anthropoid taxa. The study sample consisted of 291 first post‐transitional vertebrae of wild‐caught individuals representing 27 extant anthropoid species (16 genera). Vertebrae were 3D scanned, and 19 landmarks were digitized. PAF shape was tested for the presence of a phylogenetic signal using the multivariate version of the K‐statistic (Kmult), and a chronometric consensus phylogenetic tree was mapped onto the major axes of shape space using species means to produce a phylomorphospace. Results showed that phylogenetic signal is statistically significant in PAF shape (Kmult = 0.3; p < 0.0001), and phylogenetic separation is apparent in the phylomorphospace, with some exceptions. However, certain aspects of PAF shape also appear to be associated with locomotor behavior within major taxonomic groups, such as hominoids and platyrrhines. Our results suggest that both phylogenetic relatedness and function may contribute to PAF shape variation in anthropoids.

The morphological consequences of segmentation anomalies in the human sacrum

Article

Full-text available

Dec 2021

Objectives Despite the high frequency of segmentation anomalies in the human sacrum, their evolutionary and clinical implications remain controversial. Specifically, inconsistencies involving the classification and counting methods obscure accurate assessment of lumbosacral transitional vertebrae. Therefore, we aim to establish more reliable morphological and morphometric methods for differentiating between sacralizations and lumbarizations in clinical and paleontological contexts. Materials and Methods Using clinical CT data from 145 individuals aged 14–47 years, vertebral counts and the spatial relationship between the sacrum and adjoining bony structures were assessed, while the morphological variation of the sacrum was assessed using geometric morphometrics based on varied landmark configurations. Results The prevalence of lumbosacral and sacrococcygeal segmentation anomalies was 40%. Lumbarizations and sacralizations were reliably distinguishable based on the spatial relationship between the iliac crest and the upward or downward trajectory of the linea terminalis on the sacrum. Different craniocaudal orientations of the alae relative to the corpus of the first sacral vertebra were also reflected in the geometric morphometric analyses. The fusion of the coccyx (32%) was frequently coupled with lumbarizations, suggesting that the six-element sacra more often incorporate the coccyx rather than the fifth lumbar vertebra. Conclusions Our approach allowed the consistent identification of segmentation anomalies even in isolated sacra. Additionally, our outcomes either suggest that homeotic border shifts often affect multiple spinal regions in a unidirectional way, or that sacrum length is highly conserved perhaps due to functional constraints. Our results elucidate the potential clinical, biomechanical, and evolutionary significance of lumbosacral transitional vertebrae.

Ticks, Hair Loss, and Non-Clinging Babies: A Novel Tick-Based Hypothesis for the Evolutionary Divergence of Humans and Chimpanzees

Article

Full-text available

May 2021

Jeffrey G. Brown

Human straight-legged bipedalism represents one of the earliest events in the evolutionary split between humans (Homo spp.) and chimpanzees (Pan spp.), although its selective basis is a mystery. A carrying-related hypothesis has recently been proposed in which hair loss within the hominin lineage resulted in the inability of babies to cling to their mothers, requiring mothers to walk upright to carry their babies. However, a question remains for this model: what drove the hair loss that resulted in upright walking? Observers since Darwin have suggested that hair loss in humans may represent an evolutionary strategy for defence against ticks. The aim of this review is to propose and evaluate a novel tick-based evolutionary hypothesis wherein forest fragmentation in hominin paleoenvironments created conditions that were favourable for tick proliferation, selecting for hair loss in hominins and grooming behaviour in chimpanzees as divergent anti-tick strategies. It is argued that these divergent anti-tick strategies resulted in different methods for carrying babies, driving the locomotor divergence of humans and chimpanzees.

DIFFUSE IDIOPATHIC SKELETAL HYPEROSTOSIS IN CAPTIVE GORILLAS (GORILLA SPP.): APPEARANCES AND DIAGNOSIS

Article

Nov 2020

Roberto Portela Miguez

Diffuse idiopathic skeletal hyperostosis (DISH) is a disorder of unknown cause, in which new bone forms in soft tissues attached to the skeleton. Originally described in humans, in whom it is quite common, it is usually asymptomatic. New bone may completely bridge across joints, especially in the spine. However, it can be difficult to distinguish from diseases such as spondyloarthritis and spondylosis. With safer and increased use of radiography in diagnosis, the unfamiliar skeletal changes of asymptomatic DISH may now be coincidentally revealed during investigation of other disorders and result in misdiagnosis and unnecessary treatment. There have been case reports of its occurrence in great apes, but this is the first study to illustrate its appearances in a series of 11 skeletons of western and eastern lowland gorillas (Gorilla gorilla gorilla and Gorilla beringei graueri) from zoos in Europe and the United States. The study combines a review of available clinical and postmortem records with examination of the skeletons and radiologic investigation, such as computed tomography (CT). The results indicate that the disorder is probably common in older (>30 yr) captive gorillas, but that it is asymptomatic. It was not symptomatic during life in any of these animals. Several cases had unexpected features, such as extensive involvement of the thorax and extra-articular sacroiliac and tibiofibular joint fusions that are not typical in humans. By illustrating these skeletons, the study should aid differentiation of DISH from spondylosis (syn spondylosis deformans) and spondyloarhritis. It illustrates those features that are atypical of human DISH. CT scanning is valuable in such cases for examining diagnostically important areas such as sacroiliac joints. Increased awareness of DISH should help with understanding its cause, both in gorillas and humans.

DIFFUSE IDIOPATHIC SKELETAL HYPEROSTOSIS IN CAPTIVE GORILLAS (GORILLA SPP.): APPEARANCES AND DIAGNOSIS

Article

May 2020
J ZOO WILDLIFE MED

Diffuse Idiopathic Skeletal Hyperostosis (DISH) is a disorder of unknown cause, in which new bone forms in soft tissues attached to the skeleton. Originally described in humans, in whom it is quite common, it is usually asymptomatic. New bone may completely bridge across joints, especially in the spine. However, it can be difficult to distinguish from diseases such as spondyloarthritis and spondylosis. With safer and increased use of radiography in diagnosis, the unfamiliar skeletal changes of asymptomatic DISH may now be coincidentally revealed during investigation of other disorders and result in misdiagnosis and unnecessary treatment. There have been case reports of its occurrence in great apes, but this is the first study to illustrate its appearances in a series of eleven skeletons of western and eastern lowland gorillas (Gorilla gorilla gorilla and G. beringei graueri) from zoos in Europe and the USA. The study combines review of available clinical and post-mortem records with examination of the skeletons and radiological investigation, such as CT. The results indicate that the disorder is probably common in older (>30yr.) captive gorillas but that it is asymptomatic. It was not symptomatic during life in any of these animals. There were unexpected features in several cases, such as extensive involvement of the thorax, extra-articular sacroiliac and tibiofibular joint fusions that are not typical in humans. By illustrating these skeletons, the study should aid differentiation of DISH from spondylosis (syn spondylosis deformans) and spondyloarthritis. It illustrates those features that are atypical of human DISH. CT scanning is valuable in such cases for examining diagnostically important areas such as sacroiliac joints. Increased awareness of DISH should help with understanding its cause, both in gorillas and humans.

Potential adaptations for bipedalism in the thoracic and lumbar vertebrae of Homo sapiens: A 3D comparative analysis

Article

Nov 2019

A new Miocene ape and locomotion in the ancestor of great apes and humans

Article

Full-text available

Nov 2019
NATURE

Many ideas have been proposed to explain the origin of bipedalism in hominins and suspension in great apes (hominids); however, fossil evidence has been lacking. It has been suggested that bipedalism in hominins evolved from an ancestor that was a palmigrade quadruped (which would have moved similarly to living monkeys), or from a more suspensory quadruped (most similar to extant chimpanzees)1. Here we describe the fossil ape Danuvius guggenmosi (from the Allgäu region of Bavaria) for which complete limb bones are preserved, which provides evidence of a newly identified form of positional behaviour—extended limb clambering. The 11.62-million-year-old Danuvius is a great ape that is dentally most similar to Dryopithecus and other European late Miocene apes. With a broad thorax, long lumbar spine and extended hips and knees, as in bipeds, and elongated and fully extended forelimbs, as in all apes (hominoids), Danuvius combines the adaptations of bipeds and suspensory apes, and provides a model for the common ancestor of great apes and humans. Danuvius guggenmosi moved using extended limb clambering, thus combining adaptations of bipeds and suspensory apes and providing evidence of the evolution of bipedalism and suspension climbing in the common ancestor of great apes and humans.

Miocene Ape Spinal Morphology: The Evolution of Orthogrady

Chapter

Aug 2019

Masato Nakatsukasa

The postcranial skeleton of living apes is characterized by a number of derived features that are attributable to the frequent forelimb-dominated orthograde positional behavior such as suspension or vertical climbing. Their axial skeletons exhibit a common specialization, e.g., a decreased number of lumbar vertebrae concomitant with an increase in sacral vertebrae, loss of an external tail, spinal invagination into the thoracic and abdominal cavities, and craniocaudally short and dorsoventrally deep lumbar vertebral centrum. So far, over 30 genera of apes have been discovered from Miocene fossil localities in Africa and Eurasia. However, axial skeletal specimens are available in only a handful of apes. Fossil apes (~19–15 Ma, Kenya) from the beginning and mid-part of the Miocene in Africa (Ekembo and Nacholapithecus) were essentially deliberate arboreal pronograde quadrupeds and retained primitive catarrhine axial skeletal morphology: long and dorsomobile lumbar spine, short sacrum, and absence of spinal invagination (as inferred from ventral position of the lumbar transverse process), though Nacholapithecus shows a hint of an early transition to orthograde positional behavior. However, they did not have an external tail, and their tail loss is almost certainly a shared derived feature with living apes. The penultimate lumbar vertebra of Morotopithecus (20.6 Ma, Uganda) exhibits craniocaudally short and dorsoventrally deep centrum and dorsal position of the transverse process. While these features resemble those in living apes, the evolutionary pattern of the dentognathic morphology and paleobiogeography of Miocene apes suggest that derived lumbar anatomy of Morotopithecus is a product of parallel evolution. European ape fossil record illustrates a progressive evolution toward orthogrady. The stem great ape which spread into Eurasia from Africa between 17 and 16 Ma was pronograde-like contemporary African fossil apes. Pierolapithecus (~12 Ma, Spain) is the earliest known orthograde (but perhaps non-suspensory) ape in Europe although its spine might be less dorsostable compared to extant great apes. Hispanopithecus (9.6 Ma, Spain) had acquired a full suite of orthograde and suspensory characters comparable to extant great apes. Oreopithecus (~8–7 Ma, Italy) also has a fully orthograde spine although its lumbar spine has some distinct features from Hispanopithecus. Some authors have proposed that orthogrady evolved in European and African ape lineages (and Asian as well) independently. However, some others propose that a European orthograde ape dispersed into Africa during the Late Miocene gave rise to the extant African apes and humans. Besides this issue, opinions are divided whether the dorsostable spine in the extant African apes is homologous or homoplastic. Postcranial anatomy of Ardipithecus ramidus suggests to some that the last common ancestor of the extant African apes and humans had an intermediate body plan between pronogrady and orthogrady (“multigrady”) with spinal invagination but without enhanced dorsostability as that in extant great apes. However, an argument continues with regard to this interpretation. Postcranial fossils of African Miocene apes are totally absent after ~12 Ma until the appearance of the earliest putative humans. For further clarification of the evolution of the hominoid spine, new discoveries of postcranial elements of Late Miocene African apes are needed.

Increased variation in numbers of presacral vertebrae in suspensory mammals

Article

Full-text available

May 2019
Nat. Ecol. Evol.

Restricted variation in numbers of presacral vertebrae in mammals is a classic example of evolutionary stasis. Cervical number is nearly invariable in most mammals, and numbers of thoracolumbar vertebrae are also highly conserved. A recent hypothesis posits that stasis in mammalian presacral count is due to stabilizing selection against the production of incomplete homeotic transformations at the lumbo-sacral border in fast-running mammals, while slower, ambulatory mammals more readily tolerate intermediate lumbar/sacral vertebrae. We test hypotheses of variation in presacral numbers of vertebrae based on running speed, positional behaviour and vertebral contribution to locomotion. We find support for the hypothesis that selection against changes in presacral vertebral number led to stasis in mammals that rely on dorsomobility of the spine during running and leaping, but our results are independent of running speed per se. Instead, we find that mammals adapted to dorsostability of the spine, such as those that engage in suspensory behaviour, demonstrate elevated variation in numbers of presacral vertebrae compared to dorsomobile mammals. We suggest that the evolution of dorsostability and reduced reliance on flexion and extension of the spine allowed for increased variation in numbers of presacral vertebrae, leading to departures from an otherwise stable evolutionary pattern.

Step width and frontal plane trunk motion in bipedal chimpanzee and human walking

Article

Oct 2018

New fossil remains of Homo naledi from the Lesedi Chamber, South Africa

Article

Full-text available

May 2017
eLife

The Rising Star cave system has produced abundant fossil hominin remains within the Dinaledi Chamber, representing a minimum of 15 individuals attributed to Homo naledi. 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 H. naledi. 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 H. naledi, and evidence of H. naledi from both recovery localities shows a consistent pattern of differentiation from other hominin species.

3D geometric morphometrics of thorax variation and allometry in Hominoidea

Article

Sep 2017
J HUM EVOL

Ever since the seminal papers of Keith and Schultz, hominoid primate ribcages have been described as either " funnel-" or " barrel-shaped. " Following this dichotomic typology, it is currently held that Homo sapiens and hylobatids (gibbons and siamangs) share a barrel-shaped ribcage and that they are more similar to each other than to the funnel-shaped thoraces of great apes (Gorilla, Pan, and Pongo). Other researchers hypothesized that thoracic width and the invagination of the thoracic spine into the thorax are related to allometry. However, analyses that take into account the complex three-dimensional (3D) shape of the ribcage are lacking. Here, we address hypotheses about thorax shape and evolution using 3D morphometrics of thoraces in anatomical connection obtained by computed tomography scans of 23 hominoid cadavers and 10 humans and examining thorax compartments composed of seven ribs (1-7 thorax) and of 11 ribs (1-11 thorax). In the 1e7 thorax analyses, the human thorax is uniquely flat because of torsion of the upper and central ribs, differing from all non-human hominoids including hylobatids. In the 1e11 thorax analyses, humans are markedly different from African great apes, with hylobatids and orangutans intermediate. In full shape space analyses, affinities between orangutans and humans on the one hand and between hylobatids and African great apes on the other are evident. Therefore, we reject the hypothesis that humans and hylobatids bear any special affinities in overall 3D thorax shape to each other. We find that larger thoraces are wider and flatter, with a more invaginated spine, supporting the allometric hypothesis. Hominoid thorax variation shows complex interactions between allometry, rib curves, torsion, and declination, and the morphology of the costo-vertebral joint and the thoracic vertebral column. When considering functional specializations alongside phylogenetic relationships, an overly simplistic dichotomy between funnel-shaped and barrel-shaped thoraces is not supported.

Challenges and perspectives on functional interpretations of australopith postcrania and the reconstruction of hominin locomotion

Article

Dec 2022
J HUM EVOL

In 1994, Hunt published the 'postural feeding hypothesis'-a seminal paper on the origins of hominin bipedalism-founded on the detailed study of chimpanzee positional behavior and the functional inferences derived from the upper and lower limb morphology of the Australopithecus afarensis A.L. 288-1 partial skeleton. Hunt proposed a model for understanding the potential selective pressures on hominins, made robust, testable predictions based on Au. afarensis functional morphology, and presented a hypothesis that aimed to explain the dual functional signals of the Au. afarensis and, more generally, early hominin postcranium. Here we synthesize what we have learned about Au. afarensis functional morphology and the dual functional signals of two new australopith discoveries with relatively complete skeletons (Australopithecus sediba and StW 573 'Australopithecus prometheus'). We follow this with a discussion of three research approaches that have been developed for the purpose of drawing behavioral inferences in early hominins: (1) developments in the study of extant apes as models for understanding hominin origins; (2) novel and continued developments to quantify bipedal gait and locomotor economy in extant primates to infer the locomotor costs from the anatomy of fossil taxa; and (3) novel developments in the study of internal bone structure to extract functional signals from fossil remains. In conclusion of this review, we discuss some of the inherent challenges of the approaches and methodologies adopted to reconstruct the locomotor modes and behavioral repertoires in extinct primate taxa, and notably the assessment of habitual terrestrial bipedalism in early hominins.

Bipedal locomotion in zoo apes: Revisiting the hylobatian model for bipedal origins

Article

Full-text available

Mar 2022

Bipedal locomotion is a hallmark of being human. Yet, the body form from which bipedalism evolved remains unclear. Specifically, the positional behavior (i.e., orthograde vs. pronograde) and the length of the lumbar spine (i.e., long and mobile vs. short and stiff) of the last common ancestor (LCA) of the African great apes and humans require further investigation. While fossil evidence would be the most conclusive, the paucity of hominid fossils from 5-10 million years ago makes this field of research challenging. In their absence, extant primate anatomy and behavior may offer some insight into the ancestral body form from which bipedalism could most easily evolve. Here, we quantify the frequency of bipedalism in a large sample (N=496) of zoo-housed hominoids and cercopithecines. Our results show that while each studied species of ape and monkey can move bipedally, hylobatids are significantly more bipedal and engage in bipedal locomotion more frequently and for greater distances than any other primate sampled. These data support hypotheses of an orthograde, long-backed, and arboreal LCA, which is consistent with hominoid fossils from the middle-to-late Miocene. If true, knuckle-walking evolved in parallel in Pan and Gorilla , and the human body form, particularly the long lower back and orthograde posture, is conserved.

Mineral content analysis in the rib cross‐sections of Homo sapiens and Pan troglodytes and its implications for the study of Sts 14 costal remains

Article

Feb 2022

From an evolutionary perspective, the ribcage has changed substantially in the subfamily Homininae. Among many other features, the amount of mineralized tissues of the rib cross‐section at the midshaft could be informative about potential biomechanical changes during Homininae evolution. These changes would be related to the different loading stresses that each costal level has to deal with. Nevertheless, this knowledge remains hypothetical and has never been properly addressed. This issue was assessed by analysing via micro‐CT the internal rib anatomy of the complete sets of ribs belonging to ten Homo sapiens and ten Pan troglodytes adult individuals. Additionally, five fossil ribs of Australopithecus africanus Sts 14 (costal levels 5–9) were also included to evaluate similarities with the two tested extant species. The mineralized area of P. troglodytes rib cross‐sections was higher than that of H. sapiens. However, its serial change along the rib sequence (1–12/13) was similar in both species. The mineralized area of the Sts 14 rib cross‐sections was closer to H. sapiens than to P. troglodytes for costal levels 7–9 (Sts 14w) but not for levels 5 and 6, where it was distinct from both comparative samples. The variation in the amount of mineralized tissues along the rib sequence in H. sapiens and P. troglodytes might indicate a common upper‐lower thorax division probably linked to the insertions of the diaphragm. This variation is similar between ribs Sts 14w and the corresponding modern human costal levels, which could be potentially related to closer breathing kinematics in the lower thorax of Sts 14 and H. sapiens.

Examination of magnitudes of integration in the catarrhine vertebral column

Article

May 2021

The evolution of novel vertebral morphologies observed in humans and other extant hominoids may be related to changes in the magnitudes and/or patterns of covariation among traits. To examine this, we tested magnitudes of integration in the vertebral column of cercopithecoids and hominoids, including humans. Three-dimensional surface scans of 14 vertebral elements from 30 Cercopithecus, 32 Chlorocebus, 39 Macaca, 45 Hylobates, 31 Pan, and 86 Homo specimens were used. A resampling method was used to generate distributions of integration coefficient of variation scores for vertebral elements individually using interlandmark distances. Interspecific comparisons of mean integration coefficient of variation were conducted using Mann-Whitney U tests with Bonferroni adjustment. The results showed that hominoids generally had lower mean integration coefficient of variation than cercopithecoids. In addition, humans showed lower mean integration coefficient of variation than other hominoids in their last thoracic and lumbar vertebrae. Cercopithecoids and Hylobates showed relatively lower mean integration coefficient of variation in cervical vertebrae than in thoracolumbar vertebrae. Pan and Homo showed relatively lower mean integration coefficient of variation in the last thoracic and lumbar vertebrae in the thoracolumbar region, except for the L1 of Pan. The results suggest fewer integration-mediated constraints on the evolution of vertebral morphology in hominoids when compared with cercopithecoids. The weaker magnitudes of integration in lumbar vertebrae in humans when compared with chimpanzees likewise suggest fewer constraints on the evolution of novel lumbar vertebrae morphology in humans.

3D shape analyses of extant primate and fossil hominin vertebrae support the ancestral shape hypothesis for intervertebral disc herniation

Article

Full-text available

Dec 2019
BMC EVOL BIOL

Background: Recently we proposed an evolutionary explanation for a spinal pathology that afflicts many people, intervertebral disc herniation (Plomp et al. [2015] BMC Evolutionary Biology 15, 68). Using 2D data, we found that the bodies and pedicles of lower vertebrae of pathological humans were more similar in shape to those of chimpanzees than were those of healthy humans. Based on this, we hypothesized that some individuals are more prone to intervertebral disc herniation because their vertebrae exhibit ancestral traits and therefore are less well adapted for the stresses associated with bipedalism. Here, we report a study in which we tested this "Ancestral Shape Hypothesis" with 3D data from the last two thoracic and first lumbar vertebrae of pathological Homo sapiens, healthy H. sapiens, Pan troglodytes, and several extinct hominins. Results: We found that the pathological and healthy H. sapiens vertebrae differed significantly in shape, and that the pathological H. sapiens vertebrae were closer in shape to the P. troglodytes vertebrae than were the healthy H. sapiens vertebrae. Additionally, we found that the pathological human vertebrae were generally more similar in shape to the vertebrae of the extinct hominins than were the healthy H. sapiens vertebrae. These results are consistent with the predictions of the Ancestral Shape Hypothesis. Several vertebral traits were associated with disc herniation, including a vertebral body that is both more circular and more ventrally wedged, relatively short pedicles and laminae, relatively long, more cranio-laterally projecting transverse processes, and relatively long, cranially-oriented spinous processes. We found that there are biomechanical and comparative anatomical reasons for suspecting that all of these traits are capable of predisposing individuals to intervertebral disc herniation. Conclusions: The results of the present study add weight to the hypothesis that intervertebral disc herniation in H. sapiens is connected with vertebral shape. Specifically, they suggest that individuals whose vertebrae are towards the ancestral end of the range of shape variation within H. sapiens have a greater propensity to develop the condition than other individuals. More generally, the study shows that evolutionary thinking has the potential to shed new light on human skeletal pathologies.

Evolutionary selection and morphological integration in the vertebral column of modern humans

Article

Full-text available

Nov 2019

Objectives: The main objective is to quantify integration, modularity, and response to selection in the presacral vertebral column of modern humans. Materials and methods: Seventeen linear variables on each presacral vertebra were collected in 108 modern humans producing a total of ~39,000 measurements. Then, we studied patterns and magnitudes of integration at regional, vertebral, and intra-vertebral levels. Additionally, we calculated the ability of vertebrae to respond to selection by quantifying differences in evolvability, flexibility, and constraint throughout the spine. Results: The results indicate that caudal vertebrae are more evolvable than those located more cranially in the presacral vertebral column, following an increasing pattern of evolvability from the cervical to the lumbar region. Additionally, the atlas and fifth lumbar vertebra show the lowest values of integration, while central thoracic vertebrae display the highest magnitudes of integration. Discussion: These results could be related to three main factors: body plan organization expressed by the Hox genes, the strong developmental constraints that determine the number of mammalian vertebrae, and, finally, the functional requirements of an adaptation to bipedal locomotion in the human lineage.

The lumbo-sacral transitional vertebra (LSTV) sacrum with negligible sacral kyphosis: a case report with an evolutionary review CASE REPORT

Article

Full-text available

May 2019

Monkey and other hominids species have 5 sacral segments in 10% cases. The similar frequencies for each 6-segmented and 4-segmented sacra in human are known as lumbo-sacral transitional vertebra (LSTV). Achieving the erect posture in human has necessitated much skeletal modification, but these are more apparent in the lumbosacral region. Sacral kyphosis is a distinguishing feature of the human sacrum, which helps to differentiate them from the animal. The monkey has a sacral index near 80, and humans a sacral index is near 100. The sacral index was 88 in six-segmented sacra with negligible sacral kyphosis, having sacralisation of the 5th lumbar vertebra. Therefore, SI is 88 and lack of sacral kyphosis challenge its human origin. On the contrary, gross morphology, actual sacral index, and comparison with apes gave sufficient evidence of human origin. Later excluding 5th Lumbar vertebra, the sacral index is 107.34 and might belong to a male which corresponds with bone bank record.

Skeletal Anomalies in The Neandertal Family of El Sidrón (Spain) Support A Role of Inbreeding in Neandertal Extinction

Article

Full-text available

Feb 2019

Neandertals disappeared from the fossil record around 40,000 bp, after a demographic history of small and isolated groups with high but variable levels of inbreeding, and episodes of interbreeding with other Paleolithic hominins. It is reasonable to expect that high levels of endogamy could be expressed in the skeleton of at least some Neandertal groups. Genetic studies indicate that the 13 individuals from the site of El Sidrón, Spain, dated around 49,000 bp, constituted a closely related kin group, making these Neandertals an appropriate case study for the observation of skeletal signs of inbreeding. We present the complete study of the 1674 identified skeletal specimens from El Sidrón. Altogether, 17 congenital anomalies were observed (narrowing of the internal nasal fossa, retained deciduous canine, clefts of the first cervical vertebra, unilateral hypoplasia of the second cervical vertebra, clefting of the twelfth thoracic vertebra, diminutive thoracic or lumbar rib, os centrale carpi and bipartite scaphoid, tripartite patella, left foot anomaly and cuboid-navicular coalition), with at least four individuals presenting congenital conditions (clefts of the first cervical vertebra). At 49,000 years ago, the Neandertals from El Sidrón, with genetic and skeletal evidence of inbreeding, could be representative of the beginning of the demographic collapse of this hominin phenotype.

Functional and developmental influences on intraspecific variation in catarrhine vertebrae

Article

Nov 2018

Objectives We tested whether patterns of intraspecific variation in catarrhine vertebral shape are consistent with developmental or functional predictions. Intraspecific variation was compared across column regions, morphological features, and species. Transitional regions and later ossifying morphological features were predicted to exhibit increased variation. The lumbosacral region, biomechanically important morphological features, and species with high locomotor demand and/or dedicated pronogrady were predicted to exhibit decreased variation. Materials and Methods We used a modified Levene's test to compare intraspecific variation in dimensions of the neural canal, vertebral bodies, and spinous and transverse processes in lower thoracic to proximal sacral vertebrae. The sample included all hominoid genera and one cercopithecoid (Chlorocebus). Results We found little difference in variation across regions of the vertebral column. In hominoids, vertebral body dimensions were the least variable, neural canal dimensions the most variable, with spinous and transverse processes generally intermediate. Among species, there was a general though not always significant pattern for Chlorocebus to exhibit the least variation, followed by Homo or Hylobates. Discussion Patterns of variation across morphological features may reflect the complex interaction of functional constraints, developmental timing, and/or variable biomechanical forces. Pongo's elevated variation in spinous process length suggests a release from functional constraint, consistent with its suspensory locomotion and reduced spinous processes. Interspecific differences in vertebral variation based on locomotor demand or posture are generally consistent with patterns previously reported for vertebral formula and other aspects of morphology. Future research would benefit from an expanded taxonomic sample and more detailed analyses of vertebral modularity and developmental timing.

Testing biomechanical models of human lumbar lordosis variability

Article

May 2017
AM J PHYS ANTHROPOL

Objectives: Lumbar lordosis (LL) is a key adaptation for bipedalism, but factors underlying curvature variations remain unclear. This study tests three biomechanical models to explain LL variability. Materials and Methods: Thirty adults (15 male, 15 female) were scanned using magnetic resonance imaging (MRI), a standing posture analysis was conducted, and lumbar range of motion (ROM) was assessed. Three measures of LL were compared. The trunk's center of mass was estimated from external markers to calculate hip moments (M hip) and lumbar flexion moments. Cross-sectional areas of lumbar vertebral bodies and trunk muscles were measured from scans. Regression models tested associations between LL and the M hip moment arm, a beam bending model, and an interaction between relative trunk strength (RTS) and ROM. Results: Hip moments were not associated with LL. Beam bending was moderately predictive of standing but not supine LL (R 2 5 0.25). Stronger backs and increased ROM were associated with greater LL, especially when standing (R 2 5 0.65). The strength-flexibility model demonstrates the differential influence of RTS depending on ROM: individuals with high ROM exhibited the most LL variation with RTS, while those with low ROM showed reduced LL regardless of RTS. Discussion: Hip moments appear constrained suggesting the possibility of selection, and the beam model explains some LL variability due to variations in trunk geometry. The strength-flexibility interaction best predicted LL, suggesting a tradeoff in which ROM limits the effects of back strength on LL. The strength-flexibility model may have clinical relevance for spinal alignment and pathology. This model may also suggest that straight-backed Neanderthals had reduced lumbar mobility.

The torso integration hypothesis revisited in Homo sapiens : Contributions to the understanding of hominin body shape evolution

Article

Full-text available

Sep 2018

Objectives: Lower thoracic widths and curvatures track upper pelvic widths and iliac blades curvatures in hominins and other primates (torso integration hypothesis). However, recent studies suggest that sexual dimorphism could challenge this assumption in Homo sapiens. We test the torso integration hypothesis in two modern human populations, both considering and excluding the effect of sexual dimorphism. We further assess covariation patterns between different thoracic and pelvic levels, and we explore the allometric effects on torso shape variation. Material and Methods: A sex‐balanced sample of 50 anatomically connected torsos (25 Mediterraneans, 25 Sub‐Saharan Africans) was segmented from computed tomography scans. We compared the maximum medio‐lateral width at seventh–ninth rib levels with pelvic bi‐iliac breadth in males and females within both populations. We measured 1,030 (semi)landmarks on 3D torso models, and torso shape variation, mean size and shape comparisons, thoraco‐pelvic covariation and allometric effects were quantified through 3D geometric morphometrics. Results: Females show narrow thoraces and wide pelves and males show wide thoraces and narrow pelves, although this trend is more evident in Mediterraneans than in Sub‐Saharans. Equal thoracic and pelvic widths, depths and curvatures were found in absence of sexual dimorphism. The highest strength of covariation was found between the lowest rib levels and the ilia, and allometric analyses showed that smaller torsos were wider than larger torsos. Conclusions: This is the first study testing statistically the torso integration hypothesis in anatomically connected torsos. We propose a new and more complex torso integration model in H. sapiens with sexual dimorphism leading to different thoracic and pelvic widths and curvatures. These findings have important implications in hominin body shape reconstructions.

Gorilla beringei (Primates: Hominidae)

Article

Oct 2018

Stephanie L. Canington

Gorilla beringei Matschie, 1903 is a great ape commonly called the eastern gorilla. Highly sexually dimorphic, this diurnal knuckle-walking quadruped is 1 of 2 species of Gorilla, the largest living primates. It is endemic to northwest Rwanda and southwest Uganda as G. b. beringei, and to eastern Democratic Republic of the Congo as G. b. beringei and G. b. graueri. G. beringei is known to both highland and lowland montane forests and subalpine environments, though only G. b. beringei is called the “mountain gorilla.” Those inhabiting higher elevations are more folivorous than those at lower elevations. Groups are highly cohesive polygamous social units, varying in size and composition. G. b. beringei and G. b. graueri are both listed as “Critically Endangered” by the International Union for the Conservation of Nature and Natural Resources.

Was the last common ancestor aping a chimp or just monkeying around?

Article

May 2018

Scott Alan Williams

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

Article

Feb 2018

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.

Morphological integration in the gorilla, chimpanzee, and human neck

Article

Full-text available

Feb 2018

Objectives: Although integration studies are important to understand the evolution of organisms' traits across phylogenies, vertebral integration in primates is still largely unexplored. Here we describe and quantify patterns of morphological integration and modularity in the subaxial cervical vertebrae (C3-C7) in extant hominines incorporating the potential influence of size. Materials and methods: Three-dimensional landmarks were digitized on 546 subaxial cervical vertebrae from 141 adult individuals of Gorilla gorilla, Pan troglodytes, and Homo sapiens. Integration and modularity, and the influence of size effects, were quantified using geometric morphometric approaches. Results: All subaxial cervical vertebrae from the three species show a strong degree of integration. Gorillas show the highest degree of integration; conversely, humans have the lowest degree of integration. Analyses of allometric regression residuals show that size is an important factor promoting integration in gorillas, with lesser influence in chimpanzees and almost no effect in humans. Discussion: Results point to a likely ancestral pattern of integration in non-human hominines, whereby the degree of integration decreases from cranial to caudal positions. Humans deviate from this pattern in the cranialmost (C3) and, to a lesser extent, in the caudalmost (C7) vertebrae, which are less integrated. These differences can be tentatively related to the emergence of bipedalism due to the presence of modern human-like C3 in australopiths, which still preserve a more chimpanzee-like C7.

Regulation of posterior Hox genes by sex steroids explains vertebral variation in inbred mouse strains

Article

Nov 2021

John F Mulley

A series of elegant embryo transfer experiments in the 1950s demonstrated that the uterine environment could alter vertebral patterning in inbred mouse strains. In the intervening decades, attention has tended to focus on the technical achievements involved and neglected the underlying biological question: how can genetically homogenous individuals have a heterogenous number of vertebrae? Here I revisit these experiments and, with the benefit of knowledge of the molecular‐level processes of vertebral patterning gained over the intervening decades, suggest a novel hypothesis for homeotic transformation of the last lumbar vertebra to the adjacent sacral type through regulation of Hox genes by sex steroids. Hox genes are involved in both axial patterning and development of male and female reproductive systems and have been shown to be sensitive to sex steroids in vitro and in vivo. Regulation of these genes by sex steroids and resulting alterations to vertebral patterning may hint at a deep evolutionary link between the ribless lumbar region of mammals and the switch from egg‐laying to embryo implantation. An appreciation of the impact of sex steroids on Hox genes may explain some puzzling aspects of human disease, and highlights the spine as a neglected target for in utero exposure to endocrine disruptors. The uterine environment can alter vertebral patterning. Here I argue that this occurs via regulation of Hox genes by sex steroids. If sex steroids can alter vertebral patterning, then so might in utero exposure to endocrine‐disrupting chemicals (EDCs), highlighting the spine as an unappreciated target of EDCs.

Homeotic change in segment identity derives the human vertebral formula from a chimpanzee-like one

Article

Jul 2021
AM J PHYS ANTHROPOL

Objectives: One of the most contentious issues in paleoanthropology is the nature of the last common ancestor of humans and our closest living relatives, chimpanzees and bonobos (panins). The numerical composition of the vertebral column has featured prominently, with multiple models predicting distinct patterns of evolution and contexts from which bipedalism evolved. Here, we study total numbers of vertebrae from a large sample of hominoids to quantify variation in and patterns of regional and total numbers of vertebrae in hominoids. Materials and methods: We compile and study a large sample (N = 893) of hominoid vertebral formulae (numbers of cervical, thoracic, lumbar, sacral, caudal segments in each specimen) and analyze full vertebral formulae, total numbers of vertebrae, and super-regional numbers of vertebrae: presacral (cervical, thoracic, lumbar) vertebrae and sacrococcygeal vertebrae. We quantify within- and between-taxon variation using heterogeneity and similarity measures derived from population genetics. Results: We find that humans are most similar to African apes in total and super-regional numbers of vertebrae. Additionally, our analyses demonstrate that selection for bipedalism reduced variation in numbers of vertebrae relative to other hominoids. Discussion: The only proposed ancestral vertebral configuration for the last common ancestor of hominins and panins that is consistent with our results is the modal formula demonstrated by chimpanzees and bonobos (7 cervical-13 thoracic-4 lumbar-6 sacral-3 coccygeal). Hox gene expression boundaries suggest that a rostral shift in Hox10/Hox11-mediated complexes could produce the human modal formula from the proposal ancestral and panin modal formula.

Pelvic shape variation among gorilla subspecies: Phylogenetic and ecological signals

Article

Oct 2019
J HUM EVOL

Gorillas occupy habitats that range in elevation from 0 to 3850 m. Populations at higher elevations tend to be less arboreal than lowland populations. Variation in habitat-specific behaviors among closely related populations makes gorillas a unique model to study the relationship between locomotion and morphology. The pelvis reflects differences in locomotion in other primates, and thus may also reflect locomotor differences among gorillas. We tested the hypothesis that pelvic morphology exhibits clinal variation across elevation within Gorilla. Using 3D geometric morphometrics and principal components analysis (PCA), we characterized pelvic shape in three gorilla subspecies representing 14 localities across gorillas' full elevation range: western lowland gorillas (Gorilla gorilla gorilla), mountain gorillas (Gorilla beringei beringei), and Grauer's gorillas (Gorilla beringei graueri). We found that the first principal component (PC1) usually reflects differences between western and eastern gorillas in the lateral margin of the ilium and, in males, the obturator foramen. When sexes are considered together, the second principal component (PC2) indicates some separation between G. b. beringei and G. b. graueri, albeit with considerable overlap, corresponding to the shape of the iliac crest. When sexes were analyzed separately, there was no distinction. Phylogenetic generalized least squares regression was used to evaluate the relationship between elevation and pelvic shape under varying phylogenetic assumptions. Models were compared to assess how phylogenetic adjustment affects model fit. Neither of the first two PCs nor overall shape yielded a significant relationship with elevation in any of the pooled-sex and individual-sex samples. This suggests that covariation between pelvic morphology and elevation is sex-specific and dependent on phylogenetic assumptions. Our results find complex interactions between sex, phylogeny, elevation, and pelvic morphology, suggesting that there is not one ecomorphological pattern that characterizes all gorillas.

The Spine of Australopithecus

Chapter

Aug 2019

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.

The Study of the Human Spine and Its Evolution: State of the Art and Future Perspectives

Chapter

Aug 2019

The vertebral spine is a key element of the vertebrate anatomy and it fulfills two main roles. First, it protects the spinal cord and associated blood vessels. Second, it is a structural column that influences both body posture and locomotion. The study of the evolution of the human spine thus provides information on how the distinct posture and locomotion of our species—striding bipedalism with an upright trunk—developed. In this volume we provide the most updated information on the morphology and evolution of the human spine. This volume mainly focuses on the skeletal aspect and contextualizes it within the evolution of the spine in hominoids, but it also provides orthopedic information as well as an overview of new methodological approaches in study of the spine. The objective of this introductory chapter is to provide an overview of the book, to summarize the state of the art on this subject, and to propose new avenues for future research.

How to Build a 3D Model of a Fossil Hominin Vertebral Spine Based on Osseous Material

Chapter

Full-text available

Aug 2019

Reconstruction of the spinal curvatures of extinct hominins is essential in order to understand their posture and function. Despite its importance, researchers face many difficulties in reconstructing spinal posture based solely on osseous material due to the absence of soft tissues.

The Modern and Fossil Hominoid Spinal Ontogeny

Chapter

Aug 2019

Sandra A Martelli

This chapter presents an overview of the pre- and postnatal ontogeny of the modern human and modern great and lesser ape vertebral column. Understanding of the growth patterns which lead to the distinct and species-specific adult vertebral column morphology of modern humans and great and lesser modern apes is important to interpret fossil hominoid vertebral material in its phylogenetic and functional context.

Numbers of Vertebrae in Hominoid Evolution

Chapter

Aug 2019

Vertebral formulae, the combination of regional numbers of vertebrae making up the bony spine, vary across vertebrates and within hominoid primates. Reconstructing the ancestral vertebral formulae throughout hominoid evolution has proved a challenge due to limited fossil evidence and disagreement among researchers. Proposed “long-backed” and “short-backed” ancestors have implications for the evolution of bipedalism and human evolutionary history generally. Here, we analyze a large dataset of hominoid vertebral formulae, including previously unstudied species and subspecies. We find more variation within and between species than expected, particularly in hylobatids (gibbons or lesser apes) and in gorilla and chimpanzee subspecies. Our results suggest that combined thoracic and lumbar numbers of vertebrae are somewhat phylogenetically structured, with outgroup taxa (two species of Old World monkeys, or cercopithecoids) retaining the primitive number of 19 thoracolumbar vertebrae, hylobatids generally possessing 18 thoracolumbar vertebrae, and hominids (great apes and humans) having 17 or 16 thoracolumbar vertebrae. When compared to cercopithecoids, and to putative stem hominoids, extant hominoids show evidence for homeotic change at both the lumbosacral (e.g., decrease in lumbar vertebrae; increase in sacral segments) and in the position of the transitional vertebrae. Homeotic changes are probably also responsible for the differences between African apes and modern humans, with differences in the number of thoracic and lumbar within a 17-segment thoracolumbar framework.

The Vertebrae, Ribs, and Sternum of Australopithecus sediba

Article

Full-text available

Jan 2019

Australopithecus sediba is known from two partial skeletons, Malapa Hominins 1 and 2 (MH1 and MH2), a juvenile male and an adult female, respectively. Forty-eight elements of the axial skeleton, including vertebrae, ribs, a sternum, and a sacrum, are known from MH1 and MH2. Here, we describe these ~2.0 Ma fossils and provide raw data and plots of standardized measurements. We revisit the serial positions of the previously described vertebrae and ribs proposed in their initial announcements and provide revised identifications. Additionally, we include in our descriptions and analyses new axial material. Finally, we also test the hypothesis that multiple species are represented in the MH1 and MH2 material and specifically that MH1’s lumbar vertebrae belong to a member of the genus Homo, whereas those of MH2 belong to Australopithecus. We do not find support for this hypothesis, and instead attribute differences between MH1 and MH2 to their age difference and incomplete growth of the vertebral body in juvenile MH1.

Sexual Dimorphism and the Origins of Human Spinal Health

Article

Jan 2018
ENDOCR REV

Recent observations indicate that the cross-sectional area (CSA) of vertebral bodies are on average 10% smaller in healthy newborn girls than in newborn boys - a striking difference that increases during infancy and puberty, and is greatest by the time of sexual and skeletal maturity. The smaller vertebral CSA in females is associated with greater spinal flexibility, and could represent the human adaptation to fetal load in bipedal posture. Unfortunately, it also imparts a mechanical disadvantage that increases stress within the vertebrae for all physical activities. This review summarizes the potential endocrine, genetic, and environmental determinants of vertebral cross-sectional growth and current knowledge on the association between the small female vertebrae and increased risk for a broad array of spinal conditions across the lifespan.

A volumetric technique for fossil body mass estimation applied to Australopithecus afarensis

Article

Aug 2017
J HUM EVOL

The evolution of vertebral formulae in Hominoidea

Article

Sep 2017

Primate vertebral formulae have long been investigated because of their link to locomotor behavior and overall body plan. Knowledge of the ancestral vertebral formulae in the hominoid tree of life is necessary to interpret the pattern of evolution among apes, and to critically evaluate the morphological adaptations involved in the transition to hominin bipedalism. Though many evolutionary hypotheses have been proposed based on living and fossil species, the application of quantitative phylogenetic methods for thoroughly reconstructing ancestral vertebral formulae and formally testing patterns of vertebral evolution is lacking. To estimate the most probable scenarios of hominoid vertebral evolution, we utilized an iterative ancestral state reconstruction approach to determine likely ancestral vertebral counts in apes, humans, and other anthropoid out-groups. All available ape and hominin fossil taxa with an inferred regional vertebral count were included in the analysis. Sensitivity iterations were performed both by changing the phylogenetic position of fossil taxa with a contentious placement, and by changing the inferred number of vertebrae in taxa with uncertain morphology. Our ancestral state reconstruction results generally support a short-backed hypothesis of human evolution, with a Pan-Homo last common ancestor possessing a vertebral formulae of 7:13:4:6 (cervical:thoracic:lumbar:sacral). Our results indicate that an initial reduction in lumbar vertebral count and increase in sacral count is a synapomorphy of crown hominoids (supporting an intermediate-backed hypothesis for the origins of the great ape-human clade). Further reduction in lumbar count occurs independently in orangutans and African apes. Our results highlight the complexity and homoplastic nature of vertebral count evolution, and give little support to the long-backed hypothesis of human evolution.

Hox genes and the evolution of vertebrate axial morphology

Article

Full-text available

Feb 1995

A common form of evolutionary variation between vertebrate taxa is the different numbers of segments that contribute to various regions of the anterior-posterior axis; cervical vertebrae, thoracic vertebrae, etc. The term ‘transposition’ is used to describe this phenomenon. Genetic experiments with homeotic genes in mice have demonstrated that Hox genes are in part responsible for the specification of segmental identity along the anterior-posterior axis, and it has been proposed that an axial Hox code determines the morphology of individual vertebrae (Kessel, M. and Gruss, P. (1990) Science 249, 347–379). This paper presents a comparative study of the developmental patterns of homeobox gene expression and developmental morphology between animals that have homologous regulatory genes but different morphologies. The axial expression boundaries of 23 Hox genes were examined in the paraxial mesoderm of chick, and 16 in mouse embryos by in situ hybridization and immunolocalization techniques. Hox gene anterior expression boundaries were found to be transposed in concert with morphological boundaries. This data contributes a mechanistic level to the assumed homology of these regions in vertebrates. The recognition of mechanistic homology supports the historical homology of basic patterning mechanisms between all organisms that share these genes.

Why do almost all mammals have seven cervical vertebrae? Developmental constraints, Hox genes, and cancer

Article

Full-text available

Apr 1999
J Exp Zool

Frietson Galis

Mammals have seven cervical vertebrae, a number that remains remarkably constant. I propose that the lack of variation is caused by developmental constraints: to wit, changes in Hox gene expression, which lead to changes in the number of cervical vertebrae, are associated with neural problems and with an increased susceptibility to early childhood cancer and stillbirths. In vertebrates, Hox genes are involved in the development of the skeletal axis and the nervous system, among other things. In humans and mice, Hox genes have been shown also to be involved in the normal and abnormal (cancer) proliferation of cell lines; several types of cancer in young children are associated with abnormalities in Hox gene expression and congenital anomalies. In these embryonal cancers the incidence of a cervical rib (a rib on the seventh cervical vertebra, a homeotic transformation of a cervical vertebra towards a thoracic‐type vertebra) appears to be increased. The minimal estimate of the selection coefficient acting against these mutations is about 12%. In birds and reptiles variations in the number of cervical vertebrae have frequently occurred and there is often intraspecific variability. A review of the veterinary literature shows that cancer rates appear lower in birds and reptiles than in mammals. The low susceptibility to cancer in these classes probably prevents the deleterious pleiotropic effect of neonatal cancer when changes in cervical vertebral number occur. In mammals there is, thus, a coupling between the development of the axial skeleton and other functions (including the proliferations of cell lines). The coupling of functions is either a conserved trait that is also present in reptiles and birds, but without apparent deleterious effects, or the coupling is new to mammals due to a change in the functioning of Hox genes. The cost of the coupling of functions in mammals appears to be an increased risk for neural problems, neonatal cancer, stillbirths, and a constraint on the variability of cervical vertebral number. J. Exp. Zool. (Mol. Dev. Evol.) 285:19–26, 1999. © 1999 Wiley‐Liss, Inc.

Independent regulation of vertebral number and vertebral identity by microRNA-196 paralogs

Article

Full-text available

Jul 2015

Significance The vertebral column provides essential structural and protective functions. The total number of vertebral elements and their specific morphologies are remarkably reproducible within a given species, yet can be tailored to the requirements of separate vertebrate species. Major genetic determinants driving formation of the vertebral column are known, but how they are regulated to achieve a highly reproducible structure remains to be fully elucidated. In this report, we show that the miR-196 family of microRNAs are essential in defining correct vertebral number and vertebral identity in mouse. We reveal the molecular landscape controlled, either directly or indirectly, by miR-196 activity, to demonstrate that miR-196 impacts many key developmental signalling pathways and reinforces a timely trunk-to-tail Hox code transition.

Neither chimpanzee nor human, Ardipithecus reveals the surprising ancestry of both

Article

Full-text available

Apr 2015

Australopithecus fossils were regularly interpreted during the late 20th century in a framework that used living African apes, especially chimpanzees, as proxies for the immediate ancestors of the human clade. Such projection is now largely nullified by the discovery of Ardipithecus. In the context of accumulating evidence from genetics, developmental biology, anatomy, ecology, biogeography, and geology, Ardipithecus alters perspectives on how our earliest hominid ancestors--and our closest living relatives--evolved.

Evolution of the Hominoid Vertebral Column: The Long and the Short of It

Article

Full-text available

Jan 2015

The postcranial axial skeleton exhibits considerable morphological and functional diversity among living primates. Particularly striking are the derived features in hominoids that distinguish them from most other primates and mammals. In contrast to the primitive catarrhine morphotype, which presumably possessed an external (protruding) tail and emphasized more pronograde trunk posture, all living hominoids are characterized by the absence of an external tail and adaptations to orthograde trunk posture. Moreover, modern humans evolved unique vertebral features that satisfy the demands of balancing an upright torso over the hind limbs during habitual terrestrial bipedalism. Our ability to identify the evolutionary timing and understand the functional and phylogenetic significance of these fundamental changes in postcranial axial skeletal anatomy in the hominoid fossil record is key to reconstructing ancestral hominoid patterns and retracing the evolutionary pathways that led to living apes and modern humans. Here, we provide an overview of what is known about evolution of the hominoid vertebral column, focusing on the currently available anatomical evidence of three major transitions: tail loss and adaptations to orthograde posture and bipedal locomotion. © 2015 Wiley Periodicals, Inc.

EVOLUTION OF THE HOMINOID VERTEBRAL COLUMN BY

Article

Full-text available

Fast running restricts evolutionary change of the vertebral column in mammals

Article

Full-text available

Jul 2014

Significance Our study explains one of the riddles of mammal evolution: the strong conservation of the number of trunk vertebrae. The vertebral column and its high evolvability are considered to be of central importance for the evolution of vertebrates, which is why the constancy is both puzzling and important. We hypothesize, on biomechanical and developmental grounds, that evolutionary change is virtually impossible in fast running and agile mammals. The rationale is that several mutations are necessary to change trunk vertebral counts, with single mutations usually leading to irregular lumbosacral joints that severely hamper running and jumping capability. Our observations indeed show that selection against these initial changes is strong in fast and agile mammals and weak in slower and sturdier ones.

The Vertebral Column of Australopithecus sediba

Article

Full-text available

Apr 2013
SCIENCE

Two partial vertebral columns of Australopithecus sediba grant insight into aspects of early hominin spinal mobility, lumbar curvature, vertebral formula, and transitional vertebra position. Au. sediba likely possessed five non-rib-bearing lumbar vertebrae and five sacral elements, the same configuration that occurs modally in modern humans. This finding contrasts with other interpretations of early hominin regional vertebral numbers. Importantly, the transitional vertebra is distinct from and above the last rib-bearing vertebra in Au. sediba, resulting in a functionally longer lower back. This configuration, along with a strongly wedged last lumbar vertebra and other indicators of lordotic posture, would have contributed to a highly flexible spine that is derived compared with earlier members of the genus Australopithecus and similar to that of the Nariokotome Homo erectus skeleton.

The third partial skeleton of a late Pliocene hominin (Stw 431) from Sterkfontein, South Africa

Article

Full-text available

May 2003

Partial skeletons of ancient hominins are extremely rare. When located, they present unique opportunities for palaeo-anthropological enquiry. From East African Pliocene and early Pleistocene sites, two associated skeletons, AL. 288-1 assigned to Australopithecus afarensis,1,2 and OH 62 (Homo habilis)3 are well-known. Other examples are KNM-ER 1500, 4 the diseased skeleton, KNM-ER 1808,4-6 and the very complete and also diseased skeleton of the Nariokotome boy,7 from west of Lake Turkana, Kenya, both of the latter being classified as H. erectus. From the dolomitic limestone cave of Sterkfontein, South Africa, until 1987 only two partial skeletons, Sts 14 (A. africanus)8 and a cluster of specimens found in July-August 1986,9 were available. The 1987 discovery, of which a preliminary description is given here, comprised some 48 bone fragments which, when pieced together, represented 18 bones of a manifestly single adult hominin skeleton, probably male (Stw 431).10 To these three partial skeletons must be added the partially excavated fine skeleton Stw 573 from Member 2 in the Sterkfontein Formation.11,12 The Sterkfontein site is unique in having yielded, thus far, four partial skeletons of hominins. Thus, of only six australopithecine skeletons that have been brought to light in Africa, four have stemmed from Sterkfontein. Stw 431 was recovered in situ by the late A.R. Hughes, S. Sekowe, M. Makgothokgo, and other field assistants from Member 4, Bed B, of the Sterkfontein Formation. On grounds of its provenance, as well as on Occam's razor and with compatible morphology, it is attributed to A. africanus. The skeleton shows an interesting complex of primitive and derived features, throwing further light on the mosaic character of hominin evolution. While the pelvis is broadly similar to that of modern humans in some respects, the elbow more closely resembles those of early hominins than that of modern humans. These features, together with the relatively small size of the lumbar vertebrae and sacrum, provide insights into the locomotor repertoire of A. africanus. They support suggestions that the australopithecines, although adapted for bipedalism, were not consistent or obligate bipeds. Resemblances between comparable postcranial bones of Stw 431 and of Hadar suggest close morphological similarity between A. africanus and A. afarensis.

Miocene Hominids and the Origins of the African Apes and Humans

Article

Full-text available

Oct 2010

David Begun

In the past 20 years, new discoveries of fossil apes from the Miocene have transformed our ideas about the timing, geography, and causes of the evolution of the African apes and humans. Darwin predicted that the common ancestor of African apes and humans would be found in Africa. Yet the majority of fossil great apes are from Europe and Asia. I briefly review the fossil record of great apes and then examine the main competing hypotheses of our origins, African or European, inspired by these recent discoveries, concluding that elements of both ideas are likely to be correct. Given current interpretations of the paleobiology of fossil apes and relationships among living hominids, I suggest that the last common ancestor of chimpanzees and humans was morphologically unique, but more chimpanzee-like than hominin-like: a knuckle-walker with a chimpanzee-sized brain, canine sexual dimorphism, and many probable behavioral similarities to living chimpanzees.

The skeleton of the trunk and limbs of higher primates

Article

A.H. Schultz

Observations on the growth, classification and evolutionary specialization of gibbons and siamangs

Article

Jan 1933

A.H. Schultz

The Thoracic and Lumbar Vertebrae

Chapter

Jan 1993

Man's posture: Its evolution and disorders

Article

Jan 1923
Br Med J

A. Keith

The Postcranial Bones

Chapter

Jan 1993

The human sacrum

Article

Jan 1893

A.M. Paterson

The definition of thoracic and lumbar vertebrae

Article

Jan 1952

Brachiation in New World monkeys and in anthropoid apes

Article

Jan 1963

G.E. Erikson

Die Wirbelsäule der Japaner

Article

Jan 1913
Z Morphol Anthropol

K. Hasebe

Vertebral column and thorax

Article

Jan 1961

A.H. Schultz

Numerical vertebral variation in the human adult and embryo

Article

Jan 1904

C.R. Bardeen

Comparative biologic-anatomical investigations on the vertebral column and spinal muscular of mammals. Verhandelingen der Koninklijke Nederlandshe Akadamie van Wetenschappen, Afd. Naturekunde

Article

E.J. Slijper

Article

Jan 1932
Bull Mus Comp Zool

Materials for the Study of Variation Treated With Especial Regard to Discontinuity in the Origin of Species

Article

Jan 1894

William Bateson

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

Article

Jun 2015

Motions of the Running Cheetah and Horse

Article

Nov 1959

Milton Hildebrand

Postcranial Adaptation in Nonhuman Primates

Article

Nov 1994

Early Hominid Posture and Locomotion.

Article

Sep 1974
Man

Numerical Variation of Vertebrae in Japanese Macaques, Macaca fuscata

Article

Jan 1994
ANTHROPOL SCI

Mitsuru Aimi

Based on 882 skeletal specimens comprising 444 males and 438 females, the vertebrae of Japanese macaques, Macaca fuscata fuscata, were examined. Numerical variation was determined by counting ribs and by counting facets. No sexual difference was significant in overall distribution of frequencies. The number of cervical vertebrae was invariably seven. The ranges of variation in thoracic, lumbar, sacral, and caudal vertebrae were 12-13, 6-8, 2-4, and 7-11, respectively. The maximum number of caudals exceeds 12, though unconfirmed. The ranges of variation in thoracolumbar, lumbosacral, and thoracolumbosacral vertebrae were 18-20, 9-11, and 21-24, respectively. These variations cannot be fully explained by thoracization, lumbarization, and/or sacralization. The range of variation in vertebrae with thoracic type of prezygapophyseal facets was 8-11, which is wider than that reported previously. Vertebrae are repetitive units with numerical variation. It is impossible to homologize each vertebra among individuals. A new paradigm is needed in order to understand the numerical variation of the vertebral column. © 1994, The Anthropological Society of Nippon. All rights reserved.

“Lucy” (A.L. 288-1) had five sacral vertebrae

Article

Oct 2014
AM J PHYS ANTHROPOL

A “long-backed” scenario of hominin vertebral evolution posits that early hominins possessed six lumbar vertebrae coupled with a high frequency of four sacral vertebrae (7:12-13:6:4), a configuration acquired from a hominin-panin last common ancestor (PLCA) having a vertebral formula of 7:13:6-7:4. One founding line of evidence for this hypothesis is the recent assertion that the “Lucy” sacrum (A.L. 288-1an, Australopithecus afarensis) consists of four sacral vertebrae and a partially-fused first coccygeal vertebra (Co1), rather than five sacral vertebrae as in modern humans. This study reassesses the number of sacral vertebrae in Lucy by reexamining the distal end of A.L.288-1an in the context of a comparative sample of modern human sacra and Co1 vertebrae, and the sacrum of A. sediba (MH2). Results demonstrate that, similar to S5 in modern humans and A. sediba, the last vertebra in A.L. 288-1an exhibits inferiorly-projecting (right side) cornua and a kidney-shaped inferior body articular surface. This morphology is inconsistent with that of fused or isolated Co1 vertebrae in humans, which either lack cornua or possess only superiorly-projecting cornua, and have more circularly-shaped inferior body articular surfaces. The level at which the hiatus' apex is located is also more compatible with typical five-element modern human sacra and A. sediba than if only four sacral vertebrae are present. Our observations suggest that A.L. 288-1 possessed five sacral vertebrae as in modern humans; thus, sacral number in “Lucy” does not indicate a directional change in vertebral count that can provide information on the PLCA ancestral condition. Am J Phys Anthropol, 2014. © 2014 Wiley Periodicals, Inc.

Structure and scaling of the lumbar vertebrae in African bovids (Mammalia: Artiodactyla)

Article

Feb 1987

The structure and dimensions of the lumbar vertebrae from 18 genera of African bovids (with a body weight range of 4–900 kg) were studied with reference to allometric and biomechanical factors. Centrum height scales with body weight according to McMahon's elastic similarity theory, but centrum width scales geometrically with body weight. Thus, the dimensions of bones need not scale according to a single principle. Transverse process orientation, as measured in two planes, varies allometrically with body weight; this trend may reflect size‐related differences in abdominal girth and spinal musculature. Bovids exhibit decreasing lumbar mobility in the sagittal plane with increasing body size, a phenomenon related to an increase in centrum height and the appearance of interlocking mechanisms (postzygapophysial ridges and prezygapophysial labra). Geometric scaling of centrum width and zygapophysial curvature is evidence that lateral flexion of the spine occurs throughout the family. In all taxa examined, the last lumbar vertebra exhibits an absolutely wider centrum and straight postzygapophyses, thus reducing lateral mobility at the lumbosacral joint. In heavier bovids, the observed restriction of lumbar flexion and extension to the lumbosacral joint is a consequence of the distribution of the shapes of the centra and the interlocking mechanisms of the zygapophyses.

A fragmentary pelvis of Paranthropus robustus of the Plio-Pleistocene site of Drimolen (Republic of South Africa)

Article

Mar 2002
Geobios

The vertebral remains of the late Miocene great ape Hispanopithecus laietanus from Can Llobateres 2 (Valles-Penedes Basin, NE Iberian Peninsula)

Article

Jun 2014

In vivo axial rotation at the thoracolumbar junction: An investigation using low dose CT in healthy male volunteers

Article

Aug 1989
CLIN BIOMECH

Few studies report in vivo data on segmental spinal rotation due to complexities in resolving axial plane motion. Unilateral segmental rotation at the thoracolumbar junction in 18 healthy male volunteers was assessed using a low dose CT protocol. Subjects were positioned in end-range right trunk rotation and, following a digital scanogram, were scanned in the plane of the superior vertebral end-plates of T10-L3. The change in vertebral orientation between mobile segments, assumed to represent 'rotation', was calculated using standardized CT image references and vertebral landmarks. Greatest rotation appeared to occur with coronally oriented joints and the least change between segments where a mortice joint or the thoracolumbar transition was demonstrated. The mean trend was similar for individuals with either an abrupt or gradual change from coronal to sagittal plane orientation of their zygapophysial joints. Although not statistically significant, the gradual pattern demonstrated generally greater rotation at each segmental level compared to those subjects with an abrupt transition pattern. In contrast, routine supine thoracolumbar junction scans of patients showed lesser mean physiological rotation between all segments examined.

Thoracolumbar vertebral number: The first skeletal synapomorphy for afrotherian mammals

Article

Mar 2007

There is overwhelming molecular support for the monophyly of a supra‐ordinal clade of living African placental mammals, the Afrotheria, but there is not a single unequivocal morphological synapomorphy for this group. We conducted a survey of thoraco‐lumbar vertebral numbers across mammals, based on the examination of specimens representing 86 living and 12 fossil species and a thorough review of the anatomical literature. A total of 19 thoraco‐lumbar vertebrae is plesiomorphic for mammals, eutherians and metatherians. Metatherians show no variation in this plesiomorphic condition, suggesting the presence of a developmental constraint, in view of the contrasting variability of the equally old eutherian clade. Several deviations from the plesiomorphic condition have evolved independently in the course of placental phylogeny. Optimization of the information on a published phylogenetic framework based on molecular sequence data reveals that an increase in the number of thoracolumbar vertebrae is the first unambiguous skeletal synapomorphy of Afrotheria.

Attainment of the Upright Posture of Man

Article

Jan 1940
NATURE

F. WOOD JONES

Man's posture: Its evolution and disorders

Article

Nov 1922

Arthur Keith

The Influence of Bodily Locomotion in Separating Man from the Monkeys and Apes

Article

Henry Fairfield Osborn

Trunk movements during locomotion in the marsupial Monodelphis domestica (Didelphidae)

Article

Feb 1992
J MORPHOL

Peter Pridmore

The small didelphid cmarsupial, Monodelphis domestica , uses a lateral sequence walk during slow treadmill locomotion and gradually shifts to a trot as speed increases. At higher speeds it changes abruptly to a half-bound. Cinematographic records suggest significant lateral bending but no sagittal bending of the trunk during the slow walk and a reduced amount of lateral bending during the fast walk. There is slight lteral, but no sagittal, bending during the trot. Sagittal bending is obvious during the half-bound, but no lateral bending is evident. Cineradiography confirms that the vertebral column of the trunk bends laterally during the slow walk. Bending occurs throughout the trunk region, but seems to be most pronounced in the anterior lumbar region. Associated with this bending of the trunk is substantial rotation of the pelvic girdle in the plane of yaw. Pelvic rotation is synchronized with the locomotor cycle of hindlimbs. Each side of the pelvis rotates forward during the recovery phase of the ipsilateral hindlimb and backward during the contact phase of this limb. Information on locomotor trunk movements in other limbed tetrapods is limited. The pattern of trunk bending found in Monodelphis , however, is consistent with that reported in the placental mammal Felis catus and in some lepidosaurian reptiles. This suggests that sagittal bending did not replace lateral bending during the evolution of mammals, as is sometimes suggested. Rather, bending in the vertical plane seems to have been added to lateral bleeding when the ancestors of extant mammals acquired galloping and bounding capabilities. Peer Reviewed http://deepblue.lib.umich.edu/bitstream/2027.42/50285/1/1052110203_ftp.pdf

Palaeoanthropology: Hesitation on hominin history

Article

May 2013
NATURE

William H Kimbel

Extensive studies of fossil skeletons of Australopithecus sediba provide fascinating details of the anatomy of this hominin species, but do not convincingly indicate its position on the evolutionary route to modern humans.

Contributions toward a more complete knowledge of the axial skeleton in the Primates

Article

Jul 2010
J ZOOL

St. George Mivart

Vertebral numbers and human evolution

Abstract

No full-text available