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The endocast of StW 573 (“Little Foot”) and hominin brain evolution
Abstract
One of the most crucial debates in human paleoneurology concerns the timing and mode of the emergence of the derived cerebral features in the hominin fossil record. Given its exceptional degree of preservation and geological age (i.e., 3.67 Ma), StW 573 (‘Little Foot’) has the potential to shed new light on hominin brain evolution. Here we present the first detailed comparative description of the external neuroanatomy of StW 573. The endocast was virtually reconstructed and compared to ten southern African hominin specimens from Makapansgat, Malapa, Sterkfontein and Swartkrans attributed to Australopithecus and Paranthropus. We apply an automatic method for the detection of sulcal and vascular imprints. The endocranial surface of StW 573 is crushed and plastically deformed in a number of locations. The uncorrected and therefore minimum cranial capacity estimate is 408 cm3 and plots at the lower end of Australopithecus variation. The endocast of StW 573 approximates the rostrocaudally elongated and dorsoventrally flattened endocranial shape seen in Australopithecus and displays a distinct left occipital petalia. StW 573 and the comparative early hominin specimens share a similar sulcal pattern in the inferior region of the frontal lobes that also resembles the pattern observed in extant chimpanzees. The presumed lunate sulcus in StW 573 is located above the sigmoid sinus, as in extant chimpanzees, while it is more caudally positioned in SK 1585 and StW 505. The middle branch of the middle meningeal vessels derives from the anterior branch, as in MH 1, MLD 37/38, StW 578. Overall, the cortical anatomy of StW 573 displays a less derived condition compared to the late Pliocene/early Pleistocene southern African hominins (e.g., StW 505, SK 1585).
... Scans were processed into meshes using Artec Studio v. 13 software (Artec3D, Luxembourg). We compared these specimens with other australopith endocasts from Makapansgat and Sterkfontein (Beaudet et al., 2019), which are curated at the University of the Witwatersrand and were previously digitized from m CT scans (n ¼ 11; Supplementary Online Material [SOM] Table S1). To help identify sulcal impressions, we consulted several human and chimpanzee brain atlases (Connolly, 1950;Borden et al., 2015;Falk et al., 2018;Ardesch et al., 2019;Van Essen et al., 2019), as well as 3D meshes of 200 chimpanzee cerebra from the National Chimpanzee Brain Resource (https://www.chimpanzeebrain.org/mri-datasets; ...
... We used two other methods to help identify sulcus impressions, which are characterized by a more gradual change in surface topography distributed over a larger area. First, we used an automatic detection method for identifying both meningeal vessel and cerebral imprints, based on an algorithm dedicated to the detection of topographical variation in three dimensions (Yoshizawa et al., 2007(Yoshizawa et al., , 2008Beaudet et al., 2016Beaudet et al., , 2019. Second, we used the 'Thickness' module in Avizo to generate a color map of the endocranial surface of the MLD 3 parietal bone, depicting distance to the ectocranial surface (SOM Figs. ...
... Regardless, MLD 3/3a presents a simple middle meningeal vascular network, with a few branches that do not reticulate. This simple vasculature lacking a distinct middle branch is also seen in Australopithecus natural endocasts Sts 60 and Sts 1017 from Sterkfontein (Falk, 1979;Beaudet et al., 2019). In addition to the meningeal network, a small depression along the posterior medial edge of the natural endocast, in the area missing from the parietal bone, likely represents the margin of the sagittal sinus. ...
... Falk (1980) found the relationship between the superior temporal sulcus and the middle and descending rami of this sulcus in the Australopithecus africanus Taung 1 fossil to be chimpanzee-like, although Holloway (1981) disagreed with Falk's positioning of the superior temporal sulcus on this endocast. Beaudet et al. (2019) further examined the brain endocasts of South African australopithecines and found that in four Australopithecus specimens from the Sterkfontein Caves the superior and middle temporal sulci are parallel and nonoverlapping in Sts 1017, StW 573, Sts 5 and Sts 60, as observed in chimpanzees. ...
... Screenshots of both the left and right hemispheres in lateral view were captured for each of the nine extant specimens. 3D models of the fossil hominin endocasts and the imprints detected in Beaudet et al. (2019) were viewed in ParaView (version 5.10.0). Sulci were identified and studied on one hemisphere (the best preserved) for each specimen. ...
... Sulcal and gyral names and abbreviations were Table 1 List of specimens studied in this chapter. Beaudet et al. (2019) taken from Connolly (1950). We identified the Sylvian fissure (S); the sub-central posterior sulcus (scp); the superior temporal sulcus (ts); the middle temporal sulcus (tm); the three caudal rami, namely, the anterior/superior parallel (a1), middle/ angularis (a2) and descending/anterior occipital (a3) rami; the post-central sulcus (pt), which is divided into the superior post-central sulcus (pts) and inferior post-central sulcus (pti), which may or may not be connected; the intraparietal sulcus (ip); the processus acuminis (e) and the intermedius anterior sulcus (ina); the inferior occipital sulcus (oci). ...
The spoken word does not fossilize. Despite this, scientists have long sought to unearth the origins of language within the human lineage. One of the lines of evidence they have pursued is functional brain areas, such as Broca's and Wernicke's areas, which are associated with speech production and comprehension, respectively. Sulcal layout of Broca's area clearly differs between humans and our closest living relatives, the chimpanzees, enabling its homolog in fossil hominins to be deemed more chimpanzee-like (i.e., closer to the ancestral form) or more human-like (i.e., derived form) with relative ease. Yet, no such differences have been found for Wernicke's area. This study compares sulcal and gyral organization of Wernicke's area across extant human brains (n=4), extant chimpanzee brains (n=5) and fossil hominin endocasts (n=4). Some chimpanzee brains had indications of leftward Wernicke's area asymmetry in the form of a shorter Sylvian fissure and/or caudal superior temporal gyral bulging in the left hemisphere. Overlap between the superior and middle temporal sulci in human but not chimpanzee brains may be due to a relatively larger Wernicke's area in humans. Fragmentation of the main body of the superior temporal sulcus exclusively in human left hemispheres was ascribed to a leftward Wernicke's area asymmetry in this species. Endocast examination found that, while Paranthropus robustus exhibit human-like overlap between the superior and middle temporal sulci, Australopithecus africanus do not, although they do exhibit chimpanzee-like caudal superior temporal gyral bulging. Such findings signal, albeit loosely, a more human-like Wernicke's area in Paranthropus than Australopithecus.
... prometheus specimen), and the base of the cranium is narrow [Clarke and Kuman, 2019]. Endocranial volume is small compared to other, albeit later, Australopithecus [Beaudet et al., 2019a]. These features, alongside general postcranial dimensions , also suggest that StW 573 is female. ...
... At present, there is no conclusive evidence whether the asymmetry reflects healed premortem injury to the left arm [as suggested by Heile et al., 2018] or remodelling on the basis of handedness in vivo, a phenomenon far less common in non-human great apes [Schultz, 1937]. Indeed, the endocast shows that a left occipital petalia, an expansion of the occipital lobe into the right side of the cortex and a feature associated in living humans with handedness, was present [Beaudet et al., 2019a]. ...
... The postcranial evidence reported in Heaton et al. [2019] and Carlson et al. [2020] and reviewed and examined further here, suggests that Au. prometheus was competent arboreally, a conclusion reinforced by the innerear mechanism, atlas cranial facet orientation and carotid foraminae of StW 573 [Beaudet et al., 2019a[Beaudet et al., , b, 2020. The lateral semicircular canal is mediolaterally large, as in non-human great apes but not Homo, although the apical part of the cochlea has loose turns, resembling the case in humans. ...
The StW 573 skeleton of Australopithecus prometheus from Sterkfontein Member 2 is some 93% complete and thus by far the most complete member of that genus yet found. Firmly dated at 3.67 Ma, it is one of the earliest specimens of its genus. A crucial aspect of interpretation of locomotor behaviour from fossil remains is an understanding of the palaeoenvironment in which the individual lived and the manner in which it would have used it. While the value of this ecomorphological approach is largely accepted, it has not been widely used as a stable framework on which to build evolutionary biomechanical interpretations. Here, we collate the available evidence on StW 573's anatomy in order, as far as currently possible, to reconstruct what might have been this individual's realized and potential niche. We explore the concept of a common Australopithecus "bauplan" by comparing the morphology and ecological context of StW 573 to that of paenocontemporaneous australopiths including Australopithecus anamensis and KSD-VP-1/1 Australopithecus afarensis. Each was probably substantially arboreal and woodland-dwelling, relying substantially on arboreal resources. We use a hypothesis-driven approach, tested by: virtual experiments, in the case of extinct species; biomechanical analyses of the locomotor behaviour of living great ape species; and analogical experiments with human subjects. From these, we conclude that the habitual locomotor mode of all australopiths was upright bipedalism, whether on the ground or on branches. Some later australopiths such as Australopithecus sediba undoubtedly became more terrestrial, allowing sacrifice of arboreal stability in favour of manual dexterity. Indeed, modern humans retain arboreal climbing skills but have further sacrificed arboreal effectiveness for enhanced ability to sustain striding terrestrial bipedalism over much greater distances. We compare StW 573's locomotor adaptations to those of living great apes and protohominins, and agree with those earlier observers who suggest that the common panin-hominin last common ancestor was postcranially more like Gorilla than Pan.
... Similarly, automatic segmentation methods for generating virtual endocasts are now available in paleosciences (e.g., Endex, Endomarker, Michikawa et al., 2017;Profico et al., 2020;Subsol et al., 2010). However, analytical tools for the automatic recognition and identification of cerebral imprints in endocasts are still scarce (e.g., automatic detection of sulcal imprints, Beaudet et al., 2016Beaudet et al., , 2019ade Jager et al., 2019). ...
... Sulci from the brain hull and the endocast were detected using an automatic method that is based on the algorithm introduced by Yoshizawa et al. (2008) for the detection of topographical variations (i.e., ridge and ravine lines) in 3D meshes (Beaudet et al., 2016(Beaudet et al., , 2019aBeaudet and Gilissen, 2018;de Jager et al., 2019 could be considered to be the salient parts of the brain hull surface, these structures could be detected via a differential geometry-based approach. Accordingly, at each point of the 3D mesh, the principal curvatures can be computed and the sulci would then correspond to some of their extrema (Subsol, 1999). ...
... Sulci from the brain hull and the endocast were manually identified using a MATLAB R2013a v8.1 (Mathworks) program (https:// gitlab.com/jeand umonc el/curve -editor; Beaudet et al., 2016Beaudet et al., , 2019a de Jager et al., 2019) and endocast atlases from previous publications (Connolly, 1950; de Jager et al., 2019). A label represented by a colour was attributed to each category of sulci. ...
Endocasts (i.e., replicas of the inner surface of the bony braincase) constitute a critical proxy for qualifying and quantifying variations in brain shape and organization in extinct taxa. In the absence of brain tissues preserved in the fossil record, endocasts provide the only direct evidence of brain evolution. However, debates on whether or not information inferred from the study of endocasts reflects brain shape and organization have polarized discussions in paleoneurology since the earliest descriptions of cerebral imprints in fossil hominin crania. By means of imaging techniques (i.e., MRIs and CT scans) and 3D modelling methods (i.e., surface-based comparisons), we collected consistent morphological (i.e., shape) and structural (i.e., sulci) information on the variation patterns between the brain and the endocast based on a sample of extant human individuals (N = 5) from the 3D clinical image database of the Steve Biko Academic Hospital in Pretoria (South Africa) and the Hôpitaux Universitaires Pitié Salpêtrière in Paris (France). Surfaces of the brain and endocast of the same individual were segmented from the 3D MRIs and CT images, respectively. Sulcal imprints were automatically detected. We performed a deformation-based shape analysis to compare both the shape and the sulcal pattern of the brain and the endocast. We demonstrated that there is close correspondence in terms of morphology and organization between the brain and the corresponding endocast with the exception of the superior region. By comparatively quantifying the shape and organization of the brain and endocast, this work represents an important reference for paleoneurological studies
... Similarly, automatic segmentation methods for generating virtual endocasts are now available in paleosciences (e.g., Endex, Endomarker, Michikawa et al., 2017;Profico et al., 2020;Subsol et al., 2010). However, analytical tools for the automatic recognition and identification of cerebral imprints in endocasts are still scarce (e.g., automatic detection of sulcal imprints, Beaudet et al., 2016Beaudet et al., , 2019ade Jager et al., 2019). ...
... Sulci from the brain hull and the endocast were detected using an automatic method that is based on the algorithm introduced by Yoshizawa et al. (2008) for the detection of topographical variations (i.e., ridge and ravine lines) in 3D meshes (Beaudet et al., 2016(Beaudet et al., , 2019aBeaudet and Gilissen, 2018;de Jager et al., 2019 could be considered to be the salient parts of the brain hull surface, these structures could be detected via a differential geometry-based approach. Accordingly, at each point of the 3D mesh, the principal curvatures can be computed and the sulci would then correspond to some of their extrema (Subsol, 1999). ...
... Sulci from the brain hull and the endocast were manually identified using a MATLAB R2013a v8.1 (Mathworks) program (https:// gitlab.com/jeand umonc el/curve -editor; Beaudet et al., 2016Beaudet et al., , 2019a de Jager et al., 2019) and endocast atlases from previous publications (Connolly, 1950; de Jager et al., 2019). A label represented by a colour was attributed to each category of sulci. ...
Endocasts (i.e., replicas of the inner surface of the bony braincase) constitute a critical proxy for qualifying and quantifying variations in brain shape and organization in extinct taxa. In the absence of brain tissues preserved in the fossil record, endocasts provide the only direct evidence of brain evolution. However, debates on whether or not information inferred from the study of endocasts reflects brain shape and organization have polarized discussions in paleoneurology since the earliest descriptions of cerebral imprints in fossil hominin crania. By means of imaging techniques (i.e., MRIs and CT scans) and 3D modelling methods (i.e., surface-based comparisons), we collected consistent morphological (i.e., shape) and structural (i.e., sulci) information on the variation patterns between the brain and the endocast based on a sample of extant human individuals (N = 5) from the 3D clinical image database of the Steve Biko Academic Hospital in Pretoria (South Africa) and the Hôpitaux Universitaires Pitié Salpêtrière in Paris (France). Surfaces of the brain and endocast of the same individual were segmented from the 3D MRIs and CT images, respectively. Sulcal imprints were automatically detected. We performed a deformation-based shape analysis to compare both the shape and the sulcal pattern of the brain and the endo-cast. We demonstrated that there is close correspondence in terms of morphology
... Vascular imprints in hominin endocasts and foramina through the cranial base have featured in discussions about taxonomy 49,50 , thermoregulation 51 and blood flow rate 52 . Studies of the vascular imprints in fossil hominin endocasts identified specific patterns in early hominins, with Paranthropus being characterized by an enlarged occipital-marginal sinus, while the middle branch of the middle meningeal vessels cannot be found in Australopithecus 49,50 , but see 53 . The reorganization of the vascular system in early hominins has been interpreted by some as evidence for the emergence of a thermoregulation system for cooling down the brain under conditions of hyperthermia (the "radiator" theory 51 ). ...
... It is a matter of debate in paleoanthropology to what extent evolutionary changes in sulcal patterns are causally linked to species differences in overall brain volume. Early australopiths had sulcal patterns more similar to extant great apes in form 19,53 , while later, larger-brained members of Homo had sulci that more closely resemble modern humans 17 , but the sulcal pattern in later australopiths and early Homo is still debated 88 . Clarifying the timing and functional consequences of these sulcal changes requires new resources, more fossils, more comparative data from extant ape brains for reference, and innovative approaches from other disciplines. ...
Fossil endocasts record features of brains from the past: size, shape, vasculature, and gyrification. These data, alongside experimental and comparative evidence, are needed to resolve questions about brain energetics, cognitive specializations, and developmental plasticity. Through the application of interdisciplinary techniques to the fossil record, paleoneurology has been leading major innovations. Neuroimaging is shedding light on fossil brain organization and behaviors. Inferences about the development and physiology of the brains of extinct species can be experimentally investigated through brain organoids and transgenic models based on ancient DNA. Phylogenetic comparative methods integrate data across species and associate genotypes to phenotypes, and brains to behaviors. Meanwhile, fossil and archeological discoveries continuously contribute new knowledge. Through cooperation, the scientific community can accelerate knowledge acquisition. Sharing digitized museum collections improves the availability of rare fossils and artifacts. Comparative neuroanatomical data are available through online databases, along with tools for their measurement and analysis. In the context of these advances, the paleoneurological record provides ample opportunity for future research. Biomedical and ecological sciences can benefit from paleoneurology’s approach to understanding the mind as well as its novel research pipelines that establish connections between neuroanatomy, genes and behavior.
... id¼endex). Sulcal and vascular imprints were automatically detected using a method for the detection of topographic variation in 3D meshes (Yoshizawa et al., 2007(Yoshizawa et al., , 2008Beaudet et al., 2016Beaudet et al., , 2019Dumoncel et al., 2021). The 3D surface of Border Cave 1 was also registered with the 3D surface of Cro-Magnon 1 for further comparison using the 'Align' module of Avizo v9.0 software (Visualization Sciences Group Inc.) ...
... The frontal lobes are relatively broad as in Middle and Late Pleistocene human specimens such as Bodo and Cro-Magnon (Fig. 3) and not pointed as in early Pleistocene hominins (Falk et al., 2000;Holloway et al., 2004;Beaudet et al., 2019). The overall shape of the endocast approximates the globular shape illustrated in our sample by Cro-Magnon (Fig. S1) and the extant human individual (Fig. 4), and by the endocast of Hofmeyr based on Figure 10 published by Grine et al. (2010). ...
Besides providing a unique archaeological assemblage that documents the early emergence of complex behaviour in the human lineage, Border Cave (South Africa) is noteworthy for having yielded hominin remains of at least nine individuals, including the partial cranium Border Cave 1. While the exact provenance of Border Cave 1 is unknown, sequence stratigraphy and ESR dating converge towards an age from about 82 ka to 170 ka. Here we present novel information about the brain, braincase and bony labyrinth of Border Cave 1 and discuss related evolutionary implications. We compare Border Cave 1 to specimens of Early and Middle Pleistocene Homo as well as to fossil and extant Homo sapiens. Virtual segmentation techniques were used to reconstruct the brain and bony labyrinth endocasts, assess the distribution of cranial bone thickness, and identify the vascular and sulcal imprints preserved on the inner surface of the braincase. Our results show that the overall morphology of the brain endocast approximates the globular shape of the modern human brain and differs from the long and low brains seen in Middle Pleistocene fossil hominins. The vascular imprints preserved on the right hemisphere indicate that the middle branch derives from the anterior branch, which is a pattern shared with Neanderthals and modern humans. Bone thickness distribution in the Border Cave 1 cranium resembles the patterns seen in Cro-Magnon 1 and Abri Pataud 1, which both share a diffuse distribution of thickened areas over the frontal region. Finally, the relative size and curvature of the semicircular canals of the bony labyrinth conform to the ancestral configuration shared between Early and Late Pleistocene fossil hominins from Africa and the Levant, as well as modern humans, and distinct from the more derived condition documented within Neanderthals. We discuss the implications of our findings for understanding the bioge-ography, evolution, and, to some extent, behaviour of fossil Homo sapiens.
... In late 2017, we witnessed the long-awaited unveiling of the near-complete skeleton StW 573 of an individual belonging to the genus Australopithecus, recovered from the cave of Sterkfontein in the Cradle of Humankind UNESCO World Heritage Site in South Africa more than twenty years prior. This year marked the flood of highly anticipated articles about the morphological characteristics of the individual, nicknamed "Little Foot" (Beaudet et al. 2019a;Beaudet et al. 2019b;Clarke and Kuman 2019;Heaton et al. 2019), its date of 3.67 million years old , and the complex taphonomic context of the specimen, extracted through a more than twenty-year-long meticulous excavation and cleaning process (Clarke 2019). Comparing the StW 573 inner ear with that of an assemblage of Australopithecus, Homo, and Paranthropus fossils, Beaudet et al. (2019b) show that this aspect of its morphology is Australopithecus-like and suggest that it may represent the ancestral condition of Australopithecus is southern Africa. ...
... A number of features identified from its virtually reconstructed endocast, including a small minimum cranial capacity of 408 cm 3 and aspects of its reconstructed sulcal pattern that is shared with chimpanzees, indicate that StW 573 preserves a more ancestral form than later Au. africanus (Beaudet et al. 2019a). As for its lower and upper limbs, StW 573 shares similar limb proportions with that of the "Lucy" Australopithecus afarensis skeleton , indicating clear bipedality, and some indication of a combination of ape-and human-like features in the upper limb (Crompton et al. 2018). ...
Over the past few decades, paleoanthropology has undergone a transformative shift away from studies focused solely on traditional assessments of skeletal anatomy. Prior to this shift, a review highlighting a year of research may have primarily consisted of a description of new fossil discoveries; in 2019, however, this review also incorporates novel subject matters such as ancient DNA, paleoproteomics, and studies applying a wide array of new analytical methods and theoretical frameworks to paleoanthropological questions. Through these new advances, the nonlinearity and complexity of hominin evolution has been illuminated, emphasizing the importance of interdisciplinary work in progressing the field. In addition, similar to the broader discipline of biological anthropology, the topic of decolonization has been reflected on and discussed. Further, researchers in paleoanthropology are grappling with important issues related to open access and data sharing. In light of this widening scope, this review centers on a collection of studies that focus on five key themes: (1) new discoveries; (2) data sharing and ethics; (3) human origins research; (4) paleogenomics, and new advancements in paleoproteomics; and (5) introspection on a colonial history. Paleoanthropology is coming of age, and in 2019 especially, published research has been reflective of this. [Evolutionary anthropology; human evolution; year in review; human origins].
... Our study reveals relatively smaller cross-sectional areas of transverse foramina and the carotid canal in StW 573 compared with extant Homo. Given that the vertebral arteries are bigger in species with bigger brains and the cranial capacity in StW 573 is similar to the extant chimpanzee values 24,47 , these results may be expected. It is interesting to consider that brain perfusion in extant great apes is suggested to be higher than in Australopithecus 48 . ...
... AL 333-83 represents a partial atlas that preserves most of the left side, including the inferior and superior articular facets and a portion of the posterior arch, but it is missing the left transverse process 27 (Fig. 2). Additionally, for measuring dimensions of the carotid canal, we investigated 10 southern African fossil hominin crania from the sites of Makapansgat (Member 4), Sterkfontein (Member 4) and Swartkrans (Member 1) (Supplementary Tables S1, S2; for further details see Beaudet et al. 40,47,57 www.nature.com/scientificreports www.nature.com/scientificreports/ ...
Functional morphology of the atlas reflects multiple aspects of an organism’s biology. More specifically, its shape indicates patterns of head mobility, while the size of its vascular foramina reflects blood flow to the brain. Anatomy and function of the early hominin atlas, and thus, its evolutionary history, are poorly documented because of a paucity of fossilized material. Meticulous excavation, cleaning and high-resolution micro-CT scanning of the StW 573 (‘Little Foot’) skull has revealed the most complete early hominin atlas yet found, having been cemented by breccia in its displaced and flipped over position on the cranial base anterolateral to the foramen magnum. Description and landmark-free morphometric analyses of the StW 573 atlas, along with other less complete hominin atlases from Sterkfontein (StW 679) and Hadar (AL 333-83), confirm the presence of an arboreal component in the positional repertoire of Australopithecus. Finally, assessment of the cross-sectional areas of the transverse foramina of the atlas and the left carotid canal in StW 573 further suggests there may have been lower metabolic costs for cerebral tissues in this hominin than have been attributed to extant humans and may support the idea that blood perfusion of these tissues increased over the course of hominin evolution.
... Despite the small cranial capacity (a minimum of 408 cm 3 ; Beaudet et al., 2019), the profile of the StW 573 braincase in posterior view (Figs. 12 and 18; Table 6) has almost vertical sides that turn superomedially around parietal bosses. This is very different from the profiles of the equally small-brained StW 53 (a male A. africanus) and AL 333-45 (A. ...
... It is possible, then, that the smaller cheek teeth in the 3.67 Ma StW 573 represents an ancestral condition from which the later megadont A. prometheus derived. This could also explain the smaller brain size for StW 573, discussed earlier (see Beaudet et al., 2019). This hypothesis would benefit from further investigation and an enlarged sample of Australopithecus fossils from that earlier time period at Sterkfontein. ...
Here we present the first full anatomical description of the 3.67 million-year-old Australopithecus skull StW 573 that was recovered with its skeleton from the Sterkfontein Member 2 breccia in the Silberberg Grotto. Analysis demonstrates that it is most similar in multiple key morphological characters to a group of fossils from Sterkfontein Member 4 and Makapansgat that are here distinguished taxonomically as Australopithecus prometheus. This taxon contrasts with another group of fossils from those sites assigned
to Australopithecus africanus. The anatomical reasons for why these groupings should not be lumped together (as is frequently done for the South African fossils) are discussed in detail. In support of this taxonomy, we also present for the first time a newly reconstructed palate of A. africanus (StW 576 from Sterkfontein Member 4), which has a uniquely complete permanent dentition. The StW573 skull also has
certain similarities with other earlier Australopithecus fossils in East Africa, assigned to Australopithecus afarensis and Australopithecus anamensis, which are discussed. One of its most interesting features is a pattern of very heavy anterior dental wear unlike that found in A. africanus but resembling that found in A. anamensis at 4.17 Ma. Because the StW 573 skull is associated with a near-complete skeleton that is also described for the first time in this special issue, we are now able to use this individual to improve our
understanding of more fragmentary finds in the South African fossil record of Australopithecus.
... This change in the cortical organization of the occipital lobe has been related to a relative expansion of the parietal association cortex (Holloway, 2001). The most recent evidence, from StW 573, about Australopithecus from southern African is consistent with an apelike location for the lunate sulcus (Beaudet et al., 2019). The only evidence available about the lunate sulcus in P. robustus, from SK 1585, suggests that its location is modern human-like (Holloway, 1972). ...
... A similar pattern of asymmetry of the third frontal convolution has been recorded in fossil hominins (i.e., Au. africanus, P. aethiopicus, H. rudolfensis, H. habilis, H. ergaster/erectus, H. floresiensis, Neanderthals, H. heidelbergensis/rhodesiensis) and in modern humans and bonobos, but the degree to which it is expressed varies among taxa (Balzeau et al., 2012b). Similarly, the left/ right asymmetry of the cerebral hemispheres (i.e., petalia) that is present in modern humans is also seen in great apes and in fossil hominins, including the 3.67 Ma specimen StW 573 (Beaudet et al., 2019;Holloway et al., 2004b;LeMay et al., 1982). ...
When compared to the brains of our closest living relatives, chimpanzees and bonobos, the brains of modern humans are larger and differently shaped. This chapter reviews what we know about the evolutionary history of these differences. We can make an educated guess about the size and shape of the brains of the hypothetical common ancestor of modern humans and chimpanzees/bonobos, but between ca. 8 million years ago and the present day evidence about the size and shape of the brain comes from either natural endocasts, which are literally brain-shaped rocks, or from individuals for which enough of the brain case is preserved to provide estimates of endocranial volume and/or the relative proportions of the different regions of the cerebral hemispheres and the cerebellum. The tempo and mode of brain size increase in the hominin clade has been the subject of spirited debate, but we suggest that some of this controversy is the combination of an overreliance on frequentist statistical tests and researchers addressing these issues at different taxonomic scales. The existence and significance of shape changes are also controversial topics, made more so by the dearth of reliable evidence.
... Despite the small cranial capacity (a minimum of 408 cm 3 ; Beaudet et al., 2019), the profile of the StW 573 braincase in posterior view (Figs. 12 and 18; Table 6) has almost vertical sides that turn superomedially around parietal bosses. This is very different from the profiles of the equally small-brained StW 53 (a male A. africanus) and AL 333-45 (A. ...
... It is possible, then, that the smaller cheek teeth in the 3.67 Ma StW 573 represents an ancestral condition from which the later megadont A. prometheus derived. This could also explain the smaller brain size for StW 573, discussed earlier (see Beaudet et al., 2019). This hypothesis would benefit from further investigation and an enlarged sample of Australopithecus fossils from that earlier time period at Sterkfontein. ...
Here we present the first full anatomical description of the 3.67 million-year-old Australopithecus skull StW 573 that was recovered with its skeleton from the Sterkfontein Member 2 breccia in the Silberberg Grotto. Analysis demonstrates that it is most similar in multiple key morphological characters to a group of fossils from Sterkfontein Member 4 and Makapansgat that are here distinguished morphologically as A. prometheus. This taxon contrasts with another group of fossils from those sites assigned to A. africanus. The anatomical reasons for why these groupings should not be lumped together (as is frequently done for the South African fossils) are discussed in detail. In support of this classification, we also present for the first time a palate (StW 576 from Sterkfontein Member 4) newly reconstructed by RJC, which has a uniquely complete adult dentition of an A. africanus. The StW 573 skull also has certain similarities with other earlier Australopithecus fossils in East Africa, A. afarensis and A. anamensis, which are discussed. One of its most interesting features is a pattern of very heavy anterior dental wear unlike that found in A. africanus but resembling that found in A. anamensis at 4.17 Ma. While StW 573 is the only hominid fossil in Sterkfontein Member 2, we conclude that competitive exclusion probably accounts for the synchronous and sympatric presence of two species of Australopithecus in the younger deposits at Makapansgat and Sterkfontein Member 4. Because the StW 573 skull is associated with a near-complete skeleton that is also described for the first time in this special issue, we are now able to use this individual to improve our understanding of more fragmentary finds in the South African fossil record of Australopithecus.
... Our dating and stratigraphy (2) show that Member 4 sediments are intact and that the historic faunal assemblage is mixed because some younger fossils from overlying Member 5 (not recognized at the time) were collected from blasted breccias and assumed to belong to Member 4. In limited areas affected by deep solution pockets, younger fossils were also mistakenly assigned to Member 4 because no record was kept of these sediments. In addition, significant differences in Australopithecus and Chasmaporthetes fossils are consistent with Member 2 being paleontologically older than Member 4 (2,9,10). ...
... The cerebellum is readily visible in dorsal views of the endocranial cast in all extant and extinct proboscideans, but the occipital lobe is ill-defined ( Fig. 15.1). This greatly differs from the condition seen in humans, in which the occipital lobe is well developed and overlies the cerebellum in dorsal view (Jerison 1973;Holloway 2013;Beaudet et al. 2019). In this regard, Shoshani et al. (2006) indicated that as the occipital lobe is the center of vision, vision is not an elaborated sense in elephants (but see Pettigrew et al. 2010;Maseko et al. 2013a, b). ...
The elephant brain is famous for its higher than average encephalization quotient, memory capacities, large cerebellum, large facial and trigeminal nerves, and the extensive repertoire of complex behaviors and social interactions it produces, the last of which being supported by infrasonic communication. The evolutionary history of Proboscidea is amongst the best-documented among mammals but knowledge of the group’s paleoneurological history remains comparatively fragmentary. Here, we summarize and build upon more than 150 years of research on the evolution of the proboscidean nervous system. We find that the morphology of the endocranial cast and bony labyrinth of the basal-most proboscideans is consistent with the generalized plesiomorphic conditions for placental mammals (e.g. linearly organized brain parts, low encephalization quotient, presence of a secondary common crus), whereas their conditions become essentially elephant-like in the Elephantimorpha around the Oligocene. This suggests that a higher encephalization quotient and adaptations to low-frequency hearing (e.g. loss of the secondary bony lamina) evolved in parallel with the formation and evolution of a trunk, adaptation to a drier environment, and a higher body mass. We hypothesize that these structures co-evolved as a response to the changing climate in the Oligocene.
... These similarities include a bell-shaped outline in posterior view, a very long nuchal plane, a wide interorbital distance, a large canine relative to cheek teeth, a diastema (gap) between the upper canine and the incisor, and a small cranial capacity. The estimated brain size of StW 573 is ∼408 cc (Beaudet et al. 2019b), and it is 365-370 cc in MRD-VP-1/1. Such parallels between the very early Ethiopian Australopithecus and that of South Africa are intriguing. ...
... These similarities include a bell-shaped outline in posterior view, a very long nuchal plane, a wide interorbital distance, a large canine relative to cheek teeth, a diastema (gap) between the upper canine and the incisor, and a small cranial capacity. The estimated brain size of StW 573 is ∼408 cc (Beaudet et al. 2019b), and it is 365-370 cc in MRD-VP-1/1. Such parallels between the very early Ethiopian Australopithecus and that of South Africa are intriguing. ...
The earliest South African hominids (humans and their ancestral kin) belong to the genera Australopithecus, Paranthropus, and Homo, with the oldest being a ca. 3.67 million-year-old nearly complete skeleton of Australopithecus (StW 573) from Sterkfontein Caves. This skeleton has provided, for the first time in almost a century of research, the full anatomy of an Australopithecus individual with indisputably associated skull and postcranial bones that give complete limb lengths. The three genera are also found in East Africa, but scholars have disagreed on the taxonomic assignment for some fossils owing to historical preconceptions. Here we focus on the South African representatives to help clarify these debates. The uncovering of the StW 573 skeleton in situ revealed significant clues concerning events that had affected it over time and demonstrated that the associated stalagmite flowstones cannot provide direct dating of the fossil, as they are infillings of voids caused by postdepositional collapse.
... All great ape brains exhibit a lunate sulcus (L), which marks the anterior boundary of the primary visual cortex (Brodmann area 17) (Fig. 1A), whereas human brains are characterized by complete loss of L (14), reflecting an expanded parieto-occipital cortex (13,15) (Fig. 1B). L rarely leaves endocranial imprints (7,16,17), such that, in fossil hominin endocasts, absence of evidence of L is not evidence of absence, and it remains unclear when during human evolution this cortical area started expanding (3,4,7,9,(18)(19)(20). ...
Brain evolution in early Homo
Human brains are larger than and structurally different from the brains of the great apes. Ponce de León et al. explored the timing of the origins of the structurally modern human brain (see the Perspective by Beaudet). By comparing endocasts, representations of the inner surface of fossil brain cases, from early Homo from Africa, Georgia, and Southeast Asia, they show that these structural innovations emerged later than the first dispersal of the genus from Africa, and were probably in place by 1.7 to 1.5 million years ago. The modern humanlike brain organization emerged in cerebral regions thought to be related to toolmaking, social cognition, and language. Their findings suggest that brain reorganization was not a prerequisite for dispersals from Africa, and that there might have been more than one long-range dispersal of early Homo .
Science , this issue p. 165 ; see also p. 124
... This led Clarke [1][2][3]12 to propose the presence of a second Australopithecus species at Sterkfontein Member 4, which he attributed to A. prometheus, a species name originally given to fossils from Makapansgat 13 . Recent studies of the StW 573 "Little foot" skeleton from Sterkfontein Member 2 renewed debates on the functional biology and taxonomy of the Plio-Pleistocene hominins from South Africa 12, [14][15][16] . Nevertheless, the presence of two closely related Australopithecus taxa at Sterkfontein Member 4 is not widely accepted 17,18 because of conflicting interpretations and the fragmentary preservation of the fossils. ...
The presence of multiple Australopithecus species at Sterkfontein Member 4, South Africa (2.07 to 2.61 Ma) is highly contentious. Quantitative assessments of craniodental and postcranial variability remain inconclusive. Using geometric morphometrics, we compared the sacrum of the small-bodied, presumed female subadult Australopithecus africanus skeleton Sts 14 and the large, alleged male adult StW 431 against a geographically diverse sample of modern humans, and two species for each of the genera Gorilla , Pan and Pongo . The probabilities of sampling morphologies as distinct as Sts 14 and StW 431 from a single species ranged from 1.3 to 2.5% for the human sample, and from 0.0 to 4.5% for the ape sample, depending on the analysis performed. Neither differences in developmental or geologic age nor sexual dimorphism could account for the differences between StW 431 and Sts 14 sacra. These findings support earlier claims of taxonomic heterogeneity at Sterkfontein Member 4.
... We did not include cranial capacity data for the recently published specimen StW 573 from the Silberberg Grotto at Sterkfontein because its taxonomic status is still under debate, and its endocast has not yet been virtually reconstructed to correct for distortion during the fossilisation process. 54 We also simulated A. africanus cranial capacity growth by looking at per cent changes necessary to grow Taung to different A. africanus 'target' adults, thereby simulating different models for growth increases in Taung's cranial capacity 10,11 (Table 5). We compared these percentages to values for comparative samples to assess the likelihood that Taung's remaining brain growth would be sufficient to produce target adult cranial capacity values. ...
Cranial capacity, a proxy for the volume of the brain and associated cranial contents, is an important yardstick used to compare early hominin species because increasing brain size is a key characteristic of our lineage. In 1925, Raymond Dart claimed that a natural endocast found at the Buxton Limeworks near Taung, South Africa (which he named Australopithecus africanus), showed signs of neural reorganisation, but its juvenile status complicated comparison to other hominoid species. In an attempt to put its brain size and reorganisation into a comparative context, subsequent researchers have tried to estimate Taung’s adult cranial capacity by comparison to coarse-grained hominoid growth data. In this study, we simulated brain growth in A. africanus using asymptotic growth models in known-age mountain gorillas, chimpanzees and modern humans, and show that, at just under 4 years old, Taung’s brain had already finished or nearly finished growing according to hominoid developmental schedules. Percentage-growth remaining estimates are lower here than in previous studies using cross-sectional ontogenetic samples of unknown chronological age. Our new adult estimates (between 404 cm3 and 430 cm3 overall and 405–406 cm3 for chimpanzee models) are smaller than previous estimates with a ‘starting’ cranial capacity of 404 cm3, supporting the hypothesis that Taung’s adult brain size would have fallen toward the lower end of the A. africanus range of variation and strengthening the case that Taung was female.
Significance:
• This is one of several recent studies to show that brain growth is completed in African apes and humans earlier than previously appreciated.
• New adult cranial capacity estimates for Taung are lower than previous estimates, supporting the hypothesis that Taung was female.
• Cessation of brain growth in hominoids at earlier ages than previously reported suggests that adult cranial capacities for hominin juvenile specimens have been overestimated.
Open data set:
http://dx.doi.org/10.17632/wyfvwd4s22
... In mammals, brains larger than 700 g have evolved infrequently, being found primarily in extant humans, cetaceans and elephants 1 . The temporal/evolutionary history of human brain size and shape has been studied in detail [2][3][4][5] , with the 700 g barrier on brain size evolution being surpassed with the appearance of Homo ergaster/erectus, approximately 1.8 million years ago 1 . The suborder Cetacea has many species that also exhibit large brains, both absolute and relative to body mass 6,7 . ...
As the largest and among the most behaviourally complex extant terrestrial mammals, proboscideans (elephants and their extinct relatives) are iconic representatives of the modern megafauna. the timing of the evolution of large brain size and above average encephalization quotient remains poorly understood due to the paucity of described endocranial casts. Here we created the most complete dataset on proboscidean endocranial capacity and analysed it using phylogenetic comparative methods and ancestral character states reconstruction using maximum likelihood. our analyses support that, in general, brain size and body mass co-evolved in proboscideans across the Cenozoic; however, this pattern appears disrupted by two instances of specific increases in relative brain size in the late Oligocene and early Miocene. These increases in encephalization quotients seem to correspond to intervals of important climatic, environmental and faunal changes in Africa that may have positively selected for larger brain size or body mass.
... More attention has been paid to the cranium, although it, too, is largely undisclosed save for references in which Clarke (2008) attributed it to Australopithecus prometheus, drawing favorable comparisons to the Stw 252 and Stw 505 crania in terms of its robust zygomatic arch, lack of supraorbital thickening, and the presence of a small posteriorly restricted sagittal crest. Recently, Beaudet et al. (2019a) examined the endocast of Stw 573 and determined that it falls within the range of size and morphological variation displayed by other A. africanus specimens. Beaudet et al. (2019b) reported upon the structure of the bony labyrinth of this specimen but were unable to differentiate it from the variation exhibited by other Australopithecus specimens from Sterkfontein and Makapansgat. ...
The possibility that the fossils attributed to Australopithecus africanus represent more than a single species is of significance because of the pivotal role that A. africanus has played in discussions about hominin evolution. The A. africanus hypodigm that is currently widely recognized evinces considerable variation in a number of craniodental characters, and this has led to speculation that more than one australopith taxon may be represented among the specimens from Sterkfontein. Although crania, mandibles and teeth have dominated these taxonomic discussions, the Sterkfontein postcranial remains also have been invoked. While several workers have proposed that some of the craniodental remains from Sterkfontein can be partitioned into two groups, there is a notable lack of agreement among them as to their actual sorting. Most of the craniodental observations that have been put forward in support of arguments for taxonomic heterogeneity of the Sterkfontein australopith assemblage have been subjective and anecdotal in nature. So too, the postcranial evidence that has been cited in support of more than one australopith species at Sterkfontein has been largely subjective, and limited to a small number of elements. The results of quantitative statistical analyses of the craniodental and postcranial fossils that have been undertaken to date are not necessarily consistent with the hypothesis of taxonomic heterogeneity.
Motion analysis, as applied to evolutionary biomechanics, has experienced its own evolution over the last 50 years. Here we review how an ever-increasing fossil record, together with continuing advancements in biomechanics techniques, have shaped our understanding of the origin of upright bipedal walking. The original, and long-established hypothesis held by Lamarck (1809), Darwin (1859) and Keith (1934), amongst others, maintained that bipedality originated in an arboreal context. However, the first field studies of gorilla and chimpanzees from the 1960's, highlighted their so-called 'knucklewalking' quadrupedalism, leading scientists to assume, semi-automatically, that knucklewalking must have been the precursor to bipedality. It would not be until the discovery of skeletons of early human relatives Australopithecus afarensis and Australopithecus prometheus, and the inclusion of methods of analysis from computer science, biomechanics, sports science and medicine, that the knucklewalking hypothesis would be most robustly challenged. Their short, but human-like lower limbs and human-like hand indicated that knucklewalking was not part of our ancestral locomotor repertoire. Rather, most current research in evolutionary biomechanics agrees it was a combination of climbing and bipedalism, both in an arboreal context, which facilitated upright, terrestrial, bipedal walking over short distances.
Background
Computed tomography (CT) scans are a convenient means to study 3D reconstructions of bones. However, errors associated with the different nature of the observation, e.g. visual and tactile (on dry bone) versus visual only (on a screen) have not been thoroughly investigated.Materials and methodsWe quantified the errors between modalities for sex estimation protocols of nonmetric (categorical and ordinal) and metric data, using 200 dry pelves of archaeological origin and the CT reconstructions of the same bones. In addition, we 3D surface scanned a subsample of 39 pelves to compare observations with dry bone and CT data. We did not focus on the sex estimation accuracy but solely on the consistency of the scoring, hence, the interchangeability of the modalities.ResultsMetric data yielded the most consistent results. Among the nonmetric protocols, ordinal data performed better than categorical data. We applied a slightly modified description for the trait with the highest errors and grouped the traits according to consistency and availability in good, intermediate, and poor.DiscussionThe investigated modalities were interchangeable as long as the trait definition was not arbitrary. Dry bone (gold standard) performed well, and CT and 3D surface scans performed better. We recommend researchers test their affinity for using virtual modalities. Future studies could use our consistency analysis and combine the best traits, validating their accuracy on various modalities.
Supplementary Online Material (SOM): Knuckle-walking in Sahelanthropus?
Interpreting morphological variation within the early hominin fossil record is particularly challenging. Apart from the fact that there is no absolute threshold for defining species boundaries in palaeontology, the degree of variation related to sexual dimorphism, temporal depth, geographic variation or ontogeny is difficult to appreciate in a fossil taxon mainly represented by fragmentary specimens, and such variation could easily be conflated with taxonomic diversity. One of the most emblematic examples in paleoanthropology is the Australopithecus assemblage from the Sterkfontein Caves in South Africa. Whereas some studies support the presence of multiple Australopithecus species at Sterkfontein, others explore alternative hypotheses to explain the morphological variation within the hominin assemblage. In this review, I briefly summarize the ongoing debates surrounding the interpretation of morphological variation at Sterkfontein Member 4 before exploring two promising avenues that would deserve specific attention in the future, that is, temporal depth and nonhuman primate diversity.
In 1987, Phillip Tobias published a comprehensive anatomical analysis of the endocasts attributed to Homo habilis, discussing issues dealing with brain size, sulcal patterns, and vascular traces. He suggested that the neuroanatomy of this species evidenced a clear change toward many cerebral traits associated with our genus, mostly when concerning the morphology of the frontal and parietal cortex. After more than 30 years, the fossil record associated with this taxon has not grown that much, but we have much more information on cranial and brain biology, and we are using a larger array of digital methods to investigate the paleoneurological variation observed in the human genus. Brain volume, the size of the frontal lobe, or the gross hemispheric asymmetries are still relevant issues, but they are considered to be less central than before. More attention is instead being paid to the cortical organization, the relationships with the cranial architecture, and the influence of molecular or ecological factors. Although the field of paleoneurology can currently count on a larger range of tools and principles, there is still a general lack of anatomical information on many endocranial traits. This aspect is probably crucial for the agenda of paleoneurology. More importantly, the whole science is undergoing a delicate change, because of the growing influence of the social environment. In this sense, the disciplines working with fossils (and, in particular, with brain evolution) should take particular care to maintain a healthy professional situation, avoiding an excess of speculation and overstatement.
The left and right hemispheres of our brains differ subtly in structure, and each is dominant in processing specific cognitive tasks. Our species has a unique system of distributing behavior and cognition between each cerebral hemisphere, with a preponderance of pronounced side biases and lateralized functions. This hemisphere-dependent relationship between cognitive, sensory or motor function and a set of brain structures is called hemispheric specialization. Hemispheric specialization has led to the emergence of model systems to link anatomical asymmetries to brain function and behavior. Scientific research on hemispheric specialization and lateralized functions in living humans focuses on three major domains: (1) hand preferences, (2) language, and (3) visuospatial skills and attention. In this chapter we present an overview of this research with a specific focus on living humans and the applications of this research in the context of hominin brain evolution. Our objective is to put into perspective what we know about brain-behavior relationships in living humans and how we can apply the same methods to investigate this relationship in fossil hominin species, and thus improve our understanding of the emergence and development of complex cognitive abilities.
All modern mammals are descendants of the paraphyletic non-mammaliaform Synapsida, colloquially referred to as the “mammal-like reptiles.” It has long been assumed that these mammalian ancestors were essentially reptile-like in their morphology, biology, and behavior, i.e., they had a small brain, displayed simple behavior, and their sensory organs were unrefined compared to those of modern mammals. Recent works have, however, revealed that neurological, sensory, and behavioral traits previously considered typically mammalian, such as whiskers, enhanced olfaction, nocturnality, parental care, and complex social interactions evolved before the origin of Mammaliaformes, among the early-diverging “mammal-like reptiles.” In contrast, an enlarged brain did not evolve immediately after the origin of mammaliaforms. As such, in terms of paleoneurology, the last “mammal-like reptiles” were not significantly different from the earliest mammaliaforms. The abundant data and literature published in the last 10 years no longer supports the “three pulses” scenario of synapsid brain evolution proposed by Rowe and colleagues in 2011, but supports the new “outside-in” model of Rodrigues and colleagues proposed in 2018, instead. As Mesozoic reptiles were becoming the dominant taxa within terrestrial ecosystems, synapsids gradually adapted to smaller body sizes and nocturnality. This resulted in a sensory revolution in synapsids as olfaction, audition, and somatosensation compensated for the loss of visual cues. This altered sensory input is aligned with changes in the brain, the most significant of which was an increase in relative brain size.
The presence of multiple Australopithecus species at Sterkfontein Member 4, South Africa (2.07 to 2.61 Ma) is highly contentious. Quantitative assessments of craniodental and postcranial variability remain inconclusive. Using geometric morphometrics, we compared the sacrum of the small-bodied, presumed female subadult Australopithecus africanus skeleton Sts 14 and the large, alleged male adult StW 431 against a geographically diverse sample of modern humans, and two species for each of the genera Gorilla , Pan and Pongo . The probabilities of sampling morphologies as distinct as Sts 14 and StW 431 from a single species ranged from 1.3 to 2.5% for the human sample, and from 0.0 to 4.5% for the ape sample, depending on the analysis performed. Neither differences in developmental or geologic age nor sexual dimorphism could account for the differences between StW 431 and Sts 14 sacra. These findings support earlier claims of taxonomic heterogeneity at Sterkfontein Member 4.
Objectives
The bony labyrinth of the inner ear has special relevance when tracking phenotypic evolution because it is often well preserved in fossil and modern primates. Here we track the evolution of the bony labyrinth of anthropoid primates during the Mio−Plio−Pleistocene—the time period that gave rise to the extant great apes and humans.
Materials and Methods
We use geometric morphometrics to analyze labyrinthine morphology in a wide range of extant and fossil anthropoids, including New World and Old World monkeys, apes, and humans; fossil taxa are represented by Aegyptopithecus , Microcolobus , Epipliopithecus , Nacholapithecus , Oreopithecus , Ardipithecus , Australopithecus , and Homo .
Results
Our results show that the morphology of the anthropoid bony labyrinth conveys a statistically significant phylogenetic signal especially at the family level. The bony labyrinthine morphology of anthropoids is also in part associated with size, but does not cluster by locomotor adaptations. The Miocene apes examined here, regardless of inferred locomotor behaviors, show labyrinthine morphologies distinct from modern great apes.
Discussion
Our results suggest that labyrinthine variation contains mixed signals and alternative explanations need to be explored, such as random genetic drift and neutral phenotypic evolution, as well as developmental constraints. The observed pattern in fossil and extant hominoids also suggests that an additional factor, for example, prenatal brain development, could have potentially had a larger role in the evolutionary modification of the bony labyrinth than hitherto recognized.
Phylogenetic relationships among extinct hominoids (apes and humans) are controversial due to pervasive homoplasy and the incompleteness of the fossil record. The bony labyrinth might contribute to this debate, as it displays strong phylogenetic signal among other mammals. However, the potential of the vestibular apparatus for phylogenetic reconstruction among fossil apes remains understudied. Here we test and quantify the phylogenetic signal embedded in the vestibular morphology of extant anthropoids (monkeys, apes and humans) and two extinct apes (Oreopithecus and Australopithecus) as captured by a deformation-based 3D geometric morphometric analysis. We also reconstruct the ancestral morphology of various hominoid clades based on phylogenetically-informed maximum likelihood methods. Besides revealing strong phylogenetic signal in the vestibule and enabling the proposal of potential synapomorphies for various hominoid clades, our results confirm the relevance of vestibular morphology for addressing the controversial phylogenetic relationships of fossil apes.
The 3.67-million-year-old StW 573 Australopithecus skeleton is important for the light it sheds on the paleobiology of South African species of that genus, including, as discussed here, how the possible pathology of the specimen informs our understanding of Australopithecus behavior. The StW 573 antebrachium exhibits bilateral asymmetry, with significantly more longitudinally curved left forearm bones than right. Arguing from a comparative perspective, we hypothesize that these curvatures resulted from a fall onto a hyperextended, outstretched hand. It is unlikely that the fall was from a significant height and might have occurred when the StW 573 individual was a juvenile. This type of plastic deformation of the forearm bones is well-documented in modern human clinical studies, especially among children between the ages of four and ten years who tumble from bicycles or suffer other common, relatively low-impact accidents. Left untreated, such injuries impinge normal supination and pronation of the hand, a condition that could have had significant behavioral impact on the StW 573 individual.
Our knowledge of human brain evolution primarily relies on interpretation of paleoneurological evidence. In this context, the endocast (i.e., replica of the internal table of the bony brain case) constitutes a proxy for reconstructing a timeline and mode of cerebral changes in human evolution. The identification of cerebral imprints, with specific focus on cortical sulci, is critical for assessing the topographic extension and structural organization of cortical areas. However, the description of these crucial landmarks in fossil endocasts is challenging. The recent introduction of high-resolution imaging techniques in (paleo)neurology offers new opportunities for tracking detailed endocranial neural characteristics. This study aims at providing an atlas documenting the variation in the extant human endocranial sulcal pattern for subsequent use as a comparative platform for the study of the fossil record. Overall, more than 90 extant human crania from the Pretoria Bone Collection (University of Pretoria, South Africa) were detailed by X-ray microtomography at a spatial resolution ranging from 94 to 123 µm at MIXRAD, located at the South African Nuclear Corporation, Pelindaba. Based on our preliminary analyses, sulci are nearly consistently identifiable on the frontal (i.e., superior, intermediate and inferior sulci) and temporal (i.e., superior and inferior sulci) lobes. Interestingly, sulci bordering critical functional areas (e.g., Broca’s cap) could be labelled as well. The construction of an atlas is a prerequisite for developing protocols involving automatic sulci recognition in endocasts. In this regard, our study introduces a promising perspective for discussing long outstanding questions in paleoneurology.
A large brain is a defining feature of modern humans, yet there is no consensus regarding the patterns, rates and processes involved in hominin brain size evolution. We use a reliable proxy for brain size in fossils, endocranial volume (ECV), to better understand how brain size evolved at both clade- and lineage-level scales. For the hominin clade overall, the dominant signal is consistent with a gradual increase in brain size. This gradual trend appears to have been generated primarily by processes operating within hypothesized lineages-64% or 88% depending on whether one uses a more or less speciose taxonomy, respectively. These processes were supplemented by the appearance in the fossil record of larger-brainedHomospecies and the subsequent disappearance of smaller-brainedAustralopithecusandParanthropustaxa. When the estimated rate of within-lineage ECV increase is compared to an exponential model that operationalizes generation-scale evolutionary processes, it suggests that the observed data were the result of episodes of directional selection interspersed with periods of stasis and/or drift; all of this occurs on too fine a timescale to be resolved by the current human fossil record, thus producing apparent gradual trends within lineages. Our findings provide a quantitative basis for developing and testing scale-explicit hypotheses about the factors that led brain size to increase during hominin evolution.
Modern humans have large and globular brains that distinguish them from their extinct Homo relatives. The characteristic globularity develops during a prenatal and early postnatal period of rapid brain growth critical for neural wiring and cognitive development. However, it remains unknown when and how brain globularity evolved and how it relates to evolutionary brain size increase. On the basis of computed tomographic scans and geometric morphometric analyses, we analyzed endocranial casts of Homo sapiens fossils (N = 20) from different time periods. Our data show that, 300,000 years ago, brain size in early H. sapiens already fell within the range of present-day humans. Brain shape, however, evolved gradually within the H. sapiens lineage, reaching present-day human variation between about 100,000 and 35,000 years ago. This process started only after other key features of craniofacial morphology appeared modern and paralleled the emergence of behavioral modernity as seen from the archeological record. Our findings are consistent with important genetic changes affecting early brain development within the H. sapiens lineage since the origin of the species and before the transition to the Later Stone Age and the Upper Paleolithic that mark full behavioral modernity.
https://doi.org/10.1126/sciadv.aao5961
Following the publication (Granger DE et al., Nature 2015;522:85–88) of an 26Al/10Be burial isochron age
of 3.67±0.16 Ma for the sediments encasing hominin fossil StW573 (‘Little Foot’), we consider data
on chert samples presented in that publication to explore alternative age interpretations. 10Be and 26Al
concentrations determined on individual chert fragments within the sediments were calculated back in
time, and data from one of these fragments point to a maximum age of 2.8 Ma for the sediment package
and therefore also for the fossil. An alternative hypothesis is explored, which involves re-deposition
and mixing of sediment that had previously collected over time in an upper chamber, which has since
been eroded. We show that it is possible for such a scenario to yield ultimately an isochron indicating
an apparent age much older than the depositional age of the sediments around the fossil. A possible
scenario for deposition of StW573 in Member 2 would involve the formation of an opening between
the Silberberg Grotto and an upper chamber. Not only could such an opening have acted as a death
trap, but it could also have disturbed the sedimentological balance in the cave, allowing unconsolidated
sediment to be washed into the Silberberg Grotto. This two-staged burial model would thus allow a
younger age for the fossil, consistent with the sedimentology of the deposit. This alternative age is also
not in contradiction to available faunal and palaeomagnetic data.
The evolution of human cognition has been inferred from anthropological discoveries and estimates of brain size from fossil skulls. A more direct measure of cognition would be cerebral metabolic rate, which is proportional to cerebral blood flow rate (perfusion). The hominin cerebrum is supplied almost exclusively by the internal carotid arteries. The sizes of the foramina that transmitted these vessels in life can be measured in hominin fossil skulls and used to calculate cerebral perfusion rate. Perfusion in 11 species of hominin ancestors, from Australopithecus to archaic Homo sapiens, increases disproportionately when scaled against brain volume (the allometric exponent is 1.41). The high exponent indicates an increase in the metabolic intensity of cerebral tissue in later Homo species, rather than remaining constant (1.0) as expected by a linear increase in neuron number, or decreasing according to Kleiber's Law (0.75). During 3 Myr of hominin evolution, cerebral tissue perfusion increased 1.7-fold, which, when multiplied by a 3.5-fold increase in brain size, indicates a 6.0-fold increase in total cerebral blood flow rate. This is probably associated with increased interneuron connectivity, synaptic activity and cognitive function, which all ultimately depend on cerebral metabolic rate.
AFTER A DECADE OF CAREFUL EXCAVATION, it is now possible to explain how the skeleton came to be in that isolated position in the cavern. Furthermore, it is apparent that the fossil does not belong to either Australopithecus africanus or to A. afarensis, but to an individual belonging to, or closely affiliated to, the second Australopithecus species that is represented in Sterkfontein Member 4 and Makapansgat.
Objectives:
The diploic channels appear to be more developed in humans than in nonhuman primates, suggesting they may be relevant in evolutionary biology. This study is aimed at providing a segmentation procedure for diploic channels and CT analysis, a quantitative description of their variation in modern humans, and paleoanthropological case-studies.
Materials and methods:
CT data were used for the 2D and 3D visualization, rendering, and measure, of diploic channels in modern and fossil hominids. We analyzed 20 modern human skulls and three Neanderthals. The effect of different resolution factors was evaluated. A specific protocol was designed to segment the vascular network and localize the main branches, reducing the noise of the cancellous bone.
Results:
We provide a quantitative description of the frontal, parietal, and occipital diploic networks in modern humans and in three Neanderthals. There is a correlation in the degree of vascularization among the different vault areas. No side differences can be detected. The diploic network is commonly connected with the meningeal artery at the temporal fossa, with the emissary veins at the occipital bone, and with the venous sinuses at the parieto-occipital areas. The channels are more developed in the parietal areas. The three Neanderthals show a vascular development, which is in the lower range of the modern human variation.
Conclusions:
Modern humans display a large variation in their morphological patterns, being the parietal area the most vascularized. The pattern of the diploic channels may be relevant in anthropology, medicine, and paleontology, taking into account their possible involvement in thermoregulation. Am J Phys Anthropol, 2015. © 2015 Wiley Periodicals, Inc.
The identification of species in the fossil record has long vexed paleontologists because of its inherent difficulty, and it has long preoccupied them because of its fundamental significance. Australopithecus africanus exemplifies this difficulty and importance. This species, as commonly defined, is viewed by some as having played a role in the evolution of the genus Homo, while others consider it to have been uniquely related to Paranthropus. A third opinion places it near the base of the evolutionary divergence of the “robust” australopith and human lineages. Various analyses find A. africanus to be phylogenetically unstable, and this is almost certainly owing to its craniodental variability. This has led to questions concerning the taxonomic homogeneity of the assemblages from Taung, Sterkfontein, and Makapansgat that comprise its hypodigm. Initial discoveries at these sites were attributed to different species and possibly genera, but subsequent studies suggested that these fossils represent a single, albeit variable taxon. This paradigm has become current conventional paleoanthropological wisdom, but observations about the degree and pattern of variability evinced by these fossils have raised anew the possibility that the A. africanus hypodigm is taxonomically heterogeneous. Various workers have proposed that at least some of these fossils belong to a different taxon, but there is notable lack of agreement over the manner in which they should be sorted. Morphometric studies tend to find little, if any, support for taxonomic heterogeneity, but they may not have directly addressed those features that have been suggested to differ. Novel innovative technological and quantitative approaches are required to adequately address the possible taxonomic heterogeneity of the A. africanus hypodigm.
The cave infills at Sterkfontein contain one of the richest assemblages of Australopithecus fossils in the world, including the nearly complete skeleton StW 573 (‘Little Foot’) in its lower section, as well as early stone tools in higher sections. However, the chronology of the site remains controversial owing to the complex history of cave infilling. Much of the existing chronology based on uranium–lead dating and palaeomagnetic stratigraphy has recently been called into question by the recognition that dated flowstones fill cavities formed within previously cemented breccias and therefore do not form a stratigraphic sequence. Earlier dating with cosmogenic nuclides suffered a high degree of uncertainty and has been questioned on grounds of sediment reworking. Here we use isochron burial dating with cosmogenic aluminium-26 and beryllium-10 to show that the breccia containing StW 573 did not undergo significant reworking, and that it was deposited 3.67 ± 0.16 million years ago, far earlier than the 2.2 million year flowstones found within it. The skeleton is thus coeval with early Australopithecus afarensis in eastern Africa. We also date the earliest stone tools at Sterkfontein to 2.18 ± 0.21 million years ago, placing them in the Oldowan at a time similar to that found elsewhere in South Africa at Swartkans and Wonderwerk.
Arachnoid granulations are normal variants that protrude into the cerebral venous sinus lumen and produce focal defects in cerebral venography, contrast enhanced CT, and MRI. It should be differentiated from other lesions within the dural sinus lumen that produce focal defects. In the present study, we investigated the frequency and positional distribution of arachnoid granulations with multi-detector row CT. Simple post processing procedures on thin slice multi-detector row CT were performed. We found arachnoid granulations in nearly half of our participants. We observed that presence of arachnoid granulations showed no tendency in two sexes. No relationship between age and multiplicity, and an inverse relationship between age and the variants' size existed. We concluded that as imaging technology continues to develop, the frequency with which normal variants are identified will also increase. Arachnoid granulations are a normal variant that all radiologists should be aware of and which should not be mistaken for pathological intra-sinus lesions. The relationship between characteristics of the variant (presence, number, size) and of the human subjects (gender, age) should be reviewed with larger samples.
The South African National Centre for Radiography and Tomography (SANCRAT), located at Necsa, strives to be leaders in utilizing ionizing radiation as imaging probes in research and development as part of the South African National System of Innovation. The centre already encompasses a Neutron Radiography and Tomography facility (SANRAD) as well as a High Energy X-ray facility (HEXRAD). Recently the centre introduced a state-of-the art micro-focus X-ray machine to the already diverse arsenal of imaging equipment in the Micro-focus X-ray Radiography and Tomography facility (MIXRAD). It is anticipated that the equipment will be extensively used by post graduate students and researchers since this dedicated equipment is the first of this kind and type being made available, nationally, to conduct research for free if the research leads to the publication of peer reviewed papers and /or an upgrade to a higher educational degree. The characteristics and performance capabilities of the MIXRAD facility are presented through several case studies that were being conducted with the instrument.
Different brain components can evolve in a coordinated manner or they can show divergent evolutionary trajectories according to a mosaic pattern of variation. Understanding the relationship between these brain evolutionary patterns, which are not mutually exclusive, can be informed by the examination of intraspecific variation. Our study evaluates patterns of brain anatomical covariation in chimpanzees and humans to infer their influence on brain evolution in the hominin clade. We show that chimpanzee and human brains have a modular structure that may have facilitated mosaic evolution from their last common ancestor. Spatially adjacent regions covary with one another to the strongest degree and separated regions are more independent from each other, which might be related to a predominance of local association connectivity. Despite the undoubted importance of developmental and functional factors in determining brain morphology, we find that these constraints are subordinate to the primary effect of local spatial interactions.
X-ray micro-CT has become a very powerful and common tool for non-destructive three-dimensional (3D) visualization and analysis of objects. Many systems are commercially available, but they are typically limited in terms of operational freedom both from a mechanical point of view as well as for acquisition routines. HECTOR is the latest system developed by the Ghent University Centre for X-ray Tomography (http://www.ugct.ugent.be) in collaboration with X-Ray Engineering (XRE bvba, Ghent, Belgium). It consists of a mechanical setup with nine motorized axes and a modular acquisition software package and combines a microfocus directional target X-ray source up to 240 kV with a large flat-panel detector. Provisions are made to install a line-detector for a maximal operational range. The system can accommodate samples up to 80 kg, 1 m long and 80 cm in diameter while it is also suited for high resolution (down to 4 μm) tomography. The bi-directional detector tiling is suited for large samples while the variable source-detector distance optimizes the signal to noise ratio (SNR) for every type of sample, even with peripheral equipment such as compression stages or climate chambers. The large vertical travel of 1 m can be used for helical scanning and a vertical detector rotation axis allows laminography experiments.
The setup is installed in a large concrete bunker to allow accommodation of peripheral equipment such as pumps, chillers, etc., which can be integrated in the modular acquisition software to obtain a maximal correlation between the environmental control and the CT data taken. The acquisition software does not only allow good coupling with the peripheral equipment but its scripting feature is also particularly interesting for testing new and exotic acquisition routines.
Paleoneurologists analyze internal casts (endocasts) of fossilized braincases, which provide information about the size, shape and, to a limited degree, sulcal patterns reproduced from impressions left by the surface of the brain. When interpreted in light of comparative data from the brains of living apes and humans, sulcal patterns reproduced on hominin endocasts provide important information for studying the evolution of the cerebral cortex and cognition in human ancestors. Here, new evidence is discussed for the evolution of sulcal patterns associated with cortical reorganization in three parts of the hominin brain: (1) the parietotemporo-occipital association cortex, (2) Broca's speech area, and (3) dorsolateral prefrontal association cortex. Of the three regions, the evidence regarding the last is the clearest. Compared to great apes, Australopithecus endocasts reproduce a clear middle frontal sulcus in the dorsolateral prefrontal cortex that is derived toward the human condition. This finding is consistent with data from comparative cytoarchitectural studies of ape and human brains as well as shape analyses of australopithecine endocasts. The comparative and direct evidence for all three regions suggests that hominin brain reorganization was underway by at least the time of Australopithecus africanus (~2.5 to 3.0 mya), despite the ape-sized brains of these hominins, and that it entailed expansion of both rostral and caudal association cortices.
StW 573, Little Foot, is the most complete Australopithecus skeleton yet discovered, with many of its bones found in their correct anatomical position. Since the discovery of the in situ skeleton in the Silberberg Grotto in 1997, several teams have attempted to date the fossil. This appeared a simple process because several flowstones are inter-bedded in the breccia above and below StW 573. Dating of these flowstones, using U–Pb (uranium-lead) isotope decay techniques, gave younger results than expected from the fauna and stratigraphic position, around 2.2 Ma (millions of years). Our recent stratigraphic, micromorphological and geochemical studies revealed that the stratigraphy is much more complicated than was previously thought, with localized post-depositional processes leading to the creation of voids within the breccia around the skeleton. These voids were then filled by multiple generations of flowstone growth. The research we present here demonstrates that the proposed dates based on the flowstone deposition can give only a minimum age for StW 573 and that the flowstone formation came after, and probably long after, the breccia deposition. If one takes account of the long evolution of these karst fillings, StW 573 appears to be significantly older than 2.2 Ma.
We use a model of modern baboon socio-ecology to explore the behavioral ecology and biogeography of the extinct Plio-Pleistocene baboons (genera Parapapio, Gorgopithecus, Dinopithecus, and Papio). The model is based on the way climate affects the baboons’ time budgets, and focuses on intersite variability in behavior rather than on species-typical patterns of behavior, as most previous approaches have done. We use climate estimates for individual fossil sites based on matching modern habitats using faunal profiles and estimates of individual species’ body masses given in the literature. The model allows us to examine the minimum and maximum sizes of groups that individual species would have been able to support at particular localities, and hence the biogeography of a species on a continental scale. In doing so, the model allows us to examine which variables are most responsible for limiting a species’ ecological and biogeographic flexibility, and through this to explore a species’ capacity for coping with climate change. Feeding time is identified as the main constraint. In general, large-bodied species would have had more difficulty surviving in as wide a range of habitats as smaller-bodied species, and this may explain the limited geographical distribution of large-bodied baboons such as Gorgopithecus and Dinopithecus.
Our knowledge of human brain evolution primarily relies on the interpretation of palaeoneurological evidence. In this context, an endocast or replica of the inside of the bony braincase can be used to reconstruct a timeline of cerebral changes that occurred during human evolution, including changes in topographic extension and structural organisation of cortical areas. These changes can be tracked by identifying cerebral imprints, particularly cortical sulci. The description of these crucial landmarks in fossil endocasts is, however, challenging. High-resolution imaging techniques in palaeo-neurology offer new opportunities for tracking detailed endocranial neural characteristics. In this study, we use high resolution imaging techniques to document the variation in extant human endocranial sulcal patterns for subsequent use as a platform for comparison to the fossil record. We selected 20 extant human crania from the Pretoria Bone Collection (University of Pretoria, South Africa), which were detailed using X-ray microtomography at a spatial resolution ranging from 94 to 123 µm (isometric). We used Endex to extract, and Matlab to analyse the cortical imprints on the endocasts. We consistently identified superior, middle and inferior sulci on the frontal lobe; and superior and inferior sulci on the temporal lobe. We were able to label sulci bordering critical functional areas such as Broca’s cap. Mapping the sulcal patterns on extant endocasts is a prerequisite for constructing an atlas which can be used for automatic sulci recognition.
The Sterkfontein Caves site is one of the richest early hominin fossil localities in Africa. More specifically, the fossiliferous deposits within the lower-lying Jacovec Cavern have yielded valuable hominin remains; prominent among them is the Australopithecus partial cranium StW 578. Due to the fragmentary nature of the braincase, the specimen has not yet been formally assigned to a species. In this context, we employ microtomography to quantify cranial thickness and composition of StW 578 in order to assess its taxonomic affinity. As comparative material, we investigate 10 South African hominin cranial specimens from Sterkfontein (StW 505, Sts 5, Sts 25, Sts 71), Swartkrans (SK 46, SK 48, SK 49) and Makapansgat (MLD 1, MLD 10, MLD 37/38), attributed to either Australopithecus or Paranthropus, as well as 10 extant human and 10 extant chimpanzee crania. Thickness variation in and structural arrangement of the inner and outer cortical tables and the diploë are automatically assessed at regular intervals along one parasagittal and one coronal section. Additionally, topographic cranial vault thickness distribution is visualized using color maps. Comparisons highlight an absolutely and relatively thickened condition of the StW 578 cranial vault versus those of other South African Plio-Pleistocene hominins. Moreover, in StW 578, as well as in the Australopithecus specimens Sts 5 and Sts 71 from Sterkfontein, the diploic layer contributes substantially to cumulative vault thickness (i.e., >60%). Within the comparative sample investigated here, StW 505 and Sts 71 from Sterkfontein Member 4, both attributed to Australopithecus, most closely resemble StW 578 in terms of cranial vault thickness values, tissue proportions, and two- and three-dimensional distributions. Including additional Plio-Pleistocene Australopithecus and Paranthropus crania from South and East Africa in future studies would further help establish morphological variability in these hominin taxa.
The only direct source of information about hominin brain evolution comes from the fossil record of endocranial casts (endocasts) that reproduce details of the external morphology of the brain imprinted on the walls of the braincase during life. Surface traces of sulci that separate the brain's convolutions (gyri) are reproduced sporadically on early hominin endocasts. Paleoneurologists rely heavily on published descriptions of sulci on brains of great apes, especially chimpanzees (humans' phylogenetically closest living relatives), to guide their identifications of sulci on ape-sized hominin endocasts. However, the few comprehensive descriptions of cortical sulci published for chimpanzees usually relied on post mortem brains, (now) antiquated terminology for some sulci, and photographs or line drawings from limited perspectives (typically right or left lateral views). The shortage of adequate descriptions of chimpanzee sulcal patterns partly explains why the identities of certain sulci on australopithecine endocasts (e.g., the inferior frontal and middle frontal sulci) have been controversial. Here, we provide images of lateral and dorsal surfaces of 16 hemispheres from 4 male and 4 female adult chimpanzee brains that were obtained using in vivo magnetic resonance imaging. Sulci on the exposed surfaces of the frontal, parietal, temporal, and occipital lobes are identified on the images based on their locations, positions relative to each other, and homologies known from comparative studies of cytoarchitecture in primates. These images and sulcal identifications exceed the quantity and quality of previously published illustrations of chimpanzee brains with comprehensively labeled sulci and, thus, provide a larger number of examples for identifying sulci on hominin endocasts than hitherto available. Our findings, even in a small sample like the present one, overturn published claims that australopithecine endocasts reproduce derived configurations of certain sulci in their frontal lobes that never appear on chimpanzee brains. The sulcal patterns in these new images also suggest that changes in two gyri that bridge between the parietal and occipital lobes may have contributed to cortical reorganization in early hominins. It is our hope that these labeled in vivo chimpanzee brains will assist future researchers in identifying sulci on hominin endocasts, which is a necessary first step in the quest to learn how and when the external morphology of the human cerebral cortex evolved from apelike precursors.
Compared to their putative insectivore-like ancestors, extant primates show an enlarged brain relative to body weight, a larger neocortex and proportionally decreased olfactory bulbs. Besides hypotheses based on the comparative neuroanatomy of extant taxa, the only direct evidence documenting such long-term evolutionary history is provided by fossil endocasts. However, due to the unpredictable yet unavoidable impact of taphonomic processes, the reliability of data from the fossil record is complicated by the nature of the investigated structures themselves. Nonetheless, palaeoneurology has recently enlarged its traditional investigative toolkit by integrating descriptive morphology with advanced methods of high-resolution 3D imaging and computing. In addition to the development of digital restoration techniques, the introduction of analytical methods for investigating topographic differences in morphostructural organization and quantitatively characterizing intra- and interspecific variation patterns provides new possibilities for the study of the primate fossil record, especially for assessing brain evolutionary tracks.
Assessment of global endocranial morphology and regional neuroanatomical changes in early hominins is critical for the reconstruction of evolutionary trajectories of cerebral regions in the human lineage. Early evidence of cortical reorganization in specific local areas (e.g. visual cortex, inferior frontal gyrus) is perceptible in the non-human South African hominin fossil record. However, to date, little information is available regarding potential global changes in the early hominin brain. The introduction of non-invasive imaging techniques opens up new perspectives for the study of hominin brain evolution. In this context, our primary aim in this study is to explore the organization of the Australopithecus africanus endocasts, and highlight the nature and extent of the differences distinguishing A. africanus from the extant hominids at both local and global scales. By means of X-ray-based imaging techniques, we investigate two A. africanus specimens from Sterkfontein Member 4, catalogued as Sts 5 and Sts 60, respectively a complete cranium and a partial cranial endocast. Endocrania were virtually reconstructed and compared by using a landmark-free registration method based on smooth and invertible surface deformation. Both local and global information provided by our deformation-based approach are used to perform statistical analyses and topological mapping of inter-specific variation. Statistical analyses indicate that the endocranial shape of Sts 5 and Sts 60 approximates the Pan condition. Furthermore, our study reveals substantial differences with respect to the extant human condition, particularly in the parietal regions. Compared with Pan, the endocranial shape of the fossil specimens differs in the anterior part of the frontal gyri.
It has long been hypothesized that the transition from Australopithecus to Homo in eastern Africa was linked to the spread of open and arid environments near the Plio−Pleistocene boundary, but data for the latest Pliocene are scarce. Here we present new stable carbon isotope data from the late Pliocene mammalian fauna from Ledi-Geraru, in the lower Awash Valley (LAV), Ethiopia, and mammalian community analyses from the LAV and Turkana Basin. These data, combined with pedogenic carbon-ate stable isotopes, indicate that the two regions were largely similar through the Plio−Pleistocene, but that important environmental differences existed during the emergence of Homo around 2.8 million years ago. The mid-Pliocene to late Pliocene interval in the LAV was characterized by increasingly C 4-dominated, arid and seasonal environments. The early Homo mandible LD 350-1 has a carbon isotope value similar to that of earlier Australopithecus from the LAV, possibly indicating that the emergence of Homo from Australopithecus did not involve a dietary shift. Late Pliocene LAV environments contrast with contempo-raneous environments in the Turkana Basin, which were more woody and mesic. These findings have important implications for the environmental conditions surrounding the emergence of Homo, as well as recent hypotheses regarding Plio−Pleistocene environmental change in eastern Africa.
Paleoneurology deals with the anatomical and morphological analysis of the endocranial cavity in fossil species. Brain size, brain proportions, sulcal patterns, and craniovascular traits can be investigated by comparing living and extinct taxa. Digital anatomy and computed morphometrics represent a major advance in this field, supplying tools for the reconstruction of cranial and endocranial spatial relationships, and for multivariate analyses of the patterns of integration behind the observed phenotypic variability. The study of the relationships between brain and braincase is crucial to understand brain morphology in terms of evolutionary neuroanatomy. In particular, primary neural changes due to intrinsic cerebral factors should be separated from secondary morphological changes due to cranial constraints.
Despite the abundance of well-preserved crania and natural endocasts in the South African Plio-
Pleistocene cercopithecoid record, which provide direct information relevant to the evolution of their
endocranial characteristics, few studies have attempted to characterize patterns of external brain
morphology in this highly successful primate Superfamily. The availability of non-destructive penetrating
radiation imaging systems, together with recently developed computer-based analytical tools, allow for
high resolution virtual imaging and modeling of the endocranial casts and thus disclose new perspectives
in comparative paleoneurology. Here, we use X-ray microtomographic-based 3D virtual imaging
and quantitative analyses to investigate the endocranial organization of 14 cercopithecoid specimens
from the South African sites of Makapansgat, Sterkfontein, Swartkrans, and Taung. We present the first
detailed comparative description of the external neuroanatomies that characterize these Plio-Pleistocene
primates. Along with reconstruction of endocranial volumes, we combine a semi-automatic technique
for extracting the neocortical sulcal pattern together with a landmark-free surface deformation method
to investigate topographic differences in morphostructural organization. Besides providing and
comparing for the first time endocranial volume estimates of extinct Plio-Pleistocene South African
cercopithecoid taxa, we report additional information regarding the variation in the sulcal pattern of
Theropithecus oswaldi subspecies, and notably of the central sulcus, and the neuroanatomical condition of
the colobine taxon Cercopithecoides williamsi, suggested to be similar for some aspects to the papionin
pattern, and discuss potential phylogenetic and taxonomic implications. Further research in virtual
paleoneurology, applied to specimens from a wider geographic area, is needed to clarify the polarity,
intensity, and timing of cortical surface evolution in cercopithecoid lineages.
The evolution of neurocranial morphology in Homo sapiens is characterized by bulging of the parietal region, a feature unique to our species. In modern humans, expansion of the parietal surface occurs during the first year of life, in a morphogenetic stage which is absent in chimpanzees and Neandertals. A similar variation in brain shape among living adult humans is associated with expansion of the precuneus. Using MRI-derived structural brain templates, we compare medial brain morphology between humans and chimpanzees through shape analysis and geometrical modeling. We find that the main spatial difference is a prominent expansion of the precuneus in our species, providing further evidence of evolutionary changes associated with this area. The precuneus is a major hub of brain organization, a central node of the default-mode network, and plays an essential role in visuospatial integration. Together, the comparative neuroanatomical and paleontological evidence suggest that precuneus expansion is a neurological specialization of H. sapiens that evolved in the last 150,000 years that may be associated with recent human cognitive specializations.
The "radiator" theory of brain evolution is proposed to account for "mosaic evolution" whereby brain size began to increase rapidly in the genus Homo well over a million years after bipedalism had been selected for in early hominids. Because hydrostatic pressures differ across columns of fluid depending on orientation (posture), vascular systems of early bipeds became reoriented so that cranial blood flowed preferentially to the vertebral plexus instead of the internal jugular vein in response to gravity. The Hadar early hominids and robust australopithecines partly achieved this reorientation with a dramatically enlarged occipital/marginal sinus system. On the other hand, hominids in the gracile australopithecine through Homo lineage delivered blood to the vertebral plexus via a widespread network of veins that became more elaborate through time. Mastoid and parietal emissary veins are representatives of this network, and increases in their frequencies during hominid evolution are indicative of its development. Brain size increased with increased frequencies of mastoid and parietal emissary veins in the ineage leading to and including Homo, but remained conservative in the robust australopithecine lineage that lacked the network of veins. The brain is an extremely heat-sensitive organ and emissary veins in humans have been shown to cool the brain under conditions of hyperthermia. Thus, the network of veins in the lineage leading to Homo acted as a radiator that released a thermal constraint on brain size. The radiator theory is in keeping with the belief that basal gracile and basal robust australopithecines occupied distinct niches, with the former living in savanna mosaic habitats that were subject to hot temperatures and intense solar radiation during the day.
Much southern African cercopithecoid postcranial material is not associated with craniodental remains. Consequently, this postcranial material cannot be confidently assigned to a particular taxon, with the result that little is known about the locomotor strategies and habitat preferences of specific Plio-Pleistocene cercopithecoids from southern Africa. However, cercopithecoid postcrania can provide important information about habitats that were present at fossil sites, even when the material is not attributed to taxa. In this paper, ecomorphic analysis is used to assign cercopithecoid postcranial material from Sterkfontein Member 4, Bolt's Farm and Swartkrans Members 1 and 2 to one of three habitat/locomotor categories: forest-living arboreal quadrupeds ('forest arboreal'), open habitat terrestrial quadrupeds ('open terrestrial') and open habitat cercopithecoids using a mix of arboreal and terrestrial quadrupedalism ('open mixed'). Cercopithecoids representing all three habitat categories were found in the samples from Sterkfontein Member 4 and Bolt's Farm, suggesting that monkeys using a range of habitats and locomotor strategies were present at these sites. However, no 'forest arboreal' cercopithecoids were found in the samples from Swartkrans Members 1 and 2, indicating that cercopithecoids at these localities probably depended largely on open habitats. The habitat and locomotor strategy data were also used in combination with locality-based listings of fossil cercopithecoid craniodental remains to suggest possible locomotor strategies for several southern African Plio-Pleistocene cercopithecoid taxa, including Parapapio broomi (possibly 'forest arboreal'), Parapapio jonesi ('open terrestrial'), Papio robinsoni ('open terrestrial') and Cercopithecoides williamsi('open mixed').
Since the discovery by Robert Broom of the first adult Australopithecus at Sterkfontein in 1936, a large quantity of fossil remains of this genus, consisting of crania, teeth and postcranial bones, has been excavated from those cave infills. They have generally been considered as belonging to one species, Australopithecus africanus, but there is now abundant proof that a second species is represented by many of the fossils. This second species should be classified as Australopithecus prometheus, the name given by Raymond Dart in 1948 to such fossils from Makapansgat (MLD 1 and MLD 2). A. prometheus is distinguished from A. africanus by having a more vertical occiput, larger, bulbous-cusped cheek teeth, a flatter face, lower frontal squame, and sagittal crest in the males. An almost complete skeleton of Australopithecus (StW 573) from an early deposit in the cave belongs to this second species, and for the first time this discovery made it possible to indisputably associate postcranial anatomy with specific cranial anatomy. It is also now possible to clearly distinguish males and females of each species, and to state with conviction that StW 53, a cranium excavated in 1976 and widely identified as Homo habilis, is in fact a male A. africanus, virtually the same as the TM 1511 cranium found by Broom 40 years earlier.
Understanding hominid brain evolution involves identifying both the physical changes that occurred, as well as understanding the reasons for the changes. There are two ways in which inferences about evolutionary changes are made. By comparing a species of interest against other modern species, one can determine what exactly is different. By studying the fossil record, one assesses the time-course of evolutionary changes. Most comparative studies have primarily focused on how humans differ from expectations based on primate trends, though ape disproportions have also been highlighted when found. In light of the evidence regarding functional implications of neuroanatomical differences, it is possible to outline likely behavioral implications of neuroanatomical evolution in apes and humans. First, changes in ape brains suggest a significant enhancement of general cognitive ability, behavioral flexibility, learning, and planning compared with monkeys. Further changes during human evolution suggest even greater enhancement of same abilities in our lineage.
Mammalogy provides exceptionally fertile grounds for advancing evolutionary theory, because its data base spans from diverse researches on living forms to a rich fossil record. I illustrate this by integrating interdisciplinary evidence and hypotheses in the habitat theory, including: 1) the context of paleoclimatic changes, and how species' distributions responded to them; 2) geographical biases in turnover rates of species; 3) the turnover-pulse hypothesis; 4) breadth of resource use as a cause of phylogenetic turnover rates. Preliminary tests using the late Neogene records of the Americas and Africa suggest that major aspects of the Great American Interchange have parallels in the African record, as predicted by the habitat theory. Comparable forces may have operated in both cases. The habitat theory of the Great American Interchange differs from the traditional emphasis on the effects of interspecific competition.
The human orbitofrontal cortex is an important brain region for the processing of rewards and punishments, which is a prerequisite for the complex and flexible emotional and social behaviour which contributes to the evolutionary success of humans. Yet much remains to be discovered about the functions of this key brain region, and new evidence from functional neuroimaging and clinical neuropsychology is affording new insights into the different functions of the human orbitofrontal cortex. We review the neuroanatomical and neuropsychological literature on the human orbitofrontal cortex, and propose two distinct trends of neural activity based on a meta-analysis of neuroimaging studies. One is a mediolateral distinction, whereby medial orbitofrontal cortex activity is related to monitoring the reward value of many different reinforcers, whereas lateral orbitofrontal cortex activity is related to the evaluation of punishers which may lead to a change in ongoing behaviour. The second is a posterior–anterior distinction with more complex or abstract reinforcers (such as monetary gain and loss) represented more anteriorly in the orbitofrontal cortex than simpler reinforcers such as taste or pain. Finally, we propose new neuroimaging methods for obtaining further evidence on the localisation of function in the human orbitofrontal cortex.
Since Dart’s analysis of the Taung skull in1925 in Nature, there has been controversy surrounding the presence of a clearly defined lunate sulcus (LS) in the australopithecines, marking the anterior extent of primary visual cortex (PVC). An anterior position signifies that the LS is in an ape-like position, such as found in Pan troglodytes. A posterior position is a more human-like characteristic (autapomorphy). If the latter occurred in Australopithecus, then the cerebral cortex underwent some neurological reorganization prior to brain enlargement, thus occurring earlier than the emergence of the genus Homo. The endocast of the Stw 505 specimen from Sterkfontein, South Africa, shows an unmistakably posterior placement of the LS. The early hominid brain was reorganized at least by the time of Australopithecus africanus, thus vindicating Dart’s early assessment. To cite this article: R.L. Holloway, C. R. Palevol 3 (2004).
II existe, d'apres l'etude du moulage endocrânien, parmi les Australopitheques deux types de topographie du reseau des veines meningees moyennes : l'un, propre a la forme gracile, sans branche moyenne : l'autre, propre a la forme robuste, avec une banche moyenne. Homo habilis s'en distingue par un modele plus complique avec l'accroissement du nombre de ramifications de la branche moyenne et la presence d'anastomoses, premier pas vers le dessin caracteristique du genre Homo. Le specimen KNM ER 1813 montre une facture correspondant au type de la forme robuste.