25 Days of Skeletal Facts: Day 24 – The Neurocranium

Happy Christmas Eve! Since we discussed the facial sketelton yesterday, today is devoted to the other part of the skull, the neurocranium, which consists of the calvaria, or the skull cap, and the basicranium, the cranial base. This typically consists of 8 bones: the frontal bone (1), the parietal bones (2), the temporal bones (2), the sphenoid (1), the ethmoid (1), and the occipital (1). If you are at all familiar with any neuroanatomy, you will notice that the lobes of the brain (frontal, parietal, temporal, and occipital) correspond to the bones of the calvaria.

Bones of the neurocranium

One characteristic of primates in general is a larger brain to body mass ratio, and this is especially true of modern humans. One of the early paleoanthropological assumptions was that big brains came before bipedalism, but this turned out not to be the case. As discussed in previous posts, species of Australopithecus were walking upright millions of years ago. As you can see from the graph below, however, their cranial capacity hovers around 500 cc, about 1/3 the size of ours. Even Homo habilis, the oldest of our genus, has a cranial capacity only slightly larger than an australopith. It isn’t until Homo erectus that we really see a larger cranial capacity approaching 1000 cc (van Ginneken et al. 2017) and then rapid brain growth from H. erectus (2 million years ago) to the appearance of modern humans (~200,000 years ago).

Figure 1. Human evolution based on skull endocasts of fossil archaic primates and early hominids from van Ginneken et al. 2017

You may also notice that modern humans are the only hominins with a tall forehead (also see image below). This is due to the expansion of our frontal lobe, which contains important center for memory, emotions, and communication. Comparatively, we modern humans really do have more big brain energy. That’s all for your neurocranium. Tomorrow we are discussing my favorite bone in the human body, see you then.

REFERENCES & MORE TO EXPLORE

Human Characteristics: Brains. Human Origins. National Museum of Natural History. Smithsonian Institution. Last updated December 2020

Neurocranium. Sieroslawska. KenHub Anatomy. Last reviewed August 2020

Hypothesis Hunter-prey correlation between migration routes of African buffaloes and early hominids: Evidence for the ” Out of Africa ” hypothesis. van Ginneken et al. Integrative Molecular Medicine. 2017

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