Paranthropus genus

The genus Paranthropus currently includes three species, Paranthropus boisei, Paranthropus robustus, and Paranthropus aethiopicus. They are collectively known as the ‘robusts’ because of their extremely large jaws and molar teeth. They are our distant ‘cousins’ rather than our direct relatives.

Age

Paranthropus aethiopicus lived between 2.3 and 2.7 million years ago. Paranthropus boisei and Paranthropus robustus lived between 1.0 and 2.3 million years ago.

_{Photogrammetry scan of Paranthropus aethiopicus cast. View full screen on Pedestal 3D}

Important fossil discoveries

In 1938, a schoolboy found some fossil fragments on a hillside at Kromdraai in South Africa. The fossils were brought to the attention of Robert Broom from the Transvaal Museum and Broom soon located more fragments, all from the same skull. Unique features of the skull included particularly large premolar and molar teeth and a robust or strongly built lower jaw, so Broom announced it as a new species Paranthropus robustus.

The first Paranthropus discovery in east Africa was made in 1959 by Mary Leakey. Since then, more than 300 Paranthropus fossils have been uncovered and three species are now included in the group.

Important specimens: Paranthropus robustus

• SK 23 – a lower jaw discovered in Swartkrans, South Africa
• SK 13/14 – an upper jaw discovered in Swartkrans, South Africa. This adolescent palate or upper jaw shows the eruption of the last molar teeth.
• SK 50 – a right half of an adult male pelvis discovered inSwartkrans, South Africa
• SK 48 – skull discovered in 1950 in Swartkrans, South Africa. This adult skull has been dated between 1.5 and 2 million years old. Accurate dates have been difficult to obtain for South African fossils because they lie in cave ground layers that have been disturbed by washed-in sediments and erosion of the cave roof.

Important specimens: Paranthropus boisei

• L 74 – a 2.3-million-year-old lower jaw discovered in Omo, Ethiopia. This fossil is the most massive example of a jaw from this species.
• KNM-ER 729 – a lower jaw of a male discovered in East Turkana, Kenya
• OH 5 – skull discovered in 1959 by Mary Leakey in Olduvai Gorge, Tanzania
  Dated to 1.8 million years old, this is the ‘type specimen’ or official representative of this species. It was originally classified as Zinjanthropus boisei and earned the nickname ‘Nutcracker Man’ because of its powerful jaws and large teeth. Layers of volcanic sediment around this skull have enabled the reliable dating of this fossil.
• KNM-ER 732 – a 1.7-million-year-old skull discovered in 1970 by Richard Leakey in Koobi Fora, East Turkana, Kenya. Compared with a male’s skull, this female has a smaller face and no sagittal crest along the top of the braincase.

Important specimens: Paranthropus aethiopicus

• The ‘Black Skull’ KNM-WT 17000 discovered in 1985 by Alan Walker in West Turkana, Kenya. This 2.5 million-year-old skull has a very projecting face compared with the other, more recent Paranthropus species.
• The type specimen is Omo 18, a toothless mandible discovered in 1968.

What the names mean

Paranthropus is based on the Greek words, ‘para’ meaning ‘beside’ or ‘near’ and ‘anthropus’ meaning ‘man’.

There are three species in the Paranthropus genus or group. The second word from each species’ scientific name is:

• aethiopicus, after Ethiopia where the type specimen Omo 18 was discovered,
• boisei, honouring Charles Boise who helped to fund Louis Leakey’s fossil hunting expeditions,
• robustus, a Latin word meaning ‘strongly built’ which refers to this species’ robust skulls and jaws.

Distribution

Fossils of both Paranthropus aethiopicus and the more recent species Paranthropus boisei have been found in the countries of Ethiopia, Kenya and Tanzania in east Africa. Fossils of Paranthropus robustus have been excavated from South Africa, including over 100 specimens from the limestone cave of Swartkrans.

Relationships with other species

None of these species is considered to be a direct ancestor of humans. P. aethiopicus may have evolved from Australopithecus afarensis or from an earlier species such as A. anamensis. Many scientists believe that P. aethiopicus was the direct ancestor of P. boisei.

The ancestry of P. robustus is debated. Some consider it to have evolved from P. aethiopicus. Others think its ancestor may have been Australopithecus africanus.

It is still debated as to whether Paranthropus is a valid grouping composed of a common ancestor and its descendants (monophyly) or an invalid grouping of similar-looking hominins (paraphyly) resulting from convergent evolution.

Other names

Some scientists call the species in this group the ‘robusts’ or ‘robust australopithecines’ and the genus name Australopithecus has sometimes been preferred instead of Paranthropus for all three species. Various other names have been used over the years. Paranthropus boisei was initially known as Zinjanthropus boisei and some P. robustus specimens were originally named Paranthropus crassidens.

Key physical features

All three species share similar physical characteristics - a relatively small body and a ‘robust’ or strongly built skull including large lower jaws with extremely large molar teeth.

Body size and shape

• P. aethiopicus appears to have been much larger than the other two species but lack of skeletal evidence makes reconstructing the exact sizes difficult. P. robustus and P. boisei were probably only slightly larger than Australopithecus africanus.
• males were significantly larger than females
• rib cage was cone-shaped like those of apes rather than the barrel-shape of human rib-cages.

Brain

• size was relatively small and ranged from 420 cubic centimetres for P. aethiopicus to 520 cubic centimetres for P. boisei and P. robustus.

Skull

• cranial features were ape-like with a flat forehead and a prominent brow ridge above the eyes.
• the face was relatively broad with flaring cheekbones. P. aethiopicus had a more projecting face than the other species in this genus, which had shorter, flatter faces.
• spinal cord passed through the centre of the skull base, indicating these species walked upright.
• males had a massive bony ridge running along the top of the skull, called a sagittal crest. This acted as an anchor for their powerful jaw muscles.

Jaws and teeth

• front teeth (incisors and canines) were very small compared with the extremely large molar teeth. The molar teeth were very effective for crushing and grinding tough plant foods
• jaws were large and robust for the attachment of powerful chewing muscles

Limbs and pelvis

• legs had human-like features that indicate an ability to walk upright
• arms were long compared with the legs
• pelvis was similar to that of Australopithecus as it was built for walking on two legs but without the refinements for the striding gait of humans.

Culture

The majority of scientists believe that these species did not manufacture stone tools, but they may have used sticks or unmodified stone to access the tubers or hard nuts that were part of their diet.

It has been suggested that these species may have lived in social groups based around a dominant male and several females, similar to modern gorillas.

Environment and diet

These species lived in regions of Africa that were dominated by open savannah grasslands and woodlands. There is evidence that the environment was becoming drier after about 1.5 million years ago.

The powerful grinding teeth and jaws of these species suggest that they ate large amounts of tough vegetation. Tooth wear patterns suggest hard foods like seeds, nuts and roots were included in the diet. They may have eaten some meat, but only in negligible amounts.