Peer review of: Fossils from Mille-Logya, Afar, Ethiopia, elucidate the link between Pliocene environmental (2020)

Reviewers' Comments: 
 
Reviewer #1: 
Remarks to the Author: 
NCOMMS 19-14456 
 
This is a clear and useful description of the recent discoveries from Mille-Logya. It is nice to see a new 
are opened up and producing fossils. Overall, I have no strong complaints with the manuscript; overall 
it follows established protocols for describing the new material and the assertions seem reasonably 
well-supported. I am encouraged to see the work being done there - in general, it seems to have 
potential to produce some very interesting and informative fossils. I do have a few notes, however. 
Notes: 
 
1. Page 9: Some clearer explanation of the taxonomy of the hominin tooth might be helpful. The 
authors say “Based on size and average enamel thickness (Fig. 3 e & f) in addition to diagnostic 
occlusal features, we attribute it to Homo sp.”. Fair enough for the occlusal features and enamel 
thickness, but the size is not really helpful, according to my read of the graph, since the new tooth is 
in with A. anamensis and A. afarensis, which is, in turn between H. habilis and H. erectus. Perhaps 
cusp proportions might be more helpful. 
Also on that graph, using only the species means gives us no sense of variation. Since the new M2 
falls in with the A. afarensis and A. anamensis, just using the means might or might not be telling us 
the whole picture. Does the new molar not overlap at all with early Homo in terms of size? 
 
2. The previous sentence reads: “An asymmetric and rhomboidal occlusal outline of the upper second 
molar has been reported to characterize Homo erectus and H. habilis<sup>35,35</sup> but is rare in 
A. afarensis Kimbel et al.<sup>42</sup>” 
I would argue that the M2 rhomboidal structure might not be so diagnostic – it is present in AL 417 
and AL 444. If it is truly different from A. afarensis, some quantitative expression of that fact might 
clarify. 
 
Just a note: citation 42 is not Kimbel et al. 
 
3. P. 9-10: Were the two ulnae from the same stratigraphic horizon? What are the ages? 
 
4. P. 13-15 and Supplement: The faunal list is helpful, and the paleoecological interpretations seem 
reasonable, but there was no attempt to quantify the habitat in terms of open-closed or wet-dry. Since 
the authors draw specific environmental conclusions, I would have liked to have seen some kind of 
multivariate analysis of the faunal data to provide us with a sense of where the Mille-Logya fossils fall 
relative to other known ecological communities (fossil and extant). Perhaps this is in an accompanying 
paper? 
 
 
 
Reviewer #2: 
Remarks to the Author: 
This manuscript provides a preliminary overview of the geology, fauna, and paleoenvironment of a 
new hominin-bearing site in Ethiopia, Mille-Logya. The site samples a little-known time period in the 
human fossil record and has the potential to contribute significantly to our understanding of the origin 
and evolution of Homo. However, the conclusions that the authors reached are not substantiated. This 
is mostly because of the lack of detail or analysis provided for the fauna. This is in direct contrast to 
the geology and age of the site, which is described and analyzed in great detail. To support their 

conclusion that Homo appeared with drier/open environments and represents an adaptive shift 
between Australopithecus and Homo, the authors needed to show that the fauna from the older 
sediments are different from those of younger sediments, that there was indeed in-situ faunal change 
with fauna in Mille-Logya, and that the paleoenvironment was different between the older sediments 
and younger sediments. To do this, the authors really needed to: 
1. Provide the data and results behind the relative abundances of the fauna. No numbers are ever 
provided – what is the number of specimens? What is the relative abundance? The authors just tell us, 
for example, that Gafura is similar to Hadar with higher proportions of bovids to suids and equids. 
2. The authors talk about the degree of faunal similarity, but it is a qualitative rather than quantitative 
assessment. They really need to do some sort of faunal similarity analysis that provides us with a 
quantitative measure of (dis)similarity, such as Dice. 
3. The authors only provide a composite faunal list even though they argue for in-situ faunal change. 
They need to provide faunal lists by localities and/or stratigraphic units. 
4. There needs to be a more detailed comparison between the fauna and paleoenvironment between 
Mille-Logya and contemporaneous sites. 
4. Relative abundances and faunal similarity can be quite biased unless we understand the taphonomic 
context of the site. As far as I can tell, no taphonomic analyses have been conducted.