Nice paper - and quick! FWIW below are my solicited comments. I hope that they help in some small way. I haven't italicised genus or species names because I wasn't sure which <i>if any</i> formatting would work.
"Barosaurus is widely thought of as merely Diplodocus with a longer neck."
Do you have a reference for this? You mentioned Barosaurus' regular inclusion in popular dinosaur books so do you mean that it's widely thought of as a long-necked Diplodocus by readers of mainstream palaeontological literature or by dinosaur workers (or some subset)?
"... but very morphologically distinct"
'... but morphologically very distinct' is better.
"... identical to Diplodocus except for a lengthened neck ..."
I don't think the neck has been lengthened. Would 'longer' or 'elongated' work better?
Table 1. The Condyle height:width ratio is absent for Vertebra R but can presumably be calculated from the supplied Condyle height and width.
Assuming that the measurements for Vertebra Q were taken with a millimetre-accurate rule or similar, it's prob better to match the implied accuracy of the other ratios and list it as '0.50'.
Cotyle height:width ratio for Vertebra R - I calculate the ratio of 195/370 to be '0.53'.
Width across parapophyses - should presumably be a capital 'P' next to the Vertebra S datum.
Vertebra Q. You point out that its overall length is not much more than that of Vertebra R but didn't comment that its centrum is 22% longer. I feel that this is worth mentioning (also see next).
Vertebra S. Here you do list both the ratio of lengths overall and that of the centra which feels a little inconsistent when you didn't do that with the previous comparison mentioned above.
In Table 1 you list the vertebrae in the order of R, Q, S, and address them in that order in the subsequent text. However, in this sentence "Its preservation is very different from that of vertebrae Q and R ..." you list Q and R in the reverse order. I feel that it would be clearer (assist with mapping the data in one's mind) to consistently list them in the same order whenever referring to them together. If you agree, you will need to consider changing it twice more in this same paragraph.
"... compared with 51% and 56% for Q and R ..."
As stated above, I get 53% for the Vertebra R ratio.
Para 7 - "Vertebrae Q and R have no trace ..."
Order of Q and R again.
"Presence of a ventral keel ..."
'The presence of a ventral keel ...' is perhaps better.
Reconstructions of the cervical vertebrae.
Does "forward shearing" always have a clear unambiguous meaning when describing vertebrae; ie that it's (presumably) the uppermost part which has been pushed forward?
"So the broad zygapophyseal facets, diapophyseal wings and posterior migration of the cervical rib loop ..."
You appear to have use Oxford commas throughout the paper but are missing one just after 'wings'.
"... vertebra Q, which we tentatively identify as C12,.."
On page 16 at the end of 'Serial position of the cervical vertebrae' you tentatively identify Vertebrae S as C12 and Q as C13 (and this appears to follow logically from everything that precedes).
"... or it might be simple individual variation"
"... or it might simply be individual variation" is possibly better unless you mean to stress that the individual variation is not complex.
This is a nicely illustrated paper of an important specimen. A few areas of minor change are suggested, particularly in addressing issues of geological context, specimen association, and scaling / allometry. Additionally, because so much of the topic has systemetic relevance, a revised diagnosis should be presented for Barosaurus lentus. Finally, some of the descriptions could be augmented in places to create a more comprehensive treatment of the specimen.
p. 1: "Barosaurus is widely thought of as merely Diplodocus with a longer neck." - This statement really needs some context. Has anyone actually said this in print? I recognize that these sorts of memes are often passed from researcher to researcher, but does anyone actually believe this? (later in the paper are some statements that might indicate this, but they really should be up front). Is there a recent diagnosis of the taxon that would indicate such things? Is this a longer neck relative to torso length? Femur length? Is it real, or just a meme?
- Vertebra T is dismissed as too incomplete, but shouldn't it still get a brief description and photos? Or are we talking so incomplete as to be doubtful as a vertebra?
- Because you focus a great deal on anatomy of the neck in Barosaurus, and distinguishing it from Diplodocus, you really should provide a revised diagnosis for Barosaurus. This is partway given in the conclusions, but it is not anything of real utility. If one of the goals of the paper is to provide new information on the neck of Barosaurus, this information should be put to use! As an overall note, I would recommend including a full systematic paleontology section, with taxonomic authorities, referred material, stratigraphic horizons, autapomorphic and differential diagnoses, etc. Minimal work, maximal utility to the reader.
- Figure 2. Include a scale bar (here and elsewhere). Yes, parallax is an issue. As a compromise, indicate where the scale bar is relative to the specimen, as a way to acknowledge parallax. For figures like Figure 4, the lack of a scale bar is a serious deficit. When I see vertebrae of different shapes and from different taxa, I immediately think about scaling effects and the like. Without a scale bar and some way to tell intuitively which vertebrae are largest and which are smallest, the reader is left in the dark. In fact, scaling effects are pretty much ignored in this paper. How do the sizes of the vertebrae in Barosaurus stack up relative to those of Diplodocus, Apatosaurus, etc.? How big are the vertebrae of AMNH 6341 vs. YPM 429? They are said to be roughly the same size (p. 19), but if measurements are available (or can be estimated), this should be quantified.
- Figure 3. The orientation of anterior and posterior views are odd. I would put them into "standard" position, with dorsal to the top and ventral to the front. Also, add letters to the figure to indicate which view is which. The same goes for other figures in this paper.
- Give strong consideration to including interpretive line drawings that label portions of the figure, or at a minimum, some labeling on the photographic plates. Not every reader is going to know where the lateral laminae are, and things such as the neural spine are not immediately obvious on some views of some vertebrae (particularly where the neural spine is very subdued). In the absence of a line drawing, consider labeling parts of the figures. For instance, in Figure 4 the bifurcation of the neural spine is an important feature, but it is really hard for this non-sauropodologist to pick out the neural spine in some of the photos. In figure 6, it is really hard to pick out the prezygapophyseal facet. Etc.
- Figure 4. Include letter labels. This is far more intuitive than trying to pick out top and bottom specimens, etc.
- Figure 5. I appreciate the desire to illustrate this specimen (it is beautiful), but it is so minimally referenced in the text as to seem a little superfluous. Do you really need 6 views to get across the relevant points? Granted, I like things to be illustrated in detail, but it seems odd to have 6 views of a vertebra from a taxon that is only distantly related to Barosaurus.
- Does YPM 429 have a broader context? Where was it found? Which rock formation? As is, it is just dropped into the discussion, which not a lot of context. Given the later questions about association of the specimen, surely there must be some field notes at the YPM that talk about this. Or maybe not? Something to check into. Given the concerns about association, field data are critical. Were they found in the same quarry? This is mentioned in one part (p. 10), but then the whole issue of a quarry map is discarded for the section on association at p. 14. Are there other sauropods from the same site? These sort of data are critical, but not realy addressed at the appropriate points in the text.
- How do the AMNH and YPM Barosaurus compare in size? Are any measurements available for the AMNH specimen?
- The vertebral descriptions seem a little brief; rather than just calling out a few features, why not include a comprehensive redescription using modern terminology (which was not used by Lull or Marsh)? What are the shapes, orientations, etc., of the laminae? Of the pleurocoels? Some of these descriptions occur in some places, but I was really hoping for the definitive description of the cervical vertebrae of YPM 429. Maybe that's beyond the scope of the paper...but why not broaden the scope just a little? It would only improve the utility of the work to a broader audience!
- For AMNH 6341 vs. YPM 429, do you have any stratigraphic comparisons?Although morphology is primary, it would be important and interesting to know how these animals stack up to each other in geological time. Perhaps John Foster's thesis has some data that would be of help.
--Andrew A. Farke, 23 September 2013
What I was trying to add last night: The position of YPM 429 is tricky to figure out. The site is on the north slope of Piedmont Butte, about 15-20 miles north of Rapid City and it is covered in grass and pine trees, so it is difficult to tell where you are in the section (just not enough exposure). When I was out there years ago we did find some indeterminate sauropod material in the lower meter of the Morrison, right above the Unkpapa Sandstone. The Barosaurus quarry was at about 6-7 m above the contact (had to look that up in my own thesis -- tough to remember sections from 20 years ago). The tricky part is that all along the eastern Black Hills the Unkpapa thins gradually to the north below the Morrison and the Morrison becomes correspondingly thicker. The Morrison is also only about 30-35 m thick in the Black Hills (down to about 25 m thick in Unkpapa-less parts of the northwest Hills in Wyoming, and absent in the southern Hills where the Unkpapa is thickest). The the problem is determining where you really are in the section relative to the top and bottom of the Morrison without a full exposure, how thick the Unkpapa is there (and thus where you are relative to other Black Hills Morrison sections where the Unkpapa is absent), and assuming you can figure that out, how the thin Black Hills Morrison lines up with the thicker Morrison at places like Como Bluff and the eastern flank of the Big Horns. There is little direct way to correlate from these areas to the Black Hills, and the thinness of the Morrison in the Hills makes it difficult to determine if the formation is essentially time-equivalent with the Morrison elsewhere and just thinner, if much of the upper Morrison was eroded off prior to deposition of the Lakota, or if the Morrison of the Hills is equivalent to the upper Morrison elsewhere and the lower part of the formation was perhaps not deposited in the first place. Pete Peterson once mentioned that his best guess was that the upper part of the Morrison was eroded off, but we have no way of knowing yet. The mudstones seem to be devoid of ash so radiometric dating would be tough.
Now, about three miles south of Piedmont Butte and YPM 429 was a probable Barosaurus partial skeleton collected in 1980 (SDSM 25210) that came from an outcrop with better exposure and here I was able to get a complete section of the Morrison tied into the Unkpapa also. Conveniently, the 25210 probable Barosaurus came from about the 7-8 m level above the Unkpapa Sandstone, so assuming that the thickness of the Unkpapa doesn't change significantly between this site and YPM 429 three miles north, the relative positions of the two sauropod specimens (i.e., the position between the Sundance below and the Lakota above, considering the Unkpapa a member of the Morrison in the Black Hills, Szigeti and Fox 1981) should be very similar. The more complete section at the 25210 site then allows us to estimate approximately how high in the overall section the two sites are and at least compare to other areas relative to their respective local sections. The typical Morrison at the 25210 site is approximately 18 m thick, and the Unkpapa (if I remember Szigeti and Fox correctly) is about 12 m thick at the same outcrop, so we have YPM 429 and SDSM 25210 occurring at approximately 18-20 m up into a 30 m-thick total section (about 60-66% up from the base). If we go out on a limb and assume that, regardless of thickness, local Morrison sections are essentially equivalent in terms of relative positions, the Black Hills specimens would be slightly older than AMNH 6341 from the Carnegie Quarry, which according to Turner and Peterson (1999; figure 7) is about 76% of the way up from the base of the Morrison in the local section. (Two quarries that are from about the same relative level in their local sections as the Black Hills sites would be Sheep Creek Quarry D north of Como and Riggs Quarry 15 in Fruita, the Field Museum Apatosaurus site -- at least the back half -- which is lower Brushy Basin Member.) However, if the upper Morrison of the Black Hills has been eroded off then of course the Black Hills specimens would be even older still. And then there is the possibility that the base of the Morrison is much younger in the Black Hills than elsewhere (although there is no evidence that it is) and that the specimens might in fact be from late in Morrison time.
So basically we don't know where YPM 429 really is stratigraphically, thanks to the peculiarities of the Black Hills Morrison, but the above summarizes what we do know and outlines a few of the speculations we can make.
Didn't mean to go on for quite so long.
Abstract- "It is related to the sympatric Diplodocus". Isn't every organism? Well, that lived at the same time as Diplodocus anyway.
Pg9-10- The comparison to brachiosaurs seems like it would benefit from more extensive taxonomic coverage, a phylogenetic philosophy, discussion of how the characters vary with vertebral position in sauropods, and how they vary with neck elongation. For example, is the forward-shifted neural arch a characteristic of Titanosauriformes? Present in other camarasauromorphs? Found in any other diplodocoids? On which vertebrae of brachiosaurs? Is there a trend in neural arch placement throughout the diplodocoid neck? Is this also true of e.g. Euhelopus or Mamenchisaurus?
Pg22- "Consequently, and surprisingly, none of these analyses reported any autapomorphies in the neck of Barosaurus, its most distinctive feature. This indicates that additional characters, related to the prezygapophyses and their laminae, should be added to future analyses." Well, including unique autapomorphies in analyses is largely a waste of time, and Whitlock is one of the few authors who does this. Indeed, it seems harmful to bootstrapping, since sometimes the characters randomly excluded or doubled will be autapomorphies, which have no effect on topology. His rationale that "The inclusion of autapomorphies in an analysis of this type can also be useful in distinguishing otherwise morphologically similar taxa" is unconvincing since phylogenetic analyses are not used to distinguish taxa.
Overall, I feel the paper includes some great information but seems scattered. I know you've lamented the near universal structure of papers, but I think this one would benefit from consolidating the ideas- description of S > excellent illustrations of S > description of Q > excellent illustrations of Q > description of T (as Farke suggested) > ... > revised comparison of R to brachiosaurs > each section from page 14 onward in a Discussion.
Similarly, figures 8, 11 and 12 are almost completely superfluous. I get that in our Shiny Digital Future, page length and figure count don't matter, but it reminds me of an SVP slideshow where you need to get a point across but the audience can't rewind to the other slides that show the information. The Giraffatitan vertebra is similarly unneeded, but at least here it would be greatly appreciated if I were coding the taxon. So contra Farke, here I favor helping people over strict efficiency.
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