Amélie Beaudet and colleagues have published a comprehensive and detailed paleoneurological study on South African fossil cercopithecoids. The paper supplies three main advances. First, it provides key information on primate paleoneurology, in particular on Plio-Pleistocene monkeys, belonging to the genera Theropithecus, Parapapio, and Cercopithecoides. Paleoneurology is often more focused on humans and hominoids than on monkeys, and therefore this article is particularly welcome. Furthermore, the study is based on a surface-based method, that compares the rough geometry of the object. Surface analyses can represent an additional and interesting alternative for computing endocast comparisons. There are many complex techniques currently available in shape analysis, and we should always carefully consider that their results depend upon their specific criteria and constraints. Morphometric outputs are “ordered representations” of a given sample variation according to specific numerical and logical assumptions. Consequently, methods are crucial in determining the comparative framework. Different methods, different criteria. For example, surface analysis is not constrained by anatomical correspondence, but it is only sensitive to geometrical correspondence. Hence, the approach misses the information on anatomical boundaries between different elements and areas, distributing variation all through a homogeneous and undifferentiated object.This can be an advantage when taking into consideration form alone, or a disadvantage if one want to investigate the contribution of specific anatomical components. Finally, this study presents a semi-automatic approach for sulcal detection, that is a geometry-based method for the identification of surface relieves, curvature lines, and topographical variations. This approach may seriously represent a major advance in paleoneurology. Nonetheless, it should be taken into account that we still ignore many mechanisms behind cortical folding, and that folding patterns could be the result of passive biomechanical constraints with uncertain phylogenetic or functional meaning.
Posts Tagged 'Cercopithecoids'
Tags: Cercopithecoids, cortical folding, shape analysis
Tags: Cercopithecoids, cerebral complexity, endocranial volume, olfactory bulb
Macaques and chimps are still used in anthropology and neuroscience as “primitive models” for human evolution. This is of course a non-sense: all living species, after the divergence from a common ancestor with modern humans, have evolved and changed as humans did. The genus Macaca is as young as the genus Homo, and living macaques and living humans are recent species in evolutionary terms, approximately with a comparable age. The problem with chimps is that we miss fossils, so we ignore how and how much their lineages has changed. But we have more information on macaques, and in general on fossil cercopithecoids. A very detailed and informative study on the endocast of Victoriapithecus has been recently published, definitely a stimulating and comprehensive article for primate paleoneurology. This Old World monkey, dated to 15 Ma, had a small cranial capacity and large olfactory bulbs, but a sulcal pattern similar to modern cercopithecids. This suggests two major points. First, in Old World monkeys sulcal complexity evolved before brain size increase. Second, brain morphology evolved in cercopithecoids and hominoids through distinct processes, mixing primitive traits, different mechanisms, specific adaptations, and some convergences. These results stress further the necessity of caution and of a proper evolutionary perspective when dealing with comparative primatology and human brain evolution: macaques (and chimps) are derived species as we are, with their own independent evolutionary histories. They can provide information on biological factors which are shared among our respective lineages, but it would be an error to think that their anatomy, physiology, or genetics, represent an ancestral condition.