Morphological evolution of the hominid brain

A comparative analysis of the brain surfaces and endocasts of 35 hominid specimens including 24 operational taxonomic units was performed with the aim to search for morphological transformations of the brain surface that occurred over time throughout the hominid lineage. Our research was directed at size-independent morphological characters. We found 14 characters dealing with (1) relative proportions of the frontal lobe, (2) relative proportions of the parietal lobe, (3) relative proportions of the temporal lobe, (4) extension of the occipital lobe and position of the parieto-occipital sulcus, and (5) morphology and proportions of the frontal bec. We described and mapped these characters onto a reference phylogeny of Hominidae including 4 ape species and 20 operational taxonomic units belonging to bipedal hominins (species Australopithecus, Paranthropus, and Homo) to infer character states at the ancestral nodes. At the macroscopical level, we found that (a) the occipital lobe changed its inclination at the Pan-Australopithecus transition; (b) the frontal lobe increased its roundness during the transition between Australopithecus/Paranthropus and Homo; (c) the parietal lobe increased its relative length in a hominin clade including Homo erectus, H. floresiensis, H. cepranensis, H. neandertalensis and H. sapiens; and (d) the distal border of the temporal lobe increased its height and the posterolateral border of the temporal lobe acquired a ventrally concave outline in the clade including H. neandertalensis and H. sapiens. These observations are important in the broader context of the inference of the relationships of paleoneurology and behavioral outputs in extinct hominid species.