Paranthropus robustus
Paranthropus robustus is a species of robust australopithecine from the Early and possibly Middle Pleistocene of the Cradle of Humankind, South Africa, about 2.27 to 0.87 million years ago. It has been identified in Kromdraai, Swartkrans, Sterkfontein, Gondolin, Cooper's, and Drimolen Caves. Discovered in 1938, it was among the first early hominins described, and became the type species for the genus Paranthropus. However, it has been argued by some that Paranthropus is an invalid grouping and synonymous with Australopithecus, so the species is also often classified as Australopithecus robustus. Robust australopithecines—as opposed to gracile australopithecines—are characterised by heavily built skulls capable of producing high stresses and bite forces, as well as inflated cheek teeth. Males had more heavily built skulls than females. P. robustus may have had a genetic susceptibility for pitting enamel hypoplasia on the teeth, and seems to have had a dental cavity rate similar to non-agricultural modern humans. The species is thought to have exhibited marked sexual dimorphism, with males substantially larger and more robust than females. Based on 3 specimens, males may have been 132 cm tall and females 110 cm. Based on 4 specimens, males averaged 40 kg (88 lb) in weight and females 30 kg (66 lb). The brain volume of the specimen SK 1585 is estimated to have been 476 cc, and of DNH 155 about 450 cc. P. robustus limb anatomy is similar to that of other australopithecines, which may indicate a less efficient walking ability than modern humans, and perhaps some degree of arboreality. P. robustus seems to have consumed a high proportion of C4 savanna plants. In addition, it may have also eaten fruits, underground storage organs, and perhaps honey and termites. P. robustus may have used bones as tools to extract and process food. It is unclear if P. robustus lived in a harem society like gorillas or a multi-male society like baboons. P. robustus society may have been patrilocal, with adult females more likely to leave the group than males, but males may have been more likely to be evicted as indicated by higher male mortality rates and assumed increased risk of predation to solitary individuals. P. robustus contended with sabertooth cats, leopards, and hyenas on the mixed, open-to-closed landscape, and P. robustus bones probably accumulated in caves due to big cat predation. It is typically found in what were mixed open and wooded environments, and may have gone extinct in the Mid-Pleistocene Transition characterised by the continual prolonging of dry cycles and subsequent retreat of such habitat.
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