Trampling Over The Dikika Cut Marks

Well, I feel somewhat vindicated. Remember the post where I criticized hominin cut marks from over 3 million years ago? Others have also had an eye of suspicion and have published their concerns in PNAS this week.

I was wrong in considering the croc marking differential to the cut marks. But I was not wrong in thinking they author of the original paper made the wrong conclusions. The authors of this new paper raise up an even more logical explanation, and carried out a more thorough analysis. Here’s part of their argument from the abstract,

“The Dikika research group focused its analysis on the morphology of the marks in question but failed to demonstrate, through recovery of similarly marked in situ fossils, the exact provenience of the published fossils, and failed to note occurrences of random striae on the cortices of the published fossils (incurred through incidental movement of the defleshed specimens across and/or within their abrasive encasing sediments). The occurrence of such random striae (sometimes called collectively “trampling” damage) on the two fossils provide the configurational context for rejection of the claimed butchery marks. The earliest best evidence for hominin butchery thus remains at 2.6 to 2.5 Ma, presumably associated with more derived species than Aafarensis.”

Trampling vs. Cut Marks
Trampling vs. Cut Marks (The image in A is courtesy of R. Blasco and J. Rosell. The images in B, D, and F are modified from McPherron et al.)

Looking back at the comment thread, I got a lot of flak. Aside from being wrong about the croc markings, I won’t deny that my post was inflammatory and incited a lot of the response. But many who know just a bit about the fossil and archaeological record, may find it extraordinary to believe australopithecines were using stone tools to extract food from flesh and bone from ‘indirect’ evidence. Of more concern was the lack of exhaustive exploration into other possibilities.

I remember as an anthropology undergrad one of my professors designed a hands-on experiment for us. If memory serves me correctly, this was for a zooarchaeology class. She acquired some beef bones from the local butcher and gave us stone tools. We were instructed to extract the marrow from the bones. We hammered the afternoon away.

Part of our assignment was to use different techniques and tools. We could cut, saw, abrade, chisel, etc. After the mess was done we compared our extractions from prehistoric samples. This comparative approach allowed use to systematically compare how we modified the bone to how possibly prehistoric individuals modified bone.

The authors of the current PNAS paper did something similar. The hypothesized that trampling could have created similar modifications as seen on the 3.39 million year old Dikika bones. And what did they do? Well they got some bone and experimentally setup some trampling experiments. As one would expect, cut marks would have a \/ shaped incision. Incidentally, the bones from Dikika show a \_/ flat bottom morphology. The authors write,

“Ninety-six percent of experimental trampling grooves display a broad-based, open cross-section with the aforementioned shape, versus just 4% of experimental grooves inflicted by simple (i.e., unmodified) stone flakes used to cut meat from bones. In addition, curvy and sinuous groove trajectories characterize nearly 70% of experimental trampling marks,compared with just 10% of experimental cut marks created with simple flakes (11). Together, these experimental results provide a robust actualistic context to evaluate illustrated marks F, G, H2,and I on DK-55–3 as high-probability trampling damage and not stone tool cut or percussion marks…”

I wonder what happened to good science?

What happened to the scientific method?

Did we not learn how to set up experiments and carry out analysis?

How can a paper make all the way into Nature and not exhaust all the possibilities?

These are not rhetorical questions. I am seriously asking it. I honestly feel that there is something rife in paleoanthropological studies lately. I must sound like a broken record to say yet again, too often are papers published in haste and for fortune and glory… All which compromise the validity & ethical responsibility of the science.

    Domínguez-Rodrigo M, Pickering TR, & Bunn HT (2010). Configurational approach to identifying the earliest hominin butchers. Proceedings of the National Academy of Sciences of the United States of America PMID: 21078985

7 thoughts on “Trampling Over The Dikika Cut Marks

  1. I basically agree with what you said at the end of your post. On the other hand, I don’t think that there’s really problem when it comes to the qualitiy of science in general.
    If someone is publishing papers in which he’s stating controversial and (more importanly) bad researched hypotheses, prove that they’re wrong. As long as you’re able to do so, there is absolutely no harm done. In fact, even if it’s not obvious this stuff helps to improve our knowledge about certain things.
    The Problem starts when you start “attacking” those hypotheses on a non-scientific level, or stop attacking them at all.

  2. I agree that the scientific method is becoming absent in anthropology. Although it is funny that you site Dominguez-Rodrigo as an example of good science when his work is anything but. As an expert in early stone age taphonomy and zooarchaeology that is one of the few people to have experience with crocodile tooth-marked bone, I can tell you that the marks from Dikika are in fact crocodile tooth marks. Keep yours out for another paper as this debate is far from over. I also suggest that you not take anything Dominguez-Rodrigo claims in publication for granted.

  3. I’m sure you want to know how the scientists of the Nature paper regard this latest effort to discredit their work. The Dikika team has responded in great detail to the PNAS article, including issues related to the scientific method. From Shannon McPherron on behalf of the team (widely available now all over the web) — so stay tuned:

    “Domínguez-Rodrigo et al. have published a critique of our findings, questioning the provenience of the finds and suggesting that the marks on 3.4 Ma bones from Dikika are not the result of stone tools used by hominins, but instead accidental marks created by trampling. Trampling marks and stone tool cut marks are both produced by the action of stone working against bone, and thus they are often difficult to distinguish. Both problems were anticipated in our original publication and addressed in the main text as well as in the supplemental information. We welcome the opportunity for greater scientific dialog on the specimens from Dikika, but based on our analysis of the actual specimens we must respectfully disagree with the claims of Domínguez-Rodrigo et al. and wish to make the following key points:

    First, we disagree that because the bones were found on the surface their provenience is “unknown.” We acknowledged a very specific degree of uncertainty in the stratigraphic provenience, but this is not the same as “unknown”. Conservatively, we know that the fossils come from the sediments exposed somewhere on the DIK-55 slope (from the location of the lowermost surface find to the top of the crest in our photo in supplementary information accompanying the Nature paper). That slope is a total ~16m of strata of the total 76m exposed in Andedo, and ~100m exposed in the Andedo/Simbil Dere area, over which the entirety of the Sidi Hakoma Member is exposed. We narrowed the provenience to 16 of 76 meters or approximately 21% of the total exposure in this river, i.e. we know the provenience is within the lower ~20% of the interval between 3.42 and 3.24 Ma. This is a stratigraphic uncertainty of about 40 thousand years in an age of about 3.4 million years.

    Second, however, Domínguez-Rodrigo et al. are more specifically concerned with the sedimentary matrix and our mention of the fossils as lack adhering matrix. They note that our fossils do have some sediment adhering to them and suggest that this is normal for many fossils from the Sidi Hakoma Member at Dikika. We agree, however, they have conflated two separate arguments we were making (one about the likely provenience of the fossils and one about the state of their preservation) and two separate localities. Previously reported fossils from Dikika, such as the DIK-1 nearly complete skeleton which is encased in a block of sands that have taken over ten years to remove, come from a 4m plus thick layer of cemented sands. By contrast, the DIK-55 fossils come from a thin series of layers 10-30 cm of loose, uncemented sands (total of 1.5 m thick) – not “thick” as they state. As a result, the DIK-55 fossils are found on the surface in an excellent state of preservation, not requiring extensive cleaning, and with very little matrix still attached. This typical state of preservation for this bed narrowed down our estimate of the provenience because it is one of two sands exposed in this slope, and the only sand that produces fossils in such contrasting preservation to those from DIK-1.

    Third, they further question the provenience of the finds arguing that we should have excavated to find fossils in situ in order to determine the provenience of the published finds. We too would prefer to find fossils in situ, but this is not what happened in this case and in fact most of the stone tool modified bones prior to 2.0 ma come from surface collections with a similar degree of stratigraphic uncertainty (including those from Gona). Excavation could show that additional bones and perhaps even modified bones may be found in the sand layer to which we attribute our stone tool modified bones, but it is logically impossible to demonstrate through any further excavation that our published surface finds must have come from this sand layer.

    Fourth, on the marks themselves, Domínguez-Rodrigo et al., having failed to examine the original specimens, compare our photographs to photographs of their experimental trampled sample and experiments with conventionally flaked stone tools. Out of a very large sample of experimentally trampled specimens, they succeed at finding a small sub-set of the trampled sample that superficially resembles a small sub-set of the Dikika marks. This of course means that they failed to find any trampling damage that resembled the many other stone tool inflicted marks on Dikika. Thus, the Dikika sample, as we originally argued, falls outside the range of variation of trampling damage. As they themselves note in their paper, their massive sample of trampling damage could not produce a set of marks that overlapped in morphology with some of the key Dikika marks – particularly DIK-55-2 marks A1 and A2. This is our point exactly.

    Fifth, their approach, which they call the “configurational approach”, fails to meet a basic premise of the scientific method – independent tests of diagnosis. They did not do a blind test of inter-analyst correspondence. In our study, three highly trained analysts with wide backgrounds in taphonomy independently identified marks of the original specimens as stone tool inflicted. In this PNAS paper, three analysts who regularly work together (two of which are holding their prior analysis up as the earliest stone took marks, and thus have a clear bias), reach a conclusion as a group – this is a well-known failed and biased approach. Without the blind test of correspondence, their conclusions become “group-think” applied to picture-matching.

    Sixth, the authors fail to consider the item that could be causing the marks – unflaked stone – in their assessment. Rather, they base their assessment on standard flaked stone tools, which are not present at Dikika. As we suggested, the most likely tool was unflaked stone, which has broader less sharp edges than flaked stone. Recent experiments reported in a paper now under review show that the Dikika marks are a tight fit to marks produced by unflaked stone. By rushing a response paper to press, the authors failed to both 1) examine the specimens first-hand, and 2) design proper comparative data-sets. That is unfortunate, and just muddies the water.”

  4. The Dikika bone “marks” were made by:
    a. crude stone “tools”
    b. croc teeth
    c. trampling by some unknown something
    d. none of the above
    e. all of the above

  5. I sigh every time I read that someone has read an article and concludes..’what happened to the scientific method’. I make the same sigh when I notice the same thing when I do review what’s been published lately in my own field. I usually figure that the authors of the paper/report just wanted to get the report done quickly and to get it to the publisher asap for their cvs/next career development.

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