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DATES: to 2.3 million years ago (Tobias, 1973)
Makapansgat, Sterkfontein, and
SPECIMENS: many individuals
The braincase of Australopithecus africanus was higher and rounder than in A. afarensis and less apelike. The cranial capacity is larger, 420-500 cc (Conroy, 1998; Conroy, 1998b).
There was a further reduction of canines
and enlargement of the molars. The lower jaw projects less and approaches
the shape of the jaw of modern humans.
There was no diastema and the large molars
and premolars were covered with a thick layer of enamel.
The microscopic wear on the teeth suggests that there were tougher
materials in the diet. Carbon
isotopes in teeth suggest that their diet either included grasses or the
animals which fed on grasses (Sponheimer, 1999;
Vogel, 1999; Lewin, 1985; Leakey, 1974) .
.Microwear on hominid teeth indicates that the diet of A. africanus included tough food items and the diet of Australopithecus robustus included even tougher items (Scott, 2005).
The pelvis and leg indicate bipedal gait
but it may have been inefficient. The
arms were longer than in A. afarensis,
suggesting that A. africanus
was adapted for both life in trees and on the ground (Shreeve,
1996). The South African habitat
where the fossils were found seems to have included more woodland than
There is evidence of sexual dimorphism in size but it was probably not as great as in A. afarensis. Scanning electron microscopy has demonstrated that the patterns of bone remodeling are more like chimps than humans. Some researchers feel that A. afarensis and A. africanus are geographic variants of one species; others feel that A. africanus is not our direct ancestor but rather is related to the robust australopithecines (as the anterior pillars may indicate) (Skelton, 1986; Rak, 1985).
The following images are of an infant A. africanus specimen known as the Taung child.
DATES: to 2.3 million years ago
SPECIMENS: a few relatively complete crania, teeth, and jaws
Some of the characteristics of the famous “black skull”, especially the back portions (such as the unflexed base of cranium), are primitive as in A. afarensis. The cranial capacity was 410 cc. Derived features include a massive face, massive jaws, and a large sagittal crest at the top of the skull (the largest in any hominid). The large molars and premolars suggest a specialized diet that required a great deal of chewing. The zygomatic bones (cheekbones) are flared.
Australopithecus aethiopicus may be the ancestor of A. boisei and A. robustus. It lived in an area where the climate was drier and perhaps this dry climate was related to the tougher materials in its diet (Grine, 1993).
|Australopithecus robustus/ Paranthropus robustus|
DATES: to 1.5 million years ago
SPECIMENS: many individuals
Australopithecus robustus is similar to A. africanus but has more robust skull, jaws, and teeth. Its face was flat or dished, with no forehead and large brow ridges. Endocasts of the inside of the skull give no indication of modifications in the brain for speech. The incisors and canines are small but the molars and premolars were massive (in the second photo which follows, compare the size of the grinding cheek teeth to the incisors). The top of the skull bore a prominent sagittal crest. A. robustus and A. afarensis have an enlarged occipital/marginal venous system (the impressions left by the veins inside the skull) that are unique among hominids. The cranial capacity was 530 cc. From tooth microwear, it appears the diet included coarse material (Grine, 1988; Grine 1993).
Scratchings on bones found in association with A. robustus suggest that these bones may have been used as digging tools. Tools and scratches on animal bones indicate the inclusion of meat in the diets of early hominids. Unfortunately, it is not clear which hominids were using many of the tools found since both australopithecines and early Homo coexisted and utilized simple tools (Susman, ; Robbins, 1972; Keeley, 1981; Corvinus, 1976; Wood, 1997; Bunn, 1981; Merrick, 1973; Potts, 1981; Clark, 1979; Clarke, 1970; Tatterall, 2000; Leakey, 1971c). The fingers of A. robustus would have permitted toolmaking (Susman, 1988). One find indicates that leopards were predators of A. robustus (Brain, 1970). A. robustus is the earliest known hominid which seems to have made use of fire (Brain, 1988),
Australopithecus boisei/ Paranthropus boisei
DATES: 2.1 to 1 million years ago
SPECIMENS: many individuals, mostly cranial and dental specimens
Australopithecus boisei had a tall upper jaw with the largest hominid premolars and molars (some molars are 2 cm wide). The cranial capacity was 530 cc. It was probably as sexually dimorphic in size as the modern gorilla. There were very prominent sagittal and nuchal crests on the skull and the cheeks (zygomatic bones) had a very prominent flare. The upper body was powerful. Some consider A. boisei and A. robustus to be geographic variants of one species. The variations seen in different individuals of A. bosei should serve to caution researchers from identifying every new find as a new species of hominid (Skelton, 1986; Walker, 1986; Suwa, 1997; Carney, 1971; Leakey, 1970; Howell, 1974).
Paranthropus vs. Australopithecus
--P. aethiopicus, P. robustus, and P. boisei (the robust australopithecines) differ from A. anamensis, A. afarensis, and A. africanus (the gracile australopithecines) in a number of traits:
--first deciduous molar distinguishes Paranthropus from all other hominid species
--Paranthropus had smaller canines and incisors but larger premolars and molars, a condition unique among hominids
--in Paranthropus, the floor of the nasal cavity, palate, face, and braincase also differed from gracile australopithecines
--in Paranthropus, there is no trace of a chin or forehead and there are massive chewing muscles
--pattern of dental development
--The robust australopithecines developed a much thicker palate which functioned together with other facial modifications to absorb additional stresses while chewing (Strait, 2007).
In reference to 69 skeletal traits, A. afarensis demonstrates the primitive condition from which the others could be derived in all but 4. Because of this and its older age, A. afarensis is considered to be ancestral to both A. africanus and the Paranthropus species (Benyon, 1988; Bilsborough, 1988; McCOllum, 1999; Smith, 1986; Grine, 1993; Robinson, 1993).
Below are the gracile group and the robust group.