Stepping Out: Laetoli Footprints

I want to share something really cool and interesting with you.  Some of you may already be aware of this, some not, but whether you have or haven't I think it is something so awesome that it warrants a brief blog about it.  

In 1976, a Yale University paleoanthropologist Andrew Hill was working with Mary Leakey's research group on the excavation of an early-hominid archaeological site in Laetoli, Tanzania, when he unexpectedly stumbled across one of the most spectacular prehistoric discoveries ever made: a line of hominid footprints left in mud 3.6 million years ago.  I know right!

Up until then, the earliest known human footprints were only tens of thousands of years old.  Remarkably, Hill's Laetoli footprint trail was nearly 30 metres long and preserved in volcanic ash that had turned into a cement-like solidity as good as a plaster cast.  It left us with an action replay of one of the first species of prehistoric hominids who walked upright on two legs.  

The ideal surface material was created by a coating of volcanic ash from the nearby Sadiman volcano that had settled on a sandy surface.  When rain then fell, the sooty volcanic sediment became soft , like wet cement, and all the birds and small animals that walked on it left small prints.  But they were joined by the track of two hominids, one large and the other smaller, trailed possibly by a third (child?), whose tracks share some of the larger individuals footprints.

A further eruption of dust from the volcano served to seal up the footprints for prosperity before the rains returned and washed them away.  The light rain then turned the ash into cement, which set solid.  There, they remained until they were exposed by millions of years of gentle erosion.

These prints have led to all sorts of deductions and speculations , however they differ significantly from chimpanzee footprints and are not very different from those of modern humans, with an aligned big toe, heel, and an arched foot.  Interestingly the smaller individual of the two ( because they left shallower prints) is lopsided, bearing more weight on one side - perhaps carrying a baby?  The sequence of depressions also reveal the pattern of walking, with an initial strike followed by a push off by the front toes, again like our own stride pattern.  

The length of the footprints along the two trails are 19cm and 20cm, umm, about a boys size 1 in UK sizing, indicating that the individuals were probably about 120cm (4 ft) and 152 (5 ft) tall.  For the first time we had what amounted to a photographic of pre-human intelligent activity that could be understood in terms of our present day movements, how awesome!

A summer stroll on the beach could create the same impressions on the sand, only a marvellous accident of nature could preserve them, and we do not really want that do we.  

http://www.pbs.org/wgbh/evolution/library/07/1/l_071_03.html 


You can find more reading in:
N. Agnew and M. Demas, 'Preserving the Laetoli Footprints' , Scientific America (September 1998), pp. 45-55.  Mary D. Leaky and J. M. Harris (eds), Laetoli: A Pliocene Site in Northern Tanzania, Clarendon Press, Oxford  (1987).