A SNAPSHOT IN TIME: DETERMINING THE AGE, ENVIRONMENT, AND SOCIAL STRUCTURES OF EARLY HOMO SAPIENS USING TRACE FOSSILS IN VOLCANICLASTIC ROCKS AT THE ENGARE SERO FOOTPRINT SITE, LAKE NATRON, TANZANIA

The Engare Sero footprint site, located along the southern shore of modern Lake Natron in northern Tanzania, hosts one of the world’s most extensive and well-preserved sets of fossilized human trackways. The site includes several hundred Pleistocene-aged footprints that were pressed into volcaniclastic sediments prior to burial beneath an extensive ash deposit originating from the nearby stratovolcano Oldoinyo L’engai.

Detailed measurements of the fossilized trackways have revealed that they were likely produced by two separate groups of individuals traveling in different directions and at different speeds. Footprint sizes and stride lengths were compared to modern data sets to determine the age and probable sex of the members of each group. From these data we can form a picture of what early human foraging parties may have looked like.

The eruption that buried the human footprints also buried and preserved plant fragments, gastropod shells, and the footprints of the local fauna, including zebra, buffalo, hyena, antelope, and potentially baboon. Comparing the speciation, distribution, and density of the preserved biota to modern analogs, we can begin to also piece together a picture of the landscape through which these early humans walked.

Using field mapping and geochemical fingerprinting we have determined that Oldoinyo L’engai is the most likely source of both the foot-printed volcaniclastic sediments and the overlying tephra. The overlying tephra is at least 40cm thick at 17km from source, suggesting that it was produced by a relatively large, sustained eruption. Analog experiments have shown that rewetting of the foot-printed substrate would have almost certainly destroyed the prints meaning that the window of time from when the hominids created the prints and when they were buried and preserved could only have been a few hours to days.