I'm in Kansas and my internet is spottier here than it was in Africa. So I have a bunch of thoughts about the new Koobi Fora fossils published by Maeve Leakey and coworkers this week , and I have to wait to document them all. It just so happens that I was looking closely at a cast of the KNM-ER 1802 mandible with Lee Berger last week, comparing it to some of the Sterkfontein mandibles. There's a very interesting story there about variation in fossil samples of Australopithecus and (supposedly) early Homo.
I can't tell it yet properly. So in the meantime, I highly recommend two takes on the new fossils from two experts. Zach Cofran, who has just finished his Ph.D. and set off for a new faculty position in Kazakhstan, asks a question the Nature paper didn't: How does the new KNM-ER 62000 face compare to the otherwise very Homo-like A. sediba? ("These new fossils are as intriguing as hell") Amazing what a simple photo montage can tell you...
Adam Van Arsdale has his own substantial base of expertise coming from the Dmanisi sample of early Homo erectus, where the mandibles encompass an incredible range of morphological variation, especially with respect to mandibular size and robusticity: "The new Koobi Fora early Homo fossils".
Prior to the publication of KNM ER-60000, the Dmanisi 2600 mandible was truly exceptional in many respects relative to other mandibles assigned to early Homo. In particular, the size of its corpus and height of its ramus stood out. This new specimen from Kenya, dating from a similar time, is the best match we have yet for its features. And yet it is being linked to a fossil, KNM ER-62000, that has notable affinities (despite a significant difference in size) with KNM ER-1470, a fossil that prior to this publication also appeared somewhat morphologically exceptional relative to its peers. The authors also note similarities bewteen the new lower face (KNM ER-62000) and the Dmanisi 2700 individual. So in some ways, these fossils seem to be filling in a gap between earlier African material associated with habilis/rudolfensis and Dmanisi. And yet Dmanisi has already been widely associated with later African and Asian material assigned to Homo erectus, hence the description of it in various publications as basal Homo erectus.
My only exception to Adam's perspective is that the Koobi Fora sample itself already contains a lot of mandibular diversity. In Georgia, we have the luxury of knowing that none of the mandibles represent Australopithecus boisei, meaning that we recognize a robusticity in early Homo that may have been sifted out of descriptions of the East African sample. The earlier South African sample also has huge mandibular diversity. I think it is premature to sort these East African fossils into four or more species on the basis of one or two new specimens.
But more later.
- . New fossils from Koobi Fora in northern Kenya confirm taxonomic diversity in early Homo. Nature. 2012;488(7410):201-4.