Australopithecus afarensis

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Selam (Lucy's Baby.

Australopithecus afarensis is an extinct hominid species, which to some, is considered to be the "missing link" in human evolution. Although A. afarensis is an older species than A. africanus, it is thought to be one of the closest ancestors to the genus Homo. This is because the species shares a significant amount of traits with both chimpanzees and humans. The monumental remains known as "Lucy" stemmed from one of the most famous paleoanthropological finds in history. The potassium-argon dating found that the ancient species is thought to have lived between 3.76 and 3.49 million years ago with Lucy's remains dating to around 3.2 million years ago. The claim of discovering the potential missing link as well as the name of the species remains the subject of heated discussions within many scholarly circles. A number of scholars with Mary Leakey, in particular, would prefer the official name of this species to be Praeanthropus afarensis.

Distinguished Digs

1973: AL 129-1: Knee joint Kada Hadar, Ethiopia #REDIRECT 1
Discovered in Hadar, Ethiopia by Donald Johanson, the angle of the proximal tibia and distal femur suggests a bipedal hominid. In addition, the bicondylar angle, deep patellar groove and lateral lip of the patellar groove suggest that it is in fact a hominid.
The Hadar site consists of four general members: The Basal member dates older than 3.4 million years old while the Sidi Hakum member dates to 3.22ma and is thought to be a woodland environment. The Denen Dora member dates to 3.18ma and is thought to be a forested/swampy area while the top layer is named Kada Hadar and dates to 2.3ma. The Kada Hadar member is much more open than the other bottom layers.

1974: AL 288-1: Lucy Kada Hadar, Ethiopia
The Lucy find was a singular find and relatively complete (around 40%). Discovered by the International Afar Research Expedition (IARE), Lucy became one of the most notable finds in the history of human biological evolution. The great significance of this find is mainly due to the fact that it was the first time there existed good evidence that humans were bipedal before developing larger brains.

1978: Laetoli Site: Footprints / Holotype Tanzania
The Laetoli site is located in Tanzania and is just south of Olduvai gorge. The site was being excavated by Mary Leakey and her team in 1975 when thirteen specimens of Australopithecus afarensis were discovered, including the current holotype of Australopithecus afarensis (a mandible). When returning to the site in 1978, the team uncovered over 20,000 animal tracks which included hominid footprints. The cluster of footprints found in the tuff dates from 3.76 to 3.49 million years ago.

2006: Lucy's Baby Dikika, Ethiopia
This was the first manor find by an African scientist in Ethiopia. Zeray Alemseged was responsible for this find and is equally astonishing as Lucy. This find was one of the most complete skeletons ever found, which included a scapula, and dated to around 3.31-3.35 million years old. The thyroid bone in the throat was not even fused yet which suggested a very early age of maturation (thus, the name Lucy's baby).

Physical Attributes

Cranial Relatively small brain with an average cranial capacity of 434cc. It has an encephalization quotient of 2.5 and is quite chimpanzee-like when looking at it from behind. The compound temporal neutral crests demonstrates a smaller brain capacity and its face is more prognathus when compared to the Australopithecus africanus. Although the cranium is more primitive than the Australopithecus africanus, it remains classified as a gracile Australopith instead of a chimpanzee.

Dental The canines show similar wear patterns as humans. This may show a possible link between humans and Australopiths. Although the canines are a bit smaller than chimpanzees, they are also bigger than other Australopiths which suggests dimorphism. there is minimal metaconid development but they have asymmetric shape which are more like chimpanzees. There is a megadontia quotient of 1.7 and have a shallow palate which is human-like. Although there are human-like characteristics, the tooth rows are more parallel and narrow which is more ape-like. This shows a possible link between human-like characteristics and ape-like morphologies.

Body size Males average a weight of 100 lbs while females average a weight of 64lbs. This indicates a significant amount of sexual dimorphism. Some studies have suggested that there exists such a great deal of dimorphism that it could in fact be two different species. This has been refuted because although body sizes differ, the morphological features are continuous.

Bipedal Locomotion
Evidence for bipedal locomotion is seen when examining the pelvis structure, knee joint and foramen magnum. The bones are strong and the pelvis is very human-like. When examining the bottom of the foot; there exists a non-opposable hallux (straight big-toe)with a longitudinal arch (for a springy foot). Although a lot of these features indicate a human-like biped, they still posses long arms, short legs and very curved fingers, which may indicate a significant amount of time in trees.

External Links

1 AL 129-1
2 Lucy's Baby