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Australopithecus afarensis

Australopithecus afarensis (Latin: "Southern ape from Afar") is an extinct hominin that lived between 3.9 and 2.9 million years ago in Africa. A. afarensis was slenderly built and is thought to be more closely related to the genus Homo (which includes the modern species Homo sapiens), whether as a direct ancestor or a close relative of an unknown ancestor, than any other known primate from the same time. A. afarensis existed between 3.9 and 3.0 million years ago. The species is one of the better-known , merely with regard to the number of samples attributed to the species. The species was named by D. Johanson and T. White in 1978. Key fossil discoveries During the , two fossil hunting teams began uncovering evidence of ancient human ancestors in east Africa. One team, co-led by Donald Johanson, was working at Hadar in . The other team led by Mary Leakey, was over 1,500 kilometres away at Laetoli in Tanzania. Fossils discovered at the two sites were found to have very similar features and ages but they did not match the fossils of any species known at that time. A new species name, Australopithecus afarensis, was therefore created for them in 1978. 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, a 3.2 million years old partial skeleton, discovered in November 1974 at Hadar, Ethiopia, Possibly the best-known specimen of afarensis is AL 288–1. It was an adult female skeleton of, nicknamed as ‘’, 25 years old (Johanson, 1978). This species is now represented by several hundred fossils from east Africa. Important specimens

• ‘Lucy’ AL 288-1 – a partial skeleton discovered in 1974 by Donald Johanson in Hadar, Ethiopia. This relatively complete female skeleton, dated to 3.2 million years old, is the most famous individual from this species. She was nicknamed ‘Lucy’ after the song ‘Lucy in the sky with diamonds’ sung by The Beatles. This song was very popular at the time she was found. Lucy was only about 110 centimetres tall but was a fully grown adult when she died. She was bipedal which means she could walk on two legs but she probably also spent a lot of time climbing trees in search of food or shelter.

• Knee AL 129 1a + 1b discovered in 1973 in Hadar, Ethiopia. When this 3.4 million year old knee was discovered, it was the first fossil to provide evidence that our ancestors that had been walking on two legs for more than three million

Sk. Hedayet Hossain, Assistant Professor, Department of Anthropology Ramsaday college

years. The discovery of this fossil encouraged Donald Johanson’s team to return to Hadar where they ultimately found ‘Lucy’ and hundreds of other fossils of this species.

• LH 4 – a lower jaw discovered in 1974 by Mary Leakey’s team in Laetoli, Tanzania. This fossil is the type specimen’or official representative of this species.

• The ‘First Family’ - a group of A. afarensis fossils discovered in Hadar, Ethiopia in 1975. It became known as the ‘First Family’ because it contained fossils from nine adults and four children. Some unknown disaster overcame this family group, burying them all at the same time. This important find has allowed scientists to gather insights into the biology and development of a single fossil species. It also provided evidence that this species lived in small groups based on possible family bonds.

• ‘Selam’ or ‘Lucy’s baby' – a partial juvenile skeleton discovered in 2000 in Dikika, Hadar, in Ethiopia. She lived 3.3 million years ago and was about 3 years old when she died. Bones are preserved that have never before been found in this species. This is the earliest juvenile hominin skeleton ever found and should provide fantastic opportunities to uncover more about this species and about how our early ancestors developed.

• 'Lucy's big brother', nicknamed Kadanuumuu ('big man' in Afar) - a partial skeleton of a male uncovered in Afar, Ethiopia. An arm bone was first found in 2005 and other parts recovered over the next four years included shoulder blade, ribs, neck vertebra, pelvis, leg bones (complete tibia and partial femur) and a collarbone. This individual stood about 1.6 metres tall (30% larger than 'Lucy') and lived about 3.6 million years ago. Laetoli footprints These fossil footprints were discovered in Tanzania, East Africa and date to 3.6 million years ago. Fossil bones from A. afarensis have been found nearby so it is presumed that they left the tracks. The quite human-like footprints were made by hominins that walked through a layer of ash burst that had settled on the ground after a distant volcano erupted. Raindrops made the ash damp and, even now, the indentations made by these raindrops can still be seen on parts of the ash layer. At first glance, it looks like two people walked side-by-side. The one on the left was much smaller than the other and may have been a child. On closer examination, we can see that the prints on the right-hand side are blurred and were actually made by two adults - one following the other and treading into the prints left by the first. Part way along the trail the individuals pause and turn to the left before continuing. The sun soon dried the damp ash, which hardened like cement. The active volcano

Sk. Hedayet Hossain, Assistant Professor, Department of Anthropology Ramsaday college

continued to throw out ash until a layer up to 20 centimetres thick blanketed both the ground and the footprints. Over millions of years, additional sediments were deposited and some were eroded away by wind and water. Eventually some of the footsteps lay uncovered. Then a lucky fossil hunter came across them and the story began to be revealed. The footprints are of major significance as they are the first direct evidence (i.e. not fossils bones) that our ancestors were walking upright by 3.6 million years ago. The fossil footprints are very similar to our own footprints. They show that the heel was the first part of the foot to strike the ground. The big toe was aligned with the other toes and left a deep impression showing that each step ended with the toe pushing downwards. The feet also had central arches to help launch the body into each step. Key physical features

Fossils show this species was bipedal (able to walk on two legs) but still retained many ape-like features including adaptations for tree climbing, a small brain, and a long jaw. Body size and shape • females grew to only a little over one metre in height (105 – 110 centimetres) and males were much larger at about 150 centimetres in height

• rib cage was cone-shaped like those of apes Brain • brain was small, averaging approximately 430 cubic centimetres and comprised about 1.3% of their body weight

• reorganisation of the brain may have begun with some enlargement to parts of the cerebral cortex Skull • many cranial features were quite ape-like, including a low, sloping forehead, a projecting face, and prominent brow ridges above the eyes.

• unlike most modern apes, this species did not have a deep groove lying behind its brow ridge and the spinal cord emerged from the central part of the skull base rather than from the back.

• males had a bony ridge (a sagittal crest) on top of their skull for the attachment of enormous jaw muscles. In this species, the crest was very short and located toward the rear of the skull.

• a small hyoid bone (which helps anchor the tongue and voice box) found in a juvenile specimen suggests A. afarensis had a chimp-like voice box

Sk. Hedayet Hossain, Assistant Professor, Department of Anthropology Ramsaday college

• semi-circular ear canal similar in shape to African apes and A. africanus, suggesting this species was not as fast or agile on two legs as modern Jaws and teeth • jaws and teeth were intermediate between those of humans and apes:

• jaws were relatively long and narrow. In the lower jaw, the teeth were arranged in rows that were slightly wider apart at the back than at the front. In the upper jaw, the placement of the last molar results in tooth rows that curve in at the back.

• front incisor teeth were quite wide.

• canine teeth were pointed and were longer than the other teeth. Canine size was intermediate between that of apes and humans. Like apes, males had much larger canines than females.

• a gap (diastema) was often present between the canines and adjacent teeth. This ape-like feature occurred between the canines and incisors in the upper jaw, and between the canines and premolars of the lower jaw.

• premolar teeth in the lower jaw had ape-like cusps (bumps on the chewing surface). The front premolar tended to have one large cusp (ape-like) rather than two equal-sized cusps as in humans.

• back molar teeth were moderate in size and were human-like in having a ‘Y-5’ pattern. That is, they had five cusps arranged so that the grooves between the cusps form a Y-shape. Pelvis • pelvis was human-like as it was short and wide, but it lacked the refinements that enable humans to walk with a striding gait Limbs • limbs displayed human-like features that indicate an ability to walk on two legs

• femurs (thigh bones) that slanted in toward the knee

• knees with enlarged and strengthened outer condyles

• arched feet and wide heels

• big toes aligned with the other toes and not opposable

• ape-like features that suggest an ability to climb trees

• powerful arms with long forearms

• very short thigh bones

• long, curved finger and toe bones.

Sk. Hedayet Hossain, Assistant Professor, Department of Anthropology Ramsaday college

• shoulder blade socket that faces upwards like an ape’s, rather than to the side like a human’s, but shared other similarities with human shoulder blades. One of the more well-known remains from Laetoli are the Laetoli footprints. There have been many interpretations of the footprints, with different numbers and sex of individuals, and different ideas as to the form of locomotion used to create them. In the end, most people have come to accept the idea that the footprints were made by afarensis approximately 3.56 mya, which were an obligate biped. Features which show this include:

• Deep impressions showing pronounced heel strike. • Lateral transmission of force from the heel to the base of the lateral metatarsal. • A well-developed medial longitudinal arch. • Adducted big toe, in front of the ball of the foot and parallel to the other digits. • A deep impression for the big toe commensurate with toe-off. Phylogeny The most logical ancestor for A. afarensis is A. anamensis. The two species overlapped in time and geographic space. Some paleoanthropologists have always believed that genus: Homo is descended from A. afarensis. Over time, others have changed their taxonomic scenarios from A. africanus to A. afarensis (which would formerly have been a sister lineage to A. africanus) as our ancestor, and made A. africanus a side branch of the robust forms. Part of the argument for classifying A. afarensis outside of our lineage had to do with aspects of their anatomy being more derived than our own, e.g. the lateral flare of their ilia (the plural of ilium). Since the discovery of A. sediba, some scholars are back to favouring A. africanus in our ancestry. Conclusions The afarensis material is important in that it is the best known early hominid species (although as earlier anamensis and/or ramidus material becomes better known, it will lose much of its focus as the earliest known hominid material for which much is known). It shows decisive evidence for obligate bipedality and for the presence of evolutionary trends in its dentition and post-crania that seem to have it on the path to the modern human form.

Sk. Hedayet Hossain, Assistant Professor, Department of Anthropology