Footprints after the ash

A volcano erupts. Soon after tephra fall covers the surrounding terrain creating a thin layer of ash. During the eruption light rain fell causing the ash layer to a gooey mud. Animals walk through this terrain of mud leaving footprints. Fast forward 3.6 million years and what you have is preserved fossilized footprints. The preservation was made possible because the ash in the mud is wet carbonatite, which once dried hardens into a rock-hard substance. This event took place in now Laetoli Tanzania. The site was discovered in in 1976, lead by Mary Leaky, but it wasn’t until 1978 the the site would become world famous as the Laetoli Footprints, for they had discovered hominin footprints for the first time, also the oldest hominin footprints to date. But not just any footprints. These looked strikingly similar to us because we do this all the time on our own feet. These were snapshot actions of bipedal locomotion, walking on two legs.
1258847_e15982324c_bThis really was a revolutionary find. Because the leading consensus, developed in the 1800’s when the hominin fossil record was scarce, was that the initial kick start to humanity was larger brains and intelligence. But based on the expanded fossil record it was bipedalism as the initial fundamental behavior of hominin, not intelligence that came first and would eventually separate use from our closest relative the apes.

First Steps: What are feature that contribute to bipedal locomotion based on the prints?

2010657e6d99431c9c4d942253c771ecThere are many adaptions that contribute to the use of being able to walk on two feet. One example is our foramen magnum, a hole on our skull that connects to our erect spine. While apes have theirs in a posterior position for being on all fours most of the time. But what can we learn from observing the feet for bipdelism? Quite a lot! There are quite a few observations that can be made, but two main feature of bidality that are the the longitudinal foot arch and the lack of an opposable big toe. If you feel the bottom of your foot you can feel an arch and what that is suppose to do is be like a shock absorber when making contact with the ground and also give you leverage when pushing forward. Apes have flat feet, which reflect the adaptation of their feet for grasping. Apes have a divergent big toe which can be used for terrestrial walking and grasping objects. Humans don’t have a divergent big toe, because our feet are solely (pun intended) specialized for for walking and running.

laetoli-prints

The Laetoli footprints were most likely made by Australopithecus afarensis as fossils were found later near the site in the same sedimentary layer as well as in other parts of East Africa where they have been discovered. Observing the foot prints, recent studies of them using computer models, and examination of the fossils themselves resolves any doubt that A.U. afarensis was bipedal. The footprints show that they had foot arches, and no divergent big toe. The features also show they had a similar gait, manner of walking, compared to modern humans as their foot hit the ground first, heel-strike, and ending with the toes pushing off the ground, toe-off. The closeness of the footprints show a short stride meaning that the had short legs compared to archaic and modern humans.

For more information:

http://discovermagazine.com/2015/oct/19-first-impressions

http://humanorigins.si.edu/evidence/behavior/footprints

 

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