366 Evolution? The Fossils Say YES!
By the late Pliocene, hominins had become very diverse in Africa (fig. 15.3). These
included not only the primitive forms Australopithecus garhi (dated at 2.6 million years) and
A. bahrelghazali (dated at 3.4 million years) but also the best-studied australopithecine, Aus-
tralopithecus africanus. Originally described by Raymond Dart in 1924 based on a juvenile
skull (the “Taung Baby”), for decades the Eurocentric anthropology community refused to
accept it as ancestral to humans. But as more South African caves yielded better specimens to
paleontologists like Robert Broom (especially the adult female skull known as “Mrs. Ples”),
it became clear that Australopithecus africanus was a bipedal, small-brained African hominin,
not an ape. This went contrary to all the accepted notions, which postulated that human
evolution was driven by brain size, that bipedalism was secondary, and that it had occurred
in Europe or Asia. The Piltdown forgery was deliberately set up to reinforce this bias, but
by the 1950s, when Piltdown was exposed as a fraud, the evidence from Australopithecus
africanus became undeniable. Australopithecus africanus was a rather small, gracile creature,
with a dainty jaw, small cheek teeth, no skull crest, and a brain only 450 cc in volume. On
the basis of its gracile and very human-like features, Australopithecus africanus is also the best
candidate for ancestry of our own genus Homo.
In addition to Australopithecus africanus, the late Pliocene of Africa also yields a num-
ber of highly robust hominins. For a long time, they were lumped into a very broad con-
cept of the genus Australopithecus, either as distinct species or even dismissed as robust
males of Australopithecus africanus. In recent years, however, paleoanthropologists have
come to regard them as a separate robust lineage, now placed in the genus Paranthropus.
The oldest of these is the curious “Black Skull,” discovered in 1975 by Alan Walker and
his crew on the shores of West Lake Turkana, Kenya, from rocks about 2.5 million years in
age (fig. 15.5B). Although its brain is small, and it would have had a small body as well,
the skull is robust with large skull crest and massive molars and an advanced dish-shaped
face. Currently, scientific opinion places the Black Skull as the most primitive member of
Paranthropus, P. aethiopicus. It was followed by the most robust of all hominins, P. boisei,
from rocks in East Africa ranging from 2.2 to 1.2 million years in age (fig. 15.5C). This fos-
sil was nicknamed “Nutcracker Man” for its huge thick-enameled molars, robust jaws,
wide flaring cheekbones, and strong crest on the top of its head, indicating a diet of nut or
seed or bone cracking. Originally found by Mary Leakey at Olduvai Gorge in 1959, it was
named “Zinjanthropus boisei” by Louis Leakey, who made his reputation from it. The rocks of
South Africa between 1.6 and 1.9 million years in age yield the type species of Paranthropus,
P. robustus. These too had massive jaws, large molars, and large skull crests but were not as
robust as P. boisei. Paranthropus robustus lived side by side in the same South African caves
as A. africanus. It was not only more robust but also larger than that species as well, with
some individuals weighing as much as 150 pounds.
Finally, the latest Pliocene saw the first members of our own genus Homo, which are
easily distinguished from contemporary Australopithecus and Paranthropus by a larger brain
size, flatter face, no skull crest, reduced brow ridges, smaller cheek teeth, and reduced canine
teeth. The first of these to be described was Homo habilis (“handy man”), discovered in the
1960s by Louis and Mary Leakey in Olduvai Gorge, Tanzania, from beds about 1.75 million
years in age. Originally, all of the early Homo specimens were shoehorned into the species
H. habilis, but now paleoanthropologists recognize that this material is too diverse to belong
to one species, so several are now recognized. These include the very modern-looking skull
(fig. 15.5D) of H. rudolfensis (from beds ranging from 1.9 to 2.4 million years in age), which