New high-resolution computed tomography data of the Taung partial cranium and endocast and their bearing on metopism and hominin brain evolution

Abstract

Falk and colleagues [Falk D, Zollikofer CP, Morimoto N, Ponce de León MS (2012) Proc Natl Acad Sci U S A 109(22):8467-8470] hypothesized that selective pressures favored late persistence of a metopic suture and open anterior fontanelle early in hominin evolution, and they put an emphasis on the Taung Child (Australopithecus africanus) as evidence for the antiquity of these adaptive features. They suggested three mutually nonexclusive pressures: an "obstetric dilemma," high early postnatal brain growth rates, and neural reorganization in the frontal cortex. To test this hypothesis, we obtained the first high-resolution computed tomography (CT) data from the Taung hominin. These high-resolution image data and an examination of the hominin fossil record do not support the metopic and fontanelle features proposed by Falk and colleagues. Although a possible remnant of the metopic suture is observed in the nasion-glabella region of the Taung partial cranium (but not along the frontal crest), this character state is incongruent with the zipper model of metopic closure described by Falk and colleagues. Nor do chimpanzee and bonobo endocast data support the assertion that delayed metopic closure in Taung is necessary because of widening (reorganization) of the prefrontal or frontal cortex. These results call into question the adaptive value of delaying metopic closure, and particularly its antiquity in hominin evolution. Further data from hominoids and hominins are required to support the proposed adaptive arguments, particularly an obstetric dilemma placing constraints on neural and cranial development in Australopithecus.prefrontal reorganization | cranial capacity | human evolution

Paleodysmorphology and paleoteratology: Diagnosing and interpreting congenital conditions of the skeleton in anthropological contexts

“…It was argued in the past that metopism is accompanied by agenesis of the frontal sinuses, although several subsequent studies failed to confirm this (reviewed by Marciniac and Nizankowski, 1959). The oldest known case of metopism, although diagnostically disputed (Holloway et al, ), concerns the 2.5 million year old skull of an Australopithecus africanus child aged 3–4 years and found near Taung, South‐Africa (Hrdlicka, ). This ignited the idea that persistence of the metopic suture well beyond birth, as in modern humans and apparently in earlier hominids but not in chimpanzees or gorillas (our closest living relatives), reflects prolonged growth of the frontal lobes and hence advanced cognitive development (Falk et al, ).…”

Brain Reorganization Allowed for the Development of Human Language: Lunate Sulcus

“…In a recent tomography study of the Taung Australopithecus africanus fossil, Carlson and colleagues failed to find any signs of human-infant skull features (Holloway et al, 2014). Previous studies suggested that features of the Taung specimen would allow the child's brain to grow rapidly, similar to brain growth in modern home sapiens.…”

Revised estimates of Taung’s brain size growth

“…The type specimen of Australopithecus africanus, Taung, is a juvenile skull consisting of a partial face with fragmentary pieces of the basicranium attached, a mandible, and a natural hemi-endocast. 1 Taung has been the subject of intensive research focus because of its potential to resolve questions about hominin brain size and reorganisation [2][3][4][5][6][7] and A. africanus craniofacial growth [8][9][10][11] , dental maturation [12][13][14][15][16][17][18] and brain ontogeny [19][20][21] .…”