Endocranial vascular traces and paleoanthropology

Abstract

The traces left on the endocranial surface by arteries and veins can supply evidence on physiological processes associated with brain biology in fossil hominids. Morphological differences in these networks and consequent thermoregulation patterns can support inferences on brain evolution and metabolism. Despite the relevance of these topics, issues associated with selective brain cooling in humans remain largely elusive. Digital anatomy currently provides tools and methods to investigate these traits in modern and fossil samples, and computed modeling allows reliable methods to evaluate anatomical changes and differences according to the principles of functional craniology and integration. These same characters and methods have also relevance in forensic anthropology, archaeology, and medicine. In this study, we used cranial samples of anatomically modern humans from different historical periods (early medieval, late medieval and modern age) to evaluate bias and limits associated with the anatomical reconstruction and evaluation of vascular traits from bone remains. In particular, we focused on those traits generally considered in paleoanthropology, like middle meningeal vessel imprints, foramina/tunnels of emissary veins, traces of venous sinuses and other structures which can be scored and measured from bone and computed tomography. Vascular features were visually assessed from the semiautomatic backface projected CT reconstructions, and then compared with physical specimens when available. The endocranial area of physical specimens was also approached with digital endoscope. The digital analyses were able to show intraosseous connections of various venous channels that cannot be inferred by exclusive inspection of the ectoand endocranial surfaces. Besides reconnections of multiple mastoid emissary foramina, the mastoid tunnel transferring occipital artery and vein in the close proximity of mastoid emissary foramen was frequently present. This passage for occipital artery was easily confused with mastoid foramen and in several cases the tunnel was reconnected with mastoid emissary foramen and/or sigmoid sinus groove. Other traits such as imprints of middle meningeal vessels showed frequent presence of tunnels above lesser sphenoid wing hardly traceable with endoscopic examination. Moreover, middle meningeal vessels in the area of sphenoparietal sinus produced numerous reconnections with diploic system. This preliminary survey showed a complex intrinsic vascular network, especially in the area above mastoids, where digital anatomy proved to be necessary to make any further interpretation of the external vascular characters. The analysis of the inner vascular network is then mandatory when dealing with paleoanthropological hypothesis, for which the study of the ectocranial traits alone is not sufficient and can be even misleading.