SK 48: The Swartkrans Skull

Discovery and Site History

SK-48 was discovered by Robert Broom (1866-1951), a Scottish physician who had hunted fossils in many parts of South Africa and was particularly interested in the mystery of human evolution. Broom became curator of vertebrate paleontology at the Transvaal Museum in Pretoria and learned of human-like skeletal material being found in mining excavations during the South African gold rush. In 1936 in a mine at Sterkfontein he found parts of the skull of an Australopithecus. Then in 1938 the mine manager showed Broom a lower jaw and tooth found by a schoolboy in Kromdraai, less than a mile away. Broom and the boy sifted earth and found a number of bones and teeth that made up most of another skull, but the new finds were very different from the ones he had found or seen earlier. The sites at Sterkfontein and Kromdraai also were different in age and in the fauna found there. Broom thus established a new genus and species for the Kromdraai type of Australopithecine: Paranthropus robustus, or "robust near-man". Not everyone agreed with Broom's classification, however, and to this day the taxonomy of the Australopithecines is debated.

Broom, in his 70s, kept working and found more fossils of the robust type. These included SK-48 and other Australopithecines, which he found in a cave at Swartkranz just across the valley from Sterkfontein. Broom's work on the Swartkranz hominids was continued by others. Paranthropus fossils at Swartkranz were dated to 1.8 to 1.0 million years ago and overlapped in time with Homo erectus fossils in the area. Paranthropus skeletal anatomy suggested that this species had a vegetarian diet, and stone flakes and choppers found in association with Paranthropus suggested that this species was a tool user and possibly a toolmaker.

FAQs about Paranthropus

Pananthropus robustus (SK48)

• Discovered at Swartkranz by Robert Bloom in 1948
• Australopithecine of robust type, also known as Australopithecus robustus
• Compared to older, less robust fossils of Australopithecus africanus
• P. robustus fossils first discovered by Robert Bloom at Krondraai in 1938
• Evolved during the late Pliocene; lived between 2.0 and 1.0 million years ago
• Partly contemporaneous with early Homo erectus sites in southern Africa
• Associated with bone, flake, and pebble chopper tools

Diagnostic Characteristics of South African Australopithecines

TRAIT	AUSTRALOPITHECUS AFRICANUS	PARANTHROPUS ROBUSTUS
Height	F: 3.8 ft (115 cm)	F: 3.6 ft (110 cm)
	M: 4.5 ft (138 cm)	M: 4.3 ft (132 cm)
Weight	F: 55-66 lb (25-30 kg)	F: 71-88 lb (32-40 kg)
	M: 90-132 lb (41-60 kg)	M: 88-176 lb (40-80 kg)
	(F about 54% of M)	(F about 60% of M)
Brain size	454 cc mean	530 cc mean
	(Range, both sexes: 405-515cc)	(Range unknown)
Cranium	Prognathic face; lacks sagittal crest; low, flat forehead; low-vaulted braincase; lacks flexure (arching) of cranial base (needed for speech)	Face is wide, flattish, and "dished"; sagittal crest; low, flat forehead; low-vaulted braincase; some flexure of cranial base
Dentition	Parabolic toothrow; short, incisorlike canines; no diastemata; lower P3s have two cusps; smaller grinding teeth than P. robustus	Parabolic toothrow; short, incisorlike canines; small anterior teeth; no diastemata; lower P3s have two or more cusps; very large grinding teeth
Diet	Mostly fruits and leaves; also, possibly grasses, sedges, some meat	Harder, tougher items than A. africanus (more nuts? Gritty tubers?); some meat?
Limbs	Longer and larger arms and shorter legs than modern humans; apelike tibia; grasping big toes	Longer arms and shorter legs than modern humans; humanlike nongrasping big toes
Pelvis	Short, broad ilia; pelvic bowl nearly complete; short ischial shafts realigned in modern manner; pelvis wide between hip joints	Short, broad ilia; weak iliofemoral ligaments (?); shortening of ischial shaft (?); pelvis wide between hip joints
Locomotion	Bipedalism and arboreal climbing	Bipedalism
Known Dates	3.5 (?) - 2.5 million years bp	2.0 - 1.0 million years bp

Source: Bernard G. Campbell and James D. Loy, Humankind Emerging, Eighth Edition (Allyn & Bacon, 2000), p. 218.

Anatomy Lesson

prognathic face-the lower part of the face and the jaws jut out in front of the upper part of the face. P. robustus had a flat face instead.

sagittal crest-bony ridge at top of skull to which jaw muscles attach. P. robustus had massive, heavy jaws, indicating a largely vegetarian diet.

parabolic toothrow-curved row of teeth rather than U-shaped. P. robustus had this trait.

diastemata-gaps between the canines and the first molar teeth in the upper jaw.

zygomatic arches-cheek bones. P. robustus had a very broad face, with large cheek bones extending toward the back of the skull.

incisors and canines-front teeth and eye teeth. P. robustus had very small incisors and canines.

anterior teeth-the front teeth including incisors and canines.

Molars-back teeth. P. robustus had very large molars for chewing vegetation.

tibia-one of two leg bones, the shinbone. P. robustus had ape-like tibia.

ilia-broad flat bones of the pelvis

ischial shaft-lower bones of the pelvis

iliofemoral ligament-ligament that in humans prevents backward movement of the trunk at the hip

bipedalism-moving erect on the hind limbs only (as in walking). P. robustus was bipedal.

arboreal climbing-hand-over-hand locomotion in trees

Enduring Questions about Paranthropus robustus

• Separate genus?
• Decended from A. africanus?
• Relationships to Paranthropus fossils of East Africa?
• Ancestor of modern humans?
• Relationship to H. erectus?
• Made tools?
• Used fire?