It has been 69 years since the world-famous Mrs Ples – the most complete skull of an Australopithecus africanus – was discovered in South Africa at 1947 by palaeontologist Robert Broom at the Sterkfontein caves at the Cradle of Humankind, in Gauteng.

New research, primarily conducted by palaeontologists Dr Francis Thackeray and Dr Jose Braga, is attempting to prove that Mrs Ples is actually a male that they refer to as “Master Ples”.

The duo have been working closely with the South African Nuclear Energy Corporation (Necsa) to determine – through exploring the inside of the cranium, and other parts of the anatomy – what the palaeontologists believe is the actual gender of the fossil.

“We have been trying to understand its anatomy through skull measurements and, with help from Necsa, we can now look inside the skull to learn something new,” Thackeray tells Engineering News.

He adds that new images have been obtained from computed tomography (CT) scans, and the virtual endocast of Mrs Ples – a digital image of the inside of the skull – has been reconstructed in three dimensions.

“The skull has been dated to more than two-million years, based on palaeomagnetism and association with fossils of certain species of animal, including those of baboons and antelope of known age.”

Thackeray points out that, although these scans have been undertaken in the past, they never had the high resolution that is currently available.

“Previous CT images were recorded with slice thicknesses of 1 mm or 2 mm, but new scanners allow for submillimetre resolution, and techniques for analysis are improving rapidly,” he explains, adding that the most recent scans, analysed at Paul Sabatier University, in Toulouse, France, are based on applications also used to analyse images obtained from satellites in space.

Recent imagery, Thackeray notes, shows asymmetry on the left side of the brain of Mrs Ples, which implies that the australopithecine was probably right-handed, since it is the left side of the brain that controls functions of the right side of the body.

Another trait that has been found in the skull is a very prominent glabella, which is situated above the nose and between the eyes. A large glabella is typical of australopithecine males, he says.

“It is very prominent in Mrs Ples. The degree of projection of the glabella shows that it is obviously male,” Thackeray states.

He adds that the width of the canine socket can be measured.

“Robert Broom had in fact measured the socket diameter in 1950 and had recorded a large measurement, which also indicates that it could possibly represent a male.”

Scanning allowed for the roots of the canine sockets to be studied. From CT images, combined with other evidence, it has been suggested that Mrs Ples was an adolescent male, Braga explains.

It has been discovered that Mrs Ples did not have a well-developed crest, strengthening the argument that the fossil was an adolescent, Thackeray says.

“We have discovered that there are anatomical lines that come close to the sagittal plane. “These ‘temporal lines’ relate to muscles from the lower jaw to the sides of the skull to help Mrs Ples chew.”

He says he now has evidence to show that the muscle masses were close to the middle of the skull and, had Mrs Ples lived to be an adult, the fossil would have developed a crest. Such a crest can be found in male australopithecines.

Braga states that there have been questions regarding the gender for a while. The inner ear, which has been examined using micro CT scans with the help of Necsa, is very large, which also points to its being a male.

“We will hopefully be able to prove this very soon,” he concludes.