Fig. 2 in The sixth sense in mammalian forerunners: Variability of the parietal foramen and the evolution of the pineal eye in South African Permo-Triassic eutheriodont therapsids

Fig. 2. Evolution of the frequency of the presence of the parietal foramen ( Fq), and average (Av) and median (Med) size of the parietal foramen across the phylogeny of Therapsida. Number of specimens examined (n) is indicated for each group. Asterisks indicate the branches of the tree where a relaxation of constraints resulting from a functionless third eye is hypothesized (zone of variability). See material and methods section for the more details about the phylogenetic tree.