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Dental maturational sequence and dental tissue proportions in the early Upper Paleolithic child from Abrigo do Lagar Velho, Portugal — PNAS

This is a paper in which the authors investigate the dentition of the Abrigo do Lagar Velho child, excavated from a rock-shelter in Portugal, back in November 1998 by Cidália Duarte and João Zilhão, later assisted by Professor Erik Trinkaus. The unusually robust cranial and post-cranial features prompted the researchers to suggest that this specimen, LV1, was a hybrid of Neanderthal and AMH ancestry, a theory which has since come under intense attack from subsequent genetic researchers who contend there is almost no evidence in our modern genome of Neanderthal admixture, especially where mtDNA sequences have been investigated. This in turn has been countered by the argument that it is hardly surprising we see so little evidence tens of millennia later, as the Neanderthal influence could by now simply not have survived intact down through so many generations of humans, due to those direct descendants of limited interbreeding dying out along the way at the expense of AMH – more of which later.

The paper by Priscilla Bayle et al opens with this abstract…

Neandertals differ from recent and terminal Pleistocene human populations in their patterns of dental development, endostructural (internal structure) organization, and relative tissue proportions. Although significant changes in craniofacial and postcranial morphology have been found between the Middle Paleolithic and earlier Upper Paleolithic modern humans of western Eurasia and the terminal Pleistocene and Holocene inhabitants of the same region, most studies of dental maturation and structural morphology have compared Neandertals only to later Holocene humans.

To assess whether earlier modern humans contrasted with later modern populations and possibly approached the Neandertal pattern, we used high-resolution microtomography to analyze the remarkably complete mixed dentition of the early Upper Paleolithic (Gravettian) child from Abrigo do Lagar Velho, Portugal, and compared it to a Neandertal sample, the late Upper Paleolithic (Magdalenian) child of La Madeleine, anda worldwide extanthumansample.Someaspects of the dental maturational pattern and tooth endostructural organization of Lagar Velho 1 are absent from extant populations and the Magdalenian specimen and are currently documented only among Neandertals.

Therefore, a simple Neandertal versus modern human dichotomy is inadequate to accommodate the morphostructural and developmental variation represented by Middle Paleolithic and earlier Upper Paleolithic populations. These data reinforce the complex nature of Neandertal-modern human similarities and differences, and document ongoing human evolution after the global establishment of modern human morphology.

…and continues with this from the introduction:

It was with the goal of assessing whether the dental developmental patterns and microstructure of these earlier modern humans contrasted with later modern humans, and possibly approached the condition seen in the Neandertals, that we anaanalyzed the remarkably complete dentition of the Lagar Velho 1 child (19). Discovered in Portugal in 1998, this fossil is the >90% complete skeleton of a child (4–5 years old on the basis of dental maturation and limb bone lengths) ritually buried in a recess in the back wall of a rock shelter, at the base of an ∼3-m thick Gravettian to Solutrean stratigraphic sequence. The 14C-dated components of the burial context concur in placing the burial ∼24.5 ka 14C BP (∼30,000 calendar years ago), some five millennia after the replacement/assimilation of the last Neandertal populations of Iberia (20, 21). Preserving 46 of the possible 48 teeth (from calcified germs to complete teeth), all except one upper P4 and one lower P4 (and the four yet-to-calcify M3s) (19), the Lagar Velho 1 dentition provides a unique opportunity to assess these odontological aspects.

The Gravettian/Solutrean boundary obviously occurred sometime between the start of the Gravettian c.28 kya and the start of the Solutrean, c.21 kya,and it’s interesting to note that the 4-5 year old child appears to have been given what is described as a ritual burial, presumably around 24/25kya, some 20,000 years after the earliest recorded evidence of AMH in Europe.

This would make it a contemporary of the Gorham’s Cave Neanderthals at Gibraltar, but older than those whose remains have been proposed as even later surviving Neanderthals at La Carihuela, as well as another even younger site at Esquilleu that has yet to be confirmed in north of Spain, in both of which instances, Neanderthals appear to have not mixed with the AMH population, but survived living the Neanderthal life along with their traditional Mousterian stone tools

Those three sites tell their own story – La Carihuela holds the promise of actual Neanderthal fossils, tentatively dated to 21.5 kya, whilst Gorham’s Cave at 24,5 kya and Esquilleu, maybe a similar age as La Carihuela, contain Mousterian stone tools, and coming right at the end of the known existence of the Neanderthals, appear strongly suggestive of a Neanderthal population that was far from fully integrated into that of the AMH, either by blood or technology, thus making the putative hybrid from Portugal an exception to the general rule.

Here’s a note regarding the complex results of the research:

With the exception again of the Ui1 limited to the relative enamel thickness, both the average (AET) and relative (RET) enamel thickness values (Methods) recorded for all of Lagar Vehlo 1’s teeth follow the EH estimates, systematically setting it apart from the Neandertals because of their lower values (Figs. S2 and S3). In this respect, notably for the two deciduous and permanent molars, the extant human-like pattern of enamel distribution displayed by this child’s dentition is also evinced by the comparative thickness cartographies (Fig. S4).

For all of the absolute and relative variables describing dental tissue proportions, except the EDJ surface area, the results shown by the Lagar Velho 1’s lower first permanent molar (LM1) conform to those from its deciduous Lc and Lm2; they closely resemble the extant human figures. In all three cases, the potential influence of dental wear is negligible or null (Table S5). It is noteworthy that the lower canine of Lagar Velho 1 is affected by localized enamel hypoplasia (29) (Fig. 1C and Fig. S1C). Accordingly, the values displayed by both Upper Paleolithic children for the percent of the crown volume that is dentine and pulp and for the relative enamel thickness (Table S3) should be further shifted closer to the extant human values.

As a point of interest, this paper follows on from another, Anterior Tooth Growth Periods in Neandertals Were Comparable to those of Modern Humans, for which this is the abstract, and the rest of the paper is freely accessible too.

Summarised by Alan Boyle at Cosmic Log, we see:

Researchers led by Priscilla Bayle of France’s Museum of Natural History used X-ray micro-tomography to create 3-D images of the child’s teeth. They found that the front teeth were delayed in their degree of formation, compared with the state of the teeth farther back on the jaw. The front teeth also had more dentin and pulp than the teeth of more recent humans, but less enamel.  These characteristics don’t fit the pattern seen in today’s human population, or even the pattern for 12,000-year-old human teeth. They come closer to fitting the pattern for Neanderthals, the researchers said.

The University of Bristol’s João Zilhão, who found the skeleton and is a co-author of the study, said in a news release that the tooth analysis joins a growing body of evidence “that shows these ‘early modern humans’ were ‘modern’ without being ‘fully modern.’”  The university said the report “raises controversial questions about how extensively Neanderthals and modern human groups of African descent interbred when they came into contact in Europe.”

However, the study itself stops short of directly addressing those questions. Instead, the researchers say their findings “reinforce the complex nature of Neanderthal-modern human similarities and differences, and document ongoing human evolution” even after the rise of modern humans. They suggest further studies of juvenile teeth, going back 100,000 to 200,000 years, could make a significant contribution to charting the human family tree.

Although the authors decline to declare that this represents clear evidence of AMH and Neanderthal interbreeding, it’s difficult to ascribe a meaningful alterntative, especially when we consider the post-cranial elements of the specimen, whose limb proportions conform more closely to the Neanderthal model. Although some researchers have tried to pass this off as being evidence for nothing more than a ‘chunky kid’, a holistic approach which takes in discrete elements from both cranial and post-cranial morphology, in my opinion conclusively points us in the direction of AMH and Neanderthal admixture.

Such consideration of the skeletal remains as a whole certainly helped clarify the debate surrounding H. floresiensis, aka the Hobbit from Flores, where debates which only considered the cranial features persuaded some that the specimen was a diseased modern. Reality, however begged to differ, and since the publication of detailed research, especially on the out-sized feet and peculiar wrists of the hobbit, it seems abundantly clear that whoever else she may have been, LB1 was no anatomically modern human.

In the case of the Lagar Velho child, I think the most interesting results to come will be when its entire genome has decoded, if and when that ever happens – whether that tells us conclusively if this was indeed a hybrid child remains to be seen, but assuming that research of this type is carried out, we should at least have several more details of the overall picture.

Although this paper is freely accessible, you might find it easier to find it in this comment by Martin Cagliani, author of  Mundo Neandertal, who has very kindly provided it – hat tip to Maju/Luis for the heads-up to that. A link for the supplementary material appears below, and is also well worth checking out.

Bristol University Press Release

Fate of the Neandertals – João Zilhão, Archaeology.org, July/August 2000

Learning to Love Neanderthals – Robert Kunzig, Discover Magazine, August 1999

References:

1.Dental maturational sequence and dental tissue proportions in the early Upper Paleolithic child from Abrigo do Lagar Velho, Portugal — PNAS by Priscilla Bayle, Roberto Macchiarelli, Erik Trinkaus, Cidália Duarte, Arnaud Mazurier and João Zilhão

Published online before print January 4, 2010, doi: 10.1073/pnas.0914202107

2.Download Supporting Information (PDF)

3. Anterior Tooth Growth Periods in Neandertals Were Comparable to those of Modern Humans – by Debbie Guatelli-Steinberg,*†‡ Donald J. Reid, Thomas A. Bishop, and Clark Spencer Larsen

Proc Natl Acad Sci U S A. 2005 October 4; 102(40): 14197–14202. Published online 2005 September 23. doi: 10.1073/pnas.0503108102.

4. No Evidence of Neandertal mtDNA Contribution to Early Modern Humans – Serre D, Langaney A, Chech M, Teschler-Nicola M, Paunovic M, et al. (2004) No Evidence of Neandertal mtDNA Contribution to Early Modern Humans. PLoS Biol 2(3): e57. doi:10.1371/journal.pbio.0020057

Back in August of this year, two words I frequently encountered when trying to visit sites of interest in Andalucía, southern Spain, were“Cerrado” (closed) and “No”, which as a tourist you take in your stride, leg it to the nearest hostelry and reconsider the rest of the day from the perspective of its slightly less interesting alternatives. As an eminent archaeologist working on what is potentially one of the more important sites in Spanish archaeology, with the prospect of confirming the latest known Neanderthals to have lived anywhere in the world, you might hope for more positive words from those tasked with permitting your work to go ahead unhindered. But as we see from the sorry tale unfolding below, this is not always the case, especially where the cave of La Carihuela is concerned.

Martin Cagliani at Mundo Neandertal points us towards this story, in which Spanish archaeologists are complaining that the local Junta (legislative assembly) of Andalucía will not allow the re-excavation of the Mousterian layers in the cave which it closed in 1996, (although work seems to have been conducted at least as late as 1998 by Carrión, linked PDF, Fig.2) where it is claimed there are Neanderthal remains dating to around 21,500 years bp, located within the cave of La Carihuela, about 45 km from Granada. If confirmed, this would make these Neanderthals far younger even than those whose artefactual traces have been found at Gorham’s Cave on Gibraltar dating to around 24,500 bp, at the same time perhaps taking the species’ existence right up to the Last Glacial Maximum.

The news article referred to is in Spanish, and is reported at Público.es, from which I’ll roughly translate some of the more pertinent points, while there’s also a freely accessible paper (PDF) on the subject of pollen sequences in the cave, as well as a description of its layout, the stratigraphic sequences within the galleries,  published in 2006, to which I’ll briefly refer throughout.

The report begins by describing how the cave might be the site of the very last Neanderthals tthat once walked this planet, because following the discovery of a male (Neanderthal) skull back in the 1950s, in the vicinity of Mousterian stone tools, it was realised shortly thereafter that according to pollen analyses, the layer from which the fossil had been retrieved might date to as late as 21,500 years bp.

Excavations began in earnest during the late 1970s, and by the early 1990s, a team of 30 researchers were working there, putting it on a par with Atapuerca, near Burgos in the north,  for the amount of effort invested in the site. But in 1996, following what is described as an arbitrary decision by local authorities, this work came to a sudden halt, and despite repeated requests from the archaeological community to reopen the cave, the Junta has remained obstinately silent on the case, allegedly not even picking up the phone to engage in the debate, according to D. Gerardo Vega Toscano. Profesor Titular, Dpto. de Prehistoria. UCM, Madrid.

He remarks that the scientists in this case are effectively at the mercy of the politicians, who basically don’t give two hoots whether the cave is the last refuge of the Neanderthals, or simply a hole in the ground.

One wonders from reading this whether the Junta is a fit and appropriate body to hold sway over such affairs, and moreover where the Spanish Ministry of Culture stands in this – surely it should be they who decide the scientific importance and appropriate funding levels required by such sites, and I find it hard to believe that no-one from the Ministry has seen fit to intervene.

Vega Toscano is for his part unconvinced of the very late date of 21,500 bp proposed for the remains, which he cites as absurd, opining instead that a date of 28,000 years bp is a more realistic proposition – it should be noted here that the estimate based on the pollen samples uses 28,440 bp and 21,430 bp as its parameters, with the real date presumably falling somewhere in between the two. The oldest known actual remains of Neanderthals are from Zafarraya, occupied between 31,000-27,000 bp, and the remains at La Carihuela should provide secure dates assuming that the specimens are in good enough condition.

Gorham’s Cave on Gibraltar is also known as a late Neanderthal refuge, with a most recent date of 24,500 bp ascribed there to Mousterian artefacts, while in Portugal at Lagar Velho, what appear to be the remains of a hybrid Neanderthal child are also put at 24,500 bp, so there seems no reason why a similar date shouldn’t apply at La Carihuela, and maybe 21,500 years bp, or a millennium or two beforehand, in the overall context isn’t completely out of the question. The fact that Mousterian technologies appear to have continued to be employed right up to the very end is interesting in itself, suggesting a lack of contact between archaic and anatomically modern populations – whether further investigations within Carihuela will reveal late-surviving Neanderthals were using bone or antler implements in addition to their own Mousterian tool-kits remains to be seen, but seems doubtful.

Contrary to the opinions of Vega Toscano, there is however support for the much later Neanderthal survival dates, as the article goes on to report the opinions of José Carrión, Professor of Botany at the University of Murcia, who remarks that 21,000 years bp marks the start of the Glacial Maximum, when temperatures plunged ever deeper for the following 3,000 years, a situation he believes could have tipped Neanderthals over the edge, coinciding with the extinction of fauna such as the mastodon and sabre-toothed tiger. (Although Neanderthals had previously survived through at least 2 previous ice ages, they had done so in the absence of competition from AMH, and as far as I’m aware, no major faunal extinctions had taken place in the earlier glaciations either, or at least not to the extent that Neanderthal prey animals disappeared from the menu).

Carrión further makes the point that apart from pollen dating, the bones from La Carihuela can be dated, and so might yet reveal themselves to be younger than the Gorham’s Cave presence – whether the fossil skull mentioned earlier has been dated isn’t stated here, and whether it continues to languish unexamined in a Granada museum, isn’t clear. Other researchers have dismissed the idea that climate alone could have accounted for the demise of the Neanderthals, preferring instead to cite a multitude of inter-related factors.

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