From late May to early July, an international team of students, paleoanthropologists, geologists, and faunal experts fly to Drimolen, a chain of caves situated north of Johannesburg in South Africa and inside the “Cradle of Humankind.” Every year, this fossil excavation team, of which I am a member, arrives with revived hope of unearthing intact and complete human ancestor skulls. We begin our search as soon as we step off the plane, knowing that our real break could happen at any moment, hidden among the rocks and gravel.
Samantha Well, a student excavator, discovered the adult male skull of a Paranthropus robustus, lying upside down with the upper teeth visible, in 2018. Angeline Leece and Stephanie Baker, two of our finest excavators, slowly and persistently excavated the fossil over the next week before it could remove it, even though it was still partially encased in sediment. Over the next two weeks, I continued their excellent work by scraping the remaining residue and reassembling the hundreds of individual fragments to free the skull from its two-million-year-old sedimentary sarcophagus. Although scientists already knew about the species Paranthropus robustus, a cousin to our lineage, the finding of such a complete skull prompted a rethinking about all we believed we knew about our extinct ancestor.
One of the most exciting aspects of finding human fossils is that it allows us to resolve previously unanswered scientific questions about our common ancestors. These current concerns based on the speed and mode of human microevolution—small shifts within a species—in reaction to a changing environment two million years ago in the case of the new Paranthropus robustus cranium, named DNH 155. According to Darwin’s principle of slow adaptation through natural selection, populations can evolve, but we seldom have the resolution to “see” how these changes happened so long ago. To put it another way, we have a fantastic zoomed-out view of the human evolutionary image. Still, when we zoom in to determine more minor scale shifts, the image becomes pixelated and difficult to see. The DNH 155 cranium’s discovery essentially gives us a limited yet high-resolution snapshot of small-scale microevolutionary changes that occurred within distinct, sequential populations.
Excavating a fossil is a lot like unwrapping a present: you never know what you’re going to find. The “wrapping” in the case of the DNH 155 cranium was two-million-year-old cave sediments, and the “unwrapping” was a laborious and dangerous operation that took weeks. About this (and just like a present), our team had cause to believe from the start that we will have the honor of discovering something very unique. The trouble with archaeology and paleoanthropology, on the other hand, is that the process of excavating a fossil or artifact is fundamentally harmful. The sediments surrounding such finds will reveal a lot about the age and context of the fossils, so we need to develop new ways to preserve this record.
Since fossil human ancestors only emerge from the earth in one piece, the case with the DNH 155 skull was much more complicated. The DNH 155 cranium was in hundreds of fragments, some as tiny as a pinky fingernail, and each one was extremely delicate. Since it is impossible to excavate a fossil twice (and thus lose the original context), we must get it right the first time. As a result, 3-D scanners have changed the game.
IN PROGRESS DIGITAL CONSTRUCTION
My primary responsibility on the job is to rebuild fossils, so I was charged with bringing the DNH 155 skull together. It took a week to thoroughly clean the skull fragments from their initial resting position inside the Drimolen Main Quarry, as well as all the sand that was gluing the pieces together. The Artec Space Spider, a specialist handheld 3-D scanner, was used for digitizing each of the nearly 300 fragments as they painstakingly extracted them. The scanner fires light patterns that deform depending on the terrain of the target it’s hitting and bounce back to the scanner, similar to how a bat uses sonar, except instead of echo, light is jumping back and forth. It used this technology to produce high-resolution photographic records of each fragment of the cranium’s position within the sediment if it dislodged some of the pieces suddenly. By manually placing the elements together, it completed the first step of rebuilding. However, even after manual repair, certain sections of the skull were unable to be mounted because the touch point was too small or a small portion of the edges had been missing. It used the Artec software to place the pieces about one another in these situations digitally. DNH 155’s face, in particular, cannot be securely connected to the remainder of the skull. The use of modern technology accomplished this fusion. While the fragments may have been fused, doing so would have been dangerous and possibly resulted in irreversible damage to the fossil. Without 3-D technology, the reported reconstruction of the DNH 155 skull would not have been feasible, which would have been a significant blow to other researchers’ ability to assess the fossil in the future.
FOSSIL DATA DEMOCRATIZATION
The research program to uncover the mysteries of this unusual skull included more than just reconstruction. Many scholars who focus on South African fossils are unable to visit Johannesburg to examine the originals. It is particularly true for researchers who are not affiliated with a prosperous university and students who are financially strapped in general. The Drimolen team has spent a considerable amount of money digitizing the DNH 155 skull and most of the Drimolen fossil assemblage for this cause. As a Ph.D. student, I’m fascinated by the potential for high-quality 3-D scanners like the Space Spider to democratize science by providing free and convenient access to research-quality data. Although the University of the Witwatersrand (in the case of the Drimolen fossils) controls permits and access to such data, our ultimate goal is to share our data with researchers, especially early-career researchers, who are working on a topic related to South African hominin fossils. Paleoanthropology has a reputation for being a combative and sometimes divisive field. I assume that 3-D technology and the highly portable data it provides have the potential to pull together a new generation of researchers and promote previously impossible collaborations. Gerhard Weber, a paleoanthropologist, called for such a movement twenty years ago. We’re not quite there yet, but we’re on the right track.