Unveiling secrets of the Swartkrans Cave | new fossils of a tiny human ancestor

A groundbreaking fossil discovery at Swartkrans Cave has revealed that an early human ancestor walked upright, providing new insights into its size and vulnerability to predators.

A team of international researchers from the Evolutionary Studies Institute at the University of the Witwatersrand (Wits University) made the discovery at the SwartKrans Cave. 

The researchers include Travis Pickering, Matthew Caruana, Marine Cazenave, Ron Clarke, Jason Heaton, A.J. Heile, Kathleen Kuman, and Dominic Stratford. They  found that the fossils belonged to a single, young adult Paranthropus robustus, which was much smaller than previously thought, making it highly vulnerable to predators.

The study, published  in the Journal of Human Evolution, not only confirms that the species walks upright like modern humans but also highlights its remarkable small size.

According to Wits University, Paranthropus robustus lived in South Africa around two million years ago, alongside Homo ergaster, a direct a direct ancestor of modern people.

They explained the fossils of Paranthropus robustus are found in abundance at Swartkrans Cave, situated about halfway between Johannesburg and Pretoria. 

“Much has been revealed about the diet and social organisation of this extinct species based on studies of its many skulls and hundreds of teeth, which have been recovered from Swartkrans since scientific excavations began there in 1948,” Wits University said in a statement.

“The species had extremely heavy jaws and thick enamel-coated teeth, suggesting that, when times were lean, it was capable of subsisting on low quality foods that were difficult to chew.”

They added that  some of the skulls and teeth of Paranthropus robustus were exceptionally large, while others are robust but not as large as those in the first group. 

“This suggests that Paranthropus robustus was characterised by larger males and smaller females, indicating a mating system called polygyny, in which a single dominant male mates with multiple females,” they detailed.

They said Swartkrans has over the years yielded fewer bones from the rest of the Paranthropus robustus skeleton, limiting our understanding of its stature, posture, and locomotion, essential characteristics related to finding food and mates.

“A major new find from Swartkrans, the first articulating hipbone, thigh bone, and shin bone of Paranthropus robustus, changes that,” the university explained.

Professor Pickering from the University of Wisconsin-Madison, who led the research said the individual, was likely female, and stood just one meter tall and 27 kg. "This makes it even smaller than adults from other diminutive early human species, including those represented by the famous ‘Lucy’ (Australopithecus afarensis, about 3.2 million years old) and ‘Hobbit’ (Homo floresiensis, about 90,000 years old) skeletons, from Ethiopia and Indonesia, respectively.

“The small size of the new Paranthropus robustus individual would have made it vulnerable to predators such as sabretooth cats and giant hyenas known to have occupied the area around Swartkrans Cave. This notion is confirmed by the team’s investigation of damage on the surface of the fossils, which includes tooth marks and other chewing damage identical to that made by leopards on the bones of their prey.

They said the implements were used for a variety of purposes, including butchering animals for their meat and digging for edible roots and underground insects. 

The current research will now focus on whether Paranthropus robustus, contemporaneous Homo ergaster, or both, was the maker and user of those important tools but the Swartkrans team believes that Paranthropus robustus very likely possessed the cognitive and physical capabilities to do both.

The team’s continued investigation of the fossils which includes CT-scan analyses of internal bone structures, which will provide additional information on the growth and developmental patterns of Paranthropus robustus, as well as adding details to our growing appreciation of its locomotor behaviours.

Weekend Argus