Endocranial Occipito-Temporal Anatomy of SD-1219 from the Neandertal El Sidrón Site (Asturias, Spain)

Authors

  • Antonio Rosas,

    Corresponding author
    1. Departamento de Paleobiología, Museo Nacional de Ciencias Naturales (CSIC), Calle José Gutiérrez Abascal 2, Madrid, Spain
    • Department of Paleobiology, Museo Nacional de Ciencias Naturales (CSIC), C/José Gutiérrez Abascal 2, 28006 Madrid, Spain
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    • Fax 34-948-425740

  • Angel Peña-Melián,

    1. Departamento de Anatomía y Embriologa Humana I. Facultad de Medicina, Universidad Complutense de Madrid, Madrid, Spain
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  • Antonio García-Tabernero,

    1. Departamento de Paleobiología, Museo Nacional de Ciencias Naturales (CSIC), Calle José Gutiérrez Abascal 2, Madrid, Spain
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  • Markus Bastir,

    1. Departamento de Paleobiología, Museo Nacional de Ciencias Naturales (CSIC), Calle José Gutiérrez Abascal 2, Madrid, Spain
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  • Marco De La Rasilla,

    1. Departamento de Historia, Universidad de Oviedo, Calle Teniente Alfonso Martínez s/n, Oviedo, Spain
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  • Javier Fortea

    1. Departamento de Historia, Universidad de Oviedo, Calle Teniente Alfonso Martínez s/n, Oviedo, Spain
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Abstract

We addressed the brain drainage system as inferred by the endocranial morphology of the occipito-temporal region of the El Sidrón Neandertal specimen SD-1219. Morphological details of the endocranial surface and its anatomical implications were analyzed for the reconstruction of the dural sinus drainage pattern and its comparison with Neandertals and other hominids. The specimen SD-1219 shows a pattern in which the superior sagittal sinus goes into the right transverse sinus. Comparative analyses with a large sample of fossil hominids reveal a pattern of the SD-1219 fossil that is typical for Neandertals. The analysis of the proportions of the occipital lobes prints within the occipital fossae reveals that the left occipital pole projects toward the right. This possibly indicates brain asymmetry (petalia) in this Neandertal individual, similar to that observed in some modern human brains. Conversely, no such asymmetry was observed in the cerebellar fossae. A particular feature of this fossil is the presence of two crests, located at the middle of the left cerebellar fossa that can be related to either an imprinting of a cerebellar fissure or some bone response to mechanical influence on internal bone surface morphology during cerebellar development. Specific aspects of the paleoneurology of Neandertals are discussed. Further quantitative studies on the endocranial morphology of the occipito-temporal and -mastoid region will shed light on the paleoneurological significance of this important anatomical region for the understanding of human evolution. Anat Rec, 291:502–512, 2008. © 2008 Wiley-Liss, Inc.

Brain shape of Neandertals (H. neanderthalensis) has been thought to be different to that of modern humans (H. sapiens; Holloway,1980; Grimaud-Hervé,1997,2004; Bruner et al.,2003). For instance, the formation of a prominent “chignon” has been related to cerebral growth rates relative to bone formation growth rate (Trinkaus and LeMay,1982; Lieberman,1995). In a more general sense, the external aspect of the occipito-temporal region is one of the most derived anatomical areas in the evolution of the Neanderthal lineage. Also, the temporal area records significant changes in the evolution of Neandertals (Martínez and Arsuaga,1997; Harvati,2003). The internal side of the occipital bone and adjacent areas have been subject of different studies (Grimaud-Hervé,2004), showing that the main difference between Neandertals and modern human endocasts is the proportionally smaller Neandertal cerebellum (Weaver,2005), especially as compared to the occipital lobes of the brain (Hublin,1984).

On the other side, the topological pattern of venous sinuses drainage of the encephalon has been associated to evolutionary changes in the thermoregulation of an increasing brain (Falk,2004), although it is still not clear whether the size and shape differences between Neandertals and modern human brains give rise to differences in the drainage pattern. However, because the dural venous drainage is related to relative proportions and three-dimensional (3D) configuration of the encephalon (Aiello and Dean,1990), it can be expected that evolutionary changes in brain morphology might have some relationships to the venous drainage pattern. In this context, the study of internal anatomy of the occipito-temporal region in Neandertals is of great interest. The original description and endocranial comparative anatomy of the Neandertal specimen SD-1219 from El Sidrón site (Asturias, Spain) is presented in this study.

Since 2000, a collection of ∼43,000-year-old human fossils is being systematically recovered at El Sidrón cave site (Asturias, Spain) and it represents the most significant Neandertal sample in the Iberian Peninsula (Fortea et al.,2003; Rosas et al.,2006). The site is located in a small transversal gallery (Galería del Osario) belonging to the El Sidrón karst system, and the archeological material is being recovered from a restricted surface not larger than 10 m2. Bone assemblage is mostly composed of human remains (∼1,400 human fossils), with very few faunal remains. All the skeletal parts are represented in the sample, including the hyoid bone and pedal distal phalanges, and there is a moderate occurrence of Mousterian stone tools. At least nine individuals are represented in the sample (Rosas et al.,2006,2007) and ancient mtDNA (Lalueza-Fox et al.,2005,2006) and nuclear DNA (Krauss et al.,2007; Lalueza-Fox et al.,2007) is being extracted from dental and bone remains.

MATERIAL AND METHODS

The descriptive anatomy of the SD-1219 specimen (Figs. 1, 2) was assessed from the original fossil, supported by 3D reconstructions, computed tomography (CT) images and stereomicroscopic inspection. Terminology of bones and dural sinuses is used according to the work on modern humans by Testut (1911), Poirier and Charpy (1920), and International Anatomical Terminology (2001). The comparative sample is composed of adult or late adolescent Pleistocene hominids (see Table 1). The sample consists of high quality casts produced from the original fossils, virtual specimens from the Virtual Anthropology Collection of the Museo Nacional de Ciencias Naturales -CSIC- (Madrid, Spain), and the NESPOS data base (www.nespos.org). Virtual reconstructions and casts were used for visually assessing the dural sinus drainage pattern and for taking sinus breadth measurements. When available, breadth measurements were taken at four different anatomical regions: (1) superior sagittal sinus, (2) transition curve between superior sagittal sinus and transverse sinus, (3) right transverse sinus, and (4) left transverse sinus. Breadth measurements were taken between the apical part of the bony crests that conform the print left by the venous sinus. Additionally, supporting descriptive bibliography has been used to support the assessment of the drainage pattern (Condemi,2001; Schwartz and Tattersall,2002,2003; Holloway et al.,2004).

Figure 1.

A: Internal view of the SD-1219. B: Virtual reconstruction of the specimen with description of characters: (1) foramen magnum; (2) crest of attachment of falx cerebri; (3) right slope of 2; (4) left slope of 2; (5) grove for superior sagittal sinus; (6) grove for right transverse sinus; (7) internal occipital protuberance; (8) right cerebral fossa; (9) right cerebellar fossa; (10) left cerebral fossa; (11) left cerebellar fossa; (11a) superior soft crest; (11b) inferior soft crest; (12) crest of attachment of tentorium cerebelli; (13) groove for left transverse sinus; (14) groove for left sigmoid sinus; (15) anterior surface of petrous part; (16) squamous part of temporal bone; (17) parietal bone; (18) crest of attachment of falx cerebelli; (19) crest of attachment of tentorium cerebelli; (20) lateral part of occipital bone.

Figure 2.

A: Left lateral view of the endocranial surface. B: Virtual reconstruction of the left lateral view of the endocranial surface: (1) occipito-parietal suture; (2) groove for parietal branches of middle meningeal vessels; (3) crest of attachment of tentorium cerebelli; (4) groove for left transverse sinus; (5) groove for left sigmoid sinus; (6) mastoid foramen; (7) left cerebral fossa; (8) left cerebellar fossa; (9) crest of attachment of falx cerebri; (10) internal occipital protuberance; (11) crest of attachment of falx cerebelli; (12) groove for superior petrosal sinus; (13) posterior surface of petrous part; (14) internal acoustic opening; (15) anterior surface of petrous part; (16) squamous part of temporal bone; (17) right occipital condyle; (18) lateral part of occipital bone; (19) foramen magnum.

Table 1. Comparative sample of Pleistocene Homo specimens, with the observed dural sinus drainage pattern and sinuses breadth measurements.
SpecimenSpeciesPatternSSSSSS-TSRTSLTSSort of Data
  1. SSS: superior sagittal sinus; SSS-TS: transition curve between superior sagittal sinus-transverse sinus (right or left); RTS: right transverse sinus; LTS: left transverse sinus. All measurements in mm.

  2. Sinuses Patterns symbols and correspondence to Delmas and Chifflet (1950) classification:

  3. equation imageSSS continues by RTS. LTS also present but with no appreciable connection with SSS. Asymmetric type 3 right dominant.

  4. equation imageSSS continues by LTS. RTS also present but with no appreciable connection with SSS. Asymmetric type 3 left dominant.

  5. equation imageSSS continues by RTS. LTS not marked. Asymmetric type 3 right dominant.

  6. equation imageSSS continues by LTS. RTS not marked. Asymmetric type 3 left dominant.

  7. equation imageSSS continues by both RTS and LTS Symmetric type 1.

  8. equation imageNot clear, uncertain.

  9. equation imageAbsent part.

  10. equation imageSSS continues by RTS which deviates from the sagittal crest of attachment of falx cerebri. LTS also marked but with no appreciable connection with SSS. Asymmetric type 3 right dominant.

KNM-ER 1813H. habilisequation image5.804.404.604.10Virtual
KNM-ER 3733H. ergasterequation image6.9011.807.607.40Virtual
KNM-ER 15000H. ergasterequation image7.309.306.907.00Virtual
OH-9H. ergasterequation image4.377.18Virtual
Dmanisi 2280H. erectusequation imageCast
Sangiran 2H. erectusequation image7.408.407.60Virtual
Sangiran 4H. erectusequation imageVirtual
Sangiran 12H. erectusequation image10.5510.909.03Cast
Nanjing IH. erectusequation image7.184.115.38Cast
ZKD XIIH. erectusequation image7.4817.088.624.37Cast
ZKD IIIH. erectusequation image7.658.907.066.99Cast
KabweH. heidelbergensis s.l.equation image8.2010.609.90Virtual
NdutuH. heidelbergensis s.l.equation image6.7011.807.905.60Virtual
ReilingenH. heidelbergensis s.s.equation image8.1011.106.70Virtual
SwanscombeH. heidelbergensis s.s.equation image6.8010.405.009.00Virtual
SteinheimH. heidelbergensis s.s.equation image8.209.906.405.80Virtual
VérteszöllösH. heidelbergensis s.s.equation image5.658.826.7313.50Cast
Gibraltar-1H. neanderthalensisequation image7.108.206.206.20Virtual
Biache-1H. neanderthalensisequation image7.5010.766.714.16Cast
La Chaise S12H. neanderthalensisequation image9.508.938.76Cast
La Chaise S9H. neanderthalensisequation image4.785.647.75Cast
La Chaise BD6H. neanderthalensisequation image9.459.5910.794.73Cast-Virtual
VindijaH. neanderthalensisequation image7.477.466.68Cast
Guattari-1H. neanderthalensisequation image9.9211.3410.074.68Virtual
Hortus XLIXH. neanderthalensisequation image10.0910.268.927.78Original
Salzgitter-1H. neanderthalensisequation image6.1612.9210.20Virtual
Le Moustier-1H. neanderthalensisequation image8.598.366.40Virtual
Tabun-1H. neanderthalensisequation image6.0011.008.80Virtual
Spy-1H. neanderthalensisequation image8.5012.204.207.80Virtual
Spy-2H. neanderthalensisequation image6.6710.717.105.29Virtual
SD- 1149H. neanderthalensisequation image8.01Original-Virtual
SD- 1219H. neanderthalensisequation image8.408.148.255.36Original
Mladec 1H. sapiensequation image9.2012.7010.46.00Virtual

The virtual comparative sample is based on CT data from the original fossils and involves both medical imaging data (DICOM file format) and/or other 3D polygonal mesh files (i.e., STLs). The 3D models were generated by specialized software (Amira 4.1 & Mimics 9.0), using always the best reconstruction quality available. In a virtual environment, the original data were processed differently to obtain a clear identification of drainage pattern as well as maximizing accuracy of measurements on the virtual specimens. These methods allow an enhanced visualization of anatomical detail and also supply identification and access to hidden or distorted structures, a circumstance relatively frequent when dealing with fossils (i.e., sedimentary matrix-fillings, fragmentation). The sinuses breadths were taken in the virtual specimens with the specific 3D measurement tools of the software. On the casts, the measurements were taken with a digital calliper.

RESULTS

Description of SD-1219

The El Sidrón SD-1219 specimen is a cranial fragment that consists of major part of the occipital bone (with much of the basilar part missing; Figs. 1, 2). The area of the foramen magnum is slightly fragmented and shows an irregular perimeter. A fragment of the left parietal bone is preserved at the superior left area of the specimen. It is well articulated with the squamous part of the occipital as well as with the adjacent parts of the left petrosal temporal bone. The petrous part of temporal bone consists of a heavily weathered mastoid process, a nearly complete petrosal pyramid (until the internal acoustic opening), and a likewise incomplete part of the temporal squama. The endocranial surface of the specimen is dominated by the cerebellar and cerebral fossae (incomplete on the right side), separated by pronounced crests and sulci that converge at the internal occipital protuberance (cruciform eminence). A deep groove for the superior sagittal sinus is present at the superior part of the occipital squama, close to the midsagittal plane. This groove clearly deviates from the midline toward the right and caudally, so that the distance to the midline is considerably increased at the level of the internal occipital protuberance.

Venous Senuses Imprints

A sharp crest can be observed at the midsagittal plane, which apparently corresponds to the falx cerebri attachment and which is independent from the superior sagittal sinus groove. This crest is strongly marked so that it contributes to demarcate a remarkably deep left cerebral fossa. The crest for the attachment of the falx cerebri reaches the internal occipital protuberance, where it becomes much smoother and gives the impression to continue at the internal occipital crest (the insertion of the falx cerebelli). The internal occipital protuberance (cruciform eminence) is related to the confluens sinuum. The sagittal crest of the falx cerebri attachment shows asymmetric margins. The left margin is steeper and continues laterally toward the left cerebral fossa, whereas the right is becoming broader caudally and encloses a triangular area between the sagittal crest and the left margin of the superior sagittal sinus groove. This triangular area shows various tiny crests orientated parallel to the sagittal crest (Fig. 1).

Located at the right side, the wide groove of the superior sagittal sinus is continuous at the level of the internal occipital protuberance with the groove for the right transverse sinus. This sinus, in its horizontal trajectory, curves obliquely between the right cerebral and cerebellar fossae in a caudolateral sense, invading parts of the right cerebellar fossa. Unfortunately, its further trajectory and the origin of the sigmoid sinus groove are not preserved. Between the most caudal part of the superior sagittal sinus and the internal occipital protuberance, a smooth crest is observed, which is probably the insertion of the tentorium cerebelli that continues laterally with the groove of the right transverse sinus.

Occipital Fossae

The occipital fossae are separated, on the left side, by a horizontal osseous crest that is well marked and originates in the region superior to the internal occipital protuberance. This horizontal crest, which corresponds to the insertion of the tentorium cerebelli, becomes smoother laterally as it approximates the temporal bone, where the left sigmoid sinus originates. Therefore, and different to the right side, the left occipital fossae are separated by a crest, rather than by the horizontal sulcus of the left transverse sinus.

The left cerebral fossa is very deep, an impression that is enhanced by the sharp sagittal crest of the falx cerebri attachment and the transverse crest of the attachment of the tentorium cerebelli. The most profound part of the left cerebral fossa, that is, the print of the left occipital pole, is slightly shifted to the right side. Also, at the surface of this fossa, the wide and smooth sulci that correspond to the gyri of the occipital lobes can be easily identified.

The left cerebellar fossa is also wide, although shallower than the cerebral fossa. Left cerebral and cerebellar fossae are not separated by sulci, except at the more lateral region that corresponds to the origin of the sigmoid sinus groove (Fig. 1). The surface of the cerebellar fossa is smooth, with the exception of two finely delineated and parallel fine crests can be identified as bony thickenings. The first crest originates medially to the internal occipital protuberance and continues caudolaterally toward the internal inclination of the sigmoid sinus groove (Fig. 3). The second crest is located caudally and parallel to the first one. The origin of the second crest cannot be located because of missing bone. In the sagittal region, at the internal occipital crest, there is no sulcus that could indicate the presence of an occipital sinus. Additionally, there are no impressions that could indicate a marginal sinus or a plexiform formation in the surrounding area of the foramen magnum.

Figure 3.

View of the left cerebellar fossa. The arrowhead points at the mastoid foramen; arrows indicate superior and inferior soft crests; light dots mark the groove for the left transverse and sigmoid sinus.

The contralateral cerebellar and cerebral fossae cannot be easily described because a great part of the occipital squama is missing. However, it can be deduced from the preserved parts that the left cerebral fossa is deeper than the right one, while both cerebellar fossae are very similar.

At the endocranial surface of the temporal bone, two surfaces can be observed. The anterior surface of the petrous part that relates to the base of the brain is very wide and continuous laterally with the part of the temporal squama (Fig. 2). The posterior surface of the petrous part that is related to the cerebellum is also wide and ends at the level of the internal acoustic opening. Between both surfaces, on the superior crest of the petrous part, the groove for the superior petrosal sinus is observed and limited by two fine crests. The petrosal sinus trajectory runs along the superior border until it reaches the groove of the sigmoid sinus posteromedially.

The sigmoid sinus is defined by a deep and wide groove below the petrous part of temporal that terminates in the jugular foramen. In the middle third of its trajectory, and at the internal margin, a small foramen can be observed (Fig. 3) which connects with another one to the exocranial surface and likely corresponds to the mastoid foramen of the mastoid emissary vein. Close to the sigmoid sinus, the foramen condylaris can be identified, but there is no evidence for the existence of an emissary vein. The internal surface of the parietal bone fragment is dominated by the grooves of the parietal branches of the middle meningeal vessels (Fig. 2).

Quantitative Results

The breadth of the superior sagittal sinus in its middle third is 8.40 mm, a value within the variation range of modern humans (8–9 mm; Testut and Laterjet,1979). The breadth of the right transverse sinus is 8.25 mm, similarly within the modern human range (Testut and Laterjet,1979). These data are similar to those presented for other specimens of the genus Homo, which, in turn, are similar to those of modern humans (Table 1; Fig. 4).

Figure 4.

Scatterplot of the dural venous sinuses breadths. Only fossil specimens with a similar pattern to SD-1219 were selected (superior sagittal sinus continues in the right transverse sinus).

Dural sinuses pattern type 3 right dominant of Delmas and Chifflet (1950) is found in a 60% of the whole sample, and up to 80% of the Neandertals subsample (Table 1). Breadth of the superior sagittal sinus is 7.84, and 8.1 for the right transverse sinus. As long as this comparative sample allows saying, no differences among the different species of Homo can be detected. In addition, two variants could be distinguished, whether the breadth of the SSS is larger than that of the RTS (variant a), or the contrary (variant b). These two possible situations help to characterize species or groups, as all of them present cases of both variants. Particularly, asymmetric type 3 Neandertals (n = 11) include six cases of “variant a” and five correspond to “variant b.” The same occurs in cases of type 3 left dominant. For instance, breadth of the SSS is larger than that of the LTS in Nanjing I. The contrary is seen in Swanscombe.

DISCUSSION

Cranial Dural Venous Sinuses

Our analysis of the venous sinuses of the dura mater of SD-1219 permits one to infer a model of sinuses that corresponds likely to the asymmetric type or type 3 of Delmas and Chifflet (1950), right dominant of Singh et al. (2004), type 2 dominant without occipito-marginal component of Hollinshead, (1961) and Campillo (2002), or type 1 (detached sinuses) of Poirier and Charpy (1920). This pattern is common in Neandertals (Holloway et al.,2004), but also in other hominids (85%), including modern humans (80%; Kimbel,1984; Beards et al.,1998; Mehta et al.,2000; Grimaud-Hervé,2004; Bruner,2003; Table 1). In the inferred pattern, continuity exists between the superior sagittal sinus and the right transverse sinus. In the present case, the width of the superior sagittal sinus is slightly larger than the width of the right transverse sinus. This pattern may suggest a volumetric flow similar to those described by Mehta et al. (2000). Interestingly, this is not always the case, as these values can be inverted (Table 1). Another characteristic of SD-1219 is the marked deviation of the final part of the superior sagittal sinus toward the right. This finding is not rare in Neandertals. In 13 of 15 cases, such a configuration can be observed (Table 1), although only 6 correspond to type 3 (asymmetric right dominant) of Delmas and Chifflet (1950). This strong deviation toward the right leads to delamination of the falx cerebri, as it approaches the internal occipital crest. This situation gives rise to the formation of several laminae. One or more of these would contain the superior sagittal sinus, whereas the rest of these laminae reflect the falx cerebri attachment at the right margin of the sagittal crest. The superior sagittal sinus is on top of the superior margin of the right occipital lobe and runs across the right occipital pole (Fig. 6). This latter side appears less depressed than the left. According to this finding, the segment of the transition between the superior sagittal sinus into the right transverse sinus appears also anteriorly displaced (Figs. 5, 6). Regarding the craniocaudal location of the transverse sinuses, Poirier and Charpy (1920) suggested that, in modern humans, the right transverse sinus is slightly more elevated than the left. However, in SD-1219, the opposite is the case. The right transverse sinus is located more caudally than the left in the superior region of the inferior cerebellar fossa (Fig. 6).

Figure 5.

Computed tomography reconstructions of the caudal half of the endocranial surface of the SD-1219. A: Axial section of SD-1219 at the middle part of the cerebral fossa: (1) crest of attachment of falx cerebri; (2) right slope of 1; (3) left slope of 1; (4) groove for superior sagittal sinus; (5) right cerebral fossa; (6) left cerebral fossa, note the slight thickness of the bone in this region. B: A three-dimensional reconstruction of the occipital fossae: arrowhead points to the groove for the superior petrosal sinus.

Figure 6.

Virtual endocast of SD-1219, where the content of the four fossae can be appreciated. A: Posterior view. B: Posterior right-oblique view. C: Right lateral-oblique view of the left cerebellar fossa. (1) superior sagittal sinus and right transverse sinus; (2) right cerebellar hemisphere; (3) crest of attachment of tentorium cerebelli; (4) internal occipital protuberance, note that there are no prints of the plexiform net; (5) crest of attachment of falx cerebelli; (6) longitudinal cerebral fissure; (7) short segment of left transverse sinus; (8) left sigmoid sinus.

On the other hand, a continuity between the straight sinus and the left transverse sinus can be assumed. As already mentioned, in SD-1219 the left transverse sinus does not leave impressions between the cerebellar and cerebral fossae. Instead of a sulcus, the attachment crest of the tentorium cerebelli is observed. Laterally, the crest is substituted by a sulcus that goes into the grove of the left sigmoid sinus (Fig. 6C). The 3D reconstruction of the endocast shows that the sigmoid sinus receives a short segment of the left transverse sinus (Figs. 1, 3, 6).

Alternatively, it could also be hypothesized that the left transverse sinus does not exist, because there are no corresponding endocranial impressions. In modern humans, the frequency of such an absence ranges between 5% and 12% (Beards et al.,1998). In that case, it should be expected that the venous drainage, which normally goes to the left transverse sinus from the cerebellum, the brainstem, and occipital and temporal lobes, would be deviated into the left sigmoid sinus, incrementing the superior petrous sinus and/or other additional drainage systems, such as the occipito-marginal system (Dora and Zileli,1980; Bruner,2003). However, there are no clear endocranial impressions that would support this hypothesis. Thus, it is preferable to assume the existence of the left transverse sinus, which is displaced either along the superior surface of the tentorium cerebelli attachment crest or runs on top of this crest. In this latter case, the only contact with the squamous part of the occipital bone would then be in its most lateral area, shortly before giving rise to the left sigmoid sinus.

Around the internal occipital protuberance, there is no evidence for a plexiform pattern of the confluens sinuum (Testut,1911) or other communications between the right and left venous systems. It is more likely to assume that the two systems were detached. In such a case, either a few foramina would exist in common walls of the sinuses, or, if separated, a communication would exist in the form of narrow canals (Rouvière and Delmas,2005; dashed lines in Fig. 7). However, no such evidence is present in SD-1219. Although in modern humans it has been suggested that the mentioned communication is frequent (Poirier and Charpy,1920; Testut,1921, Rouvière and Delmas,2005), in SD-1219 there is no impression for this pattern, which in Figure 7 is indicated by discontinuous lines.

Figure 7.

Virtual reconstruction of the dural venous sinuses. A: Anterior view. B: Right view. (1) sagittal superior sinus; (2) right transverse sinus; (3) hypothetical straight sinus; (4) left transverse sinus; (5) left sigmoid sinus; (6) superior petrosal sinus; (7) internal jugular vein; (8) hypothetical communication between right and left venous systems; (9) emissary mastoid vein.

The proposed model suggests, thus, a separation between left and right circulations. This explanation gives rise to a dynamic drainage system, in which the superior sagittal sinus drains a major part of the cortex venous blood into the right jugular vein. However, it has been demonstrated that, in modern humans, the venous circulation is complex (Poirier and Charpy,1920; Testut,1921; Rouvière and Delmas,2005), a fact that is related to the high numbers of anastomotic branches. These anastomoses can redirect the venous drainage flow into whatever physiologically necessary direction. This finding has been demonstrated by studies of venous circulation dynamics in the light of effects of certain pathological processes that lead to interruption of a specific drainage pattern (Mattle et al.,1990; Hoffman et al.,2002). It seems, however, that the problem of functional asymmetries of jugular veins is still open (Lazorthes et al.,1978).

There is some evidence of a communication between endo- and exocranial venous circulation. A small foramen of the mastoid emissary vein is observed with a diameter similar to that of modern humans. The existence of a condylar emissary vein can be ascertained by the external part of the corresponding foramen. The internal part is still filled with sediment and can thus not be recognized in SD-1219 (not shown in the figures). It should be noticed that it is difficult to observe impressions and sulci that could indicate other venous communications between the internal and exocranial space.

Finally, there is no correlation between the breadth of the grooves of the SSS and RTS. No clear aggregation defining Homo species or groups considered in Table 1 can be observed in the scatterplot (Fig. 4). Breadth values of the different sinuses randomly distribute across the specimens of the genus Homo. In summary, despite the brain shape differences between Neandertals and modern humans, apparently there is no difference in the gross pattern of the venous drainage system.

Asymmetry

SD-1219 shows some asymmetric features. An axial section through the maximum depth of the left cerebral fossa (Fig. 5) shows that the corresponding thickness at the right fossa is higher. This finding indicates that the left occipital pole of SD-1219 is shifted posteriorly and, thus, characterized by a left-occipital petalia, as illustrated in the virtual endocast (Fig. 6). Also left occipital pole of SD-1219 is rotated toward the right. Compatible with this spatial position, the superior sagittal sinus lies directly on the right occipital lobe in a slightly anterior position (Figs. 5, 6). Such a configuration is usually accompanied by a deviation of the right frontal pole toward the left, the so-called Yakovlevian anticlockwise torque (Toga and Thompson,2003), and is quite common in Neandertals and also in modern humans (Holloway et al.,1982). However, obviously such a hypothetical frontal left deviation as suggested here, and its corresponding petalia cannot be assessed without the associated frontal bone. However, it would suggest, as mentioned, an anticlockwise rotation of the fronto-occipital hemispheric axis (Bruner et al.,2003), which happens in 80% of Neandertals (Holloway,1997).

It has been suggested that the relationship between petalia or brain asymmetry and behavioral aspects is difficult and speculative (Holloway,1981). Only if clear limits between different functional compartments of the brain could be established, which is difficult on endocasts, some statements could be made (Andreasen et al.,1993; Conroy and Smith,2007). Another aspect of asymmetry is the already discussed venous sinus drainage pattern. Such a kind of asymmetry is generally linked to the ontogenetic development of an individual brain (Peña Melian,2000) and indicates the morphological preponderance of a given brain hemisphere (Delmas and Chifflet,1950).

Cerebellum

The left cerebellar fossa is wide, whereas the preserved part of the right one lacks details that indicate asymmetry. Figure 3 shows two smooth and parallel crests on the left side, which cannot be observed at the right side due to missing bone. These two crests might relate to some of the principal fissures of the caudal surface of the cerebellar hemisphere or could be the result of mechanical processed during the ontogeny of the fossa. As far as it can be assessed from literature, such crests have never been observed in other Neandertals or hominid fossils.

It is known that, in modern humans, the cerebellum is notably larger than in other primates; specifically, 2.8 times larger than expected for a primate with body size of a human (Rilling,2007). However, if the volume of the human cerebellum is compared with the volume of the cortex, it is relatively smaller compared with other hominoid primates. This finding might be because of the extreme encephalization of the cortex in humans and because not all regions of the cortex project into the cerebellum (Deacon,1988; Rilling and Insel, 1999). In Neandertals, something similar could have happened although it is not known whether such changes have affected the cerebellum or the cerebral cortex. It is known that Neandertals had smaller anterior and posterior semicircular canals and a larger lateral semicircular canal compared with modern humans (Hublin et al.,1996; Spoor et al.,2003). These proportional differences might reflect different patterns of head movements compared with modern humans. Likewise, these variations can also be interpreted in the context of differences in the movement of the body, which should then be reflected in the vestibulo- and spino-cerebellar regions. Recently, Weaver (2005) has shown, although on a limited data set, that Neandertals are characterized by a small cerebellum, both absolute and relative to overall brain size. It is unknown whether there is a direct relationship between the variation of the semicircular canal dimensions (Hublin et al.,1996; Spoor et al.,2003) and evolutionary modifications of cerebellum size (Weaver,2005), but such considerations indicate that the functional complex “inner ear-cerebellum” should be an important focus of paleoneurological research in Neandertals.

Acknowledgements

We thank all the people working at the El Sidrón site excavation for their dedication. We thank Elena Santos for her technical advice. We are grateful to Profs. Henry and Ma Antoinette de Lumley for access their cast collection. We also thank Reinhard Ziegler (Staatliches Museum für Naturkunde Stuttgart), Chris Stringer and Robert Krusynski (Natural History Museum, London), Fred Spoor (University College London), Ema Mbua (Kenya National Museums), Luca Bondioli (Museo Nazionale Preistorico Etnografico Luigi Pigorini), Roberto Macchiarelli (University of Poitiers), Maria Teschler, (Naturhistorisches Museum Wien), Dan Lieberman (Peabody Museum, Harvard), Patrick Semal (Royal Belgian Institute of Natural Sciences, Brussels), Friedemann Schrenk (Senckenberg Museum, Frankfurt), for gently providing CT data.

Ancillary