Anthropology.net

Saturnalia is over, and the Feast of St. Stephen is almost upon us, so before the latter rolls round, this is just a quick note to wish everyone all the best over the Christmas holidays, and even if this time of year doesn’t signify anything of note to you, we hope you have a good time regardless.

Posting here should slowly pick up again, after what has been a quiet week, so in the meantime, make sure the chimney is unblocked to avoid getting sued by Santa, the windows open to catch a glimpse of Olentzero, or failing that, maybe make sure the guest and gift reception mode of your teleportation device is switched on.

I’m cross-posting this from everyone, the community blog of PLoS ONE, who are asking all those with an interest to involve themselves in this initiative from the White House Office of Science and Technology Policy, (OSTP), who state the following:

Yesterday we announced the launch of the Public Access Forum, sponsored by the White House Office of Science and Technology Policy.  Beginning with today’s post, we look forward to a productive online discussion.

One of our nation’s most important assets is the trove of data produced by federally funded scientists and published in scholarly journals. The question that this Forum will address is: To what extent and under what circumstances should such research articles—funded by taxpayers but with value added by scholarly publishers—be made freely available on the Internet?

The Forum is set to run through Jan. 7, 2010, during which time we will focus sequentially on three broad themes (you can access the full schedule here). In the first phase of this forum (Dec. 10th-20th) we want to focus on the topic of Implementation.

You’ll need to read the rest of the linked page for further clarification – the first stage, Implementation, ends on December 20th, 2009, and here’s what PLoS ONE are advising:

The White House Office of Science and Technology Policy has invited comment on broadening public access to publicly funded research and they want to hear from you. Please post your contributions to this blog.

Their Request for Information (RFI) lasts for just 30 days and expires on 7 January 2010, so we’d like to encourage you to get involved sooner rather than later. This is an opportunity for us to shape a broader public access policy – how it should be implemented, what type of technology and features are needed, and how to manage the process.

Adding your thoughts to the blog will help ensure that the administration form a balanced (the comment thread is moderated) view of stakeholders’ interest. E-mail comments will also be accepted and will be posted to the blog by the moderators.

There are 3 main topics where the administration would appreciate your input (they also welcome general comments) and each one is open for a set period of time:

1. Implementation – expires 20 December 2009. Which Federal agencies are good candidates to adopt Public Access policies? What variables (field of science, proportion of research funded by public or private entities, etc.) should affect how public access is implemented at various agencies, including the maximum length of time between publication and public release?

2. Features and Technology – 21-31 December 2009. In what format should the data be submitted in order to make it easy to search and retrieve information, and to make it easy for others to link to it? Are there existing digital standards for archiving and interoperability to maximize public benefit? How are these anticipated to change?

3. Management – 1-7 January 2010. What are the best mechanisms to ensure compliance? What would be the best metrics of success? What are the best examples of usability in the private sector (both domestic and international)? Should those who access papers be given the opportunity to comment or provide feedback?

Thanks for supporting this initiative.

I’m not sure whether this is a project in which only those with US citizenship can participate, bearing in mind that this concerns the question of whether US taxpayers should be entitled to free Web access to published material which they have funded, but I imagine that whatever measures are eventually put in place, their influence on the rest of the world will be soon be apparent. In any case, I daresay input of opinion (via the OSTP comments section) from a global audience can only help to more clearly define the way ahead.

Physorg are reporting an exciting find of what are described as 30 ‘pebble culture’ lithic tools,  dating back over 1.5 million years, at a site which has been dated argon dated to 1.57 million years old, thanks to an ancient volcanic eruption whose lava flow preserved the ancient ground surfaces.

Although no human remains have been found, many associated fossilized mammal remains came to light at two locations 50 meters apart from one another, with the second producing the lithic assemblage, bearing signs of wear from use -  prompting French archaeologists to claim  the finds constitute some of the earliest stone tools known anywhere in Europe. After having being alerted by a local man in the Hérault Valley, Languedoc -Roussillon , who had found ancient teeth and bones in a basalt quarry some 15 years ago, the site was revisited, and another excavation begun nearby.

The research is published in Comptes Rendus Palevol, under the title, Une nouvelle faune de vertébrés continentaux, associée à des artefacts dans le Pléistocène inférieur de l’Hérault (Sud de la France), vers 1,57 Ma, which translates to A new vertebrate fauna associated with lithic artefacts from the Early Pleistocene of the Hérault Valley (southern France) dated around 1.57 Ma,  authored by Jean-Yves Crochet et al, and for which this is the abstract:

A new vertebrate fauna associated with lithic artefacts from the Early Pleistocene of the Hérault Valley (southern France) dated around 1.57 Ma. Some lithic artefacts associated with an Early Pleistocene (Upper Villafranchian) vertebrate fossil assemblage have been found from a quarry exploited for basalt in the lower Hérault Valley (Languedoc, southern France) at the Lézignan-le-Cèbe locality.

A preliminary patrimony expertise led us to identify about 20 vertebrate taxa, and the autumnal rainfalls revealed the presence of roughly 30 lithic artefacts of “pebble culture” type. A basalt layer dated at 1.57 My directly overlies the fossiliferous level, extends along the little hill (locus 2) yielding artefacts. These new promising data offer new perspectives to improve our understanding of Early Pleistocene ecosystems (and possibly ancient hominin occupation) of southern Europe.

Although the paper is behind a paywall, I found this ‘Article In Press’ (PDF) version, which has an abridged English text along the main body in French, about which I’ll add a few related notes.

The site of Locus 1 is described as underlying an ancient lava flow, (hence the argon dating),  and bears fossil vertebrate teeth which are poorly preserved, whilst Locus 2, 50 metres to the west, is a small hill comprising fluvial and volcanic components, has less but better preserved fossils. Near the top of the hill is a paleosol, (an ancient soil layer covered by volcanic material), bearing quartzitic pebbles and artefacts. The dating methods used are as follows:

CO2 laser probe 39Ar-40Ar step-heating analyses were performed on whole rock single grains from 12 samples collected from four close areas on the lava flow covering the study site. All experiments displayed concordant plateau ages between 1.536±0.063 Ma and 1.627±0.136 Ma. As all inverse isochrone calculations yielded initial (36Ar/40Ar) ratios undistinguishable of the atmospheric ratio, excess argon can be ruled out. The weighted mean of isochrone ages, at 1.57±0.01 Ma (1), is in perfect agreement with the weighted mean of plateau ages at 1.56±0.02 Ma (1) and is probably the best estimate of the emplacement age of the lava flow. This age at 1.57±0.01 Ma (1) postdates the study site.

Amongst the fossilised fauna, a wide range of mammal taxa were identified – Leptobos etruscus, a type of buffalo, Eucladoceros ctenoides vireti, an extinct bush antlered deer, Equus altidens, which I think is a species of zebra, Dicerorhinus etruscus etruscus, rhinocerous, Canis etruscus, a wolf species, Meles thorali which is described as a Eurasian badger, Homotherium crenatidens representing the sabre-toothed cat community, a type of hyena known as Pachycrocuta brevirostris, Prolagus sp. a small, rounded herbivore related to the modern pika, a rodent by the name of Microtus, cf. Allocricetus Apodemus, and Talpa fossilis, a species of mole, and Aves indet, which I take to mean unidentified birds. This faunal suite is said by the authors to correspond to that known for the Early Pleistocene in central France.

On next to the artefacts, which are described as:

The lithic assemblage includes 20 artefacts of pebbleculture type. The supports and striking platforms are quartzitic pebbles, large basaltic flakes and fragments, and smaller flint pebbles. All flakes are exclusively produced by direct percussion, employing a hard stone hammer. Unilateral alterations can be observed on the periphery of certain flakes. The pebbles are developed in chopping-tools, and their edges often show traces of repetitive impacts. The lithic assemblage found at the locus 2 shows similar primary technical features to those from the other Early Pleistocene European sites.

The authors conclude by saying that much work still needs to be done – they state that the faunal remains recovered so far only offer a partial view of the contemporary suite, and although some of the fossils show damage from carnivores, others from Locus 1 appear to have been intentionally broken, quite possibly by those or similar choppers and chopping tools found at Locus 2  – the bones are still undergoing taphonomic analysis to determine whether such breakages were induced by humans, became damaged by carnivores or geologic processes.

To put these 1.57 million year-old pebble tools in an overall context, the earliest known lithic assemblages anywhere date to c.2.5 million years, known as the Oldowan industry from Eastern Africa, whilst those found in Georgia at Dmanisi date to c.1.7 million years. The earliest known stone tools elsewhere in Europe are mainly from Spain, notably the sites of Atapuerca to the north near Burgos, about 1.2 mya, and Orce to the south in Andalusia. From the description given, the tools from Lézignan-la-Cébe appear to correspond to the Acheulean industry, and if  they are defined as belonging to the chopper/chopping tool industry (apparently part of the overarching Acheulean), they’d have aspects in common with Asian lithic industries, dating to the Middle/Late Pleistocene. The oldest known stone tools anywhere in Europe, dating to an estimated 1.8 million years are described at Chilhac, Auvergne, also in modern day France.

Work at the Lézignan-la-Cébe site is set to continue in 2010.

image from paper: Fig. 4. Artefacts de Lézignan-la-Cèbe

Reference:

Une nouvelle faune de vertébrés continentaux, associée à des artefacts dans le Pléistocène inférieur de l’Hérault (Sud de la France), vers 1,57 Ma.,

(trans: A new vertebrate fauna associated with lithic artefacts from the Early Pleistocene of the Hérault Valley (southern France) dated around 1.57 Ma.)

Jean-Yves Crochet, Jean-Loup Welcomme, Jérôme Ivorra, Gilles Ruffet, Nicolas Boulbes, Ramon Capdevila, Julien Claude, Cyril Firmat, Grégoire Métais, Jacques Michaux, Martin Pickford, Comptes Rendus Palevol Volume 8, Issue 8, December 2009, Pages 725-736, doi:10.1016/j.crpv.2009.06.004

My apologies once again to yet another host of Four Stone Hearth for failing to submit something – in this case, Krystal D’Costa who is running the current edition at her blog, Anthropology in Practice – you’d think that 2 weeks would be plenty long enough to get a submission together, but either the passage of time is accelerating, or my perception of it is rapidly decreasing.

Regardless of that, there are plenty of good posts packed into her edition, in which The Gift by Marcel Mauss gets an early mention  – it’s one of those books I’ve dipped into here and there on many an occasion, and one that makes for excellent reading, especially at this time of year. It even contains a handy Maori proverb, quite apt I suppose, for this or any other time of the year…

Ko Maru kai atu, Ko maru kai mai, ka ngohe ngohe

…which according to Mauss means “Give as much as you take, all shall be very well.”

On which note, please head over to the latest edition of Four Stone Hearth to read the selection of assembled posts – as well as submissions from familar contributors such as Aardvarchaeology and The Primate Diaries, there are two other blogs previously unknown to me, namely Archosaur Musings and An Anthropologist Goes Techno, as well as three posts from the host herself, to whom thanks are due for publishing this edition.

The final 4SH of this year is due out on December 30th, whilst the whole of 2010 is as yet an open opportunity for anyone wishing to host this anthropology blog carnival during that time – details of how to apply can be found here.

image: Marcel Mauss from hilobrow.com

Having already posted two articles which call into question the findings of Richard Firestone et al, in their 2007 paper Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling,  I decided to contact Dr. Firestone to try and add some balance to the current debate; it’s all very well reporting on new research which appears to flatly contradict previously published work, but I think it very important to give the original research team an opportunity to voice their opinion of the new findings. Because there were differences in the various methodologies employed by the various teams of researchers, it should be no surprise that the findings were at variance with one another. However, it is unusual for subsequent research to completely contradict previous research conducted only a couple of years beforehand, so clearly there is need for further clarification from both sides.

As such I am extremely grateful to François Paquay, L. Tyler Faith and Todd Surovell for forwarding me their papers, and more recently to Dr. Richard Firestone for taking the time to so quickly reply to my request via email for some comment of his own. As we shall see, he strongly disagrees with the new findings and the way in which the research was conducted, emphatically standing by his original conclusions. It will be for readers here to decide for themselves the merits of the competing claims in this fascinating conundrum that addresses the mystery surrounding one of the greatest mammalian and avifaunal extinction events in recent geologic time, a mere 10,000-12,000 years ago, in North America.

I should add here, and partly in response to Terry Toohill who pointed out in a recent comment that I had thus far failed to mention Australia in my extinction posts, that I’m currently reading through papers regarding the Pleistocene extinctions in Australia, and I hope to publish something here in the near future. The debate there has by tradition been confined to climate change and human overkill, but as we shall see, recent research there indicates the true story may not be that simple – for example, a large decrease in mammal species diversity has been detected between 120kya and 90 kya, long before humans were on the continent in any significant numbers, more of which in due course.

I’m going to begin with the second of the recent comet papers, An independent evaluation of the Younger Dryas extraterrestrial impact hypothesis, in this instance authored by Todd Surovell et al, and for which this is the abstract:

Based on elevated concentrations of a set of “impact markers” at the onset of the Younger Dryas stadial from sedimentary contexts across North America, Firestone, Kennett, West, and others have argued that 12.9 ka the Earth experienced an impact by an extraterrestrial body, an event that had devastating ecological consequences for humans, plants, and animals in the New World [Firestone RB, et al. (2007) Proc. Natl. Acad. Sci.USA 104:16016–16021]. Herein, we report the results of an independent analysis of magnetic minerals and microspherules from seven sites of similar age, including two examined by Firestone et al. We were unable to reproduce any results of the Firestone et al. study and find no support for Younger Dryas extraterrestrial impact.

As we saw, the paper by Paquay et al stated that the researchers were unable to find sufficiently elevated levels of iridium, one of the prime marker candidates for a cometary or asteroidal impact, also noting a lacking abundance of other indicators that would be expected to be present both on land and in seawater. The story is taken up by Surovell et al, who  analysed 7 sites, also revisiting two of the sites in the original Firestone study, namely Topper and Blackwater Draw, in order to evaluate the claims for an extraterrestrial impact event. As Surovell et al note:

The primary evidence for impact is the apparent presence of a suite of markers that occur in increased concentrations in sediments dating to ca. 12.9  1.0 ka from sites across North America including 10 Clovis-age archaeological sites and 15 Carolina Bays on the Atlantic Coastal Plain (1–5). Clovis occupation features date within a narrow time range between 13.3 and 12.8 ka; some are buried by organic-rich sediments or soils, commonly termed ‘‘black mats’’ (6, 7). Markers found in YD black mats and contemporaneous sedimentary contexts include magnetic microspherules, magnetic grains, iridium and nickel, charcoal, soot and polycyclic hydrocarbons, carbon spherules, fullerenes and ET helium, glass-like carbon, and nanodiamonds. Some markers are more widespread than others.

A series of critiques of the original Firestone et al. article (1) have been published recently (8–10). Pinter and Ishman (8) argue that the suite of markers used to indicate impact are inconsistent with ‘‘any single impactor or any known event.’’ Furthermore, they provide alternative explanations for many of the observed marker peaks. For example, glassy and metallic microspherules are known components of atmospheric dust derived from the constant influx of micrometeorites.

An independent evaluation of the charcoal evidence was recently published by Marlon et al. (9). Examining concentrations of charcoal from 35 pollen cores across North America, they found no evidence for large-scale, continent-wide wildfires specifically associated with the onset of the YD.

This same paper was reviewed back in October by John Hawks, and this is part of what he had to say:

…Most critiques attempt to find an alternative explanation for a set of original observations. In this paper, Surovell and colleagues merely attempt to replicate the original observations at multiple sites, and fail…it’s about as hard-hitting as you’re going to see in a scientific research paper.

In the current case, the results are very simple: they went looking for a spike in the number of impact-generated particles coincident with the Younger Dryas. They looked at seven sites with long and continuous records of sedimentation across that interval. They found the supposed impact-generated particles, but not patterned with any kind of spike.

By way of a quick recap, here’s the abstract of Firestone et al‘s original paper, which is freely accessible.

A carbon-rich black layer, dating to ≈12.9 ka, has been previously identified at ≈50 Clovis-age sites across North America and appears contemporaneous with the abrupt onset of Younger Dryas (YD) cooling. The in situ bones of extinct Pleistocene megafauna, along with Clovis tool assemblages, occur below this black layer but not within or above it. Causes for the extinctions, YD cooling, and termination of Clovis culture have long been controversial. In this paper, we provide evidence for an extraterrestrial (ET) impact event at ≅12.9 ka, which we hypothesize caused abrupt environmental changes that contributed to YD cooling, major ecological reorganization, broad-scale extinctions, and rapid human behavioral shifts at the end of the Clovis Period.

Clovis-age sites in North American are overlain by a thin, discrete layer with varying peak abundances of (i) magnetic grains with iridium, (ii) magnetic microspherules, (iii) charcoal, (iv) soot, (v) carbon spherules, (vi) glass-like carbon containing nanodiamonds, and (vii) fullerenes with ET helium, all of which are evidence for an ET impact and associated biomass burning at ≈12.9 ka. This layer also extends throughout at least 15 Carolina Bays, which are unique, elliptical depressions, oriented to the northwest across the Atlantic Coastal Plain.

We propose that one or more large, low-density ET objects exploded over northern North America, partially destabilizing the Laurentide Ice Sheet and triggering YD cooling. The shock wave, thermal pulse, and event-related environmental effects (e.g., extensive biomass burning and food limitations) contributed to end-Pleistocene megafaunal extinctions and adaptive shifts among PaleoAmericans in North America.

As mentioned at the top of this post, I though it would be good to hear a response from Richard Firestone – the critics have been damning, so of course we want to hear how well or how badly this has gone down with the original proponents of the cometary impact theory. What follows is a direct quote via email from Dr. Firestone, on behalf of himself and fellow authors:

Surovell et al failed to confirm the YD Impact data because their sampling methods were fatally flawed.  We discovered that the impact layer was very narrow, often millimeters thick, and used painstaking microstratigraphy to find it.  Although the impact layer initially was deposited just before the formation of the black mat, the magnetic and organic fractions containing the most compelling information often moved about due to turbation of the sediment following deposition.

Surovell et al did no microstratigraphy and analyzed substantially wider sediment layers that included mostly normal sediment.  Thus their results greatly diluted the impact layer contribution to their samples.  Also, Surovell et al chose to recognize only magnetic microspherules that are round and shiny.  It is well known that meteoritic dust is generally not perfectly round, often pitted and dull, and generally weathered.  Despite all of these failures the distributions of magnetic grains and microsph erules shown by Surovell et al at all of their sites do show increases at the time of the YD impact which are consistent with our own results after correction for the sampling dilution effects.  Surovell et al’s conclusions are clearly influenced by their own bias and not by a fair analysis of their own data.

Paquay et al claim to find no evidence for PGE elements in there sediment samples.  We too found much weaker evidence for iridium in the sediment samples than in the magnetic fractions because the iridium is only found in the magnetic material which is a small fraction by weight of the total sediment even in the best cases where microstratigraphy was applied.  As was the case with Surovell et al, Paquay et al took very broad sediment samples diluting their results.  They used a shotgun approach to sample selection with no assurance that they had even sampled the YD Impact layer.  This is especially important because the thin impact layer often disappears from point to point due to the effects of wind, rain, and time.

Despite these experimental problems Paquay et al do report high concentrations of PGE elements at a site where we reported them and then dismiss them as normal despite the fact that their results were higher than were seen at some K/T sites.  Before we publishe d our PNAS paper, Sharma et al (Dartmouth) independently found convincing evidence for large Osmium anomalies in Pacific Ocean sediments dated to about 12,000 years ago.  His paper was rejected by PNAS because “no impact occurred at that time”.  Sharma has since found additional evidence for PGE’s in the YD Impact layer which are reported at the SF AGU meeting this year.   Weaker evidence of excess Iridium associated with the YD layer in Greenland ice has also been found by Paul Mayewski.

To summarize, the results published by Surovell et al and Paquay et al are both fatally flawed by their sampling techniques that failed utilize the microstratigraphy necessary to identify the YD impact layer.  Both authors thus analyzed highly diluted samples, published data showing smaller peaks in magnetic grains, microspherules, and PGE’s consistent with our own results, and then persisted on describing their results as within normal variations.  We find these results biased towards a specific conclusion and inconsistent with a broad range of impact markers found at dozens of sites across North America and into Europe.  Attempts by others to independently report results confirming our research have systematically been rejected by reviewers primary on the basis that no impact occurred.

Clearly there is a significant divergence between what the different researchers were able or unable to find, and the way in which what has been found may have been interpreted – whether one body of research or another was sufficiently detailed or painstaking is for others with more knowledge of the technologies involved than I possess to assess.

I’m not sure where the debate goes from here – as such as I have no personal interest in whether a comet hit or not, but I’d definitely like to know one way or the other. As noted elsewhere, a cometary impact might go some way to explaining the rather alarming speed with which the Younger Dryas appeared and disappeared. If however, the causes of that and the huge extinction event were indeed terrestrial, we have very great cause to be concerned for our own wayward climate in the present, especially with regard to the fact that we appear to be in the midst of the Sixth Great Extinction.

Conversely, if an extraterrestrial impact is proven, there is little or nothing we can do even with our modern technology to avoid another event in the future. With our densely populated urban societies dependent agriculture, we are even more vulnerable now than in the Late Pleistocene to events which could mark our own extinction.

On a final note, a paper published this morning at PLoS ONE, Quantifying the Extent of North American Mammal Extinction Relative to the Pre-Anthropogenic Baseline makes for some related further reading – regardless of past events, it is abundantly clear that we modern humans have damaged this planet and reduced its biodiversity to potentially dangerous levels. The planet of course will continue to exist far into the future, cometary impacts, greenhouse warming and glaciations notwithstanding  – whether we and the current suite of life are destined to be part of that future is by no means certain.

My thanks once again to all those who were kind enough to forward papers and comment to this brief series of posts on North American Pleistocene extinctions – the mystery would appear to be far from solved to the satisfaction of all, and more will doubtless be written here in the future, such as it may be.

References:

Quantifying the Extent of North American Mammal Extinction Relative to the Pre-Anthropogenic Baseline, Carrasco et al PLoS ONE 4(12): e8331. doi:10.1371/journal.pone.0008331 Open Access

Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling, R. B. Firestone et al, Published online before print September 27, 2007, doi: 10.1073/pnas.0706977104    PNAS  October 9, 2007   vol. 104  no. 41  16016-16021  Open Access

Absence of Geochemical Evidence for an Impact Event at the Bølling Allerød/Younger Dryas Transition, by François Paquay et al, Published online before print December 10, 2009, doi: 10.1073/pnas.0908874106

An independent evaluation of the Younger Dryas extraterrestrial impact hypothesis, Todd A. Surovell et al, Published online before print October 12, 2009, doi: 10.1073/pnas.0907857106

The latest offering from the Archaeology Channel is now online, and in this 22 minute video produced by Timothy Knowlton, which in brief is described thus:

An association of Tz’utujil Maya people from Santiago Atitlán, Guatemala, struggle to establish a cultural center and archaeological site museum at the nearby lakeside site of Chuitinamit, once home to the Pre-Hispanic Maya King Tepepul and now badly looted.  Including a tour of the museum, this film documents their accomplishments thus far and current endeavors in the face of artifact looting and natural catastrophe in the form of Hurricane Stan, which struck in 2005.

We get a pretty interesting tour of the museum in which traditional clothing and associated artefacts are shown and described, but it’s a much starker experience as we are shown around nearby sites that have been looted – this time the culprits don’t appear to be avaricious collectors with an eye for the illegal antiquities trade, rather local people who see items such as stelae, altars and sacrificial stones as ideal material for local construction projects. According to the film, such people contend that these ancient artefacts have no cultural relevance to them, and considering that many people struggle to earn anything approaching a decent wage, it’s hardly surprising they exploit free building materials when opportunity arises.

Those artefacts have now disappeared and can never be replaced, and whether there are plans to educate people in order that they understand and protect their own heritage is uncertain, although it could of course be argued that even those people who do come to realise the value of similar artefacts will still be poor over the coming years, and understandably will likely view heritage they can recover from local sites as an income stream – just as has been the case in recent years in places like Iraq, Cambodia and so on.

Obviously we hope that the efforts of those appearing in the video as our guides will fare better in the coming years, and be able to stem the flow of losses currently afflicting this site and many others in a similar predicament.

There are several outgoing links from the video page, and the image of Chuitinamit, also known as Chiyá, is from one of them, Authentic Maya.

This  seems a good opportunity to mention a news item that appeared last week from the University of California, Santa Barbara, which features archaeologist Anabel Ford, who is also a director of the university’s MesoAmerican Research Center. It is her contention that contrary to the idea that the Maya brought about their own downfall about 1,000 years ago by imprudent slash-and-burn treatment of their lands, they were in fact highly sophisticated in their land management. In a recent paper, Origins of the Maya Forest Garden: Maya Resource Management, Ford begs to differ with previously held views, as we see from the abstract:

There is growing interest in the ecology of the Maya Forest past, present, and future, as well as in the role of humans in the transformation of this ecosystem. In this paper, we bring together and re-evaluate paleoenvironmental, ethnobiological, and archaeological data to reconstruct the related effects of climatic shifts and human adaptations to and alterations of the lowland Maya Forest. In particular, we consider the paleoenvironmental data from the Maya Forest area in light of interpretations of the precipitation record from the Cariaco Basin.

During the Archaic period, a time of stable climatic conditions 8,000–4,000 years ago, we propose that the ancestral Maya established an intimate relationship with an expanding tropical forest, modifying the landscape to meet their subsistence needs. We propose that the succeeding period of climatic chaos during the Preclassic period, 4,000–1,750 years ago, provoked the adaptation to settled agrarian life. This new adaptation, we suggest, was based on a resource management strategy that grew out of earlier landscape modification practices.

Eventually, this resulted in a highly managed landscape that we call the Maya Forest Garden. This highly productive and sustainable system of resource management formed the foundation for the development of the Maya civilization, from 3,000 to 1,000 years ago, and was intensified during the latter millennia of a stable climatic regime as population grew and the civilization developed. These strategies of living in the forest evolved into the milpa cycle—the axis of the Maya Forest garden resource management system that created the extraordinary economic value recognized in the Maya Forest today.

Reference: Origins of the Maya Forest Garden: Maya Resource Management – Anabel Ford and Ronald Nigh, Journal of Ethnobiology 29(2):213-236. 2009 doi: 10.2993/0278-0771-29.2.213

Synchronous extinction of North America’s Pleistocene mammals — PNAS

Following on from my recent post regarding the apparent lack of evidence for a Clovis comet, I want to address this recent paper by J. Tyler Faith, in which he and his fellow authors offer statistical evidence to suggest that the mammalian extinction event at the very end of the Pleistocene largely took place between 12 kya and 10 kya.

I had originally intended to review this paper alone, but after only a cursory amount of reading around, it soon became clear I needed to address some of the other research into this mysterious time, without recourse to an extraterrestrial impact to explain the sudden disappearance not only of large bodied mammals, but also significant numbers of birds at the same time, an anomaly that cannot be explained away simply by inferring overkill of mammals by human predators, hyperdisease or climate change as the main agents of destruction.

Rather than try to offer a specific answer to this massive extinction question of my own, I have instead attempted here to include consideration of a range of factors and circumstances over a longer period of time and from further afield (in Eurasia) to help explain the unique context in which the American extinctions took place. For reasons of necessitated brevity, I have in some cases only referred in passing to some papers, most of which are open access.  But suffice it to say, all these papers are worth reading in their entirety, if only to emphasize the idea that there is probably an intricate network of causal complexity that best accounts for the North American terminal extinction event, rather than a single, albeit spectacularly compelling cause that now as in the past,  is notable for its extremely elusive nature, and which in all likelihood, doesn’t actually exist.

This paper, by Faith et al, addresses the long-standing debate surrounding the timing of the megafaunal extinction event in the terminal Pleistocene, and in so doing trying to identify the contributory factors that led to the demise of 31 genera of fauna at that time. Here’s the abstract:

The late Pleistocene witnessed the extinction of 35 genera of North American mammals. The last appearance dates of 16 of these genera securely fall between 12,000 and 10,000 radiocarbon years ago (13,800–11,400 calendar years B.P.), although whether the absence of fossil occurrences for the remaining 19 genera from this time interval is the result of sampling error or temporally staggered extinctions is unclear. Analysis of the chronology of extinctions suggests that sampling error can explain the absence of terminal Pleistocene last appearance dates for the remaining 19 genera. The extinction chronology of North American Pleistocene mammals therefore can be characterized as a synchronous event that took place 12,000–10,000 radiocarbon years B.P. Results favor an extinction mechanism that is capable of wiping out up to 35 genera across a continent in a geologic instant.

In particular Faith et al set out to answer the question of whether it was an event drawn out over many millennia or one that involved simultaneous extinctions in the terminal Pleistocene  – with the implication that if this was a  staggered event there may be a gradual change in the environment that was the cause, whereas a for sudden event, one or more extraordinary explanations need to be sought.

Indeed, they conclude that their statistical models indicate the latter scenario, although other (undefined) scenarios were possible, with some extinctions – between 0 and 8 genera -  taking place prior to 12 kya, and that further the idea of comet strike or human hand are generally considered to be two of the most likely of an unknown number of as yet inconclusive theories that might have contributed to this simultaneous extinction event.

The authors propose that sampling error may account for the lack of information, concluding that two main causes might be responsible for the disappearance of these animals in the space of two thousand years, roughly equating to between 12 kya and 10 kya – an extraterrestrial impact, or overkill by humans. As noted elsewhere, the Last Apppearance Date for a species in the fossil record, doesn’t necessarily mean that every single animal had died by then, but that numbers may have been so reduced as to make them  ‘palaeontologically invisible’ but they were still in effect, extinct as a viable population – this invisibility is something that may turn out to be relevant to the question of credibly identifying a very early pre-Clovis human presence in the Americas, especially when addressing some of the claims of 50 kya, from sites such as Topper, and 40 kya from Mexico and Baja California.

However, as we have seen, and assuming the recently published data are correct, there is at present very little if any substantive geochemical evidence for a comet or asteroid strike. And as has been noted previously, it’s hard to imagine there were enough humans on the ground in Pleistocene America to effect such a widespread die off, regardless of whatever lithic technology they deployed – or even that they would deliberately have killed order of magnitudes more animals than they could eat or would have needed to process into manufactured artefacts, such as clothing from hides or utensils from teeth, ivory, sinews and gut etc.

The researchers used two simulations to assess the synchronous extinction theory, the first of which is referred to as the continental simulation, described thus:

In our first simulation, referred to as the continental simulation, each of the 1,955 stratigraphic occurrences are assigned randomly a pre- or post- 12,000 radiocarbon years B.P. date based on the observed relative frequency of terminal Pleistocene taxon dates in the fossil record (3.4% for the complete set of radiocarbon dates and 1.3% when excluding radiocarbon dates of intermediate reliability). For each of 10,000 iterations, the number of genera receiving a terminal Pleistocene taxon date is calculated. All of the 31 genera included in the analysis are assumed to survive to the terminal Pleistocene, and all occurrences are assumed to be equally likely to receive a terminal Pleistocene taxon date.

The continental simulation essentially estimates how many genera that we can expect to recover from the terminal Pleistocene if all of them had survived to that time, given the empirically derived probability of observing a terminal Pleistocene fossil occurrence. We ran two separate trials of the continental simulation, both including and excluding radiocarbon dates that received intermediate evaluation scores (30).

Next they describe their biogeographic simulation:

Our second simulation, referred to as the biogeographic simulation, recognizes that the extinct Pleistocene genera were not distributed uniformly across the continental United States and that some regions are more likely to provide a terminal Pleistocene taxon date than others. For example, the distribution of Hydrochoerus and Holmesina within the U.S. is limited to the southeast (28), an area that yields relatively few terminal Pleistocene taxon dates (Table S4).

Because of their biogeographic ranges, these taxa are less likely to have been recovered from terminal Pleistocene deposits if they had survived to that time. This issue is addressed in our biogeographic simulation, which recognizes seven physiographic zones within the continental United States (31) (Fig. 2). In this simulation, the stratigraphic occurrences of a given genus are assigned randomly to a physiographic zone based on its relative abundance in that region (Table S4). In turn, the probability that a simulated occurrence will be assigned a terminal Pleistocene taxon date is based on the relative frequency of terminal Pleistocene fossil occurrences known from that zone (Table S4). For each of 10,000 iterations, the number of taxa receiving a terminal Pleistocene date is calculated. The biogeographic simulation also explores the possibility of preterminal Pleistocene extinctions.

To do so, we prohibited between 0 and 15 randomly selected genera from receiving a terminal Pleistocene taxon date over 16 separate trials of 10,000 iterations. The biogeographic simulation estimates how many taxa that we can expect to recover from the terminal Pleistocene if anywhere from 16 to 31 genera had survived to that time. As with the continental simulation, we ran two trials of the biogeographic simulation, once using all of the terminal Pleistocene taxon dates and once excluding radiocarbon dates of intermediate reliability (30).

The authors conclude that all their models can be interpreted as being in accordance with an abrupt event at the end of the Pleistocene, although in contrast to the two previous papers, they contend that a cometary impact may have been one of four main options for consideration as a contributory factor – some of the others being overkill by humans, hyperdisease and climate change.

Read the rest of this entry »

Apologies for the sparsity of posts here in recent days,  but while I’m finishing another post on Pleistocene extinctions, I hope this linked essay and the related papers will be of more than temporary interest to readers here. As part of the Royal Society’s 350th anniversary celebrations, they have just made available online a series of papers, Personal Perspectives in the Life Sciences for the Royal Society’s 350th Anniversary, as explained here:

This is a collection of personal perspectives by leading scientists on topics of high current relevance and interest written specifically to mark the 350th anniversary of the Royal Society. The authors were selected on the basis of their knowledge and experience in a topical area of life sciences research and they were invited to present their personal analysis of the status of the topic, promising and less promising approaches being used at the moment and, where possible, some bold conclusions. The topical areas highlighted were those that were mentioned most commonly by Royal Society Fellows and University Researchers as being of high interest and importance for future study. These topics range from environmental sustainability, including relevant areas of economics, ecology and behaviour, through complex process related to gene function and neural processing, to applications of stem cell research, social cognition and ageing.

I spotted this essay by Conway Morris and chose it as he has in the past had some pretty interesting things to say about evolutionary convergence and constraints, with particular reference to what kinds of intelligent life we might one day encounter in an extraterrestrial context – he surmised in a documentary, ‘What We Still Don’t Know – Are We Alone?, (video 49 mins) that if by chance we do ever come face to face with alien civilisations, we might find their citizens to be oddly similar to ourselves – to wit:

“I think wherever you go you’ll open the hatch and somebody will be looking back at you…. It’s difficult to think it won’t have a head, the nervous system is a jolly good invention. Quite a big brain. The eyes have got to be close to the brain. Eerily similar. As soon as we get under that alien skin, we’ll realise it’s us all over again”

I wonder to what extent that feeling of eeriness would be a useful analogy when considering how anatomically modern humans (AMH) and Neanderthals felt when they first began to encounter each other in Upper Palaeolithic Europe, the extinction of the latter species notwithstanding.

This snippet from the linked paper argues:

Here, I will suggest that one central tenet of the current neo-Darwinian synthesis, that evolution is for all intents and purposes open-ended and indeterminate in terms of predictable outcomes, is now open to question. Thus, not only is life suspended between permanently uninhabitable regions that are either locked into crystalline immobility or in continuous and chaotic flux, but that the lines of evolutionary vitality thread through a landscape that leaves evolution with surprisingly few choices.

The basis of this view relies on the phenomenon of evolutionary convergence. This concept is, of course, not only entirely familiar to evolutionary biologists, but also provides some of the strongest arguments in favour of adaptational explanations. However, much less appreciated is the ubiquity of this convergence, with examples spanning the entire biological hierarchy from molecules to social systems and cognitive processes. In support of this thesis, which I explore at far greater length elsewhere, I briefly touch on (i) what, if any, key steps in the evolution of life are entirely fortuitous and (ii) what, if any, biological innovations are unique?

It’s always good to see someone thinking on their feet, and although the topic of alien life might not be to everyone’s taste, or even considered relevant here, I definitely think it’s well worth taking a look at our own experience of life on this planet and extrapolating how it might have evolved elsewhere, especially if it turns out that the laws which govern life on Earth are within universal constraints that give rise to similar life forms across vast distances, on the galactic and universal scale.

I’m a little pushed for time, and so can’t do justice to the linked paper, or the others featured in the Royal Society Biological Sciences special edition, but as ever, I expect at least some of the topics therein will be covered here in the future, whatever it may hold in store.

Reference: Evolution: Like Any Other Science it is Predictable – Simon Conway Morris, doi: 10.1098/rstb.2009.0154    Phil. Trans. R. Soc. B  12 January 2010   vol. 365  no. 1537  133-145

In recent years a theory has emerged that seeks to explain three mysterious events that took place at around 13,000 years ago (kya) – the sudden cooling phase known as the Younger Dryas, at the end of the Bølling Allerød warm interstadial,  the sudden termination of the Clovis culture in North America, along with the mass extinction event there that saw the demise of over 30 genera of Pleistocene fauna, although this last event had been in progress from c.40 kya, and also affected further flung parts of the world such as Eurasia and Australia. (I’ll address this last point more fully in a forthcoming post ).

Previous theories postulated that a complex mix of terrestrial – albeit not clearly defined – factors had been responsible for these catastrophic events, which were viewed as having had separate causes, but were especially devastating because of their combined synchronicity.

Following research at numerous archaeological sites, notably by Firestone, West and Kennett, (open access paper), it was proposed that around this time a comet either hit the planetary surface, possibly on the Laurentide ice sheet, or exploded in mid air, initially causing widespread and ferocious burning, followed by a prolonged period of plunging temperatures which laid waste to the North American landscape, killing off much of the fauna, including humans, who had survived the primary fireball, in what has been proposed to have been a period akin to a nuclear winter.

Evidence cited in support of this idea included raised levels of iridium and the presence of nano-diamonds on the ground, both of which are identified as markers for an extraterrestrial impact, as well as a so-called ‘black mat’, a carbon rich layer plainly visible in various archaeological trenches across numerous sites contemporaneous with these events.

More recently, two teams of researchers set out to evaluate the evidence, both of whose findings cast serious doubt on the comet theory, but leave unexplained the presence of nano-diamonds,with one team suggesting that if a cometary impact was responsible, the comet itself must have been radically different from anything currently known to science.

Two papers have been published at PNAS, and I’ll attempt to convey their import here – my thanks go to both teams for very kindly forwarding me copies of the full texts, (which currently reside behind comet-proof paywalls) so without further ado, here they are. First we have ‘Absence of Geochemical Evidence for an Impact Event at the Bølling Allerød/Younger Dryas Transition’, by François Paquay, a Doctoral graduate student in the Department of Geology and Geophysics at the University of Hawaii at Manoa (UHM), and his team, from which this is the abstract:

High concentrations of iridium have been reported in terrestrial sediments dated at 12.9 ka and are interpreted to support an extraterrestrial impact event as the cause of the observed extinction in the Rancholabren fauna, changes in the Paleoindian cultures, and the onset of the Younger Dryas cooling [Firestone RB, et al. (2007) Proc Natl Acad Sci USA 104:16016–16021]. Here, we report a platinum group element (PGE: Os, Ir, Ru, Rh, Pt, Pd), gold (Au) concentrations, and 187Os/188Os ratios in time-equivalent terrestrial, lacustrine, and marine sections to seek robust evidence of an extraterrestrial contribution.

First, our results do not reproduce the previously reported elevated Ir concentrations. Second, 187Os/ 188Os isotopic ratios in the sediment layers investigated are similar to average crustal values, indicating the absence of a significant meteoritic Os contribution to these sediments. Third, no PGE anomalies distinct from crustal signatures are present in the marine record in either the Gulf of California (DSDP 480, Guaymas Basin) or the Cariaco Basin (ODP 1002C). Our data show no evidence of an extraterrestrial (ET)-PGE enrichment anomaly in any of the investigated depositional settings investigated across North America and in one section in Belgium. The lack of a clear ET-PGE signature in this sample suite is inconsistent with the impact of a large chondritic projectile at the Bølling–Allerød/Younger Dryas transition.

As we can see, the original intention of this research was to confirm the comet theory by looking again at the evidence, but as is made clear throughout the paper, that confirmation simply failed to materialise. They examined the layer beneath the ‘black mat’, noting a lack of characteristic markers such as ‘shocked minerals, spherules composed of glass (or its alteration products), or Ni-rich spinels‘.

Observing further that anomalously elevated iridium levels alone don’t necessarily confirm an extraterrestrial impact, whereas other elements present stronger evidence. Analysis of Platinum Group Elements (PGEs) combined with Osmium (Os) isotopic samples revealed that the high levels of iridium (Ir) reported at sites were not confirmed by the authors’ own analytical process. This from the paper:

The PGE abundances for Murray Springs (AZ), Blackwater Draw (NM), Howard Bay (NC), Lake Lubbock (TX), Topper (SC), and Lommel (Belgium) sections are presented in Table S1. From these same sections, but on a different powder split, a comparison of 187Os/188Os, Os concentrations and Os/Ir ratios in different depositional settings is also given (Table S1; see also Table S2).

Firestone et al. (22) have reported 169 measurements of Ir at 14 sites up to 9,200 km apart in the 14C-dated BA/YD (see Fig.S1) bulk sediments, magnetic fraction, and the black mat, but not in the over- and underlying layers. In 5 of the 12 sites reported in table 1 in ref. 22, the Ir concentrations in the bulk sediment are 0.5 ng/g, and the concentrations in four sites (Murray Springs, Blackwater Draw, Lake Hind, and Carolina Bays, Max) reach 2.3–3.8 ng/g Ir. These values are comparable to those obtained at a number of KT boundary sites (e.g., 3.7 ng/g in Petriccio, Italy; 0.85 ng/g in Brazos River, TX; 5.7 ng/g in Beloc, Haiti; 2.9 ng/g in Frenchman River, Canada; and 1.4 ng/g in Hell Creek, MT (37). The Ir concentrations in the magnetic fractions of four samples (22) (Blackwater Draw, Wally’s Beach, Lommel, and Carolina Bay, Max) show concentrations between 15 and 117 ng/g [i.e., 25% of CI chondrites, Ir  460–472 ng/g; (38, 39)].

The data presented by Firestone et al. (24) also show a clear inverse correlation between Ni and Ir (Fig. S2A). This is rather unusual as Ni and Ir are both siderophile elements, enriched in meteorites compared to the terrestrial crust. Both elements typically show the same geochemical behavior during a meteorite impact on the terrestrial crust. In numerous crater impact sites such as Popigai (40) Lapparja¨vi (41), Morokweng (42), Clearwater East (43) and at the KT boundary (25), Ir and Ni display a positive correlation (Fig. S2B).

Table S1 shows that the new analyses do not confirm the elevated Ir values published by Firestone et al. (24). The PGE concentrations measured in bulk sediments are lower by at least an order of magnitude or more. Nugget effects, which cause small-scale inhomogeneities in PGE distribution and account for a variability of concentrations in geological samples (44–46), can be fully discarded here. The use of samples 10 g precludes any nugget effect and has been demonstrated to lead to good sample reproducibility (40), confirmed by repeated analyses in this study.

The authors further claim that all samples from the Younger Dryas black mat exhibit levels considered average for continental crust, whilst the sites at Murray Springs and Blackwater Draw may have shown higher levels of osmium and iridium as a direct result of the black mat’s formation process.

Moving next from land to sea, the team examined levels of osmium isotopes present in the ocean – previous research at Chicxulub  at the KT boundary (the end of the Cretaceous 65 mya – (but check this)) showed that when high levels of osmium borne on an extraterrestrial impactor entered the ocean, the Os isotopic ratios fell. To test the comet theory, two marine environments were analysed, the Gulf of California and the Cariaco Basin, located off Venezuela. The osmium isotope values in the Gulf of California were significantly higher than those in the Cariaco Basin, indicating the lack of cometary input, whilst the lower values detected in the latter did not correspond with the timing Younger Dryas, prompting the conclusion that there was no evidence for a ‘large chondritic impact event’ that had affected the ocean in the predicted manner.

Before heading back on to dry land for the discussion, it’s worth taking a quick look at the Cariaco Basin, as its unusual properties mark it apart from the average stretch of ocean, presumably making it an ideal model for this study, as this link to the CARIACO project explains.

Broadly speaking, the first part of the discussion reiterates and expands upon the osmium isotope studies in seawater, the lack of increased Platinum Group Elements that should be present on land in the wake of an impact, as well as normal levels of iridium found in Greenland ice cores. From there we move on to those mysterious nano-diamonds, an integral component in the comet theory, but which in the context of this paper, appear to be the true anomaly in this saga.

As we have seen, a cometary impact of the types with which we are familiar, should have left both a nano-diamond and PGE signature, but all we have are the nano-diamonds. This in turn causes the authors to speculate upon the properties of a putative comet, as we see:

Results presented here show that it is unlikely that the nanodiamonds were derived from any known meteoritic projectile, in contrast to suggestions of a swarm of comets or carbonaceous chondrite (26). Specifically, mass balance calculations show that if all of the nanodiamonds in the BA/YD sections are primary meteoritic material (1,500 ppm of the bulk; (75) (covering a fluence of 30% of Earth’s surface) (Fig. S1), and were not formed upon surface impact, a chondritic projectile of 1.2 km in diameter should produce an Ir fluence of 1 ng/cm2 that is clearly missing based on our results. For clarity, we emphasize that PGE and Os isotope data are sensitive indicators of undifferentiated meteoritic material.

Alternatively, to avoid PGE enrichment, it is possible to invoke the impact of one or several differentiated, PGEs-poor, possibly still unknown type of achondritic meteorites that vaporized in Earth’s atmosphere at the BA/YD transition is one possibility. However, the probabilities of the arrival of this type of projectile to Earth is low (www.unb.ca/passc/ImpactDatabase/), and this type of bolide lacks all allotropes of nanodiamonds.

In the case of one or several surface impact(s) of achondritic projectile(s), which could explain the absence of PGEs in the studied BA/YD sections, it becomes difficult to explain the formation of nanodiamonds without a well-dated surface expression of one or several craters. So far, no BA/YD craters are yet known. Based on the existing distribution of terrestrial craters (76), one or several large craters of this very young age cannot be eroded, filled with younger sediments or erased by subduction.

Most likely such fresh impact crater(s) would have been found and confirmed many years ago. In the scenario of a 1- to 2-km diameter achondritic, PGEs-poor projectile exploding into the atmosphere or hitting only the Laurentide Ice Sheet, a crater would possibly not have been formed. However, in this case, a source of carbon is required to form the recovered lonsdaleite crystals, and the concentration of carbon in this type of meteorites is extremely low. It is possible that the nanodiamonds were formed during an airburst, but it does not explain the absence of a geochemical anomaly.

Therefore, a strong decoupling of PGEs and nanodiamonds exists which differs from other known impact events. The occurrence of high concentrations of cubic diamonds and nanodiamonds (1,340 ppb) (24) in multiple BA/YD sections, found within carbon spherules without an associated defined geochemical anomaly, is therefore not a robust diagnostic of an impact event.

Thus we have something of a mystery  – although other research has called the impact event into question, none as far as I’m aware appear so thoroughly to confound the idea as this paper. There remains however the question of what exactly created the nano-diamonds, and whether that agency was from outer space or terrestrial in origin, plus the vague possibility that the Earth was indeed hit by something whose precise nature and identity continue to elude us.

I had intended to cover another, related paper in this post, but rather than relegate it to the end of this one, I think it best to write it up separately, especially as it focusses more on the micro-spherules, or lack thereof, alluded to earlier in this post. And suffice it to say, there is a great deal more information in the reviewed paper, especially in the guise of graphs and graphics which I haven’t included here, and I’d be happy to forward a copy to anyone interested in looking at this research in greater detail.

François S. Paquay will be appearing next week at the Fall 2009 meeting of the American Geophysical Union

image from: Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling – Firestone et al, PNAS

see also: Press Release

Reassessing the Source of Long-Period Comets – by Nathan A. Kaib, Thomas Quinn

Topper Site

The Berkeley Laboratory Isotopes Project

Periodic Table

Reference: Absence of Geochemical Evidence for an Impact Event at the Bølling Allerød/Younger Dryas Transition, by François Paquay, Greg Ravizza (also from UHM), Steven Goderis and Philippe Claeys from Vrije Universiteit Brussel, Frank Vanhaeck from the Universiteit Ghent, Matthew Boyd from Lakehead University, Todd A. Surovell from the University of Wyoming at Laramie, and Vance T. Holliday and C. Vance Haynes, Jr. from the University of Arizona at Tucson.

www.pnas.org/cgi/doi/10.1073/pnas.0908874106 (correct link will be posted when available).

As mentioned previously, the Royal Society are celebrating 350 years of publication, and in recognition of this they are offering free access to a vast number of papers, both past and present – indeed the current edition of the Proceedings of the Royal Society B (Biological Sciences) treats us to a Special Issue ‘Recent advances in Chinese palaeontology,’ organized and edited by Xing Xu, Zhe-Xi Luo and Jia-Yu Rong. As well as what appears to be a whole slew of interesting articles discussing an impressive array of fossils dating all the way back to the Cambrian, the final article concerns one of our more direct ancestors, in the guise of Homo erectus.

Here’s the abstract:

A new Homo erectus endocast, Zhoukoudian (ZKD) V, is assessed by comparing it with ZKD II, ZKD III, ZKD X, ZKD XI, ZKD XII, Hexian, Trinil II, Sambungmacan (Sm) 3, Sangiran 2, Sangiran 17, KNM-ER 3733, KNM-WT 15 000, Kabwe, Liujiang and 31 modern Chinese. The endocast of ZKD V has an estimated endocranial volume of 1140 ml. As the geological age of ZKD V is younger than the other ZKD H. erectus, evolutionary changes in brain morphology are evaluated. The brain size of the ZKD specimens increases slightly over time.

Compared with the other ZKD endocasts, ZKD V shows important differences, including broader frontal and occipital lobes, some indication of fuller parietal lobes, and relatively large brain size that reflect significant trends documented in later hominin brain evolution. Bivariate and principal component analyses indicate that geographical variation does not characterize the ZKD, African and other Asian specimens. The ZKD endocasts share some common morphological and morphometric features with other H. erectus endocasts that distinguish them from Homo sapiens.

I’ll just add a few brief notes from the paper, starting with the age of the fossil ZKD V – it was originally dated to c. 230 kya, (kya = thousands of years ago) but more recent research has pushed back the date to something between 400 kya – 500 kya, “using ²⁶Al/¹⁰Be on buried quartz sediments and lithic artefacts from layers 7–10″.

This aluminium/beryllium isotopic dating  technique was in the news earlier in 2009 when it was revealed that the oldest occupants of the site may have lived as long ago  as 680,000 – 780,000 years ago, some 200 ky earlier than previous dating analyses had suggested, and further that they may have been specifically adapted to a cold climate.

The component fragments of the ZKD V skull were recovered in two separate excavations, the first of which took place in 1934 and the second in 1966. Here are details of other remains that were used in comparison to ZKD V from the paper:

Weidenreich (1935, 1943) studied the craniums of ZKD II, III, X, XI, XII and the portions of ZKD V that were then available. He suggested that the fundamental morphology of the ZKD crania remained unchanged over time. When Qiu et al. (1973) were able to study the more complete ZKD V cranium, they determined that it not only has the typical ZKD morphological characters, but also that it has what they described as more progressive features. For instance, the skull of ZKD V has a high and round temporal bone, a reduced occipital torus, and a short distance between inion and the internal occipital protuberance. Other evidence for temporal variation in ZKD H. erectus derives from studies of the human teeth (Zhang 1991) and the lithic industry (Pei & Zhang 1985).

In this paper, we analyse an unpublished endocranial cast of the ZKD V specimen and compare it with other H. erectus (ZKD II, III, X, XI, XII, Hexian, Sambungmacan (Sm) 3, Trinil II, Sangiran 2, Sangiran 17, KNM-ER 3733, KNM-WT 15 000) and Homo sapiens (Kabwe from Zambia, Liujiang from China, and a comparative modern Chinese sample). Our objective is to facilitate a more comprehensive understanding of ZKD H. erectus brain morphology and to re-examine the variability of H. erectus.

There foll0ws a more detailed discussion of the gross morphology of ZKD V, compared with cranial features of the other specimens in the study, whilst the section on bivariate morphometric analysis offers more in the way of specific measurement and statistical considerations.

Finally, a word or two on the overall context of ZKD V and its correlation to other specimens for Asia and Africa:

The taxonomic affinity of the ZKD hominins has long been questioned. Previous analyses, mostly based on study of external cranial morphology, led researchers to propose that the ZKD crania possess unique morphological and morphometric features distinguishing them from other Asian as well as African hominins (Kidder 1998; Anton 2002, 2003; Kidder & Durband 2004). According to Anton (2002), regional differentiation exists between northern Asian and southeast Asian H. erectus, and the ZKD H. erectus sample exhibits less variation than the early Indonesian sample. Other researchers argue that the cranial features thought to define Asian H. erectus are also expressed on some African specimens (Rightmire 1998). Differences between the Far Eastern and African hominins are viewed as minor and not indicative of more than one species (Braüer 1994).

Detailed endocast studies comparing Asian and other H. erectus specimens are limited in number. Begun & Walker (1993) suggested that the ZKD H. erectus endocasts are overall morphologically similar to KNM-WT 15 000. In a previous study, we found that Hexian from central-eastern China is morphologically most similar to the ZKD specimens (Wu et al. 2006). Interestingly, the nine-variable and six-variable PCA results of this study show that the six ZKD endocasts do not cluster together, and do not present a different pattern from the African or the other Asian specimens. Our research on endocast size and shape provides no support for the argument that ZKD H. erectus or other Asian H. erectus specimens represent a morphologically distinct species…

…Our studies indicate that the ZKD endocasts share some morphological and morphometric features with the African and other Asian specimens that distinguish them from the modern Chinese comparative sample. We also note that the ZKD V endocast shows some progressive features compared with the other ZKD H. erectus— ‘progressive’ in the sense that ZKD V differs in ways that foreshadow the greater overall brain height and fuller lobes that generally characterize H. sapiens. This is not unexpected given its later geological age and the possibility that as much as half a million years may be represented by the ZKD sample.

In conclusion, the researchers appear  convinced that African and Asian erectus specimens conform to a single African origin theory, although I suspect that others in the field will find sufficient detail in the data that suggest a far more complex aspect to this era of human evolution.

image: Reconstructed skull and endocast of ZKD V: (a(i)(ii)) superior view; (b(i)(ii)) left lateral view; (c(i)(ii)) anterior view; (d(i)(ii)) right lateral view; (e(i)(ii)) basal view; and (f(i)(ii)) posterior view. Reconstructed areas are shown in black. Scale bar, 4 cm.

Reference: A New Homo erectus (Zhoukoudian V) Brain Endocast From China, by Xiujie Wu1, Lynne A. Schepartz and Wu Liu, Published online before print April 29, 2009, doi: 10.1098/rspb.2009.0149 Proc. R. Soc. B  22 January 2010   vol. 277  no. 1679  337-344