Fig 6. Distribution of total brain mass for mature Oo, Tt, Dd, Zc, and H. sapiens.

Each bar represents the percentage of total brain mass in the cerebellum (pink), gray matter of the cerebral cortex (green), and the remaining areas of the brain (ROB: brainstem, white matter of the cerebral cortex) are shown in blue. Mass of the gray matter was calculated by multiplying the cortex surface area and cortex thickness (see S1 Table) by the specific gravity of the gray matter of the cerebral cortex [52]. For average cortex thickness and surface area we used our own measurements. For the human cortex thickness, we used a value of 2.5 mm. The calculated values here are similar to H. sapiens values averaged from previously published data [74]. Cerebellum masses are values from a previous publication [37]. Kb was not included because we only had a brain from an immature animal.