The hominid family originated between 10 and 5 million years ago, with a single species of bipedal ape.
As usually happens with newly established mammalian lineages:
The 1st specie gave rise by stages to a range of descendants, producing a relatively luxuriant evolutionary bush.
Individual branches were pruned away from time to time as species became extinct and new ones were added.
Eventually, the hominid bush was reduced to just Homo sapiens.
No less than 3 perhaps 6 and maybe more hominid species coexisted 2 million years ago in Africa.
Those species can be divided into 2 groups:
So far, only one species has been formally named in this group-Homo habilis.
Many scholars believed others could be identified.
- With relatively large brains and small cheek teeth.
- Large-brained species were member of the genus Homo.
If several species of Homo existed at this time, only one of them could have been ancestral to modern humans, while the rest became extinct.
Labeling of the 2nd group is more contentious. We will call them australopithecines; they all became extinct.
Anatomy and biology of the australopithecines:
- Bipedal apes with modified dentition.
- Lived in more open environmental setting, not the open plains of bushland and wooden Savannah.
- Hominid structure of teeth and jaws appear to have required more grinding that an ape’s diet.
- Male australopithecines were larger in body size. 20-40% taller, 30-40% heavier than females.
- Australopithecines were social animals.
- Foraging strategies of hominids were not dramatically different: australopithecines have been carnivores.
- Australopithecines were principally vegetarian.
- Australopithecines of 2 million years ago occurred in 2 forms:
So far, only one gracile australopithecines has been identified whereas, as many as 4 robust species have been named.
In South Africa, the gracile species is australopithecus africanus and the robust australopithecus robustus.
The robust australopithecine in East Africa is australopithecus boisei.
Naming gracile species in East Africa is more contentious; some apply the name australopithecus africanus to some specimens.
The term gracile and robust implies substantial anatomical differences between the 2 forms.
One small and delicately built.
The other bigger and more massive.
Scholars realize the difference between the 2 forms is mainly in the dental and facial adaptations to chewing.
The robust forms have bigger grinding teeth, more robust jaws and more bulky chewing muscles and muscle attachments.
- Gracile (means slender)
The remainder of the skeleton:The gracile and robust australopithecines were roughly comparable, with the robust having a slightly greater stature.
Brain size, based on small specimens, gives the robust an edge over the gracile. Both are close to 500 cm3.
Most scholars agreed hominids did not leave Africa before about 1 million years ago, when Homo erectus expanded to Eurasia.
- Teeth, jaw and cranial anatomy are one functional complex.
- Difference between the 2 forms of australopithecine is that the robust species have taken this adaptation to an extreme, having enormous, flat molars and relatively small blade-like incisors and canines.
- In all hominid, the tooth row is tucked under the face more than the apes, giving a less projecting facial profile and increasing chewing efficiency.
- Australopithecines tucking under are particularly marked.
- The robusticity of the lower jaw (mandible) that is characteristic of hominids compared with apes is particularly apparent in the robust species, reflecting more powerful chewing action.
- Extra muscle in the robust has 2 anatomical consequences:
This and the strengthening of the central part of the face by pillars of bone, gives the robust australopithecine face a characteristic dished appearance.
The difference in dental apparatus between gracile and robust australopithecines was once interpreted as a result of substantial differences in diet.
Robust was more vegetarian.
Gracile more carnivorous.
The past decade they were implies a vegetarian diet for the australopithecines.
More recent Fredrick Grine and Richard Kay concluded robust consume tougher foods than gracile.
It is consistent with evidence that robust australopithecine’s lived in drier habitats where soft fruits and leaves were more common.
Sillien recently challenged this conclusion. His analysis included the robust species included a significant amount of meat.
- One of the muscle that power the lower jaw-the temporal muscle-is anchored to a raised bony crest that run along the top of the cranium, front to back.
- This so-called sagittal crest also in gorillas is absent in gracile australopithecines.
- The great site of the temporal in robust and a second chewing muscle, the masseter, causes the cheekbones (the zygomatic arch) to be exaggerated and flared forward.
Function and overall sizes:
The australopithecine pelvis of 2 million years ago was like Lucy a million years earlier.
The thighbone is different from Homo pattern.
Head of the femur is smaller than in Homo and attached to a longer, slender neck.
Individual bones indicate although these species were bipedal, they were as adapted to climbing as was Australopithecus afarensis.
There were differences between Lucy’s hands than later australopithecines.
The handbones of australopithecus afarensis were apelike-having curved phalanges, thin tips to the finger and a short thumb.
Recent analysis of robust australopithecine hand bones indicates they were much more humanlike.
>The thumb is longer and more mobile, fingertips were broader.
The robust australopithecines probably possessed sufficient skills to make stone tools.
These are differences of opinion.<
Simple bone tools-digging sticks have been recovered from were australopithecines robustus fossils are known.
The possibility remains they were made by Homo.
The robust and gracile australopithecines were viewed as same animal but built on different scales.
- Post cranial skeletons (neck down) of gracile and robust australopithecines are similar to each other.
- Australopithecus africacus weights 41/30 kilograms.
- Australopithecus robustus, 32/40 kilograms.
- Australopithecus boisei, 49/34 kilograms.
Walker in 1985 discovered the black skull was suprising not only for its great age but also for its unexpected combination of anatomical characteristics.
The face was like the robust. The cranium, particular the top and back were like most primitive hominid Australopithecus afarensis.
Some suggest the Black skull should be recognized by naming it Australopithecus aethiopicus.
Australopithecine fossils have been discovered only in Africa specifically in East and South Africa.
1st discovery was at Taung, in South Africa.
Makapansgaat excavated in the 1950s.
Zinjanthropus discovered in 1959.