Featured image: A group of Australopithecus afarensis apes walking across newly deposited volcanic ash at Laetoli, Tanzania.

(David Bygott photo of exhibit at Oldupai Gorge Site and Visitor Center.)

Laetoli, Tanzania, 1976. Returning to paleoanthropologist Mary Leakey’s camp after a tiring day in the field, Andrew Hill revealed his “inner boy” by lightheartedly biffing a colleague with a piece of dry elephant dung. During the ensuing high-spirited elephant-turd battle, Andrew, while trying to avoid a particularly large incoming chunk, tripped and fell, and in doing so, gained a measure of fame. With his face only inches from the ground, he saw footprints; human-like footprints impressed in hardened volcanic tuff; footprints that would ultimately prove to be 3.7 million years old.

It was Andrew’s lucky day. However, Mary Leakey felt pretty good about it too, especially after she and her team investigated the site and uncovered a 75 foot (24 meter) line of footprints made by primates walking upright across powdery volcano ash. (Soft rain had preserved the footprints by cementing the ash to tuff.)

The Laetoli footprints were a major discovery. They were emotionally compelling. They also were the earliest pre-human footprints ever found. However, Mary also had another reason to celebrate. She and her team had previously found at Laetoli the well-preserved remains of an ancient species of ape of the same age as the footprints. The ape (eventually classified as Australopithecus afarensis) had an ape’s small brain but notably lacked its large mobile toes. Instead, its feet had arches typical of humans, indicating to Mary that it must have walked upright, its gait more human than ape-like. The Laetoli footprints, which showed a primate walking upright when Mary Leakey’s ape was alive, provided strong backing for her conclusions.

“Australopithecus” means Southern Ape, so named because the genus was first discovered in South Africa. The species name, afarensis, refers to Ethiopia’s Afar Depression where the type specimen (which best demonstrates the species’s defining features) was discovered.

The Laetoli footprints were an extremely valuable addition to an understanding of human evolution, demonstrating as they did that a pre-human primate species had competently walked one two feet long before evolution of the modern brain, nearly a million years before the earliest known stone tools. Mary Leakey thought them the most exciting discovery of her career.

That she felt this way says a lot because she and her husband, Louis, already were famous for paleontological discoveries at Oldupai Gorge 45 km (28 miles) north of Laetoli.

(TO BE CONTINUED.)

REFERENCES

2005. A Yale Tale: Fossil Footprints. Yale Peabody Museum of Natural History. Yale University.

Bygott, D. 1992. Ngorongoro Conservation Area Guidebook.

Masao, F.T. , et al. 2016. New Footprints from Laetoli (Tanzania) provide evidence for marked body size variation in early hominids. Evolutionary Biology. https://doi.org/10.7554/eLife.19568

The Oldupai Gorge Site and Visitors Center. http://mainly museums.com

Wikipedia