Plio-pleistocene hominids in south and east africa-Australopithecines.

Pylogentic status-characteristics-geographical distribution.

Australopithecine one divides them in two types: Australopithecus and Paranthropus.the former including gracile forms and latter robusts forms.

Multiple remains of the members of the australopithecine were discovered from different parts are given below:

Southafrica: Australopithecus africanus, pleisanthropus transvaalensis, paranthropus robustus, australopithecus prometheus, paranthropus crassidens,teleanthropus capensis.

East africa: zinjanthropus boisei, Homo habilus, Australopithecus.

Australopithecus africanus: (Taungs ape)

complete skull found in 1924 at Bechuanaland south africa.the skull contain 20 milk teeth and 4 permanent first molars.the size of the cranium and facial portion closely resembles that of the chimp.the head is dolicocephalic.the face is concave as inthe orang.the premaxilla is well marked as in the apes.the flat nasal bones resembles that of the chimp.a diastema is present in the upper jaw between the lateral incisor and the canine.cranialcapacity was 520cc.

How it differed from the present apes?

The face is small,the nasal aperture is high,the nasal bones are short.broad and separated by internasal suture;in geneal appearance the face is more in harmony with the head.

Again AUSTRALOPITHECUS approaches man in the character of the enlarged cranium;highly arched forehead;position of the orbits;downward face;position of nucal plane.faint supraorbital ridges;relatively nataroirly placed foramen magnum.

The jaw is massive.in some characters it resembles that of the apes.the molar teeth are very large but quite humanoid.

Plesianthropus transvaalensis(the sterkfontein man-ape):

in 1936 atthe cave of sterkfontein in transvaal.complete skull without jaw,some teeth and skull fragments.the cranial capacity is 600cc.the face is concave in profile.nasal bonesare long.superorbital ridges are moderately developed.premaxillary suture is visible.a diastema in between the lateral incisor and canine is present.alveolar prognatheism(Prognathism is the positional relationship of the mandible or maxilla to the skeletal base where either of the jaws protrudes beyond a predetermined imaginary line in the coronal plane of the skull.) is highly marked.molars were larger than that of chimp and man;canine is relatevily small.

Paranthropus robustus.

It was represented by apart of skull,part of somelongbones like humerus and ulna.some carpel and tarsalbones.cranial capacity 600cc,the cheek bones are projecting forward.preamxilla is marked off from maxilla.diastema(the gap between two teeth) is present,prognathism(when mandible protrudes out more than normal.) is noticed.

Australopithecus Prometheus.

Central transvaal.a fragment of a calvarium consisting of major portion of the occipital bone and the posterior part of two parietal bones wasdiscovered.the boneswere very thick,the occipatal tarus(back bulging of head) was moderately developed. a complete mandible was found later year.the jaw was chinless and the simian shelf was absent(The simian shelf is a bony thickening on the front of the ape mandible. Its function is to reinforce the jaw, though it also has the effect of considerably reducing the movement of the tongue by restricting the area available for muscles.).the teeth resembled closely the those of heidelberg men and sinanthropus.

Paranthropus crassidens:

s watkrans.many skulls,teeths,right half of a pelvis. the skull is provided with a sagittal crest (ridge of bone on the skull.)simialr tothat in male gorilla.supraorbital ridges are projecting with a prominent supraorbital torus.upper jaw id prognathous(having a projecting lower jaw or chin.).there is no premaxillary diastema.theincisor and canine are typically human in size and form.the premolars and molars are larger than modern man.the right half of the pelvis is typically human in form excepting the ischium, which resembles that of an ape.

Telanthropus capensis.

Swartkrans.a lower jaw is discovered.the jaw is almost complte except the left condyle and right condyle.the ramus of the jaw id broad andshort.the simian shelf(the inner musles that supports teeth.) is absent.the mylohyoid groove extends up the mandibular foramen,as found in human mandible.mandible resemble the hiedelberg jaw.

Zinjanthropus boisei:

Earliest know man.could make tools.communicate simple ideas in sound.at his stage man was still a food gatherer and not a hunter of large animals.Olduvai george-Tanganyika territory.complete skull without mandible.larger part of tibia.600,000 years ago.upper part of lower plsistocene.cranialcapacity 600cc.thepostorbital constriction is marked thus making the temporal fossaie large.the saggital crest is best developed.the supraorbital toruss is massive.the interorbital region is of enormous size.the face islong and broad.the facial and zygomatic portions of the maxilla are large.the nasal bones are long and narrow.

The dental series isregelar without any premaxillary diastema.the canine are notlarger than the those of the contemporary man.the premolars and molars are however very large.

The mastoid process is well developed.the nuchal crest though strongly developed is hominid in its form.the foramen magnum is situated more anteriorly than it is in the skull of contemporary man.this suggests thatZijanthropus habitually walked erectly.stature isnot estimated than 4 feet 9 inches.

Homo habilis:

Olduvai george.parts of skull,upper jaw and lower jaw.

Zinjanthropus and homohabilis seemto live during the same time.Hh however represents a more advanced type.Homo habilis represents a hominid stage of evolution between anthropithecus and homo erectus, and therefoere they want to establish a new genus for homo habilis.in respect of cranial vault,nuchal region,dentition homo habilis resembles homo sapiens.however to many homo habilis is a variety of australopithecine and may be regarded as a relatively progressive australopithecus.

All the above has been seen either as a austrlopithecus or paranthropus.

General features of Australopithecus and paranthropus.

Skull and brain:

1). brain size,ape-sized and ranged between 400 to 530 but if compared with relative body size it is more than chimpanzee and gorilla.it is smaller than human average but more than that of miocene apes hence signifies an increase in brain size.

2). increase in brain involved expansion of cerebral cortex, especially parietal and association areas.in humans these areas are related to language production suggesting that australopithecine has developed some form of symbolic communication system based on sound.the increase in cerebellum relative to rest of movements during locomotion and manipulation by hands.

3). receding fore-head.

4). sagittal crest reduced in graciles but pronounced in robust.

5).superorbital ridge reduced or absent in graciles but pronounced in robusts.development of such crest and ridges indicate developed masticatory muscles.

6). face concave resulting fromflat nasal bones and prognatheism

7).Foraman magnum located downward as in man indicating erect posture of australopiths.

Dental arcade:

Graciles were omnivores and robusts were vegetarians.many vegetarians have silica hence molars of robusts show greater wearing pattern than gracile.

The dental arcade is mainly man like with some pongid features suggesting adaptation to mainly vegetarian diet.it showed:

1). mandibles are massive and chinless like pongids but parabolic and without simian shelf like humans.

2).incisors are small and canines are only slightly projecting,slowing they were largely vegetarian.

3).premolars are large but bicuspid like modernman.

4_molars are also large but develop in series.inmodern man it also develop in a series .

Limb bones and locomotion:

Australopithecus in all probability bipedal which is supported by:

1).presence of lumber curve in the backbone

2). short and brcad ilium(of pelvis)

3). torsian angle of femur and presence of linea aspera on it for attachment of muscle.

4).straightening of knees.

5)weight bearing structure of ankle bones

6) well developed arches in foot

7)fore limbs without any signs of weight bearing activity.

Evolutionary Discussions:

Australopithecus posseses a small brain case and masssive projecting jaw and a few other minor simian features but it is characterized by overwhelming hominid features sauch as details of skull construction ,dental arcade limb bones for erect posture and bipedal locomotion and manipulation of tools.simiasn features canbe accounted for by way of common inheritance from a hominoid ancestor that also gave rise by divergent evolution to the modern anthropoid apes.on the other hand hominid characters are characters of its independent acquisition demonstrating that australopithecines were representative of the hominid and not the pongid lines of evolution.

A.afarensis sems to be the branching point of gracile autralopiths and paranthropus.the branching was supposed to have occured 3mya in to thes two bipedal hominid lines.

The paranthropus line showed a progressive increase in robustness;largerbodies a shortening of theface but with incresingly massive jaws and facial structures,incresingly longer and flatter molars and premolars with corresponding decrease in size of canines and incisors and some increase in brain size.

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