SK 46 preserves the left half of the braincase and the nearly complete palate of Paranthropus robustus. It has features typical of P. robustus, including large zygomatic arches and a prominent sagittal crest. These features are associated with large chewing muscles used in grinding tough foods.
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Paranthropus robustus is an example of a robust australopithecine; they had very large megadont cheek teeth with thick enamel and focused their chewing in the back of the jaw. Large zygomatic arches (cheek bones) allowed the passage of large chewing muscles to the jaw and gave P. robustus individuals their characteristically wide, dish-shaped face. A large sagittal crest provided a large area to anchor these chewing muscles to the skull. These adaptations provided P. robustus with the ability of grinding down tough, fibrous foods. It is now known that ‘robust’ refers solely to tooth and face size, not to the body size of P. robustus.
When scientist Robert Broom bought a fossil jaw fragment and molar in 1938 that didn’t look anything like some of the Au. africanus fossils he’d found during his career, he knew he was on to something different. After exploring Kromdraai, South Africa, the site where the curious fossils came from, Broom collected many more bones and teeth that together convinced him he had a new species which he named Paranthropus robustus (Paranthropus meaning “beside man”).
We don’t know everything about our early ancestors—but we keep learning more! Paleoanthropologists are constantly in the field, excavating new areas with groundbreaking technology, and continually filling in some of the gaps about our understanding of human evolution.
Below are some of the still unanswered questions about Paranthropus robustus that may be answered with future discoveries:
- Which species did Paranthropus robustus evolve from? Did P. robustus evolve from P. aethiopicus, or were there regionally distinct robust australopithecine lineages - meaning P. robustus evolved from the other southern African species Au. africanus?
- Bone tools presumably used by P. robustus to dig into termite mounds have been found at several South African sites. Was this tool-making, termite-mound-digging behavior something shared by all populations of this species, or was it a regional behavior?
Broom, R., 1938. The Pleistocene anthropoid apes of South Africa. Nature 142, 377-379.
Other recommended readings:
Scott, R.S., Ungar, P.S., Bergstrom, T.S., Brown, C.A., Grine, F.E., Teaford, M.F., Walker, A., 2005. Dental microwear texture analysis shows within-species dietary variability in fossil hominins. Nature 436, 693–695.
Sponheimer, M., Passey, B.H., de Ruiter, D.J., Guatelli-Steinberg, D., Cerling, T.E., Lee-Thorp, J.A., 2006. Isotopic evidence for dietary variability in the early hominin Paranthropus robustus. Science 314, 980-982.
Wood, B., Strait, D., 2004. Patterns of resource use in early Homo and Paranthropus. Journal of Human Evolution 46, 119–162.
Robust species like Paranthropus robustus had large teeth as well as a ridge on top of the skull, where strong chewing muscles attached. These features allowed individuals to crush and grind hard foods such as nuts, seeds, roots, and tubers in the back of the jaw; however, P. robustus didn’t just eat tough foods. This early human species may have been more of a dietary generalist, also eating variety of other foods such as soft fruits and possibly young leaves, insects, and meat.
While scientists have not found any stone tools associated with Paranthropus robustus fossils, experiments and microscopic studies of bone fragments show that these early humans probably used bones as tools to dig in termite mounds. Through repeated use, the ends of these tools became rounded and polished. Termites are rich in protein, and would have been a nutritious source of food for Paranthropus.
From 1940s through 1970s, lots of debate whether this species represented the males of Au. africanus. Eventually, scientists recognized that the 'robust' forms were different enough to be in their own species, originally called Australopithecus robustus. Later, the three robust species (aethiopicus, boisei, and robustus) were recognized as being different enough from the other australopithecines - and similar enough to each other - to be placed into a separate genus, Paranthropus.