Paper No. : 01 Physical/ Biological Module : 15 Development Team Principal Investigator Prof. Anup Kumar Kapoor Department of, University of Delhi Paper Coordinator Prof. Subho Roy Department of,university of Calcutta Content Writer Prof. Subho Roy Department Of, University of Calcutta Content Reviewer Prof. Barun Mukhopadhyay Indian Statistical Institute, Kolkata 1 Physical/Biological
Description Of Module Subject Name Paper Name 01 Physical/Biological Module Name/Title Module Id 15 2 Physical/Biological
Contents of this unit Introduction The Fossil types of Sahelanthropus tchadensis Orrorion tugenensis Ardipithecus ramidus afarensis Kenyanthropus platyops africanus garhi aethiopicus/paranthropus aethiopicus robustus boisei Phylogenetic Position Summary Learning Objectives Context of studying Human Evolution Who are? What are their Spatial and Temporal Distributions? What are the Varieties of? What is the Sequence of Appearance of all these Varieties? 3 Physical/Biological
Introduction All of us are quite aware about Charles Darwin and his works. After the publication of two of his famous books origin of species by means of natural selection or the preservation of favoured races in the struggle for life (1859) and descent of man, and selection in relation to sex (1871), the concept of biological evolution in general and human evolution in particular took a new turn. The later publication specifically speaks about how human beings evolved from lower order animals. From that time onwards scholars across the world were in search of the fossil of ancestors of present day human who were apes or ape-like. A number of pre-hominid fossils like, parapithecus, aegyptopithecus, dryopithecus, ramapithecus, shivapithecus, and hominid fossils like australopithecus and homo were discovered and/or restudied in this new light. The scholars also made attempt to analyse and interpret those in order to understand the evolution of human from its ape ancestry. But, no consensus has yet been formed about the sequence of human evolution because of the gaps in the fossil records. Further, the interpretation of hominid phylogeny keeps on changing with the discovery of new fossils and development of new techniques of analysis of human remains. Despite contested views, at the moment, we have an outline of the course of human evolution. The trajectory of hominid development is not straight, i.e. one species or genus subsequently gave rise to the next developed form. There were times when several species of humans and other hominids cohabited in this world. In course of evolution, a number of varieties of hominid species became extinct without evolving into a new form, while others evolved into developed form. Thus, the phylogenetic branching appears like a tree with many branches. The word australopithecus means southern apes. The fossils of this genus have been found only from different sites of south africa like Sterkfontein, Taung, Kromdraai and from east Africa like Olduvai, Laetoli and lake Turkana. appeared in this world around 4 my or might be even before, has a spectrum of varieties, all of which are extinct. This group of hominids used to live in this world before pleistocene. The members of this group were biped with reduced teeth size, especially the canine. These two characteristic features place the group in hominid category. It is believed that one of the species of the genus australopithecus evolved into homo. 4 Physical/Biological
There have been some recent discoveries of fossils from Africa (like sahelanthropus, orrorin and ardipithecus), that claim to be of the family hominidae. These varieties arrived in the world before the appearance of typical variants of australopithecus, i.e. shortly after the divergence from our common ancestor with chimpanzee. They were biped, but retain a number of ape like characteristic features. Probably from one of these new genera, australopithecus evolved. Now we will discuss on the fossil hominids discovered so far in the chronological order of appearance in the record (note that this ordering is not meant to represent an evolutionary sequence), except that the robust australopithecines are kept together. Sahelanthropus tchadensis a) facial view (b) lateral view, (c) dorsal view, (d) basal view (Source: Brunet et al. 2002) This species was discovered in 2001 from Chad in central Africa (brunet et al. 2002). The word sahel is derived from the name of the region of Africa bordering the south of Sahara, and the fossil was unearthed from this place. It is the oldest known hominid dated between 6 and 7 million years. The discovery of this fossil remains made the world to belief that hominid of Miocene period is not restricted in east and south Africa. However, Wolpoff et al. (2002) challenged the hominid status of this fossil. This species is known from a nearly complete cranium (of a male) and a number of fragmentary lower jaws and teeth. The brain size similar to that of an ape, but with reduced subnasal prognathism is popularly known as toumai (hope of life). This individual has many primitive ape like features, such as the small brain size, along with some characteristic of later hominids such as the position of foramen magnum and small canine teeth. This mixture, along with the fact that it comes 5 Physical/Biological
from around the time when the hominids are thought to have diverged from chimpanzees, suggests its closeness to the common ancestor of humans and chimpanzees. Orrorin tugenensis This species was named in July 2001 from fossils discovered in western Kenya (Senut et al. 2001), dated 6 my. The fossils include fragmentary arm and thigh bones, lower jaws, and teeth. The limb bones are about the size of a female chimpanzee. Its finders have claimed that orrorin was a human ancestor adapted to both bipedality and tree climbing, and that the australopithecines are an extinct offshoot. A later study (Galik et al. 2004) has found further evidence of bipedality in the fossil femur. Ardipithecus ramidus (Source: Senut et al. 2004) This species was discovered by a team led by Tim white, Berhane Asfaw and Gen Suwa in 1994 (White et al. 1994). Most remains are skull fragments. It has been dated 4.4 to 5.8 million years. Evidence suggests that they were possibly bipedal, and that some individuals were about 122 cm (4'0") tall. The teeth are intermediate between those of earlier apes and A. afarensis (the earliest form of australopithecus), but one baby tooth is very primitive which resembles a chimpanzee tooth more than 6 Physical/Biological
any other known hominid tooth (more recently, a number of fragmentary fossils discovered between 1997 and 2001, and dating from 5.2 to 5.8 million years, have been assigned first to a new subspecies, ardipithecus ramidus kadabba (Haile-selassie 2001), and then later as a new species, ardipithecus kadabba (Haile-selassie et al. 2004). (One of these fossils is a toe bone belonging to a bipedal creature, but is a few hundred thousand years younger than the rest of the fossils and so its identification with kadabba is not as firm as the other fossils. anamensis (Source: American Association for the Advancement of Science) In 1965, Bryan Patterson and other scholars from Harvard University discovered a single arm bone (knm-kp 271) of an early human at the site of Kanapoi in northern Kenya. They could not conclude anything from this discovery since there was no supportive evidence. Later, in the year 1994, Meave Leakey discovered some more fossil remains from the same site of lake Turkana (Leakey 1995). The material consists of skull fragments, teeth and long bones. The word anam means lake in the Turkana language. Anamensis existed between 4.2 and 3.9 million years ago, and has a mixture of primitive features in the skull, and advanced features in the body. The teeth and jaws are very similar to those of older fossil apes. A partial tibia (the larger of the two lower leg bones) shows strong evidence of bipedality, and a humerus (the upper arm bone) which is extremely humanlike (note that although the skull and skeletal bones are thought to be from the same species, this is not confirmed). 7 Physical/Biological
Fossil remains of australopithecus anamensis (knm-kp 271) Source:http://humanorigins.si.edu/evidence/humanfossils/species/australopithecusanamensis, retrieved on march 13, 2015) afarensis A number of fossils of this type have been discovered at different times (between 1975-1991) by Johanson, Johanson and Gray, Abell, and Kimbell and Rak from different places of east Africa like Hadar (Ethiopia) and Laetoli (Tanzania). Of these fossil remains, the one discovered from Hadar is nicknamed as Lucy, an adult female skeleton of 25 years old (al 288-1) (Johanson 1978). A. afarensis existed between 3.9 and 3.0 million years ago. They had an ape-like face with a low forehead, a bony ridge over the eyes, a flat nose, and no chin. They had protruding jaws with large back teeth. Cranial capacity varied from about 375 to 550 cc. The skull is similar to that of a chimpanzee, except for the more human like teeth. The canine teeth are much smaller than those of modern apes, but larger and more pointed than those of humans, and shape of the jaw is between the rectangular shape of apes and the parabolic shape of humans. However their pelvis and leg bone closely resemble modern human, and leave no doubt that they were bipedal (although adapted to walking rather than running (Leakey 1994). A foot print in the volcanic ashes from laetoli is the oldest evidence of bipedalism among the. Females were substantially smaller than males, a condition known as sexual dimorphism. Height varied between about 107 cm (3'6") and 152 cm (5'0"). The finger and toe bones are curved and proportionally longer than humans, but the hands are similar to humans in most other details (Johanson and Edey 1981). Most scientists consider this evidence that afarensis was still partially adapted to climbing in trees, others consider it evolutionary baggage. 8 Physical/Biological
Lucy (al 288-1) Source: http://humanorigins.si.edu/evidence/human-fossils/species/australopithecus-afarensis, retrieved on march 15, 2015) Kenyanthropus platyops (flat faced man of Kenya) A partial skull was discovered from Lomekwi in Kenya (Leakey 2001), dated about 3.5 million years. The size of the skull is similar to A. afarensis and A. africanus, and has a large, flat face and small teeth. This variety is contemporary to Lucy. Tim White (2003) rejected the genus Kenyanthropus and considered it as a variant of A. afarensis. Kenyapithecus platyops (er 1470) Source: http://www.talkorigins.org/faqs/homs/wt40000.html, retrieved on march 14, 2015 africanus All the fossils of this variety have been discovered from South Africa from sites like Taung and Sterkfontein. Of these, the discovery of Taung child, a skull of a child made by Raymond Dart in 1924 marks the beginning of the discovery of (Dart 1925). This 3-year-old child's skull is the first early human skull ever discovered in Africa. It took 20 years after this discovery 9 Physical/Biological
before scientists accepted the importance of Africa as a major source of human evolution. Dart claimed this fossil as an ancestor to human from its position of foramen magnum which is like modern human. A. Africanus existed between 3 and 2 million years ago. It is similar to Afarensis, and was also bipedal but body size was slightly greater. Brain size may also have been slightly larger, ranging between 420 and 500 cc. This is a little larger than chimp brains (despite a similar body size), but still not advanced in the areas necessary for speech. The back teeth were a little bigger than in Afarensis. Although the teeth and jaws of Africanus are much larger than those of humans, they are far more similar to human teeth than they are those to apes (Johanson and Edey 1981). The shape of the jaw is now fully parabolic, like that of humans, and the size of the canine teeth is further reduced compared to Afarensis. The average height of the males is 4 ft 6 inch (138 cm); and that of females is 3 ft 9 inch (115 cm). The average weight of the males is 90 lbs (41 kg) and that of the females is 66 lb (30 kg). Taung child Source: http://humanorigins.si.edu/evidence/human-fossils/species/australopithecus-africanus, retrieved on march 10, 2015 garhi This species was discovered at Bouri in Ethiopia (studied by Asfaw et al. 1999). It is a partial skull dated 2.5 my. The skull differs from previous australopithecine species in the combination of its features, notably the extremely large size of its teeth, especially the rear ones, and primitive skull morphology. Some nearby skeletal remains may belong to the same species. They show a humanlike ratio of the humerus and femur, but an ape-like ratio of the lower and upper arm. All these varieties of australopithecus discussed till now are considered as the gracile forms because of their lighter body built compared to the robust varieties (which we will discuss now). The robust varieties like, A. robustus, A aethiopicus and A. boisei had a gorilla-like bony crest down the midline of the skull, serving to anchor the enormous jaw muscles needed to chew their fibrous diet. They had huge, broad cheek teeth with thick enamel, relatively small incisor teeth, large zygomatic arches that 10 Physical/Biological
allowed the passage of large chewing muscles. They also have very heavy brows making them look far from human. Some prefer to club these three under the genus paranthropus and consider them as offshoot diverging from the ancestral line leading to humanity (Aiello & Dean, 1990). aethiopicus/paranthropus aethiopicus Discovered by Alan Walker in 1985 near west Turkana in Kenya. A. aethiopicus existed between 2.6 and 2.3 million years ago. This species is popularly known as the black skull. It is so called because the manganese deposit in the soil deposit where the skull was located stained it black and it may be an ancestor of other two robust varieties of, i.e. robustus and boisei, but it has a baffling mixture of primitive and advanced traits. The brain size is very small (410 cc), parts of the skull particularly the hind portions are very primitive, most resembling afarensis. Other characteristics are massiveness of the face, jaws and single tooth found, and the largest sagittal crest (Walker et al. 1986). aethiopicus/paranthropus aethiopicus or black skull Source: http://archaeologyinfo.com/australopithecus-aethiopicus/, retrieved on march 10, 2015 robustus Discovered from Kromdraai (Broom, 1938), from Swartkrans (Johanson and Edgar 1996) and Drimolen cave (Keysser, 2000). All these sites are in south Africa. A. robustus had a body similar to that of africanus, but a larger and more robust skull and teeth. It existed between 2 and 1.5 million years ago. The massive face is flat or dished, with no forehead and large brow ridges. It has relatively small front teeth, but massive grinding teeth in a large lower jaw. Its diet would have been mostly coarse, tough food that needed a lot of chewing. The average brain size is about 530 cc. Bones excavated with robustus skeletons indicate that they may have been used as digging tools. 11 Physical/Biological
robustus Source: http://archaeologyinfo.com/australopithecus-robustus/, retrieved on march 10, 2015 boisei /Paranthropus boisei/ Zinjanthropus boisei) This is the most robust form of australopithecus. Discovered by Mary Leakey 1959, from olduvai gorge (Tanzania), by Richard Leakey in 1969 &70 from lake turkana (Kenya) and by Swua (1997) from Konso (Ethiopia). A. boisei existed between 1.8 and 1.1 million years ago. It was similar to robustus, but the face and cheek teeth were even more massive, some molars being up to 2 cm across. The brain size is very similar to robustus, about 530 cc. Some scholars opine boisei and robust us to be variants of the same species. boisei Source: http://archaeologyinfo.com/australopithecus-boisei/, retrieved on march 10, 2015 12 Physical/Biological
Sequence of appearance Thus, we see a spectrum of varieties of. They appeared in this world during pliopliestocene epoch and were distributed mostly in south and east africa. The question that why the distribution of is restricted to East and South Africa still needs to be answered. Moreover, how these widely diversified members are related to each other and with different species of genus homo are yet to reach any consensus. Even though they have been divided by some investigators into several genera (sahelanthropus, ardipithecus, australopithecus, and paranthropus), it is still unclear whether the early hominids were simply diverse within a widely-distributed group (for example, like modern humans), or they represent more than one evolutionary line. The sequence of appearance of these fossil records reveals that sahelanthropus came around 6-7 my, orrorion around 6 my, ardipithecus 4.4-4.8 my, the gracile forms of (afarensis, africanus, garhi) between 4.2-2.0 my, Kenyanthropus around 3.5 my and paranathropus (both robustus and boisei) between 2.6 and 1.0 my. Despite these varieties, palaeoanthropologists (scientists who study human fossils) identify two major forms of australopithecus gracile and robust. Some of the scholars prefer to keep them in two different genera- australopithecus (gracile form) and paranthropus (robust form). It is believed that one of the species of the gracile forms of australopithecus evolved into genus homo, though the robust forms appeared later than the gracile forms. Summary The word means southern apes. Different sites of South Africa like Sterkfontein, Taung, Kromdraai and from East Africa like Olduvai, Laetoli and lake Turkana. Around 4 my or might be even before. The members of this group were biped with reduced teeth size, especially the canine. Earliest varieties: sahelanthropus tchadensis, orrorin, ardipithecus. Later varieties: (a) afarensis, africanus (gracile forms) (b) robustus and boisei (robust forms) Sahelanthropus came around 6-7 my, Orrorion around 6 my. 13 Physical/Biological
Ardipithecus 4.4-4.8 my Gracile forms of (afarensis, africanus, garhi) between 4.2-2.0 my Kenyanthropus around 3.5 my Paranthropus (both robust and boisie) between 2.6 and 1.0 my. It is believed that one of the species of the gracile forms of evolved into genus homo, though the robust forms appeared later than the gracile forms. 14 Physical/Biological