Monday 22 July 2013

A Shell That Is But A Shell Of Its Former Self

I'm shocked, shocked to find that mythopoeic archaeology is going on in Italy! [Apologies to Captain Renault.]
Location of Fumane Cave and two palaeontological localities mentioned in Peresani et al.
Once again, the credulous, but impartial, referees at PLoS ONE have ensured that no matter how far-fetched the inference, they're dedicated to giving it an outlet. [I'd really like to know their rejection rate. Any ideas? I kinda doubt there is one! But, that's beside the point. Because that would be argumentum ad hominem, and everybody knows that's not a valid argument!] 
Peresani M, Vanhaeren M, Quaggiotto E, Queffelec A, d’Errico F (2013) "An Ochered Fossil Marine Shell From the Mousterian of Fumane Cave, Italy." PLoS ONE 8(7): e68572. doi:10.1371/journal.pone.0068572
In this paper the authors analyze the bejeebuz out of a single, fragmentary specimen of Aspa marginata found in a Mousterian stratum. They say that the only possible conclusion is that this relatively tiny fragment of a marine shell was brought to the cave by [style-conscious] Neanderthals, [inexplicably] rubbed to create minute striations on the interior, and then smeared with hematite [to produce a nice, red lump that was somehow then displayed as a fashion statement]. These are the crucial inferences on which they base their claims.
1) The specimen is a fossil of Aspa marginata.
2) The specimen must have originated in fossiliferous rock 100 km away.
3) The specimen was originally 34 mm long and 24 mm wide.
4) The specimen has numerous minute striations on the inner lip.
5) The specimen has some hematite in numerous little surface dents.
Unfortunately for their argument, the authors have violated Rule #1—they haven't considered all of the natural processes that could account for a) the presence of a single small fragment of non-local shell, b) the striations on the lip, and c) the presence of hematite on the shell.

I want to apologize in advance for the length of this blurt, and for the length of time it has taken me to squeeze it out. It takes a long time to argue against the claims made in a paper like this, if only because the claims are based on limited 'evidence' and not much else. I've made an effort to perform the due diligence that the authors should have taken on. If they'd made the same effort as me, they would never have submitted their findings to a reputable refereed journal, much less to PLoS ONE!
[Because this blurt is so long, I'm going to make the better part of it accessible "after the fold," as they say in blogistan. That means, simply, that the article is continued on a secondary web page.]

Let's take the inferences one at a time...

Inference 1: Taxonomic identification

I have no quarrel with their species ascription. After all, I'm not a malacologist, nor an invertebrate palaeontologist. Despite my shortcomings there does seem to be some dispute in the literature as to the correct genus name—both Bufonaria marginata and Aspa marginata are used as is Bursa marginata [although, apparently, Aspa now has the edge over Bufonaria and Bursa].

Inference 2: The shell's provenance [or, to be more correct, provenience]

A. marginata has occupied the seas of Italy's part of the world since at least the Miocene [when, in fact, the Mediterranean was created by the collision of the African and Eurasian tectonic plates]. It's true that A. marginata occurs in fossiliferous sediments within 100 km or so of Fumane Cave, as the authors tell us. They're also careful to point out that in the present day the species doesn't occur the Mediterranean basin. Doesn't it seem a little odd that they've gone to the trouble of researching the present-day geographic distribution of A. marginata when they're dealing with a 47,000 year old discovery? Well, even if it doesn't seem odd to you, it does to me. I suppose it's possible that the authors wanted to rule out any possibility that their specimen was picked up on the Mediterranean littoral 47 ka. But why? For us to accept such a statement we'd have to think that marine conditions and A. marginata's trophic preferences have been static for those 47 ka. So, as my dear, dead Dad used to say: Beats the shit outa me. Furthermore, I'm surprised that they would cite the World Register of Marine Species as the source for their claim, because it seems to contradict their claim. I went to the same source and found two citations that list the Mediterranean as one of the places that this species lurks—here and here. As Frodo would say, I'm confusticated and bebothered.

If you look at Peresani et al.'s figure below, you may notice a very polished sheen on the archaeological specimen's inner surface, which I've circled in red. [Since we're given four views of the Fumane Cave specimen, the arrows are there to help you by pointing out the corresponding anatomical points on the archaeological and the comparative specimens.] I'll defer to the invertebrate palaeontologists in the group if I'm wrong. However, I think the lustre of this specimen's columella means that there has been no or very little mineralization of this specimen. In other words it appears to be an unaltered fossil, to use palaeo-speak. Such 'fossils' are a frequent occurrence in certain lithofacies. I'm also very curious as to how you would tell an 'unaltered' fossil from a contemporary one. *sigh* The lyf so short, the craft so longe to lerne.

a = archaeological specimen; b through d = comparative fossils
Unfortunately, we don't get to see inside the three comparative specimens. So, the sceptical among us are left to depend on the authors' 'authority' in this matter. And you and I know that argument from authority is not a valid form of argument.

In reality it's of little consequence whether or not the Fumane Cave specimen is truly a fossil or was a living organism at the time of the Neanderthals. There are any number of ways that a cm-sized clast of any solid could have arrived in the cave unintentionally, whether or not it was a fossil that had eroded out of bedrock. Any furry or hairy creature can transport small bits in matted hair for great distances. Had one such animal been killed or scavenged by a Neanderthal, a small fragment of shell could easily have come to rest in the cave and be preserved. The same would be true of other predators that transport carcass parts away from a death site, such as wolves and hyaenas. In this case, the authors' claim is just one of a number of possible scenarios. And a not very important one, at that.

Inference 3: Estimating the original size

I honestly don't have a clue why the authors thought it important to estimate the specimen's original size, nor do they offer a reason. Nevertheless, they take great care to justify their estimate of the original dimensions—including publishing a half-page regression curve to illustrate their six data points, seen below, and a column-width table containing the same six measurements. I feel so inadequate that I don't see the point. It's a mystery to me why the referees didn't just tell them to axe this part of their paper. I realize that in this digital age, bits and bytes are cheap, and the page count means little compared with the days of print-only publication. However, it's still true that you and I have precious little time to read unnecessary verbiage. Under the circumstances, absent a compelling explanation, I have to conclude that their treatment of the specimen's original size is a total waste of my time.

A bit of errant pedantry—Height is not spelled Heigth in any dictionary I've poked my head into. I guess proofreading is the first casualty in an electronic journal that promises "fast publication times." 
So, having thus demonstrated that they are the best darned fossil-shell, original-size estimators this side of the Pecos River, the authors get into the real purpose of their paper.

And I'll see you after the fold!

Inference 4: Surface modification

Having no doubt fantasized that their bit of shell was intentionally carried to the cave, the authors pull out all of the stops to see if it bore evidence of modification that could be in any way attributed to Neanderthal behaviour. In the top row of the figure the arrows indicate the areas illustrated in photomicrographs a through c in the lower part. The authors have definitely found some intriguing modification on a portion of the shell that would have been inside the final and largest whorl. The photos of areas b and c on the Fumane shell fragment clearly show that they weren't similarly affected. The same is true of two of the fossil specimens, shown in d and e.

The authors make no mention of it, but look at how different the surface topography of the fossil shells [i.e. d and e] is from that of the archaeological specimen [i.e. photomicrograph a]. Curious.

[This must have a bearing on the question of whether or not the Fumane specimen is an unaltered fossil. Don't you think?]

Getting back to reality, now. As you know, for any modified bits recovered from archaeological sites, the onus is on the archaeologists first to rule out natural causes before ascribing the archaeological phenomenon to human or hominid behaviour. That's Rule #1.

a (upper)-c = Fumane Cave A. marginata; a (lower) = Fumane Cave, region a (upper); b (lower) = Fumane Cave, region b (lower); c (lower) =  Fumane Cave, region c (upper); d and e = known fossil specimens, area corresponding to the modified portion of the Fumane specimen shown in a (lower). Scale = 100 microns for the photomicrographs. 
The authors tell us that the "clusters of striations were likely produced by abrasive particles incorporated in a medium that has repeatedly rubbed a distinct area of the inner lip." After marvelling at how precisely parallel are the majority of the striations, the first thing I notice is the scale of the photo that displays them. The faint scale bar in the upper left corner is 100 microns, or 0.1 mm. [I've added the yellow bar, which represents about 1.0 mm, for comparison. For the metrically challenged among you, 1 mm is about 0.0393701 in, or just a tiny bit more than 1/64th of an inch.] The point is this: most of the striations are on the order of 1 micron [approx. 3.93700787 × 105 or 1/64000th of an inch] to about 10 microns [you do the math].  That's reeeeeally small. But how small is that small? It's so small that the clasts making those marks were silt-sized and smaller!

Small, yes. But, oh so perfectly parallel! Now, look at the surface in question—it's saddle shaped. I'm gonna go out on a limb here and suggest that no "medium" rubbed by a human or Neanderthal finger could possibly leave perfectly parallel marks on that part of the shell. It would be physically impossible for a pliant, convex surface such as a finger to make such perfectly parallel striations, especially if it involved "repeatedly rubbing" the area. Just. not. possible. Of course, I'm in no position to do the actualistic research that would be necessary to support my claim. So, we'll go merrily along with them as they embellish their narrative.

[Follow along, yes. But there's no reason why I should accept their claims if their paper fails to address this fundamental question—"What in the world was the Neanderthal doing bringing home a fragmentary shell, or one that was broken after it arrived at the site? I'm sorry. It just doesn't make any sense. I know. I know. It's anthropologically outré to ask such a question, given how fluid cultural meanings are 'on the ground.' It would be different if even one other Neanderthal site contained a similarly modified shell. Under the circumstances I think it's patronizing in the extreme to suggest that a Neanderthal would consider a bit of broken shell something worth conserving, much less make into an item of jewelry.]

Okay. I'm inordinately sceptical. I wouldn't have to be if people would just start making sensible inferences and not wasting my time. But as all my critics always tell me, to be fair I need to offer a better, or at least a plausible, alternative explanation for the modification these authors describe. So, I'm trying to imagine a "medium" that could produce those marks by rubbing silt-sized and smaller particles against the nacreous inner surface of a shell. One possibility is, in fact, clay. [Wow! For the first time my interpretation of the 'data' converges on that of Peresani et al. But don't be dismayed,  dear Reader, the apparent accord lasts for only for a moment.] The authors and I can agree only because, while they don't make the connection, clay could indeed make such marks if it were impregnated with particles that were harder than the material that makes up the internal surface of A. marginata shells. Clay by itself would probably not have left such marks. Clay minerals, the predominant solids in common or garden variety clay, vary in hardness from about 1 on the Mohs scale [e.g. Montmorillonite] to 2.65 [e.g. Halloysite]. If I'm correct in presuming that the shell surface in question is nacreous [like mother-of-pearl], which has a hardness > 3, the usual clay minerals probably wouldn't have left marks on the shell. If not the usual clay minerals, what could have left those marks? I propose that if the "medium" included silt, per se, it could very well have left the striations. Silt is, by definition, quartz or feldspar. They are hard enough to have made the striations.

But if the minute, parallel striations weren't made by a Neanderthal rubbing silty clay on the shell, what could have left the marks? *inches a little further out on the limb that is already bending mightily under the weight of this blurt* How indeed would a medium like silty clay have left minute, almost perfectly parallel striations on the curved inner surface of the shell? I think the explanation is clear enough by now. Obvies, the shell was embedded in the "medium" and something forcefully moved the shell through it along a straight path. [B.T.dub, do I really need to spell it out?] All righty. Trampling could easily have created the modification that Peresani et al. have described. No need to invent a nimble Neanderthal as the actor.  Phew! I'm glad we got that settled. On to the crux of the paper.

Inference 5: Haematite in pits on the outer surface

The authors clearly demonstrate that hematite/haematite is present in numerous indentations on the Fumane specimen's outer surface. Their take on it? The "features suggest that the red substance was originally more abundant on the shell surface before being partially erased by a gentle post-depositional abrasion." Done and done. Waitaminit. When they were telling us about the marks on the inner surface we were shown beautiful microphotographs. Are we now supposed simply to accept their assertion that some mysterious "gentle post-depositional abrasion" took place and that it removed the prominences that had once had red stuff put on them? Gimme a break! I don't buy it. Even "gentle" abrasion would have left microscopic marks on the attrited areas. Why no burrowing, tunnelling, scanning EM for the outer surface?

It would have taken considerable time for a gentle abrasive agent to blunt the tops of the prominences and at the same time remove a once-more-extensive coating of red stuff. I have to say I'm baffled that the authors don't go looking for a) the marks, and b) the actor and agent of the mysterious attrition on the outer surface. What are they up to? I think the answer is straightforward. Rather than trying to explain how a sentient agent placed tiny deposits of red material in each individual divot on the shell's surface—an inference that would have been laughed at—they needed to think of a way to argue that the red stuff was relict. Et voilá, the highly unlikely, undocumented, unspoken-of, but crucial "gentle post-depositional abrasion" that removed the red-covered prominences of the shell. If not being painted on by a Neanderthal, how did the hematite get into the little pits?

Hematite [or haematite] is an abundant mineral at and below the Earth's surface. It's an iron oxide, and a much sought-after type of iron ore. It can also occur as clay-sized crystals, a secondary mineral formed by weathering processes in soil. The red soil type known as laterite is full of the stuff. And no doubt there's plenty of hematite in northern Italy. It's highly likely that the Fumane Cave shell was submerged in a hematite-rich silty clay when it was given the shove that created the striations.

I'm now officially over dealing with Peresani et al. Thanks for hanging in there. Don't forget to tell your friends about what I had to say about this load o' malarky. I can wait for 'em. I'm here 'til doomsday. Try the rib-eye. It's really good. Please leave your questions in the locked box on your way out.



Don't say I didn't warn you. I want you to know what I really think about these so-called scientists and the referees that enabled them in this effort. The authors have the gall to state that
Neandertal symbolic behavior is a controversial issue that has attracted much debate over the last thirty years
and then to reference, among others, Paul Pettit's screed about so-called burial practices that he says have their roots in the last common anceator of chimps and people like us. Peresani et al. reference the recent work by Sandgathe et al. at Roc de Marsal, that verified a prediction I made almost a quarter-century ago. But they don't have the decency, nor the class, nor the scientific integrity to mention my very large contribution to this "controversial issue." I'd like to express my utter disgust at this paper's neglect of my work, and I can do so with only two words. The second word is "you!"


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