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Such is the frequency these days of research into Neanderthals published by Professor João Zilhão, I’m beginning to wonder whether heFigure 2. Pego do Diabo: the site hasn’t created multiple copies of himself, rather in the manner of a kinder, more constructive Dr. Manhattan, in a bid to leave no cave unexplored, no Neanderthal left behind etc. Anyway, today he appears courtesy of a freely accessible paper at PLoS ONE, in which we hear news from a cave in Portugal, Pego do Diabo (The Devil’s Cave).

The gist of his latest paper, as reported at Science Daily and Physorg is that Neanderthals in west and southern Iberia survived no later that 37,000 calendar years ago, (as opposed to much later estimates indicating they could have survived up until the Last Glacial Maximum), which in the opinion of the authors means that AMH and Neanderthals co-existed in Europe for no more than 5,000 years, and furthermore, that the case for Lagar Velho I being an AMH/Neanderthal artefacts of admixture, is thus strengthened. Moreover, the authors conclude that climate change caused disruption to interactive networks, and brought AMH and Neanderthals into direct contact south of the so-called Ebro Frontier system, ultimately causing the demise of the latter.

Here’s the abstract from the paper itself:

Background

Neandertals and the Middle Paleolithic persisted in the Iberian Peninsula south of the Ebro drainage system for several millennia beyond their assimilation/replacement elsewhere in Europe. As only modern humans are associated with the later stages of the Aurignacian, the duration of this persistence pattern can be assessed via the dating of diagnostic occurrences of such stages.

Methodology/Principal Findings

Using AMS radiocarbon and advanced pretreatment techniques, we dated a set of stratigraphically associated faunal samples from an Aurignacian III–IV context excavated at the Portuguese cave site of Pego do Diabo. Our results establish a secure terminus ante quem of ca.34,500 calendar years ago for the assimilation/replacement process in westernmost Eurasia. Combined with the chronology of the regional Late Mousterian and with less precise dating evidence for the Aurignacian II, they place the denouement of that process in the 37th millennium before present.

Conclusions/Significance

These findings have implications for the understanding of the emergence of anatomical modernity in the Old World as a whole, support explanations of the archaic features of the Lagar Velho child’s anatomy that invoke evolutionarily significant Neandertal/modern admixture at the time of contact, and counter suggestions that Neandertals could have survived in southwest Iberia until as late as the Last Glacial Maximum.

The Ebro Frontier is mentioned at Physorg:

Although the reality of this ‘Ebro Frontier’ pattern has gained wide acceptance since it was first proposed by Professor Zilhão some twenty years ago, two important aspects of the model have remained the object of unresolved controversy: the exact duration of the frontier; and the causes underlying the eventual disappearance of those refugial Neanderthal populations (ecology and climate, or competition with modern human immigrants)…

…Professor Zilhão said: “I believe the ‘Ebro frontier’ pattern was generated by both climatic and demographic factors, as it coincides with a period of globally milder climate during which oak and pine woodlands expanded significantly along the west façade of Iberia.

“Population decrease and a break-up of interaction networks probably occurred as a result of the expansion of such tree-covered landscapes, favouring the creation and persistence of population refugia.

“Then, as environments opened up again for large herbivore herds and their hunters as a result of the return to colder conditions, interaction and movement across the previous boundary must have ensued, and the last of the Neanderthals underwent the same processes of assimilation or replacement that underpin their demise elsewhere in Europe five millennia earlier.”

Clearly this will come as disconcerting news to those who contend that in fact Neanderthals survived a good few millennia later than 37 cal kya, and might well argue that a single cave – or data point – can’t be construed to represent the latest appearance date of Neanderthals across the entire Iberian peninsular, and it remains to be seen whether other sites in southern and northern Iberia, such as Carihuela and Esquilleu will refute the conclusions of this paper.

Much of content of the paper itself is given over to an exhaustive description of how the cave was re-examined and some of the contents re-dated, along with brief reference to an Aurignacian lithic assemblage, the Dufour bladelets, as described here:

Bearing in mind the palimpsest nature of cave deposits, the dating of layer 2 to the time range of the Aurignacian III–IV Figure 11. Fig 2 “Dufour bladelets”: Pego do Diabo compared with the Protoaurignaciandoes not completely reject the possibility that the artifacts contained therein entered the site at some point in time during the hiatus between the deposition of layers 2 and 3, i.e., in the ca.35–43 ka cal BP interval. Confirmation that the Pego do Diabo Dufour bladelets are indeed Aurignacian III–IV therefore requires assessment of whether their metrical and formal attributes are consistent with alternative assignments to earlier stages of the technocomplex.

A persistent source of confusion in the study of the Aurignacian is the vague, catch-all original definition of the “Dufour bladelet” type: “bladelet with a curved profile, presenting a fine, marginal, semi-abrupt retouch, along one of the edges only (in which case it can be either ventral or dorsal) or along both edges (in which case it is always alternate)” [57]. As a result, over the years, practitioners have subsumed under this category an extremely varied range of microliths with very little in common in terms of blank technology, mode of retouch, and overall shape.

A case in point is the putative presence of Dufour bladelets in Châtelperronian level X of the Grotte du Renne, at Arcy-sur-Cure [77], which some have used to support the twin notions that the site is heavily disturbed and that the numerous ornaments found in level X originated in Aurignacian level VII, where Dufour bladelets are abundant [78][79]. In fact, the few level X items in question represent one end of the variation of the “retouched blade” tool type. They are not bladelets but blades (their average width is 13.5 mm), and they display a technology of blank production that is distinctively Châtelperronian [80].

The authors note that very little is known about the Aurigncian/Gravettian transition in Europe, and that this research tallies with other sites regarding the onset of the Gravettian in Europe:

The Aurignacian-to-Gravettian transition is one of the least known periods of European prehistory, explaining why the evidence from such a small site as Pego do Diabo can contribute to our understanding of this process. In particular, our results put the west European evidence in line with that from central Europe, where the earliest Gravettian is now dated to the ca.29–30 ka 14C BP interval [95].

This transition was therefore penecontemporaneous at the continental scale: the south German pattern is no instance of precocity, as in the Kulturpumpe model [95], nor is it necessarily a byproduct of post-depositional displacement of samples derived from underlying Aurignacian levels, as others have proposed [30]

…Where the emergence of anatomical modernity is concerned, Pego do Diabo establishes a secure terminus ante quem of ca.34.5 ka cal BP for the process in central Portugal, where, on current evidence [19], [39], [41], the terminus ante quem for the demise of Neandertals is ca.35.5 ka cal BP (Table S7; Figure 12).

This has major implications for the interpretation of the archaic features in the anatomy of the Lagar Velho child. With the last of the region’s Neandertals dating to five millennia before the child was borne, crossbreeding between immediate ancestors (e.g., parents or grandparents) drawn from distinct “modern” and “Neandertal” gene pools is empirically untenable. Therefore, those features must represent evolutionarily significant admixture at the time of contact.

As ever, the paper bears worth reading in full, even if as remarked over at Gene Expression, some of the detail seems a little dense to those not fully apprised in archaeological research, lithic manufacture techniques, or a familiarity with industries thereof. I’m going to end this post though at Gorham’s Cave, Gibraltar a site previously proposed to have witnessed the last known Neanderthals:

Given that no secure evidence exists elsewhere for peninsular Neandertals to have persisted beyond the 37th millennium cal BP, and that available archeological proxies place the emergence of anatomical modernity across southwest Iberia no later than the beginning of the 36th, the younger dates obtained for the Middle Paleolithic of Gorham’s Cave must be considered anomalous [50].

These dates are part of a large set of results, mostly within the expected range but widely scattered and with no correlation between age and stratigraphic depth. Combined with the microscopic size of the charcoal samples used, this pattern means that incomplete decontamination and post-depositional intrusion from the overlying Upper Paleolithic are viable explanations for the outliers.

Moreover, the samples come from a trench in the back part of the site where find densities are very low (five artifacts per cubic meter) and a non-diagnostic Upper Paleolithic stone tool component may well exist alongside the few clearly Middle Paleolithic items. Finally, Upper Paleolithic deposits of later Aurignacian affinities exist in the porch area of the site and are well dated by numerous samples to ca.34 ka cal BP (Table S7; Figure 12). This dating is in line with the evidence from Pego do Diabo, and precludes the possibility that the back area of Gorham’s continued to be used by Middle Paleolithic Neandertals beyond that point in time.

Some might wonder whether the case for Pego do Diabo is being overstated here, or that other data from Gorham’s Cave are being re-interpreted to fit with the latest data presented – either way, I somehow doubt that this will be the final word in the debate, or that the Neanderthal/AMH transition was as neat and tidy as suggested.

No contemporary human fossils were found in direct association with the artifacts at either site – but can we safely attribute all post-Mousterian lithic industries to AMH alone?

However, this figure of 5,000 years as a co-existence spell is especially interesting as it closely resembles a similar proposed 5,000 year interlude in Australia, whereby another round of re-analysis has suggested that there was an extinction of large mammals there at 40 kya, some 5,000 years after the proposed date for the arrival of humans on the continent. The story is reported in Stuff, a New Zealand news site, the details of which were sent to me by Terry T.

Giant marsupials, reptiles and flightless birds that once roamed Australia became extinct about 40,000 years ago, later than had been thought and some 5,000 years after humans arrived, a new study suggests.  Controversy has long surrounded when such creatures became extinct in Australia. New equipment that can date teeth and bones has solved the puzzle, Australian researchers said in the latest issue of the journal Science.

“For a long time, we couldn’t measure bone and teeth, or how old they (animals) were when they died, that is, when they went extinct,” paleontologist Barry Brook at the University of Adelaide in southern Australia told Reuters by telephone.

One of the new techniques used in the latest research was uranium thorium dating, which can gauge when uranium was taken up into the animal’s teeth when it was still alive.

The question as to when the last of these creatures died in Australia surfaced when other researchers began finding fossils, along with stone tools, in Cuddie Springs in New South Wales about 100 years ago and again over the past 30 years.  They analysed surrounding sediments and found that they dated back to 30,000 years ago, contradicting evidence elsewhere in Australia which showed that the animals became extinct far earlier, or at least 40,000 years ago.

Faunal remains that had previously been dated to 30,000 years by the sediments in which they were found have now been re-dated, through the use of uranium/thorium, with the new age placing them at 40,000 years old – taken in conjunction with a suggested first-appearance date 0f 47 kya for humans, the extinction event now appears to have been lightning quick, geologically speaking, with the clear implication that it was the arrival of humans that caused a continent-wide extinction event.

It seems – to me at least – extraordinary that what was probably an initially small population of humans could have had such a widespread and devastating impact on such a grand scale, and it will be interesting to see the response of others who claim to have found no evidence that the remains of extinct Pleistocene mammals there met their fate at the hands of humans. Moreover, a human presence in Australia has been proposed for as early as 50-60 kya, which would make the extinction at 40 kya a more drawn-out affair.

We return to Iberia, from where Zilhão give his team’s version of the sequence of events that led to the final days of Iberian Neanderthals:

Why, south of the Ebro drainage system, the replacement/assimilation process occurred much later than elsewhere in Western Europe, remains a “big issue.” Our hypothesis is that climatic and demographic factors are involved [13], [21][22]. North of the Pyrenees, the impact of a severely cold iceberg event (Heinrich Event 4), aggravated, in central and eastern Europe, by the effects of the Phlegraean Fields caldera explosion, must have caused a population crash.

At the same time, to the south, and especially so along the Atlantic façade, oak and pine woodlands expanded significantly during the period of the “Ebro Frontier,” which, globally, was one of generally milder climate (GIS8; Greenland Interstadial 8); by comparison with what happened in Iberia at the time of the Tardiglacial/Early Holocene transition, population decrease and a break-up of interaction networks probably occurred as a result of the expansion of such tree-covered landscapes.

The net result may have been one where, for modern human groups settling the foothills of the Cantabro-Pyrenean mountains, southward expansion (or networking) may have become neither possible nor desirable. Then, as population numbers recovered and the long GIS8 interval came to an end, with southwest Iberian environments opening up for large herbivore herds and their hunters as a result of the return to stadial conditions, interaction and movement across the previous boundary must have ensued, with inevitable consequences for the Neandertal refugia of westernmost Eurasia.

It’s important to note that a range of simultaneous contributing factors are proposed, though whether some of those Neanderthal refugia persisted in more isolated locations is something yet to be determined.

Reference:

Zilhão J, Davis SJM, Duarte C, Soares AMM, Steier P, et al. (2010) Pego do Diabo (Loures, Portugal): Dating the Emergence of Anatomical Modernity in Westernmost Eurasia. PLoS ONE 5(1): e8880. doi:10.1371/journal.pone.0008880

Editor: John Hawks, University of Wisconsin, United States of America

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