Relationship of squamosal suture to asterion in pongids (Pan): relevance to early hominid brain evolution.

Based on 244 measurements of the relationship of the squamosal suture to the landmark asterion in 49 chimpanzee skulls, it is shown that in the normal lateral view the squamosal suture is very rarely inferior to asterion. In hominid crania, the squamosal suture is always well superior to asterion. Even in Pan, that part of the squamosal suture most homologous with the remnant found on the Hadar AL 162-28 Australopithecus afarensis hominid cranial fragment is very rarely inferior to asterion. Such variability suggests that Falk's (Nature 313:45-47, 1985) orientation of the Hadar specimen is incorrect; she places asterion superior to the position of the squamosal suture if projected endocranially. The implication for the brain endocast is that, however the fragment is oriented, the posterior aspect of the intraparietal (IP) sulcus is in a very posterior position relative to any chimpanzee brain. The distance from the posterior aspect of IP to occipital pole is twice as great in chimpanzee brain casts than on the Hadar AL 162-28 endocast, even though the chimpanzee brain casts are smaller in overall size. This suggests that brain reorganization, at least as exemplified as a reduction in primary visual striate cortex (area 17 of Brodmann), occurred early in hominid evolution, prior to any major brain expansion.     

Brain expansion and rotation during hominid evolution

The question of how an endocast (or brain) is oriented within a skull that is positioned in the Frankfurt plane is investigated for African great apes, early hominids STS 71, KNM-ER 1813 and KNM-ER 1470, and modern humans using a 3SPACE digitizer. Our results suggest that, rather than being positioned in the orientation in which isolated brains (endocasts) are conventionally illustrated, brains within skulls that are oriented in the Frankfurt plane tend to be inclined so that the frontal pole is higher than the occipital pole, especially inHomo. These preliminary findings have implications for interpreting early hominid endocasts such as that of AL 162-28.     

中国古人类颅内模及脑演化研究进展

颅内模保存有脑表面的形态结构,是脑演化研究的直接证据。中国最早复原和研究的颅内模来自20世纪20年代北京周口店遗址发现的3号猿人头骨;此后虽然中国境内也相继发现了一些古人类的头骨化石,但由于古人类标本非常珍贵,不允许对其进行实体解剖,加上多数头骨破碎或者内部附有地层胶结物,导致颅内模无法成功复原。受技术水平及研究手段的限制,研究者一般只是侧重于化石外表形态结构的研究。高分辨率工业CT和3D软件的应用,可以在不损坏标本的情况下,虚拟复原出化石的内部解剖结构,使得一些重要的古人类化石标本的颅内模被复原出来,促进了脑演化的研究。近年来,本文第一作者采用新技术、新方法复原了南京直立人、柳江人等一些重要的中国古人类头骨的颅内模,通过对其颅容量、脑沟回特征、脑不对称性、脑表面的动、静脉血管压迹、各脑叶的大小、形状及比例的研究,获取了中国古人类脑形态特征变化的数据,为探讨东亚地区古人类的演化提供了参考信息。     

Endocranial suture closure in rhesus macaques (Macaca mulatta)

Endocasts from skulls of 330 rhesus monkeys (Macaca mulatta) of known age are scored for closure of nine bilateral and three unilateral sutures or segments of sutures. A variety of tests reveals a strong relationship between age and stages of suture closure, although increasingly broad confidence intervals prevent sutures from being very useful for precisely aging older macaques. The order in which endosutures begin to close, as well as that in which closure is finally achieved, is determined for macaques, and these sequences compared to those for endosutures of humans (Todd and Lyon, 1924). The basilar suture is the earliest to close, while the masto-occipital and rostral and caudal squamosal sutures achieve closure quite late in both species. On the other hand, humans and macaques differ in their schedules for the sphenofrontal suture and in the initiation of closure for the rostral portion of the squamosal suture. Two sutures close significantly sooner on the right than on the left side (the rostral squamosal and masto-occipital) and asymmetry favoring closure of the right lateral lambdoid suture also approaches significance at the 0.05 level. No sutures close significantly sooner on the left side. It is suggested that macaque sutures may close from the inside out, that endosutures are more sensitive than ectosutures for detecting sequences in which cranial sutures begin to close, and that directional asymmetries in suture closure of macaques may be related to minor asymmetries in brain/skull shape (petalias).     

The Taung endocast: a reply to Holloway

Indices of rostrality (ir, ir') are developed to assess the extent to which the medial end of the lunate sulcus (L) is rostrally positioned in photographs and figures of lateral views of primate brains and endocasts, and indices are determined for chimpanzees, SK 1585 and the Taung endocast. Ir quantifies the extent of rostrality as it has traditionally been viewed (in A-P projections) while ir' takes dorsal curvature into account. The ir of the feature that I have identified as the lunate sulcus of Taung is within one standard deviation of the mean ir for Pan and its ir' is within 1.5 standard deviations from the mean ir' for Pan. Both findings are compatible with my earlier statement that the medial end of the lunate sulcus of the Taung endocast is in a pongid-like position. Use of stereoplotting to transfer the position of L from chimpanzee endocasts and brains to australopithecine endocasts is critically assessed: Holloway stereoplotted five chimpanzee brains and then transferred their mean coordinates that describe the lunate sulcus to the Taung endocast. If stereoplotting successfully transfers the extent to which L is rostrally located, one would expect the mean L of Pan and its transferred counterpart in Taung to have identical index values of rostrality. However, the ir of the lunate sulcus that Holloway located on Taung is over two standard deviations lower than the mean ir for the five chimpanzees he stereoplotted to determine its angular coordinates, and Holloway's ir' for Taung is one standard deviation lower than the five chimpanzees' mean ir'. These discrepancies are shown to be due to shape differences, and it is concluded that stereoplotting should not be used to transfer sulci between differently shaped endocasts without correcting for these differences. I also reply to Holloway's criticisms of my use of L/H indices, palpation, techniques for sampling endocasts, and illustration of the Taung endocast. It is shown that there is room on the Taung specimen for the lateral end of L, and the pongid-like sulcal pattern of Taung is reaffirmed. Thus, we do not yet know when human-like sulcal patterns first appeared in the hominid fossil record.     

A note on the effect of asymmetry in suture closure in mature human skulls

Studies on suture closure in mature European and East African Bantu skulls revealed marked differences in the degree of suture closure on the left and right side. Asymmetrical closure of sutures may lead to erroneous conclusions being made in ageing skulls if only one-half of the skull is available for examination. Asymmetry in suture closure was rather common in recent skulls, being particularly noticeable in the bregmatic and complicate parts of the coronal suture and in intermediate portions of lambdoid sutures.     

On a new australopithecine partial endocast.

A newly discovered right parietal/temporal/frontal fragment from an australopithecine natural endocast is described and compared to other australopithecine endocasts. This specimen shows that the central sulcus was arched, rather than straight as previously believed, and reveals frontal lobe convolutions not preserved in other australopithecine endocasts.     

Unilateral and bilateral expression of a quantitative trait: asymmetry and symmetry in coronal craniosynostosis

Bilateral symmetry in vertebrates is imperfect and mild asymmetries are found in normal growth and development. However, abnormal development is often characterized by strong asymmetries. Coronal craniosynostosis, defined here as consisting of premature suture closure and a characteristic skull shape, is a complex trait. The premature fusion of the coronal suture can occur unilaterally associated with skull asymmetry (anterior plagiocephaly) or bilaterally associated with a symmetric but brachycephalic skull. We investigated the relationship between coronal craniosynostosis and skull bilateral symmetry. Three-dimensional landmark coordinates were recorded on preoperative computed tomography images of children diagnosed with coronal nonsyndromic craniosynostosis (N = 40) and that of unaffected individuals (N = 20) and analyzed by geometric morphometrics. Our results showed that the fusion pattern of the coronal suture is similar across individuals and types of coronal craniosynostosis. Shape analysis showed that skulls of bilateral coronal craniosynostosis (BCS) and unaffected individuals display low degrees of asymmetry, whereas right and left unilateral coronal craniosynostosis (UCS) skulls are asymmetric and mirror images of one another. When premature fusion of the coronal suture (without taking into account cranial dysmorphology) is scored as a qualitative trait, the expected relationship between trait frequency and trait unilateral expression (i.e. negative correlation) is confirmed. Overall, we interpret our results as evidence that the same biological processes operate on the two sides in BCS skulls and on the affected side in UCS skulls, and that coronal craniosynostosis is a quantitative trait exhibiting a phenotypic continuum with BCS displaying more intense shape changes than UCS.     

Brief communication: new reconstruction of the Taung endocast

Earlier reconstructions of the Taung endocast, from the juvenile type specimen for Australopithecus africanus, were achieved without benefit of the advanced computer technology that is available today and before morphological differences were identified that distinguish endocasts of Paranthropus from those of A. africanus. Here, we reconstruct and measure a relatively complete virtual endocast of Taung and provide a new cranial capacity estimate of 382 cm(3) and a projected adult capacity of 406 cm(3), which are smaller than previous estimates. Linear measurements and ratios were also obtained from an endocast of Sts 5 and five Paranthropus endocasts and compared with those of Taung. A number of previously unrecognized foramina, processes, and canals are identified in the bony material that adheres to the base of the Taung endocast. The newly reconstructed virtual endocast of Taung displays a number of shape features that sort it more closely with gracile than robust australopithecines, including squared-off frontal lobes in dorsal view, and the shape of the tips of its temporal poles. The Taung endocast also shares some features with Paranthropus endocasts, while other characteristics such as small temporal lobes may be due to its juvenile status. Just how much of Taung's unique morphology is due to its juvenile status may eventually be clarified by comparing its endocast with those from other juvenile australopithecines such as the 3.3-million-year-old juvenile from Dikika, Ethiopia.     

Validation of plaster endocast morphology through 3D CT image analysis

A crucial component of research on brain evolution has been the comparison of fossil endocranial surfaces with modern human and primate endocrania. The latter have generally been obtained by creating endocasts out of rubber latex shells filled with plaster. The extent to which the method of production introduces errors in endocast replicas is unknown. We demonstrate a powerful method of comparing complex shapes in 3-dimensions (3D) that is broadly applicable to a wide range of paleoanthropological questions. Pairs of virtual endocasts (VEs) created from high-resolution CT scans of corresponding latex/plaster endocasts and their associated crania were rigidly registered (aligned) in 3D space for two Homo sapiens and two Pan troglodytes specimens. Distances between each cranial VE and its corresponding latex/plaster VE were then mapped on a voxel-by-voxel basis. The results show that between 79.7% and 91.0% of the voxels in the four latex/plaster VEs are within 2 mm of their corresponding cranial VEs surfaces. The average error is relatively small, and variation in the pattern of error across the surfaces appears to be generally random overall. However, inferior areas around the cranial base and the temporal poles were somewhat overestimated in both human and chimpanzee specimens, and the area overlaying Broca's area in humans was somewhat underestimated. This study gives an idea of the size of possible error inherent in latex/plaster endocasts, indicating the level of confidence we can have with studies relying on comparisons between them and, e.g., hominid fossil endocasts.     

Heterochrony and sexual dimorphism in the skull of the Liberian chimpanzee (Pan troglodytes verus)

Allometric methods and theory derived from principles of relative growth provide new and powerful approaches to an understanding of the nature and development of sexual dimorphism among living primates. The Frankfurt collection of Liberian chimpanzee skulls and mandibles provides a large skeletal sample from a single natural population of wild shot animals, including individuals of all ages and both sexes, and allows investigation of allometric and heterochronic patterns of sexual dimorphism. Univariate, bivariate, and multivariate analyses are utilized in this study in order to ascertain the ontogenetic nature of male-female differences in the skull of the Liberian chimpanzee. The results of univariate and multivariate analyses indicate that, while overall levels of sexual dimorphism in the chimpanzee skull are small, the greatest differences are in dimensions of the viscerocranium, while neurocranial dimensions and orbital size tend to be less dimorphic. Bivariate regressions of 21 cranial variables against basicranial length document positive allometry in many facial and mandibular dimensions, and isometry or negative allometry for most neurocranial dimensions. The data confirm previous work in chimpanzees and other anthropoid primates suggesting that males and females are “ontogenetically scaled” in most cranial traits. That is, males and females share the same cranial growth trajectories, although ending up at different points. Both rate and time hypermorphosis are suggested as underlying causes of ontogenetic scaling in the Liberian chimpanzee.     

A new approach to mammalian cranial analysis, illustrated by examples of prosimian primates

Latex endocranial casts, which may be made without damaging the skull, reveal much of the information provided by a hemisected skull. Examination of drawings of endocasts superimposed on skulls may provide insight into the biological significance of skull and brain morphology. The high degree of cranial flexion and the globose brain shape of Daubentonia appear to be related to the functional demands of its gnawing mechanism. The broad frontal lobes of indriids are correlated with orbital orientation; differences in frontal lobe sulcal pattern suggest greater elaboration of the motor filed for the hand in indriids than in lemurids. Several features of lorisid cranial anatomy are discussed. It is suggested that, as a first approximation, increased splanchnocranial declination in small prosimians results from the necessity of accommodating relatively large eyes in a skull with a relatively small splanchnocranium.     

Advanced computer graphics technology reveals cortical asymmetry in endocasts of rhesus monkeys

Lengths of cortical sulci were measured on ten endocranial casts (endocasts) from skulls of rhesus monkeys, using advanced computer technology that permits analysis and imaging of surface morphology in three dimensions. Sulcal lengths were compared in left and right hemispheres and, contrary to earlier reports, the length of the left Sylvian fissure was found to be significantly longer than its right counterpart, as is the case for chimpanzees and humans. This asymmetry in humans is thought to be associated with asymmetrical representation of language functions in the left hemisphere and, although this report is the first to demonstrate a significantly longer left Sylvian fissure in rhesus monkeys, our results are in keeping with psychophysical evidence that suggests that Macaca is left hemisphere dominant for perception of meaningful vocalizations. We attribute the difference between our findings and previous reports to the sensitivity of the new computer technology used to collect data from endocasts.     

Linking form and function of the fibrous joints in the skull: a new quantification scheme for cranial sutures using the extant fish Polypterus endlicherii

The aim of this study is to connect specific sutural morphologies with the specific types of deformation they experience. To meet this goal, we quantified the morphologies of the interfrontal (IF), interparietal (IP), and frontoparietal (FP) sutures in the extant fish Polypterus endlicherii, and used our published measurements of in vivo deformation of these sutures during feeding to infer how suture morphology and function are connected. Specifically, we found that three relatively simple measures of cross-sectional suture complexity (i.e., the ratio of total sutural length to its shortest end-to-end length; amount of sutural overlap; and size of the largest interdigitation) can be used to distinguish between the IF, FP, and IP sutures, which exhibit very different cross-sectional shapes and responses to loading. Interestingly, these differences in cross-sectional morphology are not reflected by the linear traces of these sutures on the surface of the skull, implying that cross-sectional shape of a suture must be known to infer the loading conditions it experiences. Plotting the three cross-sectional metrics against one another to yield a sutural morphospace shows that the IF, IP, and FP sutures define regions that are largely distinct from one another. Our previous measurements of strain across these sutures suggested that the FP region would lie between the IF and IP regions; instead, the FP region is largely set apart from the other two fields. Based on this discovery, and on the locations of cranial muscles, we propose a new model of deformation in the skull of P. endlicherii during feeding, in which rotation parallel to the skull roof is combined with bending, subjecting the FP suture to complex shearing. Finally, although the sutures of P. endlicherii appear to be significantly less complex than those of mammals, these fish sutures show a similar range of morphologies and perform similar functions as do mammalian sutures.     

Functional implications of squamosal suture size in paranthropus boisei

It has been hypothesized that the extensively overlapping temporal and parietal bones of the squamosal sutures in Paranthropus boisei are adaptations for withstanding loads associated with feeding. Finite element analysis (FEA) was used to investigate the biomechanical effects of suture size (i.e., the area of overlap between the temporal and parietal bones) on stress, strain energy, and strain ratio in the squamosal sutures of Pan troglodytes and P. boisei (specimen OH 5) during biting. Finite element models (FEMs) of OH 5 and a P. troglodytes cranium were constructed from CT scans. These models contain sutures that approximate the actual suture sizes preserved in both crania. The FEM of Pan was then modified to create two additional FEMs with squamosal sutures that are 50% smaller and 25% larger than those in the original model. Comparisons among the models test the effect of suture size on the structural integrity of the squamosal suture as the temporal squama and parietal bone move relative to each other during simulated premolar biting. Results indicate that with increasing suture size there is a decreased risk of suture failure, and that maximum stress values in the OH 5 suture were favorable compared to values in the Pan model with the normal suture size. Strain ratios suggest that shear is an important strain regime in the squamosal suture. This study is consistent with the hypothesis that larger sutures help reduce the likelihood of suture failure under high biting loads. Am J Phys Anthropol 153:260–268, 2014. © 2013 Wiley Periodicals, Inc.     

The effect of artificial cranial deformation on the incidence of wormian bones in the lambdoidal suture

One hundred and twenty adult and 80 human fetal skulls were examined to find the relationship (if any) between the presence of wormian bones in the lambdoidal suture and artificial deformation of the skull. Wormian bones occur in deformed and undeformed skulls with no significant differences. Wormian bones detected in fetal skulls preclude cultural deformation as an important factor in the formation of these bones. It is hypothesized that a genetic predisposition (genes allowing formation of secondary ossification centers) is present and that wormian bones are under direct genetic control regardless of the presence or absence of detectable cultural deformation.     

The First Virtual Cranial Endocast of a Lungfish (Sarcopterygii: Dipnoi)

Lungfish, or dipnoans, have a history spanning over 400 million years and are the closest living sister taxon to the tetrapods. Most Devonian lungfish had heavily ossified endoskeletons, whereas most Mesozoic and Cenozoic lungfish had largely cartilaginous endoskeletons and are usually known only from isolated tooth plates or disarticulated bone fragments. There is thus a substantial temporal and evolutionary gap in our understanding of lungfish endoskeletal morphology, between the diverse and highly variable Devonian forms on the one hand and the three extant genera on the other. Here we present a virtual cranial endocast of Rhinodipterus kimberleyensis, from the Late Devonian Gogo Formation of Australia, one of the most derived fossil dipnoans with a well-ossified braincase. This endocast, generated from a Computed Microtomography (µCT) scan of the skull, is the first virtual endocast of any lungfish published, and only the third fossil dipnoan endocast to be illustrated in its entirety. Key features include long olfactory canals, a telencephalic cavity with a moderate degree of ventral expansion, large suparaotic cavities, and moderately enlarged utricular recesses. It has numerous similarities to the endocasts of Chirodipterus wildungensis and Griphognathus whitei, and to a lesser degree to ''Chirodipterus'' australis and Dipnorhynchus sussmilchi. Among extant lungfish, it consistently resembles Neoceratodus more closely than Lepidosiren and Protopterus. Several trends in the evolution of the brains and labyrinth regions in dipnoans, such as the expansions of the utricular recess and telencephalic regions over time, are identified and discussed.     

The temporal region and the supramastoid ridge in mesolithic skulls from Padina in the Iron Gate Gorge of the Danube

Studies of the morphological features of the temporal region of mesolithic skulls from Padina in the Iron Gate Gorge of the Danube revealed a very prominent and large supramastoid ridge which is the most striking feature in skulls of both sexes. Mastoid processes were larger in male skulls, but in 25% of the cases there was an overlap between the size of the processes in male and female specimens. The mastoid ridge was prominent in both sexes. The digastric fossa was always well defined in both sexes and in the two thirds of the skull specimens it was deep. The posterior root of the zygoma was prominent in all the skulls, but it was better developed in the male specimens. The parietotemporal suture in both sexes rises above the level of the pterion. There were no morphological or anthropometrical differences between the left and the right side of individual skulls outside the limits of natural asymmetry. All these morphological characteristics of the temporal region may help in racial and sexual diagnosis of the Mesolithic skulls from the Iron Gate Gorge.