Paleoneurology of an “early” Neandertal: endocranial size, shape, and features of Saccopastore 1

Virtual excavation and analysis of the early Neanderthal cranium from Altamura (Italy)

Complete Neanderthal skeletons are almost unique findings. A very well-preserved specimen of this kind was discovered in 1993 in the deepest recesses of a karstic system near the town of Altamura in Southern Italy. We present here a detailed description of the cranium, after we virtually extracted it from the surrounding stalagmites and stalactites. The morphology of the Altamura cranium fits within the Neanderthal variability, though it retains features occurring in more archaic European samples. Some of these features were never observed in Homo neanderthalensis, i.e. in fossil specimens dated between 300 and 40 ka. Considering the U-Th age we previously obtained (>130 ka), the morphology of Altamura suggests that the archaic traits it retains may have been originated by geographic isolation of the early Neanderthal populations from Southern Italy.

Endocranial anatomy of the Guercy 1 early Neanderthal from Baume Moula-Guercy (Soyons, Ardèche, France)

We provide the first comparative description of the endocranium of the Guercy 1 Early Neanderthal and examine its affinities to Preneanderthals, Neanderthals, and Homo sapiens. The Guercy 1 cranium derives from deposits chronostratigraphically and biostratigraphically dated to the Eemian Interglacial (MIS 5e). For comparative purposes, we compiled a sample of European and Southwest Asian subadult and adult Middle-to-Late Pleistocene hominins (≈MIS 12-MIS 1; N = 65). We sampled both a Preneanderthal-Neanderthal group and a Homo sapiens group. The Preneanderthal-Neanderthal group was further divided into three time-successive subgroups defined by associated MIS stages. Metric and morphological observations were made on original fossils and physical and virtual endocranial reconstructions. Guercy 1 and other Early Neanderthals, differ from Preneanderthals by increased development of the prefrontal cortex, precentral and postcentral gyri, inferior parietal lobule, and frontoparietal operculum. Early Neanderthal differ, in general, from Late Neanderthals by exhibiting less development in most of the latter brain structures. The late group additionally differentiates itself from the early group by a greater development of the rostral superior parietal lobule, angular gyrus, superior and middle temporal gyri, and caudal branches of the superior temporal gyrus. Endocranial morphology assessed along the Preneanderthal-Neanderthal sequence show that brain structures prominent in Preneanderthals are accentuated in Early-to-Late Neanderthals. However, both the Early and Late groups differentiate themselves by also showing regionally specific changes in brain development. This pattern of morphological change is consistent with a mosaic pattern of neural evolution in these Middle-to-Late Pleistocene hominins.

Neanderthal cranial remains from Baume Moula-Guercy (Soyons, Ardèche, France)

OBJECTIVES

We provide the first comparative description of the Guercy 1 cranium and isolated cranial fragments from Baume Moula-Guercy and examine their affinities to European Preneanderthals, Neanderthals, and Homo sapiens.

MATERIALS AND METHODS

The Moula-Guercy hominins derive from deposits chronostratigraphically and biostratigraphically dated to the Eemian Interglacial (MIS 5e). For comparisons we compiled a sample of European and Southwest Asian subadult-adult Middle-to-Late Pleistocene hominins (≈MIS 14-MIS 2; N = 184). This sample represents a Preneanderthal-Neanderthal group and a H. sapiens group, both of which were further divided into three time-successive subgroups defined by associated marine isotope stages (MIS). Metric and morphological observations were made on the original fossils and a virtual reconstruction of Guercy 1. Developmental age and sex and the minimum-maximum number of individuals were assessed.

RESULTS

Guercy 1 represents the remains of a late stage adolescent (≈15-16.0 years) female. Morphological and metric data combine to associate the total morphological pattern expressed in Guercy 1 with our MIS 7-MIS 5e ("Early Neanderthal") subgroup. Some features, especially those related to the frontal, suggest linkage to a paleodeme comprising the Moula-Guercy, Artenac, La Chaise Abri Suard and, possibly, the Biache-Saint-Vaast samples.

DISCUSSION

Remains of MIS 7-MIS 5e Neanderthals are rare and fragmentary, especially those dated to the Last Interglacial. The Baume Moula-Guercy sample provides new insights into the total morphological pattern expressed in MIS 5e Neanderthals. Further, our results support earlier suggestions that MIS 7-MIS 5e European hominins represent a morphotype that is distinct from both earlier and later members of the Preneanderthal-Neanderthal group.

Virtually estimated endocranial volumes of the Krapina Neandertals

OBJECTIVES

The Krapina rock shelter has yielded a large assemblage of early Neandertals. Although endocranial volume (ECV) has been estimated for four individuals from the site, several published values that appear in the literature warrant revisiting.

MATERIALS AND METHODS

We used virtual methods, including high-resolution surface models of fossils and 3D geometric morphometrics, to reconstruct endocasts and estimate ECV for five Krapina crania. We generated 10 reconstructions of each endocast to quantify missing data uncertainty. To assess the method and our ECV estimates, we applied these techniques to the Spy II Neandertal, and estimated ECV of a human reference endocast simulating the missing data of the Krapina fossils.

RESULTS

We obtained an average ECV estimate of 1,526 cm³ for Spy II, consistent with previous research. Estimated ECV of juveniles Krapina 1 and 2 average 1,419 and 1,286 cm³ , respectively. Estimates for the relatively complete adults Krapina 3 and 6 range from 1,247 to 1,310 cm³ and 1,135 to 1,207 cm³ , respectively, while the more fragmentary Krapina 5 averaged 1,397 cm³ . The missing data simulation suggests more fragmentary crania yield more uncertain and possibly overestimated ECVs.

CONCLUSIONS

We have provided new estimates of brain size of the Krapina Neandertals, including the first estimates for Krapina 2. Brain size at Krapina was similar to other pre-Würm Neandertals, within the range of but lower than the average of later Neandertals. Although the virtual approach overcomes many challenges of fossil preservation, our results are nevertheless subject to future revision.

Endomaker, a new algorithm for fully automatic extraction of cranial endocasts and the calculation of their volumes

OBJECTIVES

Reproducing cranial endocasts is a major goal of researchers interested in vertebrate brain evolution. We present a new R software, named endomaker, which allows the automatic extraction of endocasts from skull meshes along with the calculation of its volume.

MATERIALS AND METHODS

We applied endomaker on non-primate and primate skulls including the Australopithecus africanus specimen Sts-5.

RESULTS

We proved endomaker is faster, more feature-rich and possibly more accurate than competing software.

DISCUSSION

Endomaker is the only available program endowed with the possibility to process an entire mesh directory straight away, promising to expand the scope and phylogenetic breadth of comparative studies of brain evolution.

Virtual Reconstruction and Comparative Analyses of the Middle Pleistocene Apidima 2 Cranium (Greece)

The Apidima 2 fossil cranium from South Peloponnese is one of the most important hominin specimens from Southeast Europe. Nevertheless, there has been continuous controversy as to whether it represents a so-called Preneandertal/Homo heidelbergensis such as, for example, the Petralona cranium from Northern Greece or a more derived Neandertal. Recent absolute dating evidence alone cannot clarify the issue because both classifications would be possible during the respective Middle Pleistocene time span. Since only limited data were available on the cranium, there have been repeated claims for the need of a broader comparative study of the hominin. The present article presents a CT-based virtual reconstruction including corrections of postmortem fractures and deformation as well as detailed metrical and morphological analyses of the specimen. Endocranial capacity could be estimated for the first time based on virtual reconstruction. Our multivariate analyses of metric data from the face and vault revealed close affinities to early and later Neandertals, especially showing the derived facial morphometrics. In addition, comparative analyses of Apidima 2 were done for many derived Neandertal features. Here again, a significant number of Neandertal features could be found in the Apidima cranium but no conditions common in Preneandertals. In agreement with a later Middle Pleistocene age Apidima is currently the earliest evidence of a hominin in Europe with such a derived Neandertal facial morphology. The place of Apidima in the complex process of Neandertal evolution as well as its taxonomic classification are discussed as well. Anat Rec, 303:1374-1392, 2020. © 2019 American Association for Anatomy.

The endocast of the one-million-year-old human cranium from Buia (UA 31), Danakil Eritrea

OBJECTIVES

The Homo erectus-like cranium from Buia (UA 31) was found in the Eritrean Danakil depression and dated to 1 million years. Its outer morphology displays archaic traits, as well as distinctive and derived characters. The present study provides the description and metric comparison of its endocranial anatomy.

MATERIALS AND METHODS

UA 31 was originally filled by a diffuse concretion. Following its removal and cleaning, the endocast (995 cc) was reconstructed after physical molding and digital scan. Its morphology is here compared with specimens belonging to different human taxa, taking into account endocranial metrics, cortical traits, and craniovascular features.

RESULTS

The endocast is long and narrow when compared to the H. erectus/ergaster hypodigm, although its proportions are compatible with the morphology displayed by all archaic and medium-brained human species. The occipital areas display a pronounced bulging, the cerebellum is located in a posterior position, and the middle meningeal vessels are more developed in the posterior regions. These features are common among specimens attributed to H. erectus s.l., particularly the Middle Pleistocene endocasts from Zhoukoudian. The parietal lobes are markedly bossed. This lateral bulging is associated with the lower parietal circumvolutions, as in other archaic specimens. This pronounced parietal curvature is apparently due to a narrow cranial base, more than to wider parietal areas.

CONCLUSIONS

The endocast of UA 31 shows a general plesiomorphic phenotype, with some individual features (e.g., dolichocephaly and rounded lower parietal areas) which confirm a remarkable degree of morphological variability within the H. erectus/ergaster hypodigm. Am J Phys Anthropol 160:458-468, 2016. © 2016 Wiley Periodicals, Inc.

Analysis of the volumetric relationship among human ocular, orbital and fronto-occipital cortical morphology

Recent research on the visual system has focused on investigating the relationship among eye (ocular), orbital, and visual cortical anatomy in humans. This issue is relevant in evolutionary and medical fields. In terms of evolution, only in modern humans and Neandertals are the orbits positioned beneath the frontal lobes, with consequent structural constraints. In terms of medicine, such constraints can be associated with minor deformation of the eye, vision defects, and patterns of integration among these features, and in association with the frontal lobes, are important to consider in reconstructive surgery. Further study is therefore necessary to establish how these variables are related, and to what extent ocular size is associated with orbital and cerebral cortical volumes. Relationships among these anatomical components were investigated using magnetic resonance images from a large sample of 83 individuals, which also included each subject's body height, age, sex, and uncorrected visual acuity score. Occipital and frontal gyri volumes were calculated using two different cortical parcellation tools in order to provide a better understanding of how the eye and orbit vary in relation to visual cortical gyri, and frontal cortical gyri which are not directly related to visual processing. Results indicated that ocular and orbital volumes were weakly correlated, and that eye volume explains only a small proportion of the variance in orbital volume. Ocular and orbital volumes were also found to be equally and, in most cases, more highly correlated with five frontal lobe gyri than with occipital lobe gyri associated with V1, V2, and V3 of the visual cortex. Additionally, after accounting for age and sex variation, the relationship between ocular and total visual cortical volume was no longer statistically significant, but remained significantly related to total frontal lobe volume. The relationship between orbital and visual cortical volumes remained significant for a number of occipital lobe gyri even after accounting for these cofactors, but was again found to be more highly correlated with the frontal cortex than with the occipital cortex. These results indicate that eye volume explains only a small amount of variation in orbital and visual cortical volume, and that the eye and orbit are generally more structurally associated with the frontal lobes than they are functionally associated with the visual cortex of the occipital lobes. Results also demonstrate that these components of the visual system are highly complex and influenced by a multitude of factors in humans.

The shape of the human language-ready brain

Our core hypothesis is that the emergence of our species-specific language-ready brain ought to be understood in light of the developmental changes expressed at the levels of brain morphology and neural connectivity that occurred in our species after the split from Neanderthals–Denisovans and that gave us a more globular braincase configuration. In addition to changes at the cortical level, we hypothesize that the anatomical shift that led to globularity also entailed significant changes at the subcortical level. We claim that the functional consequences of such changes must also be taken into account to gain a fuller understanding of our linguistic capacity. Here we focus on the thalamus, which we argue is central to language and human cognition, as it modulates fronto-parietal activity. With this new neurobiological perspective in place, we examine its possible molecular basis. We construct a candidate gene set whose members are involved in the development and connectivity of the thalamus, in the evolution of the human head, and are known to give rise to language-associated cognitive disorders. We submit that the new gene candidate set opens up new windows into our understanding of the genetic basis of our linguistic capacity. Thus, our hypothesis aims at generating new testing grounds concerning core aspects of language ontogeny and phylogeny.

Functional craniology and brain evolution: from paleontology to biomedicine

Anatomical systems are organized through a network of structural and functional relationships among their elements. This network of relationships is the result of evolution, it represents the actual target of selection, and it generates the set of rules orienting and constraining the morphogenetic processes. Understanding the relationship among cranial and cerebral components is necessary to investigate the factors that have influenced and characterized our neuroanatomy, and possible drawbacks associated with the evolution of large brains. The study of the spatial relationships between skull and brain in the human genus has direct relevance in cranial surgery. Geometrical modeling can provide functional perspectives in evolution and brain physiology, like in simulations to investigate metabolic heat production and dissipation in the endocranial form. Analysis of the evolutionary constraints between facial and neural blocks can provide new information on visual impairment. The study of brain form variation in fossil humans can supply a different perspective for interpreting the processes behind neurodegeneration and Alzheimer’s disease. Following these examples, it is apparent that paleontology and biomedicine can exchange relevant information and contribute at the same time to the development of robust evolutionary hypotheses on brain evolution, while offering more comprehensive biological perspectives with regard to the interpretation of pathological processes.

Paleoneurology of two new neandertal occipitals from El Sidrón (asturias, Spain) in the context of homo endocranial evolution

The endocranial surface description and comparative analyses of two new neandertal occipital fragments (labelled SD-1149 and SD-370a) from the El Sidrón site (Asturias, Spain) reveal new aspects of neandertal brain morphological asymmetries. The dural sinus drainage pattern, as observed on the sagittal-transverse system, as well as the cerebral occipito-petalias, point out a slightly differential configuration of the neandertal brain when compared to other Homo species, especially H. sapiens. The neandertal dural sinus drainage pattern is organized in a more asymmetric mode, in such a way that the superior sagittal sinus (SSS) drains either to the right or to the left transverse sinuses, but in no case in a confluent mode (i.e. simultaneous continuation of SSS with both right (RTS) and left (LTS) transverse sinuses). Besides, the superior sagittal sinus shows an accentuated deviation from of the mid-sagittal plane in its way to the RTS in 35% of neandertals. This condition, which increases the asymmetry of the system, is almost nonexistent neither in the analyzed Homo fossil species sample nor in that of anatomically modern humans. Regarding the cerebral occipito-petalias, neandertals manifest one of the lowest percentages of left petalia of the Homo sample (including modern H. sapiens). As left occipito-petalia is the predominant pattern in hominins, it seems as if neandertals would have developed a different pattern of brain hemispheres asymmetry. Finally, the relief and position of the the cerebral sulci and gyri impressions observed in the El Sidrón occipital specimens look similar to those observed in modern H. sapiens.

Before the Emergence of Homo sapiens: Overview on the Early-to-Middle Pleistocene Fossil Record (with a Proposal about Homo heidelbergensis at the subspecific level)

The origin of H. sapiens has deep roots, which include two crucial nodes: (1) the emergence and diffusion of the last common ancestor of later Homo (in the Early Pleistocene) and (2) the tempo and mode of the appearance of distinct evolutionary lineages (in the Middle Pleistocene). The window between 1,000 and 500 thousand years before present appears of crucial importance, including the generation of a new and more encephalised kind of humanity, referred to by many authors as H. heidelbergensis. This species greatly diversified during the Middle Pleistocene up to the formation of new variants (i.e., incipient species) that, eventually, led to the allopatric speciation of H. neanderthalensis and H. sapiens. The special case furnished by the calvarium found near Ceprano (Italy), dated to 430–385 ka, offers the opportunity to investigate this matter from an original perspective. It is proposed to separate the hypodigm of a single, widespread, and polymorphic human taxon of the Middle Pleistocene into distinct subspecies (i.e., incipient species). The ancestral one should be H. heidelbergensis, including specimens such as Ceprano and the mandible from Mauer.

A bivariate approach to the widening of the frontal lobes in the genus Homo

Within the genus Homo, the most encephalized taxa (Neandertals and modern humans) show relatively wider frontal lobes than either Homo erectus or australopithecines. The present analysis considers whether these changes are associated with a single size-based or allometric pattern (positive allometry of the width of the anterior endocranial fossa) or with a more specific and non-allometric pattern. The relationship between hemispheric length, maximum endocranial width, and frontal width at Broca's area was investigated in extant and extinct humans. Our results do not support positive allometry for the frontal lobe's width in relation to the main endocranial diameters within modern humans (Homo sapiens). Also, the correlation between frontal width and hemispheric length is lower than the correlation between frontal width and parieto-temporal width. When compared with the australopithecines, the genus Homo could have experienced a non-allometric widening of the brain at the temporo-parietal areas, which is most evident in Neandertals. Modern humans and Neandertals also display a non-allometric widening of the anterior endocranial fossa at the Broca's cap when compared with early hominids, again more prominent in the latter group. Taking into account the contrast between the intra-specific patterns and the between-species differences, the relative widening of the anterior fossa can be interpreted as a definite evolutionary character instead of a passive consequence of brain size increase. This expansion is most likely associated with correspondent increments of the underlying neural mass, or at least with a geometrical reallocation of the frontal cortical volumes. Although different structural changes of the cranial architecture can be related to such variations, the widening of the frontal areas is nonetheless particularly interesting when some neural functions (like language or working memory, decision processing, etc.) and related fronto-parietal cortico-cortical connections are taken into account.

The pattern of endocranial ontogenetic shape changes in humans

Humans show a unique pattern of brain growth that differentiates us from all other primates. In this study, we use virtual endocasts to provide a detailed description of shape changes during human postnatal ontogeny with geometric morphometric methods. Using CT scans of 108 dried human crania ranging in age from newborns to adults and several hundred landmarks and semi-landmarks, we find that the endocranial ontogenetic trajectory is curvilinear with two bends, separating three distinct phases of shape change. We test to what extent endocranial shape change is driven by size increase and whether the curved ontogenetic trajectory can be explained by a simple model of modular development of the endocranial base and the endocranial vault. The hypothesis that endocranial shape change is driven exclusively by brain growth is not supported; we find changes in endocranial shape after adult size has been attained and that the transition from high rates to low rates of size increase does not correspond to one of the shape trajectory bends. The ontogenetic trajectory of the endocranial vault analyzed separately is nearly linear; the trajectory of the endocranial base, in contrast, is curved. The endocranial vault therefore acts as one developmental module during human postnatal ontogeny. Our data suggest that the cranial base comprises several submodules that follow their own temporally and/or spatially disjunct growth trajectories.

The middle meningeal artery: from clinics to fossils

INTRODUCTION

Although research today ranges from molecular to universe scale, many issues regarding gross anatomy remain totally neglected. Within the framework of the endocranial morphogenesis and evolution, understanding the role and variation of the middle meningeal artery relies upon the very limited, scattered, and descriptive information available. The meninges are supplied by branches originating from both the internal and external carotid arteries, often converging in the same networks and hence raising questions on the homology and embryogenesis of these vessels. The middle meningeal artery is often ligated during craniotomies, with no apparent impairment of the cerebral functional processes. The exact physiological role of this extended vascular system, together with the adaptations and selective pressure associated with its evolutionary characterization, have generally been ignored.

THE MIDDLE MENINGEAL VESSELS IN NONHUMAN PRIMATES

Anthropologists have made many attempts to quantify and qualify the differences and variation between and within human and nonhuman primates, with scarce results due to the blurry morphology of the vascular networks. Living apes and humans probably have meningeal vessels originating from different embryogenetic processes, further hampering easy phylogenetic comparisons. Generally, monkeys and apes display a larger component derived from the internal carotid artery and its ophthalmic branch.

EVOLUTION AND MORPHOLOGICAL VARIATION IN FOSSIL HOMINIDS

The fossil endocasts partially show the traces of the middle meningeal vessels, allowing some hypotheses on the evolution of these structures. In contrast with modern humans, some extinct groups show a dominance of the posterior branch over the anterior one. The most interesting features are associated with the variation of the middle branch, which supplies the parietal areas. In any case, the most striking difference between the modern and non-modern humans regard the definite increase in the number and complexity of the anastomoses and reticulation in the former. This may be either the simple result of a larger percentage of traces left by the soft tissue or be associated with a more developed vascular network.

PERSPECTIVES

Tools are needed to quantify and qualify the morphogenesis and variations of the middle meningeal artery. Supposing these vessels are not strictly necessary in the adult age, the evolutionary pressure shaping their structure may have been associated with early life stages. Apart from oxygenation, another function which deserves attention is thermoregulation, considering the metabolic loadings of the cerebral mass.