Overview:

Like other members of the Paranthropus genus, P. boisei is characterized by a specialized skull with adaptations for heavy chewing. A strong sagittal crest on the midline of the top of the skull anchored the temporalis muscles (large chewing muscles) from the top and side of the braincase to the lower jaw, and thus moved the massive jaw up and down. The force was focused on the large cheek teeth (molars and premolars). Flaring cheekbones gave P. boisei a very wide and dish-shaped face, creating a larger opening for bigger jaw muscles to pass through and support massive cheek teeth four times the size of a modern human’s. This species had even larger cheek teeth than P. robustus, a flatter, bigger-brained skull than P. aethiopicus, and the thickest dental enamel of any known early human. Cranial capacity in this species suggests a slight rise in brain size (about 100 cc in 1 million years) independent of brain enlargement in the genus Homo.

History of Discovery:

Paleoanthropologists actually found the first fossils belonging to P. boisei in 1955, but it wasn’t until Mary Leakey’s 1959 discovery of the ‘Zinj’ skull (OH 5) that scientists knew what they had found was a new species. ‘Zinj’ became the type specimen for P. boisei and, soon after, arguably the most famous early human fossil from Olduvai Gorge in northern Tanzania.

How They Survived:

This species was nicknamed Nutcracker Man for its big teeth and strong chewing muscles, which attached to the large crest on the skull. Those features show that Paranthropus boisei likely ate tough foods like roots and nuts. But dental microwear patterns seen on P. boisei teeth are more similar to living fruit-eaters with fine striations, rather than large, deep pits seen in the teeth of living species that eat grass, tough leaves and stems, or other hard, brittle foods. While the morphology of P. boisei skull and teeth indicate it could have chewed hard or tough foods, dental microwear analysis does not demonstrate that they regularly did so, suggesting a wider, more diverse diet for P. boisei. It's possible that this species only ate hard or tough foods during times when its preferred resources were scarce, relying on them as fallback foods.

This species lived in environments that were dominated by grasslands but also included more closed, wet habitats associated with rivers and lakes.

Evolutionary Tree Information:

P. boisei is usually thought to descend from earlier P. aethiopicus (who inhabited the same geographic area just a few hundred thousand years before) and lived alongside several other species of early humans during its 1.1 million year existence. P. boisei belongs to just one of the many side branches of human evolution, which most scientists agree includes all Paranthropus species and did not lead to H. sapiens.

The 1975 discovery of P. boisei specimen KNM-ER 406 and H. erectus specimen KNM-ER 3733 in the same stratigraphic layer was the first example of species coexistence. This discovery cleared up a long time controversy and confirmed that more than one species of early humans lived in the same geographical area at the same time. More finds have confirmed that this species was one of the most prevalent in Eastern Africa during the time period when early members of the genus Homo were also present. This replaced the traditional view of a single human lineage by the notion of a human family tree with many branches (like most other family trees); we’ve been adding branches though discoveries of new species ever since.

Questions:

We don’t know everything about our early ancestors—but we keep learning more! Paleoanthropologists are constantly in the field, excavating new areas, using 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 P. boisei that may be answered with future discoveries:

1. What, specifically, did P. boisei eat? The morphology and microwear of their teeth indicate different things.
2. Did P. boisei use stone tools? While we don’t think they did, P. boisei individuals have been found in stratigraphic layers with tools, and also with Homo specimens who often made tools, so there’s always a possibility.
3. What was the advantage of the big jaws and teeth of P. boisei?
4. These early humans flourished for a million years, over four times as long as our own species Homo sapiens have been around, and then went extinct---why? Scientists have one prevailing hypothesis: P. boisei was unable to adapt to a rapidly changing environment.  When Earth’s climate intense irregular with fluctuating hot and cold spells, there may have been changes in the proportions of food resources available to P. boisei.  Certain plants could have dwindled or died out. A species’ ability to adapt to changing resources, like food, is critical to their survival. Was highly specialized P. boisei unable to adapt if some of their favored plant foods disappeared due to climatic changes?

References:

First Paper:

Leakey, L.S.B., 1959. A new fossil from Olduvai. Nature 184, 491-494.

Other recommended readings:

Constantino, P., Wood, B., 2007. The evolution of Zinjanthropus boisei. Evolutionary Anthropology 16, 49–62.

Ungar, P.S., Grine, F.E., Teaford, M.F., 2008. Dental microwear and diet of the Plio-Pleistocene hominin Paranthropus boisei. PLoS One 3, e2044.