A simple and accurate method for estimating the brain volume of birds: possible application in paleoneurology.

Brain volume provides useful information for a discussion of the behavior and cognition of animals. Obtaining accurate brain volume from extinct species is difficult, however, because fossils are often partly or largely broken. The purpose of this study was to estimate the brain volumes of birds using scant osteological information. Brain volumes were calculated from magnetic resonance or computed tomography images of bird heads from 27 species representing 12 orders. Correlations between brain volume and maximum brain width, length, and height were assessed using multiple regression analysis and correlation analysis. Brain volume and maximum brain width show a strong linear correlation. Thus, in the extant Neornithes (modern birds), it is possible to estimate brain volume accurately from the maximum brain width using a standard line. We also used this method to calculate the brain volumes of fossil species to assess whether it can be used for extinct species. The brain volume values estimated by this method fit satisfactorily with the reported values in extinct Neornithes, suggesting that the method is applicable not only for extant, but also for extinct Neornithes and might be a powerful tool to obtain information not previously available from fossil specimens.