Paranthropus boisei: Mary Leakey's 'Nutcracker Man' Skull

Paranthropus boisei is an extinct hominin that lived in East Africa between about 2.3 and 1.3 million years ago, famous for its massive jaws and huge, flat cheek teeth. The first skull, known as OH 5 and nicknamed “Nutcracker Man”, was found by Mary Leakey at Olduvai Gorge in Tanzania on 17 July 1959. Its discovery, and its dating to about 1.75 million years ago, transformed the Leakeys’ careers and showed that human evolution in Africa was far older than most scientists had believed.

Background: decades of searching

Louis and Mary Leakey had worked at Olduvai Gorge since the 1930s. They had found thousands of stone tools in the gorge’s layers, which Mary studied and later defined as the Oldowan industry. Yet they had found almost no remains of the toolmakers themselves.

Funding was always short. One supporter was Charles Boise, a London-based businessman who had helped pay for the Leakeys’ research since the late 1940s. In 1959 the couple were working at a site in the lowest layer of the gorge, Bed I, known as FLK after Frida Leakey Korongo, a gully named after Louis’s first wife.

The discovery on 17 July 1959

On the morning of 17 July 1959 Louis was unwell with a fever and stayed in camp. Mary went out alone with the family’s Dalmatian dogs to search the slopes at FLK. She noticed a piece of bone protruding from the ground and, looking closer, saw parts of two large teeth in a jaw. She hurried back to camp to tell Louis.

Careful excavation over the following weeks recovered around 400 fragments of a single skull. Mary pieced them together into a nearly complete cranium, lacking the lower jaw. The skull belonged to a young adult, probably male, and became Olduvai Hominid 5, or OH 5. The Leakeys affectionately called it “Dear Boy”.

Louis described it in the journal Nature in August 1959 under the name Zinjanthropus boisei. “Zinj” came from an old Arabic name for the East African coast, and “anthropus” means man. The species name honoured Charles Boise.

A robust australopith

OH 5 looked very different from modern humans. A tall bony crest, called a sagittal crest, ran along the top of the skull and anchored enormous chewing muscles. The cheekbones flared widely, the face was broad and dish-shaped, and the molars and premolars were huge, with a chewing surface several times larger than ours. The front teeth, by contrast, were small.

The brain was about 500 to 530 cubic centimetres, similar to other australopiths and much smaller than a modern human’s. Scientists now group Paranthropus boisei with two related species: Paranthropus robustus from South Africa, first named by Robert Broom in 1938, and Paranthropus aethiopicus, known from the “Black Skull” found west of Lake Turkana in 1985 and dated to about 2.5 million years ago. Together they are called the robust australopiths.

Many researchers place all three in the genus Paranthropus, meaning “beside man”, as a side branch of human evolution. Others keep them in Australopithecus. Either way, they are cousins of our lineage rather than ancestors.

Dating the skull

The Olduvai layers contain volcanic ash, which made a new technique possible. In 1961 Louis Leakey and the geologists Jack Evernden and Garniss Curtis of the University of California, Berkeley, published potassium-argon dates for Bed I. The results put OH 5 at about 1.75 million years old.

Many scientists had expected an age of a few hundred thousand years. The new date roughly tripled the accepted timescale of human evolution and helped establish radiometric dating as a standard tool in palaeoanthropology.

The find also brought money and fame. The National Geographic Society began funding the Leakeys’ work, and their discoveries reached a wide public through its magazine and films.

What did Nutcracker Man really eat?

The nickname suggests a diet of nuts and hard seeds, and for decades that was the common view. Two lines of evidence have since changed it. Studies of microscopic wear on the teeth, published from 2008, found few of the pits expected from cracking hard foods; the wear looked more like that of animals chewing tough plants.

In 2011 a team led by Thure Cerling analysed carbon isotopes in the tooth enamel of 24 individuals. The results showed that around three-quarters of their diet came from C4 plants, a group that in East Africa consists mainly of tropical grasses and sedges. Paranthropus boisei probably spent much of its time eating large quantities of tough grasses, sedge stems and underground storage organs, grinding them with its huge molars.

Living alongside early Homo

OH 5 was not alone at Olduvai. In 1960, close by, the Leakeys found the fossils later named Homo habilis, and Paranthropus boisei also shared East Africa with early Homo erectus. For several hundred thousand years at least two or three hominin species lived in the same landscapes.

At first Louis Leakey suggested that Zinjanthropus had made the Oldowan tools found nearby. After the Homo habilis discoveries, most researchers credited the tools to Homo instead. Whether Paranthropus also made or used stone tools is still uncertain, and recent finds of tools near Paranthropus fossils have revived the question.

Paranthropus boisei disappears from the fossil record about 1.3 million years ago. Why it died out while Homo survived is unknown, though changes in climate and competition are often suggested.

Myths and facts

Myth: Nutcracker Man cracked nuts. Despite the nickname, tooth wear and chemical evidence point to a diet based mainly on grasses, sedges and other tough plants. The huge teeth were built for grinding large volumes of food rather than for breaking hard shells.

Myth: OH 5 was the first early hominin found in East Africa. Fragmentary australopith remains, such as an upper jaw found at Laetoli in Tanzania in 1939, were already known, as was the much older fossil ape Proconsul, found by Mary Leakey on Rusinga Island in 1948. OH 5, however, was the first nearly complete australopith skull from East Africa and made Olduvai world famous.

Fact: Paranthropus was a long-lived success. The robust australopiths survived for well over a million years in eastern and southern Africa, a span longer than our own species has existed so far.

By the numbers

Timeline

• c. 2.3 million years ago: Earliest fossils attributed to Paranthropus boisei.
• c. 1.75 million years ago: The individual known as OH 5 dies at Olduvai.
• c. 1.3 million years ago: Paranthropus boisei disappears from the record.
• 1959, 17 July: Mary Leakey discovers the OH 5 skull at FLK, Olduvai Gorge.
• 1959, August: Louis Leakey names Zinjanthropus boisei in Nature.
• 1961: Potassium-argon dating gives Bed I an age of about 1.75 million years.
• 1967: Phillip Tobias publishes his monograph on the skull.
• 2011: Isotope study shows a diet dominated by grasses and sedges.

Why it matters

The OH 5 skull revealed a whole branch of the human family tree that thrived for a million years and then vanished. Its dating changed the timescale of human evolution, and the shifting story of its diet shows how new scientific methods can overturn even a famous nickname.