Peer review of: Extinction of eastern Sahul megafauna coincides with sustained environmental (2020)



 

Reviewers' Comments: 
 
Reviewer #1: 
Remarks to the Author: 
This is a revised version of a paper I reviewed previously and the authors have modified some of the 
text to reflect some of the concerns I had with the earlier version, concerns shared with one of the 
other reviewers in several cases. 
 
The authors have provided a rebuttal of the concerns I had with the original, and I remain 
unconvinced by some responses, as in some cases have simply re-iterated their original position in 
different words. The response is long, so I will simply note a couple of things below in this regard. 
 
At the end of the day though, this is a very nice and thorough piece of work in most respects, and I’m 
not sure my opinion should trump theirs. I am therefore happy to recommend publication of this 
version and let history be the judge, the data is fine, it’s the nuance of the interpretation that in some 
parts I take issue with. I note that the authors now claim a minimum reliable age of 40.1±1.7ka, 
which is about what I would have thought is a reasonable firm claim anyway. I’d also add that I like 
the figures and tables as currently configured in the revised version, even if they might be pushing the 
page limit. 
 
Specifically, on two points of several I could draw out as illustration: 
(i) I pointed out that there were earlier MIS4 periods when climate deterioration, in the study area, 
using the same study as the authors, could have rendered the megafauna extinct but didn’t. The 
authors state: ‘being able to state that megafauna did not go extinct during MIS 4 is unsubstantiated’. 
This does not address the issue I raised – clearly megafauna did not go extinct during MIS4, because 
the authors present data that they continued to exist in MIS-3. My point was that climate deterioration 
as a sole driver of extinction in MIS-3 or any other time after human arrival, is probably not a viable 
explanation. 
(ii) I made the point that it was not appropriate to discount the radiocarbon dates on charcoal, which 
might be a few millennia older than the sediment, but not more. The authors responded that the 
charcoal dates were discounted because they have applied the quality rating scale of Rodrigues-Rey et 
al (2015), and the dates are ‘b’ quality and they only used a and a*. This is technically correct, but my 
point was how much older could the charcoal dates reasonably be than the age of the sediment (and 
the fossils), and the answer is a few millennia maximum and probably less. The authors then say the 
charcoal was ‘badly preserved’, and again, fine, but that would make the ages more likely minimum 
ages, and the dates do provide a constraint that suggest probably not younger than 40 and possibly 
quite a bit older. The ‘reworked’ argument I think is weak, though not entirely discountable I guess. 
(iii) I also note, on reflection, that the Gledswood dates I referred to are unpublished I think, so no 
reason for the authors to have known about them. I do think its not credible to claim that people 
weren’t around in the catchment – my view is that people were everywhere by then, but again that’s 
only my opinion. 
 
 
 
Reviewer #3: 
Remarks to the Author: 
I am happy with the authors' responses and changes to the MS. I think it's good to go. 
 
 
 
Reviewer #4: 

Remarks to the Author: 
I have read both the revised manuscript and the SI. The increased clarification by changes in the text 
is very helpful. With the excuse that the authors could not find the Mead and Metlzer reference I would 
advise they widen their search and perhaps refer to the other Mead and Meltzer reference from the 
same year. A quick google search will do it and then a visit to the library. 
 
I am still critical of the treatment of the only two sites where megafauna and a record of humans co-
occurring in Sahul have been identified: Nombe Rockshelter and Cuddie Springs. With Nombe, the 
recent dating project has confirmed the ages of the Unit where the megafauna were found. It is 
interesting that the human record is found with fragmented faunal remains. Nonetheless when an 
interaction between humans and megafauna cannot be demonstrated, it does indicates that 
megafauna survived in the highlands till quite late. There is no excuse for ignoring these results. The 
evidence is clear. 
 
Not everyone agrees that the Saltre et al dating confidence attributions are an accurate representation 
of the dating confidence. To dismiss the Cuddie Springs evidence as possibly disturbed is a clear 
indication that the authors have either not read the relevant papers or not understood them. 
 
Furthermore, it is somewhat annoying to give ESR/U-series methods such an elevated position in the 
dating suite. How this has happened I am not sure, yet in other studies ESR-U series has been up to 
10,000 years older than other dating (OSL/C14) methods. Are the authors now suggesting via Saltre 
et al that the Mungo deposits are 20,000 years older than the accepted OSL and C14, or that the 
Devils Lair sequence is also much older? Do they not see the consequences of promoting such 
interpretations because it fits their thesis? This is a rhetorical question of course. 
 
I would also suggest that the authors be more circumspect about the presence of humans. Until it is 
demonstrated (by empirical evidence) to be so then you cannot claim they were probably there. The 
work of Alan Williams has shown that the population levels across Sahul at this time were very low. 
Does that not indicate something? Furthermore, the fact there are only two megafauna sites in Sahul 
with an associated human record, which by the way these authors dismiss, does that also tell you that 
either megafauna or humans were pretty thin on the ground?