Scott Alan Williams

New York University | NYU · Department of Anthropology

Since the first discovery of human fossils in the mid‐19th century, two subjects—our phylogenetic relationship to living and fossil apes and the ancestral locomotor behaviors preceding bipedalism—have driven the majority of discourse in the study of human origins. With few fossils and thus limited comparative evidence available to inform or constra...

We describe a novel pelvic feature, the “ventral sulcus,” located on the pubic bone ventrolateral to the pubic symphysis, which is present in A.L. 288‐1 (Australopithecus afarensis) and MH2 (Australopithecus sediba). We determine how widespread the appearance of the ventral sulcus is in fossil hominins, modern humans, and other extant hominoids. We...

In humans and known fossil hominins, lumbar lordosis is produced by vertebral body wedging and other bony and soft tissue features such as the shape of the intervertebral discs. Current techniques for quantifying the wedging of vertebral bodies are limited in utility, especially when analyzing incomplete fossil material. Here, we introduce a 3D met...

Homo naledi is represented by abundant remains from the Dinaledi Chamber of the Rising Star Cave system in South Africa. While pelvic elements from the Dinaledi Chamber of the cave are fragmentary, a relatively complete ilium (U.W. 102a–138) was recovered from the Lesedi Chamber. We reconstructed and analyzed the Lesedi ilium, providing qualitative...

Variation in ulna morphology is known to differentiate specialized locomotor groups. Using elliptical Fourier analysis, we evaluate the ulnar shaft and proximal complex in 13 hominin fossils from Sahelanthropus, Ardipithecus, Australopithecus, Paranthropus, and early Homo. Principal components of shape contours were evaluated against locomotor patt...

The ulna of extant apes is distinct from other anthropoids, with knuckle-walking engendering an especially unique robusticity and curvature in the African apes. Here we use Fourier shape descriptors to compare ulna contours in a sample of 418 extant primates from 88 species against fifteen hominin fossil ulnae from Sahelanthropus, Ardipithecus, Aus...

Despite exhibiting a range of specializations in locomotion most primates have a relatively generalized postcranial skeleton, enabling extensive locomotor flexibility. However, a small number of forelimb traits, including in the morphology of the ulna, exhibit strong functional signals that may provide a link between skeletal morphology and locomot...

Lumbar lordosis is a key adaptation to bipedal locomotion in the human lineage. Dorsoventral spinal curvatures enable the body's center of mass to be positioned above the hip, knee, and ankle joints, and minimize the muscular effort required for postural control and locomotion. Previous studies have suggested that Neandertals had less lordotic (ven...

Objective: Reconstructing the social lives of extinct primates is possible only through an understanding of the interplay between morphology, sexual selection pressures, and social behavior in extant species. Somatic sexual dimorphism is an important variable in primate evolution, in part because of the clear relationship between the strength and...

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 stres...

Adaptations of the lower back to bipedalism are frequently discussed but infrequently demonstrated in early fossil hominins. Newly discovered lumbar vertebrae contribute to a near-complete lower back of Malapa Hominin 2 (MH2), offering additional insights into posture and locomotion in Australopithecus sediba . We show that MH2 possessed a lower ba...

Our understanding of the evolution of the human thorax has largely improved during the last decade through the use of virtual anthropology and 3D geometric morphometrics. For example, recent research has produced 3D reconstructions of the thorax of adult and subadult Neanderthals [1,2], but also other fossil species such as Homo erectus [3]. In the...

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 whic...

Adaptations of the lower back to bipedalism are frequently discussed but infrequently demonstrated in early fossil hominins. Newly discovered lumbar vertebrae contribute to a near-complete lower back of Malapa Hominin 2 (MH2), offering additional insights into posture and locomotion in Australopithecus sediba. We show that MH2 demonstrates a lower...

The evolution of bipedalism and reduced reliance on arboreality in hominins resulted in larger lower limb joints relative to the joints of the upper limb. The pattern and timing of this transition, however, remains unresolved. Here, we find the limb joint proportions of Australopithecus afarensis , Homo erectus , and Homo naledi to resemble those o...

Discoveries of ulnae for early hominins such as the TM 266-01-050 Sahelanthropus tchadensis and the StW 573 (“Little Foot”) Australopithecus are welcome additions to the early hominin fossil record. Significant curvature of the ulna is a normal anatomic feature among extant apes and many early hominins that has been linked to locomotor behaviors in...

Previous work suggests the significant curvature of the StW 573 (‘Little Foot’) ulna shaft represents pathological traumatic bowing from a childhood fall. Here we test this hypothesis via elliptical Fourier shape analysis in a sample of apes, modern humans, including clinical humans with this pathology. Fossil hominins also compared here include: S...

Highlights: Previous work suggests curvature of the ‘Little Foot’ ulna represents pathological bowing from a childhood fall. Shape analysis in apes, hominins and modern humans, including clinical humans rejects the traumatic bowing hypothesis. Instead, the ‘Little Foot’ ulna reflects a natural degree of curvature observed in apes and many early...

The morphology and positional behavior of the last common ancestor of humans and chimpanzees are critical for understanding the evolution of bipedalism. Early 20th century anatomical research supported the view that humans evolved from a suspensory ancestor bearing some resemblance to apes. However, the hand of the 4.4-million-year-old hominin Ardi...

We examine how derived functional signal and phylogenetic inheritance interact in the forelimb of tree sloths, to understand the relative contribution of each in the evolution of a novel morphobehavioural suite. Molecular and craniodental data demonstrate that extant tree sloths evolved suspensory behaviours and associated morphologies from a non-s...

Danuvius guggenmosi is a species of Miocene hominoid from the 11.62-million-year-old site of Hammerschmiede. On the basis of interpretations of its vertebrae and limbs, Böhme and colleagues infer that Danuvius exhibited ‘joint positions and loading patterns of both hominin bipedalism that emphasize hindlimb extension and spinal curvatures, and exta...

Like many other anatomical structures, the ribcage has changed its morphology and configuration throughout primate evolutionary history. Unfortunately, ribs usually appear broken in the fossil record, which challenges the interpretation of their morphology. In this context, it has been observed that the mineralized area of the rib cross-section at...

The tall and narrow body shape of anatomically modern humans (Homo sapiens) evolved via changes in the thorax, pelvis and limbs. It is debated, however, whether these modifications first evolved together in African Homo erectus, or whether H. erectus had a more primitive body shape that was distinct from both the more ape-like Australopithecus spec...

Recent discoveries from A. anamensis at Assa Issie (4.2 Ma) and A. afarensis from Woranso Mille (3.6 Ma) in Ethiopia, along with later fossils of A. sediba from Malapa and P. robustus from Drimolen in South Africa preserve rare aspects of vertebral anatomy from opposite poles of the postcranial axial skeleton (C1-C3; S5). Here we use 2D geometric m...

Variation in pelvic morphology has a complex genetic basis and its patterning and specification is governed by conserved developmental pathways. Whether the mechanisms underlying the differentiation and specification of the pelvis also produce the morphological covariation on which natural selection may act, is still an open question in evolutionar...

The bony pelvis is perhaps one of the most complicated structures in the body. Considering its complex structure, using three-dimensional (3D) geometric morphometrics in analyzing shape variation between primate groups is important as it maintains the 3D shape of the innominate. Locomotor modes can vary within and between species, and primates are...

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...

In this chapter, we summarize vertebral remains from early Pleistocene Homo, including H. erectus, as well as H. naledi and H. floresiensis fossils from the Middle and Late Pleistocene, respectively. Two partial immature H. erectus skeletons where vertebrae are well represented are KNM-WT 15000 (“Turkana boy”) and the D2700 individual from Dmanisi....

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 an...

Australopitheus anamensis fossils demonstrate that craniodentally and postcranially the taxon was more primitive than its evolutionary successor Australopithecus afarensis. Postcranial evidence suggests habitual bipedality combined with primitive upper limbs and an inferred significant arboreal adaptation. Here we report on A. anamensis fossils fro...

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 product...

Classic studies in Palaeoanthropology suggest that in hominins and other primates thoraces and pelves are anatomically integrated. However, this torso integration hypothesis has been only tested in isolated bones so far, but not in anatomically connected torsos. Here we aim at testing the torso integration hypothesis in two modern human populations...

The lower back is adapted to mobility and stability across mammals and reflects posture and locomotion in the framework of a species’ evolutionary history. Upright bipedalism is one such positional behavior, and due to limited fossil evidence, disagreements exist as to when, how, and in what evolutionary context bipedalism evolved. Here, we describ...

Seven A. anamensis vertebral fossils from the Assa Isse locality in Ethiopia's Middle Awash area dated to ~4.2 Ma constitute the oldest known australopith axial remains. Because the spine is the interface between major body segments, these fossils can be informative on the behavior and evolution of the first australopiths. Two C1 vertebrae are simi...

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 s...

Across mammals, encephalization and longevity show a strong correlation. It is not clear, however, whether these traits evolved in a correlated fashion within mammalian orders, or when they do, whether one trait drives changes in the other. Here, we compare independent and correlated evolutionary models to identify instances of correlated evolution...

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 c...

Mammals: An increase in body size requires an isometric increase in lung capacity/thorax size. Great Apes: We hypothesize that wide lower thoraces accommodate body size increases, while narrow upper thoraces maintain efficient forearm locomotion. Hominins: We hypothesize that wide upper thoraces accommodate body size increases and maximize the ac...

In the hominin fossil record, pelvic remains are sparse and are difficult to attribute taxonomically when they are not directly associated with craniodental material. Here we describe the pelvic remains from the Dinaledi Chamber in the Rising Star cave system, Cradle of Humankind, South Africa, which has produced hominin fossils of a new species, H...

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-sh...

Postcranial measurements. DOI: http://dx.doi.org/10.7554/eLife.24232.047

Canonical variates analysis of carpal morphology. DOI: http://dx.doi.org/10.7554/eLife.24232.048

Traits of the LES1 cranium in comparison to H. naledi and other hominin species. DOI: http://dx.doi.org/10.7554/eLife.24232.045

Cranial and mandibular measurements. DOI: http://dx.doi.org/10.7554/eLife.24232.046

Taphonomic observations by specimen from the Lesedi Chamber. DOI: http://dx.doi.org/10.7554/eLife.24232.049

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...

Modern human evolution is marked by a gradual decline in overall skeletal strength, as a result, humans are more susceptible to osteological disorders. Human chromosome region 11q12-13 has been identified multiple times as a potential region housing gene(s) associated with variation in bone mineral density (BMD). Specifically, two candidate genes–L...

H. naledi shows a mosaic morphological pattern with several derived (Homo-like) features of the skull, hands and feet, and primitive (australopith- like) features in the ribcage, shoulder, and pelvis. This pattern reflects a morphology that might be expected of a hominin at the evolutionary transition between Australopithecus and Homo. Two thoracic...

Modern humans experience rotational birth, and the size of the neonatal head and shoulders closely fits the maternal birth canal. It is unclear when this form of birth evolved. Fossils such as Sts 14—a partial Australopithecus africanus pelvis—can shed light on this issue, but it is incomplete and partly deformed. Sts 14 has been reconstructed manu...

Considered individually, many aspects of early hominin cervical anatomy appear more similar to the African great apes than to humans, suggesting an ape-like pattern of load transfer, and by extension points to significant differences with human head carriage. However, when the australopith cervical spine is examined as a whole, rather than as separ...

The rapid spread of Homo erectus from Africa, especially into the more temperate climates of Eurasia, has been variously attributed to technological, energetic, and foraging shifts. The temporal and regional anatomical variation in H. erectus suggests a high level of developmental plasticity, or the ability to modify development in response to envi...

Long bone cross-sectional properties are reflective of mechanical loading environment and have been used to make behavioral inferences. However, the genetic basis of this complex morphology remains unknown. Human chromosome region 11q12-13 has been identified multiple times as a potential region housing gene(s) associated with variation in bone min...

Nearly all mammals possess seven cervical vertebrae, and many groups retain the primitive number of 19 thoracolumbar vertebrae (TL), implying long-term evolutionary stasis. Recently, Galis and colleagues proposed that stabilizing selection for agility and fast running canalizes variation because evolutionary change in TL number can result in incomp...

The thorax and pelvis are integrated systems, important for understanding human body shape and evolution. Research has shown that in the lower thorax, sexual dimorphism and allometry produce wider ribcages in larger males and narrower ones in smaller females. If the pelvis and thorax are integrated, we would expect that the upper pelvis would simil...

Numbers of precaudal vertebrae are relatively stable in mammals, with cervical vertebrae fixed at seven in nearly all species, 19-20 thoracolumbar vertebrae (TL), and 29-30 precaudal vertebrae (PC), whereas the number of tail vertebrae is highly variable both within and between major clades. Hominoid primates have varyingly short trunks, generally...

The social brain hypothesis posits that social complexity is the primary driver of primate cognitive complexity, and that social pressures ultimately led to the evolution of the large human brain. Although this idea has been supported by studies indicating positive relationships between relative brain and/or neocortex size and group size, reported...

We describe the earliest evidence for neoplastic disease in the hominin lineage. This is reported from the type specimen of the extinct hominin Australopithecus sediba from Malapa, South Africa, dated to 1.98 million years ago. The affected individual was male and developmentally equivalent to a human child of 12 to 13 years of age. A penetrating l...

Homo erectus was the first hominin to exhibit extensive range expansion. This extraordinary departure from Africa , especially into more temperate climates of Eurasia, has been variously related to technological, energetic and foraging shifts. The temporal and regional anatomical variation in H. erectus suggests that a high level of developmental p...

First ribs – the first or most superior ribs in the thorax – are rare in the hominin fossil record, and when found, have the potential to provide information regarding the upper thorax shape of extinct hominins. Here, we describe a partial first rib from Member 4 of Sterkfontein Caves, South Africa. The rib shaft is broken away, so only the head an...

In this preliminary reconstruction of Homo naledi’s gait we begin with the null hypothesis that it walked similarly to modern humans, as the overall anatomy of this extinct hominin’s lower limb, especially its foot, is mostly modern human-like. We note the following characters as modern-like: dorsally-canting metatarsophalangeal joints facilitating...

In the hominin fossil record, pelvic remains are sparse and are difficult to attribute taxonomically when they are not directly associated with crania. Here we introduce the pelvic remains from the Dinaledi Chamber in the Rising Star cave system, Cradle of Humankind, South Africa which belong to the newly discovered species, Homo naledi. Though thi...

Presenting first results of a comparative analysis of the Australopithecus sediba costal material using 3D geometric morphometrics..

The thorax of Australopithecus sediba is hypothesized to follow a mosaic evolutionary pattern showing a greater similarity with Australopithecus afarensis and great apes in the upper thorax and a greater similarity with humans at the lower thorax and waist (Berger et al. 2011; Schmid et al. 2013). This study presents first results of a comparative...

We describe the axial skeletal material recovered from the Dinaledi chamber of Rising Star cave that, together with some pelvis and shoulder remains, document the complicated nature of trunk evolution. The axial material includes two near-complete lower thoracic vertebrae found in articulation with an 11th rib, the proximal portion of a 12th rib, a...

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 phylogeneti...