Sulcal Skirmishes - The Fossil Chronicles - page 61

this was the largest braincase volume known for gracile australopith-
ecines (which averaged about 450 cm 3 ), this size was considerably smaller
than anticipated. Something was very wrong, and Conroy's team sug-
gested that the problem might be that the published cranial capacities
of other australopithecines with whom Stw 505 had been visually com-
pared were reconstructed as larger than they should have been . 15
That suggestion sent me running to my collection of endocasts and
copies of their corresponding skulls. At the time, I was directing two
fabulous graduate students, John Redmond, Jr., who had a knack for
statistics and computers, and John Guyer, whose anatomical knowledge
and artistic skills were perfect for doing hominin reconstructions. We
soon realized that earlier workers who had filled in the missing parts
on a number of australopithecine endocasts had made them too large.
This seemed especially true for the second type of australopithecine
(Paranthropus), which Dart's colleague Robert Broom had discovered.
Paranthropus skulls were much more rugged-looking than those of grac-
ile australopithecines, as reflected in their large, flat faces, humongous
molars, and crests of bone that served as anchors for chewing muscles.
This is why they are commonly called robust australopithecines. What
Redmond, Guyer, and I discovered was that, despite their macho-
looking skulls, Paranthropus endocasts had stubby little temporal lobes
and small, pointed frontal lobes compared with those of gracile austra-
lopithecines, which dramatically affected the overall shape that recon-
structed Paranthropus endocasts should have had.
It looked to us as if a nearly complete endocast from an adult Australo-
pithecus africanus (STS 5, “Mrs. Ples”) had served as the model for miss-
ing parts in Paranthropus endocasts, which resulted in the reconstruc-
tions of their temporal and frontal lobes as unrealistically large, thus
causing their cranial capacities to be inflated. Using more appropriate
Paranthropus endocasts as models, we provided our own reconstructions
and determined new cranial capacities for these specimens, which had
implications for brain-size evolution in hominins. 16
Our results led us to question the generally accepted idea that brain