Flores

A single foot bone from a cave isn't ordinarily very remarkable. But when it's a funny-looking foot bone from a 67,000-year-old site on an island, that gets a little more attention. New in the Journal of Human Evolution, Arnand Mijares and colleagues report on a third metatarsal from a cave called Callao Cave, on the Philippines northern island of Luzon. If the date is right, this is the oldest human bone known from the Philippines, or indeed from anywhere not reachable by land from Asia -- except for the deepest bone elements from Liang Bua cave on Flores.

The presence of a human bone on an island not reachable without a water crossing naturally brings up parallels to the Flores case. The bone's small size provides an additional parallel. Mijares and colleagues compare the metatarsal to a sample of small-bodied Negrito skeletal remains from the Philippines, finding that its dimensions are smaller than any of them. It is smaller in its preserved dimensions than the small metatarsal of OH8, generally assigned to Homo habilis.

Did the bone belong to a hobbit-like creature?

Sadly, there is no direct comparison to the foot bones of LB1, the skeleton from Flores that started the Homo floresiensis craze. This would seem to be another case where the failure to disseminate scans of a specimen has impeded the analysis of new discoveries from other sites. The science suffers for it. The description of the LB1 hindlimb elements by Jungers and colleagues (2009) includes good photos of the MT3 of that specimen, which looks basically humanlike, although small and with a small proximal end in particular.

Human metatarsals have shafts that tend to get thinner as you move from the proximal to the distal end of the bone. The thinning is both in the side-to-side (mediolateral) dimension and in the top-to-bottom (dorso-plantar) dimension. The shaft in humans is relatively straight. Ape metatarsals tend to be very curved, and uniform in thickness from proximal to distal. Monkeys are between these extremes in curvature, although with substantial variability.

The Callao MT3 is humanlike in being relatively straight and thinning from proximal to distal, at least in a mediolateral dimension. But the bone actually gets thicker in the dorso-plantar dimension as it approaches the head. That's not like most human metatarsals. The proximal end and shaft, which are well-preserved, are smaller in this Callao MT3 than in the females of the Negrito comparative sample examined by Mijares and colleagues. The proximal end and shaft are quite a bit smaller than the OH8 third metatarsal. This is a very small bone.

Maybe too small. The metatarsal is reported to be smaller than OH8, with an estimated length just a hair longer than the measured length of LB1 MT3.

I'd have to look at a lot more MT3's to be sure -- which I can't do right now -- but this one looks sort of funny to me. Could it be some other kind of primate? The authors hold out some possibility that the specimen represents a subadult, but if it does, it was very close to being adult based on the preserved anatomy. So it's not a case where the bone was going to grow a lot more. As usual, I wish that the paper included more information about the range of variation in humans and other primates. If we're dealing with an odd specimen, how strange is it in the characters that stand out?

As for dating of the site, a mean of 67,000 years ago is the result of uranium-series dating of two cervid teeth in the same stratigraphic unit as the metatarsal. This method requires the application of a model of uranium absorption over the time since the teeth were deposited. This model is too complicated to describe here; the authors go through several scenarios and conclude that despite the possibility of inaccuracies, the remains are very unlikely to have been deposited as recently as 40,000 years (the approximate age represented by occupation of Niah Cave, Borneo). I have no reason to doubt the dating.

I'll leave open the question of whether a date above 60,000 years ago is unexpectedly ancient for the region. It's interesting, at least. I see nothing impossible about there having been non-hobbit-ish humans in the area at that time, as I think we'll need to revise much about the timing of dispersal of mtDNA lineages from Africa. And don't forget that mtDNA doesn't tell the important story anymore.

But by and large, I want more information on this one.

(CORRECTION: The initial version of this post followed the paper in placing the site east of Wallace's line. Wallace's line actually passes south of the Philippines.)

References:

Jungers, W.L., Larson, W., Harcourt-Smith, W., Morwood, M.J., Sutikna, T., Rokhus Due Awe, Djubiantono, T., 2009. Descriptions of the lower limb skeleton of Homo floresiensis. J Hum Evol 57:538-554. doi:10.1016/j.jhevol.2008.08.014

Mijares AS, Détroit F, Piper P, Grün R, Bellwood P, Aubert M, Champion G, Cuevas N, De Leon A, Dizon E. 2010. New evidence for a 67,000-year-old human presence at Callao Cave, Luzon, Philippines. J Hum Evol (in press) doi:10.1016/j.jhevol.2010.04.008

A new paper is pushing back the time of initial occupation of Flores by hominins to at least 1.0 million years ago. Adam Brumm and colleagues (2010) are reporting that they've found stone tools in a site from the Soa Basin of Flores, the same geological region as the previous site of Mata Menge.

The Wolo Sege excavation yielded no faunal remains, but 45 in situ stone artefacts were recovered from the conglomerate and two fine-grained metavolcanic flakes were excavated from the lower tuffaceous siltstone layer ~15–20 cm above the Ola Kile Formation (Fig. 3e, f). A single volcanic flake was also recovered from the upper overbank deposit during extraction of sediment for dating. The Wolo Sege stone artefacts are predominantly small and morphologically undifferentiated flakes struck from cobbles by direct hard-hammer percussion (Fig. 3; see also Supplementary Fig. 2), but include a bifacially and centripetally worked ‘radial’ core, similar to those characteristic of the Mata Menge assemblage of stone artefacts.

The radial core is not illustrated, but several of the flakes are figured in the paper. The conglomerate in question is overlain by a layer with a minimum date of 1.02 million years.

A date of 880,000 years ago for human occupation made for a convenient explanation of faunal turnover on the island, which happened around that time. The turnover included the extinction of the small pygmy stegodont species Stegodon sondaari, which was replaced in later faunal assemblages by the Java-derived Stegodon florensis. It also included the extinction of giant tortoises.

This suggests that the non-selective, mass death of S. sondaari and giant tortoise, associated with stratigraphic evidence for a major volcanic eruption at Tangi Talo ~0.9 Myr ago10, could represent a localized or regional extinction, and that the faunal turnover may have been a result of climate change, volcanic activity or some other natural process or event (Fig. 5).

I discussed this with my graduate seminar yesterday. The long persistence of this toolmaking culture, in what must have been a rather small human population, is weighing on my mind. Were there recurrent contacts from Java, keeping the population going? How dependent were these people on their tools?

Hominin predators can lead to unstable dynamics -- most predators will undergo predator-prey cycles, but humans can switch to other resources and continue to press a small prey species to extinction. The long persistence of tasty animals on Flores in the presence of hominins suggests that the subsistence practices of these hominins were different in some ways from later humans.

This finding doesn't really help us to resolve the issues of the later Flores record, including the relationships of the skeletal individuals with other hominins. There's been some press about the hobbits lately, but it's all paleoanthropological tree-marking -- except for the news that they'll be reopening excavations at Liang Bua.

References:

Brumm A, Jensen GM, van den Bergh GD, Morwood MJ, Kurniawan I, Aziz F, Storey M. 2010. Hominins on Flores, Indonesia, by one million years ago. Nature (advance online) doi:10.1038/nature08844

Elizabeth Culotta reports from the Stony Brook hobbitrama:

The meeting was a rare chance for U.S. researchers to hear from the team that discovered the hobbits, which they officially call H. floresiensis. Lead excavator Thomas Sutikna of the National Research and Development Centre for Archaeology in Jakarta and Mike Morwood, now of the University of Wollongong in Australia, flew across the globe for the meeting, which gathered only those researchers who already accept H. floresiensis as a new species.

One piece of news: Matt Tocheri found another capitate among the bagged bone fragments:

The bone has the same peculiar and primitive configuration seen in the capitate of the main skeleton, suggesting that at least two individuals from Liang Bua have this oddly shaped wrist bone.

I think Culotta's short description gives a good flavor of the conference. The webcast version, which I mentioned earlier in the week hasn't shown up in the archive at Stony Brook. But two of the Richard Leakey symposia have video available (Link to archive), which might be interesting viewing.

I started one of them, and the Stony Brook provost introduces the symposium by noting that they wanted their series of symposia to include specialists with strong differences of opinion, with the hope of making progress toward defining the critical issues.

I guess somewhere along the way they decided to alter that strategy....