Laetoli

In a new paper, Yohannes Haile-Selassie and colleagues describe new hominin fossils from Woranso-Mille, Ethiopia. A good thing: It gives somebody like me a rationale for describing early hominins from the point of view of Hadar. You see, Hadar is the first sample to include a really complete skeletal representation. You can present earlier sites as a series of "firsts", but that's kind of misleading. Now, the simple Ardi-Lucy comparison carries a lot of water for teaching early hominins, and if we can assume that the samples intermediate in time are mostly A. afarensis-like, so much simpler.

Oh, and one more really good thing: Standard dental measurements are provided in the text of the paper. Thank you, AJPA! We may not get all the specimens, but at least we can check the statistics.

But there's a chance that things are not so simple as they seem, that there are mysteries still waiting to jump out of this sample and scare us at night. I imagine that some people are less than thrilled about this paper, which explicitly rejects the reality of one Leakey-named species and ignores another into obscurity. One might expect me to welcome our new lumping taxonomic overlords. And yet, this little paper doesn't provide some information and comparisons that seem like curious omissions. Which makes me wonder...

The fossils from Woranso-Mille are between 3.6 and 3.9 million years old -- basically older than Laetoli and younger than Kanapoi. Since the Laetoli sample is A. afarensis, and the Kanapoi sample is A. anamensis, we can expect that the Woranso-Mille sample would say something about how these two species were related to each other. The fossils might be one species or the other, they might be intermediate between them, or they might even be something altogether different.

What is there?

The sample as described is almost exclusively dental, with only a fragment of mandible and another of maxilla tossed in the mix.

Some readers may have been under the impression there's more at this site, and indeed I am as well. I think I've even seen them for 500 milliseconds at a meeting once upon a time. Of course, maybe that was a dream. Much in paleoanthropology seems to be fading into a unicorn fairyland these days...

Wait a minute! It's for occasions like this that I have a blog! As it turns out, I took some notes on Woranso-Mille back in 2007.

Now, I have to warn you: These notes were so snarky that I didn't dare hit "publish". But there's no sense shirking responsibility for them now. Next thing I know, some crank will be hacking my server to bring all this snark into the open!

I don't have a lot to say about the new footprints from Ileret, described by Matthew Bennett and colleagues. Seems like a nicely done study, particularly given the length constraints in Science.

With respect to the comparison with Laetoli, I think that the perspective article by Robin Crompton and Todd Pataky sort of hits the important questions:

Were the Ileret footprint makers' feet the first to function just like ours? Do the Laetoli prints represent more "apelike" foot function? Do all regions of a footprint record local maxima in foot pressure, or do some record how pressure changes over time, as braking forces change to propulsive ones? None of these questions can be answered at present. It is not even clear whether a nondivergent big toe is important for the extended push-off typical of human walking or just a by-product of other anatomical changes (1, 2, 4, 8). The effect of substrate recoil or of later abrasion on the reliability of footprint measurements must also be established (6-8). But the findings of Bennett et al. herald an exciting time for studies of the evolution of human gait.

Merely quantifying significant differences in the prints doesn't really tell us much about australopithecine gait or foot function. My impression of footprints (har!) is that it's tough to analyze them.

There's much about adduction of the big toes in the press and the abstract of the paper. The text description doesn't quite support the interpretation that Ileret is identical to recent human footprints, though:

The angle of hallux abduction, relative to the long axis of the foot, is typically 14° compared to, and statistically distinct from (table S4), 8° for the modern reference prints and 27° for the Laetoli prints (Fig. 4A).

They're closer to Holocene people than to Laetoli, since the range of living prints overlaps with these. The statistics are trickier than they might look, since these are multiple trails, but each consisting of the prints of a single individual. So I'm skeptical that they really are statistically different from humans in their big toes.

But anyway, they're in-between Laetoli and humans, so that makes a good evolutionary sequence!

I'm a bit skeptical of the body size estimation in the paper. Not the regression -- that's pretty straightforward. More the interpretation that the foot size is necessarily "Homo erectus/ergaster", or that they're a "perfect fit" for the Nariokotome skeleton.

The average foot length recorded for the FwJj14E trail is 258 mm. Two hundred fifty eight millimeters is not a very big foot -- it's a shade bigger than a U.S. men's size 8. You can have a tall person with a size eight shoe, to be sure. But their height estimate of 1.75 m is not all that tall -- it's 5 foot 8 inches, which is around the 25th percentile for height for American men (and around the 90th percentile for American women).

Now, the question here is whether that's sufficient to make them "Homo erectus/ergaster" prints, or whether they might be A. boisei. That depends on whether Australopithecus had big feet. It doesn't seem to unlikely that a male A. boisei might be 1.4--1.5 m in height, and if they had relatively big feet, well then Katy bar the door!

I don't have any strong feelings -- at 1.5 million years old, these prints might be too recent to be A. boisei anyway. But it seems to me there is this question about body size estimation, when you don't have any evidence about the body proportions.

References:

Bennett MR, Harris JWK, Richmond BG, Braun DR, Mbua E, Kiura P, Olago D, Kibunjia M, Omuombo C, Behrensmeyer AK, Huddart D, Gonzalez S. 2009. Early hominin foot morphology based on 1.5-million-year-old footprints from Ileret, Kenya. Science 323:1197-1201. doi:10.1126/science.1168132

Crompton RH, Pataky TC. 2009. Stepping out. Science 323:1174-1175. doi:10.1126/science.1170916