Paranthropus robustus, an Early Pleistocene hominin species native to South Africa, has intrigued scientists for decades. Known primarily through its craniodental fossils found at Kromdraai, Drimolen, and Swartkrans cave sites, this species coexisted with Homo ergaster around two million years ago, a direct ancestor of modern humans.
The many skulls and teeth recovered from Swartkrans since 1948 have provided insights into the diet and social structure of Paranthropus robustus. Their hefty jaws and thickly enameled teeth suggest they could survive on tough, low-quality food when resources were scarce. The size differences between some robust skulls and teeth suggest a polygynous mating system, with larger males and smaller females.
However, researchers previously had limited knowledge of the species’ stature, posture, and movement because they lacked skeletal remains beyond the head.
This changed with a significant discovery at Swartkrans: the first hipbone, thigh bone, and shin bone that fit together from Paranthropus robustus.
The new Paranthropus robustus thigh and shin bones, articulated at the knee joint. Cerdit: Jason Heaton
An international team of researchers from the Evolutionary Studies Institute at the University of the Witwatersrand (Wits University), including Travis Pickering, Matthew Caruana, Marine Cazenave, Ron Clarke, Jason Heaton, A.J. Heile, Kathleen Kuman, and Dominic Stratford, has identified these fossils as belonging to a single, young adult Paranthropus robustus. Their research reveals that this individual was a habitual upright walker, much like modern humans, but was extremely small.
“It is estimated that this individual, probably a female, was only about a meter tall and 27 kg when it died, making 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,” says Professor Pickering from the University of Wisconsin-Madison, who led the research.
The small size of this Paranthropus robustus individual likely made it vulnerable to predators like sabertooth cats and giant hyenas, as confirmed by tooth marks and other chewing damage found on the fossils, similar to those made by leopards on their prey’s bones.
The newly described, leopard-chewed Paranthropus robustus hip bone fossil, superimposed on an outline of a complete hominin hip bone to show the extent of the chewing damage on it. Credit: Jason Heaton
“Although it seems this particular Paranthropus robustus individual was the unfortunate victim of predation, that does not mean the entire species was inept. We know that Paranthropus robustus survived in South Africa for over a million years and is often found in association with stone and bone tools,” says Pickering.
These tools, used for butchering animals and digging for food, suggest that Paranthropus robustus had the intelligence and physical ability to make and use them.
The research team is continuing their study by using CT scans to analyze the internal bone structures, which will provide more information on Paranthropus robustus’s growth and movement behaviors.
This new discovery enriches our knowledge of Paranthropus robustus, providing a more comprehensive picture of this ancient species and its place in the human evolutionary timeline.
Journal Reference
Travis Rayne Pickering, Marine Cazenave, R.J. Clarke, et al. First articulating os coxae, femur, and tibia of a small adult Paranthropus robustus from Member 1 (Hanging Remnant) of the Swartkrans Formation, South Africa. Journal of Human Evolution. DOI: 10.1016/j.jhevol.2024.103647