Australopithecus afarensis

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Australopithecus afarensis

Australopithecus afarensis is one of the longest-lived and best-known early human species—paleoanthropologists have uncovered remains from more than 300 individuals! Found between 3.85 and 2.95 million years ago in Eastern Africa (Ethiopia, Kenya, Tanzania), this species survived for more than 900,000 years, which is over four times as long as our own species has been around.  It is best known from the sites of Hadar, Ethiopia (‘Lucy’, AL 288-1 and the 'First Family', AL 333); Dikika, Ethiopia (Dikika ‘child’ skeleton); and Laetoli (fossils of this species plus the oldest documented bipedal footprint trails).

Similar to chimpanzees, Au. afarensis children grew rapidly after birth and reached adulthood earlier than modern humans. This meant Au. afarensis had a shorter period of growing up than modern humans have today, leaving them less time for parental guidance and socialization during childhood.

Au. afarensis had both ape and human characteristics: members of this species had apelike face proportions (a flat nose, a strongly projecting lower jaw) and braincase (with a small brain, usually less than 500 cubic centimeters -- about 1/3 the size of a modern human brain), and long, strong arms with curved fingers adapted for climbing trees. They also had small canine teeth like all other early humans, and a body that stood on two legs and regularly walked upright. Their adaptations for living both in the trees and on the ground helped them survive for almost a million years as climate and environments changed.

Image of male reconstruction based on AL444-2 by John Gurche. 3/4 view
Nickname: 
Lucy's species
Where Lived: 
Eastern Africa (Ethiopia, Kenya, Tanzania)
When Lived: 
Between about 3.85 and 2.95 million years ago
Australopithecus afarensis lived between about 3.85 and 2.95 million years ago
Year of Discovery: 
1974
History of Discovery: 

The species was formally named in 1978 following a wave of fossil discoveries at Hadar, Ethiopia, and Laetoli, Tanzania.  Subsequently, fossils found as early as the 1930s have been incorporated into this taxon.

Height: 
Males: average 4 ft 11 in (151 cm); Females: average 3 ft 5 in (105 cm)
Weight: 
Males: average 92 lbs (42 kg) ; Females: average 64 lbs (29 kg)

We don’t know everything about our early ancestors—but we keep learning more! Paleoanthropologists are constantly in the field, excavating new areas, using groundbreaking technology, and continually filling in some of the gaps about our understanding of human evolution.

Below are some of the still unanswered questions about Au. afarensis that may be answered with future discoveries:

  1. A fossil similar to Au. afarensis and dating to 3.5 million years ago has been found in Chad—did this species extend so far into central Africa?
  2. We know Au. afarensis were capable of walking upright on two legs, but they would have walked differently than modern humans do today; so, what did their bipedal locomotion look like?
  3. Did Au. afarensis usually walk upright like modern humans, or did they spend more time climbing trees like other living African apes?
  4. The species Au. afarensis existed through a period of environmental fluctuation yet showed no adaptations to the changing environment—why? Was it because they were able to migrate to where their usual food sources were located? Or were their food sources somehow unaffected?
  5. Au. afarensis shows strong sexual dimorphism in that the body sizes between males and females are quite different; however, sexual dimorphism in other primates is usually characterized by size differences in bodies and teeth. Fossil evidence shows that male Au. afarensis individuals had canine teeth comparable in size to those of females. Did male dominance in Au. afarensis individuals not include the need to bear large canine teeth, as it does in many other male primates?
  6. The teeth and jaw of Au. afarensis are robust enough to chew hard foods, but dental microwear studies show Au. afarensis individuals ate soft foods like plants and fruit instead. While most scientists think that Au. afarensis ate hard, brittle foods during tough times when vegetation was not easily found, further microwear studies show that eating hard foods did not coincide with dry seasons of little vegetation. So how do properties of Au. afarensis teeth relate to their diet?

First paper:  

Johanson,  D.C., White, T.D., Coppens, Y. 1978. A new species of the genus Australopithecus (Primates: Hominidae) from the Pliocene of Eastern Africa. Kirtlandia 28, 2-14.

 

Other recommended readings:

 

Alemseged, Z., Spoor, F., Kimbel, W.H., Bobe, R., Geraads, D., Reed, D., Wynn, J.G., 2006. A juvenile early hominin skeleton from Dikika, Ethiopia. Nature 443, 296-30.

Johanson, D.C., Edey, M.E., 1981. Lucy: The Beginnings of Humankind. St Albans, Granada.

Kimbel, W.H., Delezene, L.K., 2009. "Lucy" redux: A review of research on Australopithecus afarensis. Yearbook of Physical Anthropology 52, 2-48.

Schmid, P., 2004. Functional interpretation of the Laetoli footprints. In: Meldrum, D.J., Hilton, C.E. (Eds) From Biped to Strider: The Emergence of Modern Human Walking, Running, and Resource Transport. Kluwer Academic/Plenum, New York, pp 50-52.

 

 

 

 

 

How They Survived: 

Au. afarensis had mainly a plant-based diet, including leaves, fruit, seeds, roots, nuts, and insects… and probably the occasional small vertebrates, like lizards.

How do we know what Au. afarensis ate?

Paleoanthropologists can tell what Au. afarensis ate from looking at the remains of their teeth. Dental microwear studies indicate they ate soft, sugar-rich fruits, but their tooth size and shape suggest that they could have also eaten hard, brittle foods too – probably as ‘fallback’ foods during seasons when fruits were not available.

Evolutionary Tree Information: 

This species may be a direct descendant of Au. anamensis and may be ancestral to later species of Paranthropus, Australopithecus, and Homo.

Image of "Lucy," skeleton, right 3/4 view

‘Lucy’ (AL 288-1) is an adult female, 3.2 million-year-old A. afarensis skeleton found at Hadar, Ethiopia. Because she could walk upright on the ground and climb trees, she and other members of her species were able to use resources from woodlands, grasslands, and other diverse environments. 

Image of  Australopithecus afarensis Dikika 1, skull and partial skeleton du

This child's baby teeth had erupted in a pattern similar to a three-year-old chimpanzee’s, telling us she grew up at a rate similar to a chimpanzee. But her brain size indicates that a human growth rate was evolving. CT-scans shows small canine teeth forming in the skull, telling us this individual was female.

image of Australopithecus afarensis walking and leaving footprints

The Laetoli footprints were most likely made by Australopithecus afarensis, an early human whose fossils were found in the same sediment layer. The entire footprint trail is almost 27 m (88 ft) long and includes impressions of about 70 early human footprints.