Human Genesis

A new preprint on the Little Foot skull was posted today.  Interestingly, the article is written by Ron Clarke and Kathleen Kuman alone.  I’m used to seeing a long list of authors on most modern papers, so this one is a bit of a throwback.  The article fills in a few more details on the publication.  They refer in the acknowledgements to peer reviewers who improved the manuscript and a special issue of Journal of Human Evolution, so it looks like publication is a done deal and just a matter of finishing the editing.  These will be 2019 papers, since the 2018 volume is already published.

So what do we learn?  This is a very descriptive paper and comparisons are done primarily to other specimens.  Clarke definitely wants to use this paper to support his contention that there are two species of australopiths in South Africa.  He’s made this claim before, but the evidence is very fragmentary.  In this new paper, he and his coauthor argue that the nearly complete Little Foot skeleton gives a standard against which other fragmentary fossils can be compared.  They say that two different types of australopith fossils can be distinguished from the South African material, which they call A. prometheus (e.g., Little Foot) and A. africanus (sensu stricto, e.g., Taung child).  I don’t recall a lot of support for recognizing A. prometheus in the past, but the new descriptions of Little Foot could change that.  Time will tell.

The skull itself is nearly complete, with just a patch missing behind the foramen magnum.  The skull was found with the mandible in articulation, and it remains in articulation.  They examined the tooth surfaces by microCT.  The skull is also obviously distorted.  They describe it as having the facial bones pushed up into the frontal bone.  Notable features:

• The incisors and canines are heavily worn.  The enamel of the occlusal surface of these teeth is worn off.
• There is a diastema, a gap in the toothline, for the canines on both the upper and lower jaws.  This would be similar to the condition in gorillas and chimpanzees.  The canines on this specimen are worn down, so the diastema is not necessary, but the authors claim that it would be important for juveniles of the same species.
• The foramen magnum is positioned forward on the bottom of the skull, which is yet more evidence that this creature walked upright on two legs.
• There is a small sagittal crest, which looks kind of like a bony mohawk.  It serves as attachment for jaw muscles, and its presence implies that the jaw muscles were probably pretty big.
• The photos indicate that the mandible has no chin, which is a common feature in hominins (except for living humans, which all have chins).
• They estimate the cranial capacity to be 408 cubic centimeters, which is pretty small.  There is another partial skull, designated StW 505, that they interpret as a male with an estimated cranial capacity of 575 cc.  If that’s correct they must be very dimorphic.
• From the photos, I can see the third molars are the largest.  This is different from the modern human condition where the third molars (wisdom teeth) are the smallest.

Near the end of the paper, they offer a detailed discussion of the taxonomy, which was pretty eye-opening.  Not surprisingly, they affirm their distinction of A. prometheus and A. africanus, and they offer descriptions of each.  Then they discuss Homo habilis, which I found surprising.  There is no question that the name H. habilis has been applied to an array of fragmentary fossils, and there has been much discussion about whether or not the full group of these fossils belong to one species or more.  In particular, cranium KNM-ER 1470, originally thought to be Homo habilis, is now commonly referred to the species Homo rudolfensis.

As I said, Clarke and Kuman discuss the H. habilis fossils in the context of their separation of South African fossils into two species instead of one.  They claim that several putative H. habilis fossils match A. africanus instead, including OH 24 (Twiggy) and the South African StW 53, both of which are very fragmentary skulls.  In 2010, Darren Curnoe described StW 53 as a new species Homo gautengensis, but Clarke and Kuman don’t mention his paper.  More oddly, Clarke and Kuman claim that KNM-ER 1470 is Homo habilis, which ignores a lot of work claiming that it’s a different species altogether.  In particular, fossils reported by Maeve Leakey and colleagues support the distinction of Homo rudolfensis (including 1470) from Homo habilis.  Clarke and Kuman don’t mention this work, though.  Instead, they also claim that the partial Homo habilis skeleton OH 62, which Hartwig-Scherer worked on, is actually Australopithecus africanus.  Last but not least, they don’t even mention well-known skull KNM-ER 1813 in their discussion of Homo habilis.  This whole section on Homo habilis was really surprising to me.  They seemed to just ignore a lot of work that I was familiar with in order to support their interpretation.  That gives me pause when thinking about their treatment of A. prometheus, which deals with a lot of fossils I’m not so familiar with.  I’m very curious how professional anthropologists will respond to this whole A. prometheus proposal.

Long-suffering creationist readers are probably wondering if there’s anything more from the skull that might indicate whether Little Foot is human or ape.  I’m sure there is, but this paper didn’t give me the kind of character matrix I could conveniently use in a baraminology study.  I still find myself thinking this is an ape and not human, but time will tell.  I do not think I should just list a bunch of characteristics that I think make it an ape.  That’s a sloppy way to do this, and I know we can do better.  So we’ll have to wait a little longer for a more definitive answer.

Meanwhile, check out Clarke and Kuman’s manuscript for all the details.