PONE-D-21-38931Life before Stonehenge: the hunter-gatherer occupation and environment of Blick Mead revealed by sedaDNA, pollen and sporesPLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: No

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: N/A

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Reviewer #1: No

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Reviewer #1: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: This is the latest in a series of reports of ongoing investigations of a Mesolithic site in the valley of the Wiltshire Avon in southern England. In many respects, Blick Mead is unremarkable. Though situated at the interface between chalkland and wetland, organic preservation is poor and there are no hearths or other convincing structural features (leaving aside tree-throw hollows and a putative flint ‘platform’). Yet the site has attracted an unusual amount of attention by virtue of its proximity to Stonehenge and claims by the investigators that Blick Mead was an aggregation site to which hunter-gatherers returned periodically over millennia to engage in feasting and other ritual activities, evidenced by large amounts of (unworked) burnt flint and the preponderance of aurochs (wild cattle) among the faunal remains – a ‘persistent place’ in the Mesolithic landscape of southern England and perhaps the beginning of the Stone Henge ritual complex. While many archaeologists might regard such ideas as speculative (even fantasy), they are nevertheless difficult to refute.

The Blick Mead excavations have targeted small areas around a former spring at the leading edge of a terrace and the adjacent river floodplain. While previous reports (Refs 2 & 3) dealt primarily with the archaeological evidence, the focus of the submitted manuscript is on the results of plant sedaDNA and palynological analysis of column samples from a profile through the sediments at the floodplain edge, supported by sedimentological, OSL and XRF analyses. The results are used to promote the view that the Mesolithic site occupied an open area or ‘clearing’ in deciduous woodland (or woodland-grassland mosaic) which provided opportunities for the exploitation of browsing and grazing ungulates, principally aurochs and red deer, evidenced by their presence among the faunal remains and the occurrence of hoofprints in palaeosurfaces.

For the most part, the manuscript is clearly written, and supported by informative colour illustrations and a range of supplementary information that specialists should find valuable. Given that the application of sedimentary ancient DNA (sedaDNA) analysis as a complement to more traditional, forms of palaeoecological investigation is still not mainstream in British (or indeed European) archaeology, this aspect of the paper can be considered innovative. However, the interpretations offered are not always (in my view) robust, and there are statements that need to be amplified and/or clarified to improve the presentation:

1. Line 125-128: “Certainly, the presence of unusually high prominence of auroch artefacts in the macrofaunal assemblage, some with physical evidence of butchery, alongside numerous auroch hoofprints identified within Mesolithic soil horizons, suggests a heightened exploitation of this particular animal at Blick Mead [Line 125-128]

COMMENT: Cut-marked bones resulting from butchery are not normally considered “artefacts”. Why not simply refer to them as “cut-marked bones”? It is difficult to see how hoofprints are necessarily linked to human exploitation, or the combination of a few cut-marked bones plus hoofprints (especially given the 3-4000 yr Mesolithic occupation history) is indicative of “heightened exploitation”.

2. Line 206-208: “The late Mesolithic [OSL] dates for the middle of the sequence align with late Mesolithic C14 dates from nearby trenches 19, 22 and 24”.

COMMENT: The 2-sigma errors on the OSL dates are very large (up to ±1280 yr). So, “align” would seem to be an overstatement.

3. Line 210-212: “… reinforcing the relative archaeological chronology provided by the stone tool assemblage and demonstrating evidence of no obvious, major contamination of DNA results from later human activity”.

COMMENT: What is meant by “relative archaeological chronology”. Was this established from stone artefact typology or stratigraphy or both, and when and by whom; moreover, how does this “demonstrate” the stratigraphic integrity of the sedaDNA results – give reference citation(s). I don’t have access to the 2018 monograph on Blick Mead (Ref. 2), but in his review of that monograph report Andrew David (whose opinion I value) states, “What is clear, but is perhaps not spelled out enough in the accompanying discussion, is that the Mesolithic deposit is a chronologically mixed accumulation” (David 2019: 440). This apparent contradiction needs to be addressed.

4. Line 331: “There were three intrinsic measures of sedaDNA authenticity for this site … [et seq.]”

COMMENT: The three reasons given for discounting vertical translocation of sedaDNA are observed differences between the (sedaDNA-derived) plant assemblages from the Mesolithic age (alluvial) sediments and the underlying weathered chalk (1) and the modern flora (2), and colluviation (linked to Bronze Age (BA) agriculture on the adjacent terrace) protecting the Mesolithic horizons from later disturbance (3). None of these is entirely convincing. BA and later colluviation might explain the absence of modern plant DNA but would not have protected the Mesolithic horizons from pedogenic and other ‘disturbances’ during the Late Mesolithic to MBA (c. 5700-1500 BCE). From the context/horizon descriptions in Fig. 3A, I suspect the alluvial sediments were strongly affected by pedogenesis over a prolonged period, and that more-or-less the entire profile (from context 329 downwards into 334) is a buried soil. To be blunt, stratigraphic interpretation of palynological and sedaDNA data from buried soils is arguably no more reliable than from a modern soil. Micromorphological (thin section) analysis is widely used to investigate the properties and processes in buried soils/sediments, and often essential for identifying the extent of translocation due to root penetration, percolation, and (perhaps relevant here) animal/human trampling. Was soil microscopy and micromorphology applied at Blick Mead? If so, the results should have been included in this report. If not, this is a serious omission, which needs to be rectified before publication of the sedaDNA and palynological data.

5. METHODS/SUPPORTING INFORMATION: Overall, the descriptions of materials and methods are adequate, except for sediment geochemistry and particularly XRF. The micro-XRF (iTRAX) system is described in reference 69 (which is acceptable), but more explanation should be provided for the handheld pXRF measurements. Why was it deemed necessary to use both pXRF and μXRF? Were the pXRF measurements taken in the field or in the lab and, if in the lab, how were the samples prepared? What settings were used with the Niton XL3t – calibration model, filters, spot size, measurement times, etc. What are the detection limits for different elements using those settings? Was an empirical calibration used based on CRMs, or just the values provided by the instrument without external calibration?

MINOR CRITICISMS (Grammar/Use of English/Word Choice/Terminology)

General – “auroch” or “aurochs” are (alternative) SINGULAR nouns for Bos primigenius; “aurochsen” is the PLURAL/collective noun;

Line 19 – missing <letter o="" stroke="" with=""> in Tromsø;

Line 37 – “drylands” is one word;

Line 40 – “open clearing” – the word “open” seems superfluous;

Line 59 – DELETE “over approximately 4000 years ago” [REDUNDANT];

Line 71 – DELETE “to particular areas” (REDUNDANT); “facilitating” would be better than “easing”;

Line 90 – “windthrow” is the technical term for the uprooting and overthrowing of trees by wind;

Line 98 – “… chalkland areas THAT contain …”;

Line 116 – DELETE “to” before “towards”, i.e. “… skewed towards Neolithic …”;

Line 119 – “… Blick Mead WAS a persistent place …” [past tense];

Line 122 – Missing “a” before “unique”;

Line 125 – “… high INCIDENCE of auroch …” (not “prominence”);

Line 128 – DELETE “particular” (REDUNDANT);

Line 146 – INSERT definite article (the) before “later medieval”;

Line 155 – “The zoological assessment … identified 271 bone fragments”. The meaning is unclear. This would be better written as, “Of 2430 bone fragments recovered, only 271 were identifiable to species (S3 Table) …”

Line 159-160 – “… auroch WAS the only animal …”;

Line 162 – “Red deer WAS the second …”;

Line 163 – Italicise “Sus scrofa”;

Line 171 – “salmonid and pike” are common nouns, therefore not capitalised;

Line 172 – Change “fauna” to “microfauna”;

Line 184 – “Lathrobium sp.” – “sp.” should not be italicised;

Line 203-204 – modify text to read, “… full suite of C14 and OSL dates can be seen …”;

Line 189-190 – “Taken together the insects INDICATE …” (present tense)

Line 207 – “Late Pleistocene”. Capitalise “Late”;

Line 211-212 – “… demonstrating evidence of no obvious, major contamination of DNA results …”. Shorten this to, “… demonstrating no obvious contamination of DNA results …”

Line 233-234 – misspelling of Salicaceae; Delete “only”, thus: “…due to very low template sedaDNA…”.

Line 285 – “… the data suggest …”. “data” is plural.

Line 289 – “nutrient-enriched” [hyphenated]

Line 292 – “Between the depths of 67.82-67.98 m …”. This would read better as, “Between 67.82-67.98 depth, …”.

Line 294 – “high-stress” and “so-called” [hyphenated]

Line 302 – DELETE “possible”.

Line 314 – “…inhibited THE expansion …”;

Line 346 – DELETE “of time”.

Line 351 – “closed-canopy” [hyphenated]

Line 358 – “mineral-rich” [hyphenated]; “favourable” [British spelling, for consistency];

Line 372 – REPLACE “is” with “it”;

Line 374 – CHANGE “…had to interact with …” TO “… interacted with …”;

Line 388 – “wet woodland” [not hyphenated];

Line 390-391 – INSERT “from” between “that” and “Blick”, and DELETE “that” at beginning of line 391.

Line 392 – DELETE “fairly” [REDUNDANT];

Line 397 – DELETE “as a whole” [REDUNDANT]

Line 406 – “favourable” [BRITISH spelling, for consistency];

Line 410 – “land-use” [adjectival, therefore hyphenated];

Line 411 – “19th-century” [hyphenated];

Line 418 – REPLACE “It is likely that” WITH “Likely,”;

Line 424 – redundant “that” [that that];

Line 434 – “THE sampling procedure …”;

Line 438 – “…SEALED with duct tape …”;

Line 440 – “… THE risk of contamination …”;

Line 455 – “THE resulting barcodes …”;

Line 471 – DELETE “also”;

Line 484 – Further methodological details are included in THE S2 Text. [n.b. missing definite article]</letter>

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PONE-D-21-38931R1Life before Stonehenge: the hunter-gatherer occupation and environment of Blick Mead revealed by sedaDNA, pollen and sporesPLOS ONE

Dear Dr. Hudson,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

==============================

Please address the remaining comments in detail before re-submission.

==============================

Please submit your revised manuscript by Apr 25 2022 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

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Peter F. Biehl, PhD

Academic Editor

PLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: (No Response)

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: No

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The authors have taken on board most of the criticisms raised in my original review. However, I am still not satisfied with the information provided on soil micromorphology. A summary table has been added (S7 Table). But there are no micrographs of the soil thin sections. These should be provided as supporting information to the verbal descriptions (lines 222-250).

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Reviewer #1: No

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Life before Stonehenge: the hunter-gatherer occupation and environment of Blick Mead revealed by sedaDNA, pollen and spores

PONE-D-21-38931R2

Dear Dr. Hudson,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Academic Editor

PLOS ONE

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