How do hominin fossils get their numbers?

On Reddit I saw a great question that opens a window into the processes of finding and studying fossil remains. It's something that my students often wonder as they begin to encounter the fossil record in the laboratory for the first time:

What is the proper term for a fossil ID? Ardi, for example. What is “ARA-VP-6/500” called? An ID? A designation? Label?

Generally speaking, when a scientist uses the term “ID” they are talking about some scientific conclusion about the fossil, such as its taxonomic attribution (“species ID”) or what body part it represents (“element ID”). The numbers or other designators that are assigned to fossils are “catalog numbers” or “specimen numbers”. Almost always they include some kind of number, but you can also call them “specimen designators”.

Where do these numbers come from, and what do they mean?

Specimens and sites

Scientists and curators of fossil collections develop numbering systems to keep track of fossils, artifacts, and other kinds of samples. Curation requires a catalog with accurate information about the place and time an object was collected, its current location in storage, and other information about its context such as association with other objects. Specimen numbers often incorporate a site name or letter designation for a site, a designation for the institution, and a code designating the kind of specimen or collection.

The example from the question, ARA-VP-6/500, designates a partial skeleton of Ardipithecus ramidus from Aramis, Ethiopia, known popularly as “Ardi”. The “ARA-VP-6” refers to the locality; as described in by Giday WoldeGabriel and coworkers in a 1994 paper, this was designated as the sixth locality with vertebrate paleontology material from the Aramis and Adgantoli stream catchments. The “500” is the specimen designation. Parts attributed to the skeleton have their own designations, for example ARA-VP-6/500-115 is a maxilla fragment. A very similar number, ARA-VP-1/500, designates a fossil from the ARA-VP-1 locality, which itself represents part of the temporal and occipital bones of totally different individual.

Naming individuals

Some fossil hominins have simpler designations. For example, OH 7 stands for “Olduvai Hominid 7”, the seventh hominin fossil individual identified from archaeological investigations at Olduvai Gorge. At least 13 hand and wrist bones or fragments, a partial mandible, and portions of the left and right parietal bones of this immature individual were found. Each of these bones has a different catalog designation: for example, the scaphoid bone is FLK-NN-P, and the trapezium FLK-NN-Q. Those designators come from the site name: FLK is “Frida Leakey Korongo”, and site NN stands for “North North”. The designator OH 7 is thus not just a catalog number, it has resulted from scientific analysis that suggested the various hominin bones from the excavation floor belong to one individual.

Such assessments are often revisited by new analyses. In the case of OH 7, two of the proximal phalanges originally attributed to this individual (FLK-NN-J and FLK-NN-K) are both adult in developmental stage, recognized by Michael Day in his 1976 description of the bones. These are no longer considered to belong to the OH 7 individual. Many scientists have debated whether the hand fossils belong to the same individual as the cranial fragments and mandible. In this particular case, such long-standing debates might never really be settled.

The practice of designating an individual from an archaeological context was very common in European archaeology of the early twentieth century. For example, archaeologists often numbered the skeletons or graves from a cemetery. The archaeologist Dorothy Garrod applied a similar system when she directed work at Skhūl Cave, as did Ralph and Rose Solecki at Shanidar Cave, and which is why today we talk about Skhūl 5, Shanidar 1, and Qafzeh 11.

The OH system has been continued for close to seventy years, as later generations of scientists working in Tanzania occasionally discover new hominin fossils at Olduvai. Just last year, Catherine Taylor and collaborators described the OH 89 fossil clavicle, which was unearthed in 2005. Like Mary and Louis Leakey, today's teams continue to use other, different numbering systems for the non-hominin fossils, artifacts, and other objects that they study at different localities in the Gorge.

Numbers and evaluation

Pulling a hominin into a separate system relies on scientific assessment of the fossil, and that may take some time. For example, the Denisova 3 fossil is a hominin phalanx from Denisova Cave. This fossil attained remarkable scientific and public attention when Svante Pääbo's team successfully sequenced the first Denisovan genome from it, work that progressed so fast that the 2010 publication describing the genome wasn't able to include a number for the specimen. Nonetheless having a hominin numbering system at Denisova has proven to be valuable for further DNA work, with many small hominin fragments being first identified from protein or DNA analysis.

At some sites, teams that rely on a single system for hominin together with other fossils sometimes choose to skip up to a “round number” when they identify a hominin fossil. Turkana Basin hominins, for example, have often been assigned round numbers like KNM-WT 15000 and KNM-ER 47000. In a very large catalog, skipping up to a round number can be a strategy for making space for associated material.

Where hominin fragments are very rare in a fossil assemblage, researchers may want to designate every one of them in a memorable way. But at some sites fragments of many skeletons may be mixed together, and it's an important scientific question to figure out which pieces belong to the same individual. At Malapa, South Africa, researchers established a numbering system that provides numbers for each fossil fragment, such as U.W. 88-50 partial cranium, and numbers for the different individuals represented in the assemblage, such as MH1, the holotype skeleton of Australopithecus sediba. This system enables each fragment to be correlated easily with its discovery context while building anatomical interpretations at the level of elements and skeletons.

Administrative units

A third kind of system designates fossils at a higher-level administrative unit than a site or locality. This often comes into play in China, where the number for a hominin fossil may sometimes be designated by the county where the site is located instead of the name of the site itself. As I mentioned in a recent post about the Xuchang crania, Xuchang 1 and 2 are from the Lingjing site, where the site is named for the town where it is located, and the crania for the county.

This practice can sometimes mean that fossils with similar names are from different sites. For example, the Lantian 1 cranium is from a river terrace site named Gongwangling after the nearby village, while the Lantian 2 mandible is from a second river terrace site around 30 km away, itself named for the Chenjiawo village. These sites were once considered to be similar ages and many scientists once assumed they came from the same population. But today the geochronology suggests that they are actually very different in age with Gongwangling somewhere around 1.65 million years old and Chenjiawo closer to 700,000 years old.

Changing systems

Every numbering system seemed logical to somebody when they first started it. But it sometimes happens that a site outgrows the system. Any new system must maintain some kind of continuity with scientific publications that refer to the old system.

Sterkfontein, South Africa, is a site that has had several different numbering systems over the years. Robert Broom first collected fossils from the site and accessioned them into the old Transvaal Museum in Pretoria (today the Ditsong Museum of Natural History), giving them numbers like TM 1512. Later, he began to designate fossils with Sts, like the Sts 5 skull known popularly in South Africa as “Mrs. Ples”. In 1958 the owners of the Sterkfontein quarry donated it and the surrounding land to the University of the Witwatersrand, and that institution began excavations in 1966. From that time forward, curation of fossils from this excavation began with hominins numbered StW 1, while primate and other fossil material were curated with different systems.

Laws and fossils

Hominin fossil sites are found in many different countries, and the laws and authorities governing heritage vary country-by-country. Organized fieldwork projects generally maintain a formal relationship with a museum, university, or other government institution that will be responsible for curation of fossils, artifacts, and other objects that result from fieldwork. In many countries, that relationship must be formalized before any fieldwork permit will be issued.

Today, ethical researchers work to build capacity for future work, training the next generation of scientists and ensuring that sites are conserved. In my experience working in many different countries, scientists try to build sustainable systems that will preserve information for future research. Today's researchers are developing collections of many different kinds of objects, not only fossils and artifacts but sediment samples, thin sections, pollen, DNA, and other microscopic objects. Every one of those requires documentation that can be correlated back to their context in a site. Researchers work together with a curating institution to make sure that information can last. With complicated sites, that can mean some complicated systems are in use.

When it comes to public communication, researchers and institutions both tend to focus on the broadest and simplest way to identify a fossil. For many, this is the species name or site name. For others, it may be a nickname: “Lucy” is way more memorable than AL 288-1, “Ardi” easier than ARA-VP-6/500, and—as painful as it is for me to say it—more people remember “Mrs. Ples” than Sts 5.

Since I was a kid learning about fossil human relatives, I've taken some pride in remembering their numbers. Famous fossils like KNM-ER 1470 from Koobi Fora, Kenya, have specimen numbers with almost legendary status. Over time I've come to appreciate that these numbers and names each reflect a facet of the history of discovery. Still, nowadays I have just as much appreciation for the more common names that researchers and others have coined for fossils. They help to connect everyone with the tree of fossils that we all share in our ancestry.

References

Taylor, C. E., Masao, F., Njau, J. K., Songita, A. V., & Hlusko, L. J. (2024). OH 89: A newly described ~1.8-million-year-old hominid clavicle from Olduvai Gorge. Peer Community Journal, 4. https://doi.org/10.24072/pcjournal.372

Thackeray, J. Francis. (2020). A summary of the history of exploration at the Sterkfontein Caves in the Cradle of Humankind World Heritage Site. In B. Zipfel, B. G. Richmond, & C. V. Ward (Eds.), Hominin Postcranial Remains from Sterkfontein, South Africa, 1936-1995 (pp. 3–7). Oxford University Press.

Wang, S., Lu, H., & Xing, L. (2014). Chronological and typo-technological perspectives on the Palaeolithic archaeology in Lantian, central China. Quaternary International, 347, 183–192. https://doi.org/10.1016/j.quaint.2014.07.014

WoldeGabriel, G., White, T. D., Suwa, G., Renne, P., de Heinzelin, J., Hart, W. K., & Heiken, G. (1994). Ecological and temporal placement of early Pliocene hominids at Aramis, Ethiopia. Nature, 371(6495), 330–333. https://doi.org/10.1038/371330a0