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| Species: | Australopithecus afarensis |
| Age: | 3.6 million years |
| Date of Discovery: | 1974-1975 |
| Location: | Laetoli, Tanzania |
| Discovered by: | Mary Leakey |
Roughly three and three-quarter million years ago, a volcano erupted in what is now northern Tanzania, blanketing the landscape with volcanic ash. Rain fell, causing the ashy surface to take on the properties of plaster, and across this ground numerous animals walked, leaving their footprints in the wet volcanic ash to be preserved as it turned into a hard cement. One of the creatures that passed across this landscape 3.6 million years ago was a member of the early human species Australopithecus afarensis. In fact, at least two individuals were present, walking along side each other.
The importance of the fossil footprints at Laetoli cannot be overstated. They demonstrate incontrovertibly that 3.6 million years ago, early humans were bipedal (walking upright on two legs). Their big toes hardly diverged from the rest of the foot, this can be seen in the photograph at the top right of the imprint. In comparison, a chimpanzee has a highly diverged big toe, and is able to use it like a thumb. Additionally, it is pssoible to tell that the gait of these early humans was "heel-strike" (the heel of the foot hit first) followed by "toe-off" (the toes push off at the end of the stride); the way modern humans walk. Thus, bipedality was essentially developed by this time. Yet from other fossil finds we know that the morphology of the skull, particularly the brain, remained little changed from our ape ancestors in A. afarensis.
