Among the ancient members of the human evolutionary family, called fossil hominids by anthropologists, Paranthropus boisei cuts a striking profile. Its skull revolves around huge jaws that encase small front teeth and immense, pegshaped back teeth. A flattened face and flared cheekbones slope back to a visorlike crest over the eyes. A bony ridge runs over the top of the head, where it meets a small, triangular braincase.
A new study now indicates that P. boisei also exhibited a remarkably stubborn devotion to its distinctive look for more than 1 million years, until the Paranthropus lineage hit an evolutionary dead end. The basic features of P. boisei jaws and teeth remained unchanged during a time of marked brain growth and tooth-size reduction in direct human ancestors, contends anthropologist Bernard Wood of the University of Liverpool in England.
"I suspect P. boisei underwent little evolutionary change of any kind," Wood asserts.
The finding coincides with Wood's view that hominid species directly ancestral to modern humans also experienced few anatomical changes before their relatively abrupt evolution to succeeding species (SN: 6/20/92, p.408).
P. boisei belonged to a group of African hominids, referred to as robust australopithecines by some investigators, which first appeared about 2.6 million years ago. P. boisei lived in east Africa from around 2.2 million to 1 million years ago, in Wood's view. Some anthropologists argue that the discovery of the so-called black skull extends the antiquity of P. boisei to 2.5 million years ago, a claim that continues to spark controversy (SN: 1/24/87, p. …