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10th November 2016

DigTrace and famous Laetoli Footprints

Laetoli footprint, Laetoli reconstruction, Laetoli tracks

The laetoli tracks are some of the most iconic in the world and provide the oldest direct evidence of human bipedalism at 3.66 million years.  Discovered in the late 1970s they have fuelled controversy and research ever since (Bennett et al., 2016b).  The tracks have been buried for much of this time to aid their conservation.

DigTrace, Tanzania, Laetoli footprint, Laetoli reconstruction, Laetoli tracks

Colour rendered optical laser scan of part of the Laetoli footprint trackways. The G-1 trackway is the lower set of prints while the upper trackway (G2/3) is a composite of two or three individuals. (Source: Professor Matthew Bennett, Bournemouth University)

The site lies approximately 36 km south of the famous Olduvai Gorge in northern Tanzania and a total of over 18 track sites (mainly animal tracks) have been found.  The Laetoli Beds, cover over 1600 km² and overlie Precambrian basement.  The famous Footprint Tuff bearing the hominin tracks is found in the upper part of the ash succession.  The likely source for the volcanic ash was originally thought to be the extinct Sadiman volcano 20 km to the east, although recent work has put this into question.  The Footprint Tuff was deposited by direct ash fall, with some re-working, and the presence of rain drop impressions has led some to suggest that deposition occurred over a period of a few weeks at the transition between the dry and wet seasons. The tracks were left almost immediately after rainfall and buried by subsequent ash fall.  The distinctive composition of the tephra favoured rapid cementation assisting in the preservation of the tracks.

The main hominin (early human) footprint site (Site-G) is approximately 27 m long and consists of three trackways, two of which (G-2 and G-3) are superimposed one on top of the other, with a second track-maker (G-3) walking in the footsteps of the first (G-2).  Recently work using DigTrace on footprint scans suggests that a fourth track-maker may also be found in the G2/3 composite.  In 2016 DigTrace was also used to extract and create a mean track for the G3 individual from the composite (See: Bennett et al., 2016a).  The G-1 trail to the west of the double trackway contains 38 prints and was made by a single individual.

DigTrace was used to create two mean tracks from the individual footprints present.  Tracks are registered one on top of the other before a mean is computed.  This is one of the applications of the ‘Compare’ workbench in DigTrace.  The image on the left below is of a mean of eleven individual tracks from the G-1 trackway, while the image on the right is a mean of the G-3 track extracted from the G2/3 composite track.

DigTrace, Tanzania, Laetoli footprint, Laetoli reconstruction, Laetoli tracks

Mean tracks computed using DigTrace. On the left is the mean of the G-1 trackway, while on the right is the mean of the G-3 track extracted for the first time ever from the G2/3 composite.
(Source: Professor Matthew Bennett, Bournemouth University)

trac-maker, hominin trackways, laetoli

Reconstruction of the Laetoli trackways. Note the presence of a fourth track-maker and the potential for other hominin trackways.
(Source: Professor Matthew Bennett, Bournemouth University, modified from the reconstruction at the Olduvai Gorge Site Museum)

The track-maker has been widely attributed to Australopithecus afarensis given that small skeletal fragments have been recovered from the Laetoli Beds and it is also the only species of hominin known from the landscape at that time.  Estimates of height based on foot length suggest that the track-maker for trail G-1 had a height in the range of 1.1 to 1.15 m while the G-3 track-maker was slightly taller at 1.32-1.52 m.  There has been an extensive debate about the degree to which these tracks represent a modern anatomical foot function with the growing consensus now favouring a modern biomechanical function although the debate continues.  This was explored using DigTrace in 2016 showing that foot function has changed little in the last 3.66 million years (See: Bennett et al., 2016b).

While the hominin tracks attract all the attention there are also a large number of animal tracks with over 9525 individual tracks being identified to date and the diagram below gives some idea of the range of animals present.

During 2016 DigTrace has advance our knowledge of the Laetoli footprints and is just one example of its academic applications.

Laetoli footprint, Laetoli reconstruction, Laetoli tracks

Snapshot of the animal community present at Laetoli based on the animal tracks they left.
(Source: Professor Matthew Bennett, Bournemouth University, diagram based on data in Leakey and Harris 1987)

Sources:

Bennett, M.R., Reynolds, S.C., Morse, S.A. and Budka, M., 2016a. Laetoli’s lost tracks: 3D generated mean shape and missing footprints. Scientific reports, 6.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4763286/

Bennett, M.R., Reynolds, S.C., Morse, S.A. and Budka, M., 2016b. Footprints and human evolution: Homeostasis in foot function?. Palaeogeography, Palaeoclimatology, Palaeoecology 461, 214-223.

Leakey, M.D., Harris, J.M., 1987.  Laetoli: A Pliocene Site in Northern Tanzania. Clarendon Press, Oxford.

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