In August 1936, Robert Broom, a Scottish doctor with a keen interest in paleontology, visited a lime quarry in South Africa called Sterkfontein. In a guidebook at the time, the owner of the site, wrote, “Come to Sterkfontein and find the ‘missing link.’” It would not be long before Broom did just that.
On Broom’s third visit to Sterkfontein, the quarry’s manager George Barlow presented him with a lump of calcified sediment in the shape of a brain, complete with convolutions and venous patterns. It was of modest size, but was certainly bigger than that of a monkey or other animal whose fossils were commonly found in the caves of the area. He soon located much of the cranium as well as many of its associated teeth and determined the pieces represented a fossil human called an ape-man.
At the time, the only other example of an ape-man was the “Taung Child” skull. Due to its developmentally young age, the scientific community had been reluctant to embrace the fossil as a legitimate human ancestor, because the bones of juvenile apes and humans look more alike than their adult counterparts.
The "Taung child" skull. Image by and courtesy of Jason Heaton
Eighty years ago, on September 19, 1936, Broom published his findings, which would reshape our knowledge of our earliest ancestors. The fossils began to suggest that Africa was the ancestral homeland of our lineage, and not Europe or Asia as was previously believed. Now called the “Cradle of Humankind,” the rolling hills between Johannesburg and Pretoria have since advanced our knowledge far beyond Broom’s initial revelation and continue to further academic knowledge to this day.
The region attracted major attention long before the first human fossils were ever found there. In the 1890s, gold was discovered in the caves and later was mined for the tremendous lime resources also found there. Although the raw materials have been stripped, the fossils have proven to be the more precious resource.
In 1947, eight years after the end of the lime mining, Broom returned to Sterkfontein with zoologist John Robinson, searching strictly for fossils. Within three weeks, Broom and Robinson were rewarded with the recovery of an ape-man skull, nicknamed Mrs. Ples. Other findings quickly accrued, including a partial skeleton, the anatomy of which showed that although small-brained and apelike in many ways, the ape-men of nearly 3-million-years-ago were also upright, two-legged walkers, similar to modern humans.
By 1956, younger deposits were discovered at Sterkfontein by C.K. Brain, a geology student who also recognized primitive stone tools in these new sediments. Importantly, these tools were associated with fossils of more advanced species of our own genus, Homo.
After 10 years of inactivity at Sterkfontein, anatomist Phillip Tobias and his assistant Alun Hughes initiated systematic excavations at Sterkfontein in November 1966. It was not until 18 long months later that the first fossil human scraps were recovered. Over the next 25 years the two men would recover hundreds of fossils.
One of the most significant decisions they made was in 1978, when they began to investigate the deep underground portions of Sterkfontein, including an area called the Silberberg Grotto. Lime miners had been active in the grotto and left hundreds of blocks of calcified, fossil-rich sediment strewn across the area. Hughes collected the fossils and stored them in boxes to study later.
After Hughes died in 1991, paleontologist Ron Clarke took his place. Clarke went to the fossils that hadn’t moved from the boxes for nearly 15 years, where he discovered a misidentified and previously unknown ape-man bone. He later discovered 12 bones of the foot and leg of a single ape-man.
Paleoanthropologist Ron Clarke is now working on a the full description of a nearly complete skeleton he expects will be an anthropological Rosetta Stone. Image by and courtesy of Jason Heaton
Many bones within these South African caves found their way there through the action of carnivores who dragged animal carcasses to the caves to eat in seclusion. This messy process usually broke and scattered bones, covering them with tooth marks.
Since Clarke discovered bones in an entirely different state of preservation, he was confident that his ape-man had escaped being a carnivore’s meal; indeed, he believed that there was a complete skeleton somewhere in the depths of the Silberberg Grotto.
In June of 1997, two of Clarke’s assistants, Nkwane Molefe and Stephen Motsumi, were tasked with the impossible: trying to find a tibia where the rest of Clarke’s ape-man likely rested. He believed that since it was likely broken during the mining activities 65 years prior, that the remaining bone might still be visible.
Despite the massive, dank and dark surroundings of the Silberberg Grotto, Molefe and Motsumi found the broken tibia after just two days of searching, armed only with handheld lamps.
Over the next several years of extraction, Clarke’s prediction of an entire ape-man skeleton was confirmed. What was nicknamed “Little Foot” by Tobias, has been lifted from the depths and is being prepared and described by Clarke. Dating techniques estimate “Little Foot” to be 3.7-million-years-old, more than a million years older than the ape-men fossils first found by Broom and Robinson decades before.
When finally fully described, “Little Foot” will be an anthropological “Rosetta Stone,” allowing other isolated and broken fragments to be better understood when compared to this complete skeleton.
After 80 years, we’re honored to collaborate with Clarke in continuing his work at this iconic site. As we move forward with our exploration of the caves, one of our primary goals is to integrate excavation data from the last 50 years with high-resolution stratigraphic, sedimentological and geochemical information.
This evidence will further reveal the “big picture” of Sterkfontein’s history and our own evolutionary past, and will hopefully prove part of the proud legacy of Robert Broom’s astonishing discoveries.
http://blogs.scientificamerican.com/guest-blog/the-fossil-that-rewrote-human-prehistory/