Wednesday 9 May 2012

Skull closure in the Taung Infant.

The Taung Infant was discovered by workers at the Buxton Limeworks near Taung, South Africa in 1924 and described in a paper in the journal Nature by palaeoanthropologist Raymond Dart in 1925. It is the partial skull and endocast of the brain case of a three to four year old Australopithecus africanus, the first Australopithicine to be discovered, and the first indication that modern humans had an African origin; prior to its discovery most anthropologists believed humans originated in Asia.

In a paper published in the Proceedings of the National Academy of Sciences on 7 May 2012, a team of scientists led by Dean Falk of the School for Advanced Research in Santa Fe and the Department of Anthropology at Florida State University, describe the discovery of an unfused metopic suture in the Taung Infant, revealed by impressions of the inside of the skull on the endocast of the brain case, and its implication for our understanding of brain development in early Australopithicines.

CT Scan of the Taung endocast and face (semi-transparent, at bottom). Abreviations: (S) Sagital suture. (C) Coronal suture. (M) Metopic suture. (F) Fontanelle (soft spot where sutures have not closed), delimitated by dotted line. Falk et al. (2012).

Baby apes (including humans) are born with the Metopic Suture open, which facilitates passage through the birth canal. In Chimpanzees and Bonobos (our closest relatives) it usually closes within a year of birth, but in humans it remains open for several years, facilitating enhanced brain growth. This state had already been observed in earlier members of the genus Homo, but its discovery in Australopithecus africanus, suggests that it has been around for several million years, originating within, or possibly with, the genus Australopithecus, which showed considerable cranial enhancement on earlier hominids.

CT Scan of the skull of a Modern Human infant. Falk et al. (2012). Supplemental material.

CT Scan of an infant Chimpanzee Skull. Falk et al. (2012). Supplemental material.

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