Footprints in the Sand

Most would find the idea of sharing our planet with another distinct member of the hominin family quite odd. But 1.5 million years ago, it was normal, or so the theory went.

Now, scientists, for the first time, because of fossilized footprints made by two distinct species related to humans found on the shore of a Kenyan lake, have been able to say that Homo erectus and Paranthropus boisei – the first possibly our direct ancestor, and the second a distant relative – did actually coexist at the same time and place.

They walked together, side-by-side, possibly for thousands of years.

The discovery fills in “exciting pieces of the human evolution story,” wrote Kevin Hatala, an anthropologist and lead author of a new study, in the Conversation, along with two other authors of the study. “(The footprints) stir the imagination: They invite you to follow, to guess what someone was doing and where they were going.”

The research team reached this conclusion after examining previously found skeletal remains and matching the four sets of footprints found in the Turkana Basin, a site in northern Kenya, to two types of hominins, P. boisei, and H. erectus, according to the study. The P. boisei had smaller brains, wide, flat faces, and massive teeth. H. erectus were more similar to modern humans.

Meanwhile, the researchers discovered three isolated footprints seemingly coming from the same hominin, and one long continuous trail of footprints from another. They then relied on earlier experiments that used X-ray technology to understand the imprints in the mud.

They could tell the prints were made by people with different anatomies and gaits.

For example, the researchers determined that the three single footprints had higher arches, suggesting they were more human-like and hypothesizing that they belonged to the H. erectus species. They also noticed that the species responsible for the trail of prints had a big toe that changed position from step to step, suggesting it came from earlier relatives of humans such as P. boisei.

Footprints from a site nearby the basin also showed a similar overlap of the two hominins that occurred more than 100,000 years later. The researchers concluded that the two species lived in harmony together for a long time.

“I would expect the two species would have been aware of each other’s existence on that landscape, and they probably would have recognized each other as being ‘different,’” Hatala told the Guardian. “This raises lots of fascinating questions about how they would have interacted, and we don’t have all of those answers yet.”

He added that they weren’t competing for resources because of differing diets, something they could discern by examining the remains.

Hatala and his team say it is intriguing to think about what the two species thought of each other, and what it would have been like to live among another humanlike species that is similar, but yet so different.

“Fossil footprints are exciting because they provide vivid snapshots that bring our fossil relatives to life,” Hatala said in a statement, continuing, “We can see how living individuals, millions of years ago, were moving around their environments and potentially interacting with each other.”