Ramapithecus - 1 | Anthropology Optional for UPSC PDF Download

Phylogenetic status, characteristics and geographical distribution

Pre-Pleistocene Fossil Primates
Dryopithecus

• Early fossil finds of Dryopithecus (first definite discovery in 1856) were mainly teeth. Today we have a cranium and many log bones as well. This has not only increased our subject knowledge about Dryopithecus but also has helped to scientifically check earlier conclusions. Dryopithecus is considered to be a common ancestor of both man and modern apes.
• On the basis of earlier evidences it was believed that Dryopithecus survived from middle to the end of the Miocene period.
• Y-5 cusp pattern on his 3rd molar indicates that he was ancestor of both man and modern apes. His other body features are also similar to modern apes.
• His three species i.e. africanus, major and sivalensis must have given rise to three modern great apes of today that is Chimpanzee, Gorilla and Orang.
• Recent evidences however indicates that D. sivalensis showed absolute similarities with Ramapithecus and therefore the two has been clubbed on to a new genus Sivapithecus. His first lower premolar is sectorial that separates him from later hominids.
• In 1948 Mary Leaky found a preserved cranium which was named Proconsul but now it is considered as a member of Dryopithecus africanus.
• In comparison to present day apes, his jaws, teeth and muscles were similar and many features of his skull resemble monkeys.
• Recently walker studied his skull and estimated the weight of D. africanus to be 26 pounds whereas other anthropologists consider it to be slightly heavier i.e. approx. 33 pounds.

Dryopithecus: Important Facts

• Time span : 23m to 8m years ago.
• Arboreal habitat- both rain forests and more open areas.
• Size variable, from gibbon to gorilla.
• Large teeth, interlocking canines, Diastema.
• Y-5 Cusp Pattern.
• Limbs- mixed characteristics of both apes and monkeys.
• Indication of ape simian shelf.
• Not modified for knuckle walking.
• Evolutionary status- possible ancestor of chimpanzee, gorilla and man.
• Geographical distribution - Africa, Asia and some parts of Europe.

Walker and Tifford estimated its cranial capacity to be about 167 c.c. According to this, in proportion to body size the brain size of africanus was more than that of monkeys.
On the basis of presence of frontal sinus, it can be concluded that he was related to man and African apes.
Post-cranial fossils of Dryopithecus found in the last decade show that the many characteristics of his limbs resemble that of modern apes and monkeys. On the basis of the study of these parts it is concluded that africanus was slow walking animal and lived on trees and his limbs were not modified for Brachiation and climbing.

Ramapithecus

Discovery and Distribution of Ramapithecus

• The first discovery of Ramapithecus fossils was made by G.E. Lewis in 1932 in the Siwalik hills regions of India. He assigned one of the fossils, an upper jaw, to a new genus and species he named Ramapithecus brevirostris.
• The generic name simply means Rama's ape' Rama being the mythical prince who is the hero of Indian epic poem. The species name that Lewis chose was more meaningful for it is the Latin word for 'short snouted'.
• Next Ramapithecus fossil find was made by L.S.B. Leakey near Fort Ternan in south western Kenya in 1961. The specimen included parts of both sides of an upper jaw. Leakey gave it the name Kenyapithecus wickeri, which is synonymous with Ramapithecus brevirostris, after his friend Fred Wicker, on whose farm the fossil was found. which is synonymous with Ramapithecus brevirostris.
• The next Ramapithecus specimen was excavated by Von Freyburg, a German geologist, in Greece during World War II.
• The specimen was assigned to another new genus and species: Graecopithecus freyburgi. Freyburg's find was the complete tooth bearing part of lower jaw and at the time of its discovery it contained all the teeth.
• Next to the growing inventory of Ramapithecus fossil was a lower jaw unearthed from a Miocene deposit near Candir, some 40 miles north east of Ankara in Turkey in 1973.
• The specimen was named as Sivapithecus alpani. The species name of the Candir jaw honors the director of the Turkish Geological Survey.

Anatomical Characteristics of Ramapithecus

• Incisors and canine are inserted vertically and not in slight procumbent position as in apes.
• Little or no canine diastema.
• The canines of the Ramapithecus are not projected and they possess narrow faces.
• The dental arcade is rounded.
• The palate of the Ramapithecus is arched as in man.
• Flattened and thick enameled premolars and molars that appear to be adapted for heavy chewing and processing of hard food stuffs.
• Ramapithecus has a canine fossa ( Kenyapithecus).
• The molars possess the Dryopithecus Y-5 cusps pattern.
• Slightly divergent tooth rows. The tooth rows have been identified as parabolic by some and V-shape by some others.
• Reduction of size of third molar as compared to first and second molar.
• The ratio between the sizes of front tooth (incisors and canine) and those of cheek teeth (premolars and molars) is roughly the same which indicates the human position.
• Shelf-like ridges are present inside the lower jaw of Ramapithecus.
• Large inferior torus on mandible.
• Short maxilla that would indicate a placement of the chewing muscles that increase the chewing pressure brought to bear on the food being eaten.

Phylogenetic Position of Ramapithecus

• To understand phylogenetic position of Ramapithecus we have to take back our observations back to Dryopithecus first.
• The Dryopithecinae primates made their appearance in Europe, Asia and Africa during Miocene and Pliocene epochs. Their size ranges from gibbon like body form to the body structure of modern gorilla. Most of the remains which belong to Dryopithecinae are jaws and teeth.
• Therefore, the characters distinguishing Dryopithecinae from Hominidae are restricted to dentition. Gregory and Hellman, after conducting their dental characters, came to the conclusion that Dryopithecinae were the common ancestor of the anthropoid apes and man.
• In the year 1856, Lartet discovered from Miocene deposits, in south France, a lower jaw bone which was assigned to the genus Dryopithecus. The place of Dryopithecus in the evolutionary stem has been found out by studying the peculiar dentition - "the Dryopithecus pattern" which is characterized by five cusped lower molars. After careful study of the different species of Dryopithecus, it has been decided by many scientists that Dryopithecus fontani, Dryopithecus rheuanus and Dryopithecus darwini, were probably the ancestors of gorilla, chimpanzee and humanoid forms respectively.
• Fossils found in Europe and Asia since 1970 suggests that between 10 and 15 million years ago Dryopithecus gave rise to at least three other genera. Two of them Sivapithecus and Gigantopithecus were primates with a face as large as that of a modern chimpanzee or gorilla.
• The third genus, Ramapithecus had a small face. Of the three genera, Ramapithecus clearly shows the greatest similarity to later hominids.
• Ramapithecus has been the center of a great deal of debate concerning its possible hominid status. Pilbeam has proposed alternatively that a number of the middle and late Miocene genera to be classified together in Ramapithecines, in an attempt to both draw attention to morphological feature shared by the group which differentiate it from others and to focus discussion on adaptation and biology rather than phylogeny.
• The most widely distributed Ramapithecids genera are Ramapithecus and Sivapithecus. The taxonomy of this group is in a rather confused state, which newer materials from Pakistan will hopefully help clarify. Isolated teeth of Ramapithecus and Sivapithecus are very difficult to distinguish except on the basis of size; Ramapithecus teeth are smaller.
• What seems more probable is that both Ramapithecus and Sivapithecus are quite dimorphic dentally and that the size ranges of the two forms overlap, perhaps substantially Ramapithecus may show less canine dimorphism than Sivapithecus though more than the Pliocene hominid Australopithecus afarensis.
• A handful of Ramapithecids postcranial remains have been recovered during recent work in Pakistan, attributable to Ramapithecus, Sivapithecus and to a third form Gigantopithecus bilaspurensis. Though these remains are unfortunately fragmentary, they suggest that all the Ramapithecids were smaller than previously expected: Ramapithecus ~20kg, Sivapithecus - 40kg and Gigantopithecus - 70kg.
• Therefore, the fossil finds of Ramapithecus are regarded as the most important addition to the knowledge of relating to human evolution. Credit goes to G.E. Lewis to discover in the year 1934, the fossilized remain of Ramapithecus in the Siwalik hills of India. Dr. Simons has attributed Ramapithecus a very significant position in the line of human evolution.
• Ramapithecus raised many important points which are highly effective in search of human ancestral pattern. On examining the nature and extent of teeth, some scholars described Ramapithecus as a weapon wielding terrestrial biped. Ramapithecus, according to the competent anthropologists, represents the oldest known ancestors of the human line.
• The scientists like Simon, Pilbeam and Tattersall are the proponent of Ramapithecus as a human ancestor. The materials so far excavated in relation to Ramapithecus suggest a line between Dryopithecus group belonging to early Miocene and later real hominids. In a review based study made by Conroy and Pilbeam a plausible interpretation of the Ramapithecus has been given as the late Cenozoic ancestor of Australopithecus.
• In consequence of recent findings and interpretations Ramapithecus has been widely considered as a candidate for the first hominid. It splits up from the ape line 14 million years ago and marked the remarkable beginning of hominid line.
• The main reason for giving Ramapithecus a true hominid status is the similarity of its teeth with that of the later hominids. In discussing the status of Ramapithecus, Swartz and Jordan have remarked that when a creature is called hominid, it doesn't mean that it is a modern man, but this term is used for clearly human like forms. Ramapithecus was such a creature as understood by many authorities.

Controversy Regarding the Taxonomy of Ramapithecus

• The current view of the Ramapithecus depends upon little more than two dozen fragments, mainly of teeth and parts of jaws that have been discovered since the first find reported on by G. Edward Lewis in 1934.
• The initial discovery prompted Lewis to recognize a new form that he called Ramapithecus. This was followed in later years by a handful of fossils that were each recognized as new forms and they were given a series of separate names (Kenyapithecus, Graecopithecus, Rudapithecus, Sivapithecus) based upon the geographical localities at which they were found.
• But in 1965 Simons and Pilbeam reviewed the entire series and held the view that all these forms really comprised two species groups. One of these, Sivapithecus, was basically ape like and it was therefore put forward as an ape ancestor; the other, Rudapithecus, seemed to possess a number of hominid- like features was therefore entered as an early hominid ancestor. This view was still extent in 1977 but a series of more recent studies has cast doubt upon it.
• Thus Andrews and Cronin (1982) and Lipson and Pilbeam (1982) have all suggested that the non-Chinese Ramapithecus are really only a single species or species group, that the two forms ( Sivapithecus and Ramapithecus) are really only the males and females of sexually dimorphic species group.
• One of the reasons for putting forward this new idea is an attempt to make these data conform to those suggested by the concept of molecular clock.
• The molecular clock, assessing the time from common ancestry of two species using the notion that molecular evolution has taken place in a linear manner, suggests that human and African apes had a common ancestor at five million years ago or even closer to the present time.
• If these were true, it would be logically impossible for there to have existed prior ancestors of humans (Ramapithecines date from 8 to 14 million years ago) that were more like humans than apes. The new views of the fossils have therefore concentrated on the ape like features of Ramapithecines and of these, big sexual dimorphism is one of the most powerful, being found in every great ape known, but not markedly present in any species of the genus Homo so far identified. But the later evidences regarding Ramapithecus strongly suggests that two species are present there in Yunnan. One of these, the larger creature, (Sivapithecus), with larger dental sexual dimorphism, larger canine dimorphism, larger canine heights and areas, more herbivorous dentition, considerably smaller number of males than females has attributes that are matched by many of the apes.
• In contrast, the smaller creature, (Ramapithecus) possess smaller dental sexual dimorphism, smaller canine dimorphism, smaller canine heights and areas, more omnivorous dentition and equal numbers of males and females, and thus has attributed that would not deny it a place in a radiation of prehumen form.

Gigantopithecus

• History of Gigantopithecus is as interesting as its fossils and its evolutionary status. For centuries China's pharmacies used bones of giant animals to make medicines.
• In 1935 Koenigswald, in one of such medical stores found such remains and named them Gigantopithecus. Paleontologists/evolutionary biologists differ regarding its evolutionary status. Some consider it as giant ape, others as snowman and ancestor of Yeti of Himalayas. At present many fossils of Gigantopithecus - many mandibles (broken to almost complete) and more than a thousand teeth have been found from China, India and Vietnam.
• On the basis of remains according to Simons and others, Gigantopithecus was about 9 feet tall and weighed around 600 pounds. Though this conclusion has possibly some boosting but still size of this giant like genus can be approximated. Possibly Gigantopithecus was 6-9 feet tall and weighed 450-600 pounds. His Indian species bilaspurensis (discovered by late prof. S.R.K. Chopra of Punjab University) has been dated from 9 million to 5 million years ago whereas Chinese and Vietnamese species blacki existed in middle Pleistocene period.
• Gigantopithecus had large sized teeth and solid/hard enamel. Jolly, by his seed eater hypothesis has tried to prove that structure of teeth is based on their dietary habits & Gigantopithecus food should be dominated by hard nuts and other solid fruits.
• Many anthropologists don't agree with Jolly's view, but one thing is sure, that this middle Pleistocene quadruped cannot be the ancestor of the man. Probably around 5 lakh years ago it became extinct.

Gigantopithecus : Main Features

• Time span : 9 million to about 0.5 million years ago
• Large sized
• Large sized teeth, interlocking canines, diastema
• Dental arcade U shaped
• Species - blacki, bilaspurensis
• Geographical distribution - India, Vietnam and China
• Evolutionary status - not an ancestor of man, became extinct.

Evolutionary Status of Miocene Hominoids

• Evolutionary status of Miocene Hominoids and Hominoids before Miocene is not clear even today.
• Dryopithecus is the first evidence of ancestry of modern apes. This ape resembled modern apes in dentition but regarding rest of the physical features and locomotion it can be compared more with monkeys.
• The first clear evidence of ancestry og modern apes is clear through Aegyptopithecus but situation after this is not clear. There are many variations. Types on fossils of Dryopithecus. Because of this it is difficult to know regarding which of the Dryopithecinae with certain definite characters evolved towards direction of human evolution.
• Status of Sivapithecus as ancestor of orang is clear. Gigantopithecus was too specialized aan ape and has no place in the ancestry of man.
• Status of Gigantopithecus vis a vis other hominoids of the period is not clear. On the basis of biochemical studies of blood proteins of Primates in recent 2-3 decades, it has been concluded that evolutionary line of gibbon separated from human line about 30 million ago, whereas till about 8-6 million years ago the man, chimpanzee and gorilla had a common ancestry.
• On the basis of DNA studies etc. in last decades it can be said that direction of evolution of man and apes separated between 8 million and 6 million years ago. Unfortunately, hominid fossils of late Miocene period have not been found yet. So it is difficult to conclude who was the ancestor of later definite hominids.

Australopithecine

• Most of all the Hominid fossils of Africa comparing with the African apes have large brain, relatively reduced chewing or molar teeth and limb bones that are, except in points of details, like those of modern Homo sapiens. However, there are at least four and perhaps five species of hominid that lack expanded brain, the reduced molar teeth and the skeletal features of Homo. They antedate or overlap with earliest representatives of Homo and are known collectively as the Australopithecines. Hence, we should understand importance of this hominid fossil (Australopithecines) in tracing the evolutionary line of present day human being.
• Raymond Dart first discovered in 1924 at Taung in South Africa. The finding includes part of mandible, facial skeleton and endocranial parts of a child. Dart named the skull as Australopithecus africanus.
• The meaning of austral is south and pithecus means ape. At first discoverer of the various
• Australopithecine fossils named four to five genera, but now the consensus of scientific opinion recognizes one genus Australopithecus and two species, a slenderly built and smaller form, Australopithecus africanus (Gracile form) and larger roughly built Australopithecus robustus originally called Paranthropus.

The following are the fossils along with the sites found in South Africa and East Africa:

Fossils from East Africa:

• In East Africa, Louis Leakey made the first discovery of a hominid fossil from Bed I of Olduvai Gorge in 1959. The first discovery named Zinjanthropus boisei, now known as Australopithecus boisei is considered to be a super robust Australopithecus. Another important discovery was announced in 1964 from Olduvai Gorge and named Homo habilis.
• Other important sites in East Africa are the Omo river valley of Southern Ethiopia where both robust and gracile forms have been found. Similarly both robust and gracile forms were discovered from Hadar in Eastern Ethiopia and Turkana region of Northern Kenya. Turkana region have been studied by Richard Leakey since 1969 and over 120 hominid fossils have been discovered so far.
  
• According to Loring Brace Homo habilis is the member of Australopithecus africanus but for John Robinson it is not.
  

T. Robinson's Dietary hypothesis

• Going by the dental fossil evidence found in East and South Africa, there are two adaptive groups which can be extended to families. These two adaptive groups are gracile and robust. They are quite distinct in morphological, ecological relationship and behavior. Gracile group is Australopithecus whereas Robust group is Paranthropus.
• He sees a dichotomy in cranio - dental form separating these two Australopithecine groups. Robust group has the large post canine teeth crowns and its thick canine has larger occlusal surface, well developed roots and relatively flat occlusal surface (greater enamel has been damaged). Crownding and size reduction of the front teeth, point to a primary dietary function of crushing and grinding.
• The massiveness of the entire masticatory apparatus including the musculature and the wear of the teeth indicate a diet of rough material which needed much chewing, hence robust was herbivorous or vegetarian. Gracile forms show none of these features, rather their post canine teeth are smaller and anterior teeth would be substantial until tool making had reached a fairly advanced level.

Age and Antiquity of place

• The Taung cave once considered to be very ancient actually seems to be the most recent one, less than 0.9 million years ago. The specimen may represent one of the last surviving members of the genus Australopithecus. The absence of suitable materials precludes the use of Radioactive dating in South Africa.
• In Olduvai Gorge pre historic volcanic activities provided abandoned material for the application of Radioactive dating techniques. The Australopithecus remains are dated by potassium argon method and placed between 1.9 and 1.1 million years. Sites of the Omo valley has been dated between 2.75 and 2.5 million years, the Hadar material is dated between 3 to 3.5 million years and the Lake Turkana is around 3 to 1 million years. However gracile Australopithecus from other sites of East Africa such as Middle Awash and Lothagam extend the age range of this group of fossils to 4 million years and beyond perhaps to 5 million years.

Characteristics of Australopithecus africanus

• The supraorbital height index shows that the relative high exceeds range of variation in anthropoid ape and actually comes within the range of hominid skull.
• The occipital torus and the inion occupy a low level as in hominid skulls. In adult apes this occipital torus forms a crest high up the occipital aspects of the skull, thus extending considerably the nuchal area for attachment of neck muscles. In Australopithecus the nuchal area is restricted as in homo.
• In Australopithecus the occipital condyles are forward in position relative to the total length of the skull and the auditory aperture. The occipital condyles of pongidae are behind the midpoint of the cranial length and also behind the auditory apertures.
• In all the Australopithecus skulls in which mastoid region are sufficiently well preserved, there is a well marked pyramidal process typical of hominid form.
• The brow ridges are poorly developed compared to that of the apes.
• The facial skeleton is however, large in relation to the brain case.
• The cranial bones of Australopithecus robustus are thicker than the Australopithecus africanus and the sagittal crest is developed. The zygomatic arches are expanded and flared.
• The jaws are also relatively large but no simian shelf.

Cranial capacity

• In cranial capacity, the range of variation is quite considerable. The skull of Australopithecus afarensis and Australopithecus africanus ranges from 400 to 500 cc and Australopithecus robustus ranges from 410 to 530 cc.
• Thus the general endocranial size of Australopithecus does not differ markedly from those of gorilla and chimpanzee. However in relation to the body size Australopithecus shows larger brain capacity proportion than the apes.

Dentitions

• Australopithecus dentition is essentially of hominid type. In all the adult specimens the dental arcades is evenly curved as in Homo sapiens with no diastimic intervals. The canine is reduced in size and spatulate in forms. Canines and incisors are almost in the same level.
• The anterior upper premolars have two roots, the anterior lower premolars are non-sectorial and have one root (sectorial and two roots in apes). There is good evidence for the study of the immature specimens that the order of eruption of permanent teeth agrees with the Hominidae. In Homo sapiens the canine erupts before the second molar. This is reverse in the apes.

Pelvis

• The anterior inferior iliac spine is strongly developed.
• The ilium is much relatively broader than in the apes. The broad ilium lengthens the attachment of the gluteus muscles that makes important in maintaining balance of the trunk on the legs. The gluteus maximus becomes a fourfold extension muscle which is needed for erect bipedal locomotion. Whereas in monkeys and apes the gluteus maximus is an abductor muscle.
• The posterior extremity of the iliac crest is extended backward and downward in the sacral area.
• The angle of the sciatic notch (depression) is more acute in the pelvis of man and Australopithecus than that of the great apes. This is resulted in part due to development of prominent ischial spine.
• Ischial tuberosity is relatively high in man and Australopithecus and closer to acetabulum than that of the apes.
• Sacrum is shifted upward and closer to the acetabulum forming more or less a basin or funnel shaped pelvis which indicates the character of erect posture.

In all these characters the pelvic bone of Australopithecus contrasts with the apes and shows pattern for erect bipedalism. However the pelvis of Australopithecus is not fully developed like that of the modern man. Ischail tuberosity is not as quite closely approximated to the acetabulum as it is in Homo sapiens. The anterior superior spine extends further forward.

Limb bones

• In addition to the pelvis, the Australopithecus finds include many fossilized bones of leg, hand and feet. One group from Olduvai Gorge includes twelve of the major bones of a single foot and so perfectly preserved that the details of the foot are readily reconstructable.
• The foot of Australopithecus is much smaller than a human foot. But the metatarsals are hominid and the big toe points forward and not splayed out. The carpe bones and phalanges found in Olduvai Gorge also show hominid characters.
• Two specimens of the lower part of femur found at Stenfontein have been described. They show a combination of features such as the obliquity of the shaft, the alignment of the condyles, the forward prolongation of the intercondyler notches which confirm to the hominid femur.
• Upper extremity of one specimen, however shows certain Pongidae features, such as relatively small size of the articular head. A tibia and fibula found in Olduvai have relatively straight shafts conforming to hominid character.

Difference between Australopithecus africanus and Australopithecus robustus:

Phylogenetic Position

• Currently there are three main phylogenetic trees each with its own cadre of proponents. The problem of whether Australopithecus africanus represent early grade in homo lineage or a small brain hominid arising as a separate product of Ramapithecus radiation is yet to resolve.
• At the same time we also do not know how the two dimorphic forms i.e. gracile and robust Australopithecines are to be classed phylogenetically. Whether they reflect polytypic nature of single taxon or systematic enough to conceive as two taxa is still a question.
• There is no generally accepted phylogenetic tree for human evolution. There are several proposal branching perhaps the major distinction between them is whether homo is perceived as late arrival or as early arrival.
• In some phylogenetic, robust is consider to be on the same evolutionary line with Australopithecines and some consider robustus to be separate from the earlier gracile species in which Paranthropus robustus/promethecus is equivalent to Australopithecus robustus and Homo africanus equivalent to Australopithecus africanus.
• This Pliocene and Pleistocene fossils have shown both hominid and ape like features. However the hominid features are overwhelming. The presence of ape like features can be accounted for by way of common inheritance from a hominoid or Pongidae ancestor.
• The hominid characters however can be accounted for by way of independent acquisition demonstrating and highlighting the fact that these fossils were on a direct line of human evolution and not Pongidae line.
• There are many schools of thought prevailing with reference to the course of evolution these australopithecine have taken. The most important of these are discussed below.
• According to Donald C Johnson and Timothy white the east African fossils Australopithecus afarensis split into two branches and australopithecine line represented by A. africanus P. robustus, P. boisei and a hominid line represented by homo habilis, homo erectus and homo sapiens.
• This split was supposed to have happened 3 million years ago. The australopithecine line progressively became robust. This pattern generally called two branched theory had its variants also. For some it is A. africanus which is the common link between the australopithecine line and homoline. For still others these two branch represent parallel evolution.
• According to this two branch theory A. afarensis gave rise to A. africanus 3 million years ago of the same height living up to two million years ago.
• Next arrived A. robustus which showed marked increased in the robustness of the body face , jaws and teeth and it had lined up to 2.3 to 1.8 million years ago. Finally the last and the most robust form A. boisei lived in east Africa from roughly 1.8 to 1 million years ago.
• The second branch of this model the homo line also shows a shortening of the face but there is marked decrease in the size of both cheek teeth and the front teeth. There is a massive increase in the size of brain also. This line begins with ta transition form A. afarensis to H. habilis the first hominid who made and used tools and lived in Africa from 2-1.5 million years ago. They had human like teeth and larger brain than australopithecine (750 cc). however we can conclude that hominid evolution may not have been so simple, isolated and clear cut in tis operations.
• Instead there is a possibility that three or more hominid lineages may have been evolving and interacting with each other.
• This two branch theory was widely accepted till the discovery of the new type of hominid skull - Australopithecus aethiopithecus in northern Kenya inn 1985 by Alan Walker. This skull is considered to be the most robust form ever discovered. It had massive teeth and ape like brain.
• The dating of the this specimen indicates that the family of a. boisei didn't evolve in the last leg of the australopithecine evolution as indicated by earlier theory but it originated directly from a. afarensis. Thus the revised theory holds a three line evolutionary sequence. One to boisei line second to Homo and third to africanus, robustus line having A. afarensis as the common ancestor.
• The discovery of the youngest australopithecine - A. ramidus has added a new dimension to the three branch theory. It holds that A. afarensis is the common ancestor of Homo, P. boisei and P. robustus but it itself evolved from A. ramidus. With overspecialization of diet, competition for food with H. habilis and the latter's predation along with H.erectus led to the extinction of australopithecine group.

Why are the genera Australopithecus divided into two species?

• At first, several discoverers of the various Australopithecus fossils named four to five different genera, but now the consensus of scientific opinion recognizes one genus Australopithecus and two species, one gracile form represented by Australopithecus africanus and other robust form represented by Australopithecus robustus, originally called Paranthropus. This division is made on the basis of their morphological feature.
• The gracile form are slenderly built and smaller; gracile form have probably relatively long arm, probably less sexual dimorphism, high forehead, shorter face, brow ridges less prominent. The incisors are also small with no gap between upper incisor and canines and have big molars; cranial capacity ranges from 410-530 cc.
• The robust form are large and roughly built. They have relatively long arm with moderate sexual dimorphisms, crest on top of skull, flattish face. The robustus have thick jaws, small incisors and canine, very large molars; the premolar is also large like molars. The cranial capacity ranges from 410- 530 cc.

What is the position of Australopithecus in the line of human evolution?

• Different scholars have given different opinion about the position of Australopithecus in the line of human evolution. According to Johanson and White Australopithecus afarensis is regarded as the common ancestor of Australopithecine and Homo.
• Australopithecus afarensis rise to Australopithecus africanus and to Homo in one hand and directly to Australopithecus robustus in the other hand. Here Australopithecus africanus act as a transition form from Australopithecine to Homo.
• According to L.S.B. Leakey, the common ancestor of both homo lineage and Australopithecine divided quite early. He considers Australopithecus afarensis as not the common ancestor. The homo lineage starts separately after 3 million years and Australopithecus a little bit early but also only 3 million years.

What is T. Robinson Dietary hypothesis?

• Going by the dental fossil evidence found in East and South Africa, there are two adaptive groups which can be extended to families. These two adaptive groups are gracile and robust. They are quite distinct in morphological, ecological relationship and behavior.
• T. Robinson sees a dichotonomy in cranio-dental form separating these two Australopithecines groups. Robust group has the large post canine teeth crowns, thick enamel, larger occlusal surface, well developed root and relatively flat occlusal surface (greater enamel has been damage).
• Crowning and size reduction of the front teeth points to a primary dietary function of crushing and grinding. The massiveness of the entire mastigatory apparatus including the musculature and the wear of the teeth indicate use of a diet of rough material which needed much chewing.
• Hence robust was herbivorous or vegetarian. Gracile form shows none of these features rather their post canine teeth are smaller and anterior teeth larger. The needs for these in meat eating would be substantial until tool making had reached a fairly advanced level.