Paranthropus boisei

Paranthropus boisei is an extinct human ancestor that lived in the savannah environment of East Africa from 2.3 million until 1.2 million years ago. It is the most robust form of the robust australopithicenes, and is specialized towards heavy chewing.

The first specimen OH 5 was found by Mary Leaky at Olduvai Gorge in 1959 after 28 years of searching. It was originally named Zinjanthropus boisei or Nutcracker man, named so for its large molars and small anterior teeth. It was later renamed Paranthropus boisei, although it is also often called Australopithecus boisei.

Phylogeny

Paranthropus boisei is not actually a human ancestor but rather a cousin. It was most likely descended from Paranthropus aethipicus and some scientists consider it a subspecies of Paranthropus robustus. Many of its features are similar to Australopithecus africanus.

Characteristics

There are several characteristics that are obviously Paranthropus boisei, primarily in the craniuma and dentition, such as:

• Prognathic lower face
• Postorbital constriction reduced
• Infraorbital foramen location is variable
• Occipital Marginal sinus present
• Infrolatral orbital margin reduced
• Mental foramen opening is variable
• Lingual cusps at [margin-bucca cusps] approaching internal
• Typanic crest with inclined plate
• Sagittal crest on males
• Maxillary trigon variable
• Upper incisor reduced
• Molar cusps and cristae well developed
• Thin and delicate wall on cranium
• Cranial capacity of 450-600cc
• Large molars
• Large incisor alveolae
• Ape-like Cranial base
• Zygomatic arch of skull is wide and thick, indicating powerful masseter muscles

Postcranially, Paranthropus boisei is obviously bipedal. The thigh bone is set at a low angle to the shaft, with the shaft flattened from front to back, and there is a small hip joint surfact; all of these traits lead to better ballance. The pelvis is more human than chimpanzee: it is shortened and widened. The arms and thumbs appear to be similar to Homo habilis, and Paranthropus boisei probably had an excellent precision grip.

Diet

Small anterior teeth and large molars, as well as the wear patterns on the teeth suggest that Paranthropus boisei ate hard and fiborous foods such as nuts. It also suggests that they ate a lot of food rich in ¹³C foods found in savannahs and wetter areas. This food would include meat. The animals they were eating were most likely scavanged though, because while there are stone tools found at the sites with Paranthropus boisei, most scientists tie these stone tools to Homo habilis as they had larger brains and are more closely related to humans.

Environment

Paranthropus boisei fossils are found near ancient lakes and streams. They lived in savannah environments, forests, and flooded grasslands. Some of the animals found in the fossil beds with them are giant gelda baboon, clawless otter, white rhinoceros, black rhinoceros, bush pig, warthog, giraffe, large kudu, hartebeest, topi, wildebeest, sable antelope, springback, Grant's gazelle, two species of extinct buffallo, and four species of extinct pig.

Some of the sites they have been found at are the upper level of Bed 1 and Bed 2 at Olduvai Gorge, Upper Burgi, Okote Members of Koobi Fora Formation in East Lake Turkana, Member G of the Shangura Formation along the Omo River, and the Ethiopian Rift.