Every year, from late May to early July, a global team of students, paleoanthropologists, geologists and faunal experts, traveling from South Africa, Australia, the United States and Europe, make the trip to Drimolen, a system of caves located north of Johannesburg in South Africa and within the “Cradle of Humankind.” This fossil excavation team, which I am part of, arrives each year with renewed hope of unearthing preserved and complete skulls of human ancestors. From the moment we step off the plane, we search in earnest, anticipating our big break could happen at any minute, lying in wait among the rock and dirt.
In 2018 a student excavator, Samantha Good, came upon the adult male skull of a Paranthropus robustus, lying upside down, with the upper teeth showing. Over the next week, our two best excavators, Angeline Leece and Stephanie Baker, carefully and persistently excavated the fossil until it could be removed, still largely encased in sediment. Over the next two weeks I continued their fine work by removing the remaining sediment to free the skull from its two-million-year-old sedimentary sarcophagus, and commence the painstaking process of reconstructing the hundreds of individual fragments. While the species Paranthropus robustus, a cousin to our own lineage, is already known to science, the discovery of such a complete skull precipitated a quest to reassess everything we thought we knew about our extinct relative.
One of the most exciting things about discovering human fossils is that they provide the opportunity to address scientific questions about our own shared origins that were not previously possible to answer. In the case of the new Paranthropus robustus cranium, labeled DNH 155, these new questions all centered on the tempo and mode of how human microevolution—small changes within a species—occurred in response to an evolving climate two million years ago.
Darwin’s theory of gradual evolution by natural selection predicts that populations will change over time, but rarely do we have the resolution to “see” how these changes occurred so long ago. To put it another way, we already have an excellent zoomed-out perspective on the human evolutionary story, but when we zoom in to assess smaller scale changes, the picture becomes very pixelated and hard to see. The discovery of the DNH 155 cranium effectively provides us with a narrow but high-resolution snapshot of the small-scale microevolutionary changes that occurred between different, sequential populations.
Excavating a fossil is a little bit like unwrapping a present: you’re never entirely sure of what you’ll get. In the case of the DNH 155 cranium, the “wrapping” was two-million-year-old cave sediments and the “unwrapping” a painstaking and precarious process that took weeks. Despite that (and much like a present), our team had good reason to suspect from day one that we were going to collectively have the privilege of uncovering something very special. However, the problem with archeology and paleoanthropology is that the act of excavating a fossil or an artefact is inherently destructive. The sediments encasing such discoveries can tell us much about the age and context of the fossils themselves, and so we must invent innovate ways of preserving this record.
The situation with the DNH 155 cranium was even more complex because fossil human ancestors rarely exit the ground in one piece. In fact, the DNH 155 cranium was in several hundred pieces, some smaller than the average pinky fingernail, and each piece was incredibly fragile. Because it is not possible to excavate (and thus destroy the original context) of a fossil twice, it’s important we get things right the first time. For this reason, 3-D scanners have been a game changer.
DIGITAL CONSTRUCTION IN PROGRESS
My principal job on site is to reconstruct fossils, and so I was tasked with putting together the DNH 155 skull. It took around a week to fully remove the skull fragments and all the sediment gluing the pieces together from their original resting place within the Drimolen Main Quarry. As each of the roughly 300 fragments were painstakingly removed, they were digitized with an Artec Space Spider, a professional handheld 3-D scanner. The scanner shoots patterns of light that distort based on the geography of the object it is hitting and bounce back to the scanner—like a bat using sonar, but in this case, light rather than sound is what’s bouncing back and forth. This technology was used to create high-resolution digital records of each piece of the cranium’s location within the sediment in case any pieces unexpectedly dislodged.
The first phase of reconstruction was completed by manually putting the pieces together. But, even after manual reconstruction, there were some elements of the cranium that couldn’t be placed because the contact point was too small, or a tiny part of the edges had been lost. In these cases, the Artec software was used to digitally situate the parts in relation to one another. Specifically, the face of DNH 155 cannot safely be attached to the rest of the cranium. This fusion was achieved digitally. Although it could have been glued, joining the pieces in this fashion would have been risky and would likely have caused permanent damage to the fossil. The published reconstruction of the DNH 155 cranium would not have been possible without 3-D technology, which would have been a huge blow to the ability of other researchers to assess the fossil in the future.
DEMOCRATIZING FOSSIL DATA
Reconstruction was only one part of the research program designed to reveal the secrets of this rare skull. Many of the researchers who work on fossils from South Africa are unable to travel to Johannesburg to work on the originals. This is especially true for researchers who are not based at wealthy institutions, and for cash-strapped students in general. It is for this reason that the Drimolen team have invested significant capital to digitize the DNH 155 cranium and most of the Drimolen fossil assemblage. As a Ph.D. student myself, I am particularly interested in the potential for high quality 3-D scanners such as the Space Spider to democratize research by allowing free and easy access to research-quality data. While permissions and access to such data are controlled by the University of the Witswatersrand (in the case of the Drimolen fossils) it is our ultimate intention to share our data with researchers, particularly early-career researchers, who are pursuing a topic related to the South African hominin fossils.
Paleoanthropology has a history of being a combative and often exclusionary discipline. I believe that 3-D technology and the highly portable data it generates have the capacity to help bring together a new generation of researchers and facilitate collaborations that previously would not have been possible. Twenty years ago, paleoanthropologist Gerhard Weber called for such a revolution. We’re not quite there yet, but we are making progress.
This is an opinion and analysis article.
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