Posts Tagged 'Atapuerca'

The Pit

Eva Poza Rey and colleagues have now published a detailed paleoneurological survey of the endocasts from Sima de los Huesos, now dated at 430 ky. The study includes anatomical descriptions and a multivariate analysis of endocranial diameters. Fifteen years have passed since that early article on Sima 4 and Sima 5, showing that these two endocasts had an archaic phenotype, apparently missing any Neanderthal derived trait. This new article definitely increases the sample size, including a total of 16 endocasts. Results suggest that the endocasts from Sima de los Huesos display an intermediate morphology, between the human plesiomorphic brain form (like in Homo erectus or Homo heidelbergensis) and Neanderthals. The difference from an archaic condition would be in the posterior an inferior brain regions (posterior temporal, inferior parietal, and anterior occipital cortex), larger and wider in the Sima brains. Their endocranial size further supports the hypothesis that in Neanderthals encephalization was a gradual process. I think in the article there is probably too much space dedicated to asymmetries. Taking into considerations that all human species display a similar pattern of gross asymmetries, that differences between humans and apes could be a matter of allometry, that hemispheric differences can be very subtle and hence would require huge samples to be properly tested, and that in fossils we can only observe the superficial cortical dimensions with no information on the anatomical factors involved, I frankly can’t understand why this topic keeps on deserving so much attention in many paleoneurological papers.

The study is comprehensive and convincing, although I personally miss two points. First, there is no mention on the overall morphology of the frontal lobes, except some minor comments on the orbital gyri and frontal length in Neanderthals. Although there is no clear evidence of frontal expansion in the evolution of the human genus, Neanderthals and modern humans display relatively wider frontal cortex, probably because of a spatial constraint with the underlying orbits. In this aspect, the Sima endocasts show an archaic morphology, with narrow frontal lobes. Second, I would be really interested in a comparison with the endocast of Maba (China), which combination of traits is remarkably similar to Sima de los Huesos, showing Neanderthals features in the face but an archaic brain form. Convergence, same taxon, or shared ancestors?

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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