Quantitative analysis of somatosensory cortex development in eutherians, with a comparison with metatherians and monotremes

Abstract

Extant eutherians exhibit a wide range of adult brain sizes and degree of cortical gyrification. Quantitative analysis of parietal isocortical sections held in museum collections was used to compare the pace of somatosensory cortex development relative to body size and pallial thickness among diverse eutherian embryos, foetuses, and neonates. Analysis indicated that, for most eutherians, cortical plate aggregation begins at about 6–18 mm greatest length or about 120–320 µm pallial thickness. Expansion of the proliferative compartment occurs at a similar pace in most eutherians, but exceptionally rapidly in hominoids. Involution of the pallial proliferative zones occurs over a wide range of body sizes (42 mm to over 500 mm greatest length) or when the cerebral cortex reaches a thickness of 1.2–9.8 mm depending on the eutherian group. Many of these values overlap with those for metatherians. The findings suggest that there is less evolutionary flexibility in the timing of cortical plate aggregation than in the rate of expansion of the pallial proliferative compartment and the duration of proliferative zone activity.

• Artiodactyla
• carnivora
• chiroptera
• erinaceomorpha
• lagomorpha
• pholidota
• primata
• rodentia

Acknowledgements

The author would like to thank Dr Peter Giere of the Museum für Naturkunde (MfN), Berlin for access to the MfN collections and for all his kind help during the work. The author would also like to thank Ms Elizabeth Lockett of the NMHM, Maryland, USA, and Ms Elizabeth Harrison of the Department of Physiology, Cambridge, for access to the respective collections and for all their kind help during the work.

Declaration of interest

The author reports no conflict of interest. The author alone is responsible for the content and writing of the paper. The work was not supported by grant money.

Supplementary material available online. Supplementary table