29 June, 2017
Brains do not fossilise, but in mammals and birds, the inside of the brain cavity records what the outside of the brain would have looked like in life. Animals with a particular reliance on certain senses, such as vision, tend to have enlarged areas of the brain that deal with those senses, in much the same way as a computer designed for gaming will have a larger and more powerful graphics card than one that was built only for word processing. Differences in the external shape of casts of the brain cavity show how certain regions are larger or smaller in different animals, and these differences have long been used to infer behaviour in extinct animals.
However, a new study published in Scientific Reports has cast doubt on this practice. The research, conducted by an international team from Portugal, Germany, France, USA and Scotland, applied methods pioneered by Stig Walsh at National Museums Scotland to determine whether the size of part of the cerebellum (called the cerebellar flocculus) can be used to predict ecology and locomotion behaviour in living mammals and birds. The results suggest that the size of this brain structure is related to a variety of other factors, including the potential of the region to adapt to changes in processing tasks. The study demonstrates that statistical approaches using information from living species of animals, in which behaviour is well known, can be used to test hypotheses about extinct animals, such as dinosaurs.
Above: Reconstruction of a red squirrel skull made from X-ray computed tomography (CT) data (Fig. 3, Ferreira-Cardoso et al., 2017; open access). The brain cavity cast can be seen (blue), with the cerebellar flocculus shown in orange.
Above: Views from above of brain cavity casts of birds made from CT data (blue and orange region colours as above). This image is taken from the original work by Walsh et al. (2013; open access).