The Black Skull (KNM-WT 17000) and the Robust Paranthropus

The skull came out of the ground in 1985 on the west side of Lake Turkana in northern Kenya. Walker, Leakey, John Harris and Frank Brown described it in Nature in 1986, and at first they identified it as *Australopithecus boisei*, a heavy-jawed species already known from eastern Africa. Later comparisons supported placing it in a separate, earlier species, *Paranthropus aethiopicus*.

That makes the Black Skull rare in a very specific way. According to the Smithsonian, it is still the only known adult cranium confidently assigned to *P. aethiopicus*. Much of what anyone can say about how that species looked rests on this one head.

It is not a perfect specimen. Many of the front teeth were lost or broken after death, so the mouth looks oddly empty in photographs. The roots of the big molars and premolars survive, though, and they show how large the chewing teeth once were. The braincase was small, with a cranial capacity of about 410 cubic centimeters by the Smithsonian's figure. For a sense of scale against a modern head, our page of human skull facts covers the skull you carry around.

The short answer is about 2.5 million years, the figure the Smithsonian gives. More detailed estimates land in the same place. One later geochronological study puts it at 2.50 million years, plus or minus 70,000 years, and a 2025 review of the Omo-Turkana Basin fossil record gives 2.53 million years, plus or minus 50,000.

Those numbers are not a date taken from the bone itself. They come from geological dating of the deposits around the fossil, the layers it was buried in. That is the usual way very old fossils get their ages, and our story on how old bones are dated explains the general idea. The ranges are narrow, so the 2.5 million figure is a safe one to repeat.

It turned black underground. The skull was bone-colored when its owner was alive. During burial and fossilization, manganese-rich minerals from the surrounding soil worked their way into the fossil and stained it dark, nearly black.

That staining is a big part of why the skull is so recognizable. It looks almost like cast iron, which makes the crest and the wide cheekbones stand out sharply in photographs and museum displays.

Look at the top of the skull and you will see a tall ridge of bone running front to back. That is the sagittal crest. It gave extra space for the temporalis muscles, the big muscles on the sides of the head that close the jaw. The cheekbones flare out wide, the jaw architecture is heavy, and the molar and premolar roots are very large. All of it adds up to an animal built for forceful chewing.

What that chewing power was used for is a more open question. The anatomy shows what the jaws could do, not one exact food. Earlier interpretations leaned on nuts, seeds and hard fruits, and that idea gave the related species *Paranthropus boisei* its famous nickname, "Nutcracker Man."

Later work looked at the teeth in other ways. Dental microwear studies, such as the one by Ungar and colleagues, examine the tiny scratches and pits that food leaves on tooth surfaces. Carbon isotope studies, such as Cerling and colleagues' work on the diet of *P. boisei*, read the chemical signature that different plants leave in tooth enamel. Together they point to *P. boisei* often eating C4 resources such as grasses or sedges. The Smithsonian's *P. boisei* page notes that the microwear does not show hard foods being eaten constantly; hard items may have been fallback foods for lean times.

So, "Nutcracker Man" captures the jaws but not the whole menu. The South African species, *P. robustus*, seems to have eaten a more varied range of plant foods, with hard foods possibly kept in reserve as well, according to the Smithsonian's *P. robustus* page. If you are curious how much a set of teeth can reveal about a life, our story on what bones tell archaeologists goes further.

The Black Skull belongs to a small group of species that scientists put in the genus *Paranthropus*. The name means "beside man," which fits the way these species ran parallel to early humans. Three are commonly recognized.

The oldest of the three was named before the Black Skull turned up. In 1967 Camille Arambourg and Yves Coppens proposed *P. aethiopicus* from the Omo 18 mandible, a lower jaw from Ethiopia with no teeth left in it. A toothless jaw is a thin base for a species, and the Black Skull, found nearly twenty years later, became the main adult cranium behind it.

Names can be confusing here. Some scientists place one or more of these species in *Australopithecus* instead, so older books and labels may say *Australopithecus aethiopicus* or *Australopithecus boisei*. They mean the same fossils.

*Paranthropus* walked upright, and it shared its world with early *Homo*. In eastern Africa, fossils of *P. boisei* and early *Homo* species turn up in the same broad regions and, in some cases, in the same layers of rock. Two kinds of upright relatives were living through the same stretch of time, one with huge jaws and one that eventually led to us.

The Smithsonian presents *Paranthropus* as a side branch that did not lead to *Homo sapiens*. The details of that branch are where scientists disagree, and the disagreements are worth stating plainly:

• Many regard *P. aethiopicus* as an earlier form that gave rise to *P. boisei*. Others stress how much it resembles *Australopithecus afarensis*, the species of Lucy.
• *P. robustus* may be a southern African lineage related to *P. aethiopicus*, or a regional lineage closer to *Australopithecus africanus*, the species of the Taung Child and of Mrs. Ples.
• The genus boundary itself is debated, which is why some researchers keep these species in *Australopithecus*.

A Smithsonian Magazine piece on the Black Skull is a readable way into that argument. For the *Homo* side of the same period, see our story on the Homo erectus skull, and for the wider line-up of very old skulls, our guide to the oldest human skull.

KNM-WT 17000 belongs to the National Museums of Kenya. Its catalogue number says so: the KNM-WT prefix marks a Kenya National Museum specimen from West Turkana. The National Museums of Kenya manages the country's paleontological collections, and its Nairobi National Museum has a gallery on human origins called the Cradle of Humankind.

Museums in other countries show casts, so the dark skull you saw abroad may well have been a replica. If you hope to see the original or its display in Nairobi, confirm the current display status with the Nairobi National Museum before you go.

A few more questions come up often about this skull and its relatives.