Posts Tagged 'parietal bone'

Vault and base

This week we have published a study on the integration between the parietal and temporal morphology in the human skull. Modern humans display large and bulging parietal lobes and bones, and large and projecting temporal lobes. It is possible that the latter (the anterior displacement of the temporal lobes) can be a spatial secondary consequence of the former (the enlargement of the parietal district). This survey on adult skulls suggests that this is not the case: parietal bulging and temporal displacement are apparently independent and not related. Nonetheless, when one of these districts undergoes a major variation (bulging in the case of the parietal bone, vertical stretching in the case of the middle cranial fossa), the other undergoes a spatial rotation: shape does not change, but the orientation varies according to the global cranial modification. The enlargement/reduction of the parietal bone have thus a major effect on head orientation, and it is also associated with facial proportions. Hence, it turns out that the general enlargement of the parietal district, a species-specific character of modern human brain and skull, has probably influenced the functional axis of the head, with possible consequences on body organization and posture. These results once more recall the importance of an integrated analysis between brain and braincase and, more generally, of a system-based approach to functional craniology.

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Bones and vessels

Eisova et al 2016The vascular traces left on the bones are remnants of physiological processes associated with blood flow and functions. Craniovascular traits can be used in archaeology, paleontology, and forensic science to deal with normal and pathological variations of the circulatory system, bridging interests between evolutionary and medical fields. Current information on these characters is, at best, scarce. After our recent work on diploic channels, this week we publish another morphometric study on the vascular traces, and specifically on their relationships with parietal bone size and thickness. We provide a quantitative description of the lumen size in adult modern humans for the middle meningeal and diploic vessels, as calculated from cranial anatomy after computed tomography, for different orders of branches. Vessel size and cranial thickness can be proportional if sharing growth factors, or inversely proportional if competing through structural constraints. However, we do not find any clear relationship between vascular size, cranial size, and cranial thickness. This result suggests that bone and vessel morphogenesis are probably influenced by independent factors, at least when dealing with differences among adult individuals.

Gran Dolina

ATD6_100_168(ESaiz)This week we publish a study on a parietal bone from Gran Dolina, Atapuerca, dated to more than 800.000 years and probably belonging to the species Homo antecessor. The general morphology  suggests small dimensions and an archaic appearance, with bossing lower parietal areas (supramarginal gyrus) and flattened upper parietal areas (upper parietal lobule). The vascular network is not particularly reticulated, and it is equally developed in its anterior and posterior branches. There is a well visible parietal foramen, an accessory parietal canal, and a lot of minor vascular passages, mostly around the lambda. The bone thickness and the distribution of the diploe suggest a young age. Therefore, the information available points to a juvenile archaic human. This fragment supplies at present the only evidence on the braincase of Homo antecessor. As far as we currently know, most archaic human species do not display consistent neuroanatomical differences, apart from variation in brain size. Nonetheless, this specimen can supply valuable information if, in the future, we will be able to improve sufficiently the fossil record as to support ontogenetic series.

Maba

Maba and Saccopastore (Wu and Bruner 2016)We have now published a study of the endocranial morphology of Maba, a Chinese fossil specimen dated approximately to the end of the Middle Pleistocene. The available portions of the upper face strongly resemble European Neandertals, like Saccopastore 1, found in Italy and supposed to have the same chronology of Maba, or Krapina 3, from Croatia. Also the spatial arrangement and the structural organization between face and braincase in Maba is reminescent of Neandertals. However, the frontal and parietal bones suggest an archaic endocranial morphology, more comparable with Homo heidelbergensis.  So we have here an archaic brain form assembled onto a derived facial block. A similar situation (Neandertal traits in the face and archaic features in the vault) was also described for the sample from Sima de los Huesos (Atapuerca, Spain). If such affinity is a matter of phylogeny, the range of the paleospecies H. heidelbergensisH. neanderthalensis should be revised, and extended to China. Otherwise, the facial Neandertal traits in this Chinese populations can be but a consequence of parallelism and analogy, and the specimen can therefore represent an archaic Asian taxon. Curiously, at the same time in Africa we have the opposite combination: Jebel Irhoud, a modern face with a Neandertal braincase! Definitely puzzling …


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