Sorry for the crappy pun. Carol Ward and colleagues recently reported an associated hip joint, KNM-ER 5881, attributable to the genus Homo (1.9 million years old). Fossils coming from the same skeleton are pretty rare, but what’s more remarkable is that portions of this bone were discovered 29 years apart: a femur fragment was first found in 1980, and more of the femur and part of the ilium were found at the same location when scientists returned in 2009:
There’s also a partial ilium associated with the femur – that makes a pretty complete hip!
Despite how fragmentary the femur and ilium are, the researchers were able to estimate the diameter of the femur head and hip socket reliably. The hip joints are smaller than all Early Pleistocene Homo except for the Gona pelvis. Comparing ER 5881 the large contemporaneous KNM-ER 3228 hip bone, the authors found these two specimens to be more different in size than is usually seen between sexes of many primate species. The size difference best matches male-female differences in highly dimorphic species like gorillas.
Ward et al. find that the specimen generally looks like early Homo but that the inferred shape of the pelvic inlet is a little different from all other Early and Middle Pleistocene human fossils. The authors take this discrepancy to suggest that there was more than one “morphotype” (‘kind of shape’), and therefore possibly species, of Homo around 1.9 million years ago. While I wouldn’t just yet go so far as to say this anatomy is due to species differences, I do agree that KNM ER 5881 helps our understanding and appreciation of anatomical variation in our early ancestors. Like all great fossil discoveries, the more we find, the more we learn that we don’t know. Here’s to more Homo hips in the near future!