Photo: SK 15

This is SK 15, a lower jaw from Swartkrans, South Africa. Most scientists today attribute it to Homo erectus, but when Robert Broom and John Robinson found it, they named a new genus, Telanthropus capensis. This was the first solid demonstration that two different kinds of hominins were found at the same African fossil site. The very humanlike SK 15 contrasted with the “robust” australopithecines that make up most of the Swartkrans fossil collection.

SK 15 mandible in lateral view

However, the story is a bit more complicated. Some specialists long questioned whether SK 15 might be a small, presumably female, individual within a population where males had the form and size of the robust mandibles. That argument lost some force when later sites also demonstrated the coexistence of Homo and robust australopiths, but the variation of specimens attributed to Paranthropus robustus remains extremely extensive.

Meanwhile, a number of scientists more recently have referred SK 15 mandible to Homo habilis. Some have considered that it might represent a distinct species of Homo, more basal on the hominin phylogeny than H. habilis and H. erectus.

In other words, the taxonomic status of this specimen is really confused. To me, this is a great illustration of the problems of working with a single mandible, even though in this case the mandible is relatively complete. When you hear people talking with great confidence about the taxonomic identity of a partial mandible, SK 15 is a good case to keep in mind.