Changes through growth in sauropods and ornithopods
March 29, 2012
By one of those happy coincidences that you sometimes get, today saw the publication of not one but two dinosaur ontogeny papers: this morning I was sent a copy of Woodruff and Fowler (2012) on ontogenetic changes in the bifid spines of diplodocoids, and tonight I was alerted to Werning (2012) on Tenontosaurus growth trajectories based on osteohistology.
It’s interesting to compare them. The obvious conclusion is that, while sauropod vertebrae are intrinsically better than ornithopod long-bones, the latter make much, much better subjects for ontogeny studies.
The problem that Woodruff and Fowler have is that they’re working from a small selection of mostly isolated elements, nearly all of them damaged by breakage and/or crushing, and uncontrolled for serial position beyond some basic binning. As a result, the taxonomic identifications are really rather arbitrary and unsupported — as they say (p. 2), “for the purposes of this study, original taxonomic designations were not reexamined” — and indeed re-examination would not necessarily help much.
As a result, they are left with rather a circular argument, as follows:
- Small specimen X is Suuwassea.
- Small specimen Y is assigned to Apatosaurus, because someone once said so.
- But Y has a less bifid neural spine than adult Apatosaurus.
- So spine bifurcation increases through ontogeny in Apatosaurus.
- So small specimen X belongs to Apatosaurus, too.
- => Suuwassea is Apatosaurus [Note: I stupidly wrote "Diplodocus" here in the first posted version. Now corrected to Apatosaurus.]
I don’t find this at all convincing. (Neither does Matt: we discussed this briefly today, and at more length at the Bonn workshop where Cary presented this work.) Leaving aside the observation that the conclusion fits in neatly with the Horner Lab’s ongoing everything-is-just-a-Triceratops-growth-stage project, there isn’t really much that Cary could have done differently here: the necessary specimens (i.e. multiple near-complete associated individuals of unambiguous taxonomic identity) just don’t exist.
(Mind you, figure 7A is about the least convincing evidence of bifurcation I’ve ever seen.)
Ornithopod long bones
By contrast, Sarah Werning has a much better story to tell, largely just because she’s working with much better material. Tenontosaurus is known from many complete and near-complete individuals, there is no real uncertainty about the material all belonging to the same taxon, and the elements (long bones) are much less subject to crushing and breakage than vertebrae.
Of course it also helps that Sarah has done astonishingly careful, detailed work. I don’t think I’m giving much away when I say that this paper has been many years in the making — as the Acknowledgements say “This work was completed in partial fulfillment of the requirements for the Master of Science degree, Department of Zoology, University of Oklahoma.” And it’s been a looong time since Sarah was at Oklahoma. But I get the sense that this reflects taking the time and putting in the effort to Get It Right, rather than standard-issue procrastination.
Perhaps the most impressive part of this paper, though, is methodological:
High-resolution histological images of the cross-sections are digitally reposited online for scholarly use at MorphoBank (http://MorphoBank.org), project p494; see Table 2 for a list of slides and accession numbers. Digital images larger than 25,000 pixels in either dimension were digitally scaled (reduced to 17,000–20,000 pixels in the larger dimension) to allow processing on MorphoBank and because most image editing software does not support editing of gigapixel jpg files. These edits were made after scale bars had been added. Images in full resolution can be obtained from the author.
As you can see, these are ridiculously high-resolution images. By making them freely available, Sarah is doing everything she can to enable others to replicate or correct her work — or to use the data for other purposes that she’s not yet thought of. This is a big win for the progress of science, and I want to publicly congratulate Sarah for doing it. I would love to see this become standard behaviour.
(It’s a bit strange that the paper links onto the the MorphoBank home page rather than directly to the Tenontosaurus project. Here you go.)
PLoS ONE vs. Journal of Morphology
A final thought, before I finally go to bed. When I saw Cary’s paper in the Journal of Morphology I thought to myself, “good for him, he’s got that into a really good journal” — which is true. But then when Sarah’s came in, I found myself comparing PLoS ONE. Here’s what I came up with:
Access. A no-brainer: PLoS ONE wins hands down, being open-access while J. Morph. is paywalled.
Charges. The flip side of the first category: J. Morph. wins because (as far as I can tell from the Author Guidelines) there is no publication charge. PLoS ONE charges $1350.
Length. Another PLoS ONE win, because it imposes no limits whatsoever on length, figure count, etc. Cary’s paper is no lightweight at 11 pages, but PLoS’s liberality with page-space means that Sarah’s is well over twice as long at 25 pages. Now of course not all papers need to be long; but for those that do, cutting to a journal’s length limit is a painful and stupid process.
Image Colour. Again, PLoS ONE wins — it’s very rare these days to see a greyscale specimen image in a PLoS journal. But to be fair to J. Morph., the author guidelines do say: “All color figures will be reproduced in full color in the online edition of the journal at no cost to authors. For the printed version free color figures are at the editors discretion.” So it looks like Cary and Denver dropped the ball on this.
Image Resolution. No question. PLoS ONE wins by a mile. Click through the two representative images above: the PLoS one has 3.5 times as many pixels, and that’s after I added a 10% wide margin around the J. Morph. image. And if you want to use these illustrations as basis for new images, remember PLoS also lets you download the original full-resolution submitted image in a lossless format.
DOI Resolution. When I added the references below, I noticed that the DOI for the J. Morph. article doesn’t resolve yet, which is careless. PLoS ONE wins in this category, resolving just fine.
Impact Factor. Yes, it’s a stupid number and we all hate it. But some people still seem to take it seriously, so we may as well look. And PLoS ONE wins with 4.411 to J. Morph.’s 2.087 — more than double.
Putting it all together, based on the seven categories that I evaluated here (and no doubt I missed some), it looks like the only reason to go with J. Morph. ahead of PLoS ONE is to avoid the publication fee. By this point, PLoS ONE has made itself an absolutely mainstream journal for palaeo, and the obvious first choice for most projects.
- Werning, Sarah. 2012. The ontogenetic osteohistology of Tenontosaurus tilletti. PLoS ONE 7(3):e33539. doi:10.1371/journal.pone.0033539
- Woodruff, D. Cary, and Denver W. Fowler. 2012. Ontogenetic influence on neural spine bifurcation in Diplodocoidea (Dinosauria: Sauropoda): a critical phylogenetic character. Journal of Morphology, online ahead of print. doi:10.1002/jmor.20021 [Direct Link, since the DOI doesn't seem to work.]