Tag Archives: cranial vault

Skulls and brains in reptiles and birds

In a recent paper, Fabbri et al analyzed the relationship between brain and cranial vault shape in the transition from reptiles to birds. To assess the evolution of this relationship they used a broad sample including Aves, Lepidosauria, Crocodylia, Archosauria, and Reptilia. To assess developmental differences they included an ontogenetic sample of Alligator mississipiensis and Gallus gallus. The results showed that the relationship between the vault bones and the brain is conserved across these taxa, with the frontal bone positioned over the forebrain and the parietal bone over the midbrain or over midbrain and posterior forebrain. Nonetheless, they observed some shape variations, namely on the relative sizes of the frontal and parietal bones and in the position of the fronto-parietal suture relative to the forebrain-midbrain boundary. These two structures are significantly correlated, with the fronto-parietal suture being either anterior to (e.g. stem reptiles) or nearly aligned with (e.g. crown birds) the forebrain-midbrain boundary. In terms of ontogeny, chickens have a shorter ontogenetic trajectory than alligators, as the brain and skull of embryos are similar to the adult ones. The brain and skull of alligators develop with negative allometry, with the brain relatively large in early stages but becoming relatively small during growth. Conversely, the skull and brain of chicken grow with positive allometry, and the authors suggest the brain should be considered peramorphic in Aves. Overall the results stress the important role of the brain in shaping the cranial vault. The authors wonder whether the intimate relationship between brain and frontal and parietal bones is the key for the conservation of the cranial vault across vertebrates.

Sofia Pedro

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Amazing image from High Tech Panda!

From right to left:

Scalp, Periosteum, Bone, Dura Mater, Arachnoid, Pia Mater, Brain


Age related changes of adult cranial morphology

lebka_urbanAge-related cranial morphological changes in adult humans are generally considered as minor or negligible. However, with age the adult human cranium undergoes non-pathological processes of thickening. In the case of hyperostosis frontalis interna, for example, thickening preferentially involves the inner part of frontal bones, influencing the cranial morphology. Recently, a geometric morphometric study of recent human crania also revealed age related cranial shape changes. The shape differences in males and females ranging between 20-99 years can be mainly detected in the cranial vault and at the anterior and middle cranial fossa. In contrast, no changes were found in the posterior cranial fossa. In the vault, there are corresponding morphological changes on the outer and inner surfaces. The authors suggest that some shape modifications can reflect the increase of grey matter volume in early age groups (up to 30 years), and its loss in older age groups. Hence, such age-dependent changes are supposed to be secondary consequences of the relationship between cranial morphology and brain volume. Males generally showed more marked differences. Nevertheless, the small sample size for each age group makes this study preliminary.

Hana Pisova