Paranthropus robustus

Paranthropus robustus (or Australopithecus robustus) was originally discovered in Southern Africa in 1938. The development of P. robustus, namely in cranial features, seemed to be aimed in the direction of a "heavy-chewing complex". Because of the definitive traits that are associated with this robust line of australopithecine, anthropologist Robert Broom erected the genus Paranthropus and placed this species into it.

Paranthropus robustus is generally dated to have lived between 2.0 and 1.2 million years ago. P. robustus had large sagittal crests, jaws, jaw muscles, and post-canine teeth that were adapted to serve in the dry environment that they lived in.

Discovery
After Raymond Dart’s discovery of Australopithecus africanus, Broom had been in favour of Dart's claims about Australopithecus africanus being an ancestor of Homo sapiens. Broom was a Scottish doctor then working in South Africa who began making his own excavation in Southern Africa to find more specimens, which Dart had found earlier. In 1938, at 70 years old, Broom, excavating at Kromdraai, South Africa discovered pieces of a skull and teeth which resembled Dart's Australopithecus africanus find, but the skull had some "robust" characteristics.

The fossils included parts of a skull and teeth; all dated to 2 million years old. Fossil sites found on Paranthropus robustus are found only in South Africa in Kromdraai, Swartkrans, Drimolen, Gondolin and Coopers. In the cave at Swartkrans, the remains of 130 individuals were discovered. The study made on the dentition of the hominins revealed that the average P. robustus rarely lived past 17 years of age.

Paranthropus robustus became the first "robust" species of hominid ever uncovered well before P. boisei and P. aethiopicus. Broom's first discovery of P. robustus had been the first discovery of a robust australopithecine and the second australopithecine after Australopithecus africanus, which Dart discovered. Broom's work on the australopithecines showed that the evolution trail leading to Homo sapiens was not just a straight line, but was one of rich diversity.

Morphology
Typical of robust australopithecines, P. robustus had a head shaped a bit like a gorilla's with a more massive built jaw and teeth in comparison to hominins within the Homo lineage. The sagittal crest that runs from the top of the skull acts as an anchor for large chewing muscles. The DNH 7 skull of Paranthropus robustus, "Eurydice", was discovered in 1994 at the Drimolen Cave in Southern Africa by Andre Keyser, and is dated to 2.3 million years old, possibly belonging to a female.

The teeth of these primates were larger and thicker than any gracile australopithecine found, due to the morphology differences Broom originally designated his find as Australopithecus robustus. On the skull, a bony ridge is located above from the front to back indicating where the jaw muscles joined. P. robustus males may have stood only 1.2m (4 feet) tall and weighed 54 kg (120 lb) while females stood just under 1 meter (3 feet 2 inches) tall and weighed only 40 kg (90 lb), indicating a large sexual dimorphism. The teeth found on P. robustus are almost as large as those of P. boisei.

Broom analyzed his findings carefully and noted the differences in the molar teeth size which resembled a gorilla's a bit more than a human's. Other P. robustus remains have been found in Southern Africa. The average brain size of P. robustus measured to only 410 and 530 cc, about as large as a chimpanzee's. Some have argued that P robustus had a diet of hard gritty foods such as nuts and tubers since they lived in open woodland and savanna. More recent research suggests that this taxon was more of a dietary generalist,[1] and others have argued that they principally consumed hard and gritty resources as fallback foods only during time of nutritional stress.[2]

A 2011 study using ratios of strontium isotopes in teeth suggested that Australopithecus africanus and P. robustus groups in southern Africa were patrilocal: females tended to settle farther from their region of birth than males did.