On continua and categories in paleoecology. . .or, an example application of ODP data

Today we’re delighted to have a guest post from Dr. Chris Noto, a new assistant professor at University of Wisconsin-Parkside, and an old friend of mine from our graduate school days together at Stony Brook University. Chris has had a long-running interest in dinosaur paleoecology, and thus it only seemed natural for him to apply these interests to the ODP data. Enjoy!

Chris Noto, at home in the field

In describing the ecology of an organism our first inclination may be to simply go observe it in its day-to-day existence. Therefore, at its core, ecology is primarily a science of the living and this is reflected in the methods and theories one finds in the literature. Over the past couple decades there has been a growing interest in the relationship between organismal morphology and ecology, which is now often referred to as “ecomorphology”(Losos 1990; Ben-Moshe et al. 2001; Aguirre et al. 2002; Zeffer et al. 2003; Sacco and Van Valkenburgh 2004). This has opened entire new areas of research into the covariation between organisms and their environment, which is also the basic foundation for understanding evolutionary change over longer spans of time.

Some paleontologists have applied ecomorphological principles to reconstructing the paleoecology of certain extinct groups, including carnivorans (Palmqvist et al. 1999), birds (Hertel 1995), and especially ungulates (Solounias and Semprebon 2002; Meehan and Martin 2003; DeGusta and Vrba 2005; Klein et al. 2010). Changes in the types and/or proportions of ecomorphs in a fossil community have also been used as evidence of environmental and evolutionary responses to climate change(Van Valkenburgh 1995; Meehan and Martin 2003; Badgley et al. 2008; Noto and Grossman 2010). You will note though that a lot of this research relies on comparison to living analogs related to the fossil groups in question. How do we explore the paleoecology of groups that completely lack extant analogs?

If there’s one thing we’ve learned through all this research, it’s the fact that:

1. Certain morphological adaptations occur regardless of species (convergence) because of specific habitat constraints, and
2. Morphological differences between species will occur due to diverging ecologies, even if we don’t know exactly what ecological functions those morphological differences actually represent.

But, we won’t know those differences exist until we look for them. Paleoecology is first and foremost comparative: we take our fossils and compare them to other related taxa and living forms to better understand their place in the original community. Often we assign categories to taxa, such as “carnivore”, “biped”, etc.; however, differences between species are often better described by a continuum than a set of categories(Carrano 1999). The morphology of an organism reflects the amount of time it spends doing certain activities or performing certain functions. For example, a sloth can swim on occasion even if it is not particularly well adapted for it. Dinosaur paleoecology is finally moving in the direction of our mammalian colleagues by using quantitative measures of morphology (which allow for continua) instead of assigning discreet categories.

The ODP is one of the first large-scale projects to bring together the kind of dataset necessary to study dinosaur ecomorphology. In a recent paper I published looking at differences between dinosaur fossil communities (Noto and Grossman 2010), I was forced to use categories in assigning ecomorphs, which artificially restricted the analysis by forcing me to choose a category when uncertainty existed. In this case it was whether certain non-hadrosaur ornithopods were bipedal or quadrupedal. With ODP data, it is now possible to take a more quantitative (and nuanced) approach to this question.

To explore possible trends in ornithischians, I used humerus length and mediolateral width measurements to calculate Mike Taylor’s Gracility Index (GI; Taylor 2009) using only the largest individual from each species. These data were log transformed and plotted against the log of humerus length (to help minimize the effects of size and codependency). The resulting plot clearly separates the taxa, with more bipedal taxa having relatively gracile humeri and quadrupedal groups have more robust humeri. There are two ways to use this graph. First, we can look at the distribution of taxa from each group and see whether they fit more towards a bipedal or quadrupedal type; those intermediate to the extremes are referred to as facultative. These are my own divisions based on where I see breaks in the data. Basal ceratopsians, for example, occur mainly towards the bipedal or facultative ends of the spectrum, while derived Neoceratopsians are firmly on the quadrupedal end of things. Another way to look at the plot is how robust we may expect the humerus to be for a taxon of a given size. The dashed line is drawn across the middle of the plot. For a given humerus length we can compare GI between taxa. For example, Iguanodon has a more robust humerus (lower GI) than most ornithopods in the dataset. Furthermore, we can spot outliers, which may point to either extreme specialization or faulty data. The theropod Mononykus has an extremely robust humerus, approaching the level of Triceratops, which is related to its specialized digging forelimb. On the other hand, Cerasinops appears to have the most robust humerus of all, however as Mike pointed out to me, the original paper describes the humerus as extremely gracile and gives no width measurement. So where did the width measurement come from? This particular data point is worth another look.

Humeral robustness as a function of humeral length. Select taxa labeled in gray. Cera.=Cerasinops, Gypo.=”Gyposaurus”, Herr.=Herrerasaurus, Igua.=Iguanodon, Mono.=Mononykus, Post.=Postosuchus, Psit.=Psittacosaurus, Scut.=Scutellosaurus, Stego.=Stegosaurus, Thec.=Thecodontosaurus, Tric.=Triceratops.

As you can see, the distribution of humeral morphologies indicates a gradual continuum of locomotor strategies from fully bipedal to full quadrupedal. Quantitative data such as this could then be fed into a paleoecological analysis instead of categories, allowing for more refined analysis of ecological differences and similarities among paleocommunities over space and time. While evolutionary trends are certainly important, we must not forget the ecological context of the morphological patterns we are studying.

References

Aguirre LF, Herrel A, van Damme R et al. (2002) Ecomorphological analysis of trophic niche partitioning in a tropical savannah bat community. Proceedings of the Royal Society of London Series B-Biological Sciences 269:1271-1278

Badgley C, Barry JC, Morgan ME et al. (2008) Ecological changes in Miocene mammalian record show impact of prolonged climatic forcing. Proc Natl Acad Sci U S A 105:12145-12149

Ben-Moshe A, Dayan T, Simberloff D (2001) Convergence in morphological patterns and community organization between Old and New World rodent guilds. Am Nat 158:484-495

Carrano MT (1999) What, if anything, is a cursor? Categories versus continua for determining locomotor habit in mammals and dinosaurs. J Zool 247:29-42

DeGusta D, Vrba E (2005) Methods for inferring paleohabitats from discrete traits of the bovid postcranial skeleton. J Archaeol Sci 32:1115-1123

Hertel F (1995) Ecomorphological indicators of feeding behavior in recent and fossil raptors. Auk 112:890-903

Klein RG, Franciscus RG, Steele TE (2010) Morphometric identification of bovid metapodials to genus and implications for taxon-free habitat reconstruction. J Archaeol Sci 37:389-401

Losos JB (1990) Ecomorphology, performance capability, and scaling of West Indian Anolis lizards: an evolutionary analysis. Ecol Monogr 60:369-388

Meehan TJ, Martin LD (2003) Extinction and re-evolution of similar adaptive types (ecomorphs) in Cenozoic North American ungulates and carnivores reflect van der Hammen’s cycles. Naturwissenschaften 90:131-135

Noto CR, Grossman A (2010) Broad-scale patterns of Late Jurassic dinosaur paleoecology. PLoS ONE 5:e12553

Palmqvist P, Arribas A, Martinez-Navarro B (1999) Ecomorphological study of large canids from the lower Pleistocene of southeastern Spain. Lethaia 32:75-88

Sacco T, Van Valkenburgh B (2004) Ecomorphological indicators of feeding behaviour in the bears (Carnivora : Ursidae). J Zool 263:41-54

Solounias N, Semprebon G (2002) Advances in the reconstruction of ungulate ecomorphology with application to early fossil equids. Am Mus Novit:1-49

Taylor M (2009) A re-evaluation of Brachiosaurus altithorax Riggs 1903 (Dinosauria, Sauropoda) and its generic separation from Giraffatitan brancai (Janensch 1914). J Vert Paleontol 29:787-806

Van Valkenburgh B (1995) Tracking ecology over geological time – evolution within guilds of vertebrates. Trends Ecol Evol 10:71-76

Zeffer A, Johansson LC, Marmebro A (2003) Functional correlation between habitat use and leg morphology in birds (Aves). Biol J Linn Soc 79:461-484

A First Pass at Figures

Even though our paper is intended for a technical audience, it is still important to ensure that a broad range of readers can access and understand the information contained within the text. For instance, not even a competent dinosaur paleontologist is necessarily familiar with all of the intricacies of ornithischian clade names like “Ankylopolexia” or “Neornithischia.” Thus, we want to provide a brief bit of background for readers of the paper.

One option, of course, is to write out brief definitions of various clades as they are introduced. This works okay in some cases – for instance, we definitely want to briefly explain what an ornithischian is – but to do this for every term can get a little unwieldy. An old adage states, “A picture is worth a thousand words,” and this is just as true in scientific writing as it is in popular writing.

So, I suggest that Figure 1 for the paper include a simplified cladogram of the major clades discussed in the paper. A first pass at this is given below (click on the image to see at full resolution):

Figure 1. Phylogeny of Ornithischia (from multiple recent sources), showing major clades discussed in the text. Outlines show representative members of each clade; names in bold indicate clades with quadrupedal taxa.

There are a few things I should mention. First, the content of the figure is nowhere near finalized. However, there were a few principles I wanted to adhere to:

• Keep it simple. Because this is only an overview figure, I did not deem it practical to include all of the taxa that we discuss. Instead, I just chose the “important” ones that will appear over and over again.
• Terminology. In a few cases, such as Neornithischia, including only major named clades oversimplifies things just a little too much. For instance, there are a bunch of important neornithischians (e.g., Agilisaurus and Othnielosaurus) that don’t fit comfortably within ornithopods or marginocephalians, and I want to find ways to include such taxa. Thus, I’ve created terms like “Early neornithischians”. I realize that this may imply that they are a clade in their own right, where instead they form a comb or polytomy, but perhaps this is a simplification that just has to be made. If anyone has a suggestion for a better way to title the groups, please let me know. For now, I prefer “early neornithischians” over “basal neornithischians” and the like. “Basal” implies a ranking that just isn’t there for cladograms, but maybe other folks think this is less of a deal than I do.
• Notation of quadrupedal taxa. Because quadrupedalism vs. bipedalism is so important for the paper, I bolded relevant taxa as outlined in the caption. The icons (discussed next) provide an additional clue. If I recall correctly (Andrew McDonald is probably most up to speed on this of anyone who follows this blog), there are probably a few non-hadrosaurid ornithopods that should be inferred to be quadrupedal, too.
• Icons. I consider it very important to include at least a small figure for each taxon, so that readers who are not familiar with all of the terms can picture each clade in their mind. The icons that are shown here (from Mike Keesey’s Phylopic) are of generally high quality, but should be considered only temporary. Ideally, I would like to generate new images to go with our figure, if only because there has been such a hubbub over the running dinosaur pose recently.
• Orientation. I opted for portrait rather than landscape orientation for the figure, primarily because I thought it was a more efficient and readable format. Any thoughts?
• Time calibration. One option for the figure would be to time-calibrate it, and show the duration and estimated time of origin for each clade. I feel this might make things just a little too complex (and crowd other parts of the figure), but am open to alternative interpretations. Thoughts?

At any rate, that’s what we’ve got for now. Please chime in in the comments!

Image Sources: All images are from Phylopic, and are licensed accordingly under a Creative Commons License. Individual credits are as follows: Oscar Alcober & Ricardo Martinez (http://phylopic.org/image/246), Scott Hartman (http://phylopic.org/image/25; http://phylopic.org/image/48; http://phylopic.org/image/43; http://phylopic.org/image/33), Loewen et al. (http://phylopic.org/image/142), FunkMonk (http://phylopic.org/image/128), Lukas Panzarin (http://phylopic.org/image/140), Remes et al. (http://phylopic.org/image/146); Ville-Veikko Sinkkonen (http://phylopic.org/image/261)

Some Things to Do, and a Progress Update

We’ve had some good discussion and suggestions for ways to tweak the phylogeny, so keep them coming! At the bottom of this post, I have a new and improved version of the phylogeny.

In the meanwhile, we’re still trying to pull together a few last measurements for the analysis. We have gotten a few new data submissions, and these all require verification entries. There are also a few papers that can be combed for measurements. So, there is still an opportunity to make a contribution.

ODP Phylogeny Draft, 27 June 2011

Notes on Phylogeny

Updates on non-dinosaurian archosaurs from Nesbitt 2011 analysis:

Scleromochlus – position retained from old tree (not included in Nesbitt phylogeny)
Gracilisuchus and aetosaurs resolved arbitrarily at “base” of Pseudosuchia (position of clades not resolved in Nesbitt’s analysis)
Hallopus placed as per previous version of cladogram

Other Updates:
Polacanthus is arbitrarily placed as sister to Gastonia+Tatankacephalus (i.e., made as an ankylosaurid rather than a nodosaurid; will need discrete reference to justify this decision).
Position of Tatankacephalus follows Parsons & Parsons 2009

An updated (updated) phylogeny

As mentioned in the previous post, a few papers with new or updated phylogenies for various ornithischians have appeared in the last year. Thus, I spent a few hours going through them and updating the tree topology as well as adding taxa. The phylogeny is given below, with notes on what I did at the end of the post. Note that many of the arbitrarily-resolved nodes aren’t that critical for some aspects of the analysis; they often include fragmentary taxa (sometimes only known from cranial material). We may wish to revise some of the resolutions in order to reduce ghost lineages.

I have not yet incorporated Sterling Nesbitt’s most recent phylogeny of Archosauria, because I wasn’t able to successfully download the file. It’s top of my list once I do.

If you have suggestions to revise or improve the phylogeny, please mention them in the comments.

ODP Phylogeny Draft, 24 June 2011

Notes

General Ornithischia

General phylogeny of Ornithischia updated following 50 percent majority-rule consensus tree in Butler et al. 2011, as modified by Makovicky et al. 2011 (the latter with modifications of codings for Thescelosaurus and addition of Haya)
Position of Thescelosaurus updated following Makovicky et al. 2011, modified from Butler et al. 2011
Position of Talenkauen follows Butler et al. 2011

Updated the position of Yinlong, Micropachycephalosaurus, Stenopelix. Sister taxon relationship of Yinlong+Stenopelix follows Butler et al. 2011; relationships of Micropachycephalosaurus+Chaoyangsaurus+(Stenopelix+Yinlong)+(rest of ceratopsians) resolved arbitrarily.

Topology within Heterodontosauridae after Pol et al. 2011 and after Butler et al. 2011. Echinodon was placed as a basal heterodontosaurid heterodontosaurid (following Butler et al. 2011). The clade of Abrictosaurus+NHM A100+Heterodontosaurus+Lycorhinus was resolved arbitrarily.

Bugenasaurus and Thescelosaurus synonymized following recent work by Boyd et al. (2009).

Ceratopsia

Topology of Chasmosaurinae follows Sampson et al. 2010; placement of Ojoceratops and Eotriceratops resolved arbitrarily. Triceratops, Diceratops, and Torosaurus spp. are considered separate, following Farke 2011.

Topology of Ceratopsia follows Makovicky 2010; inclusion of Micropachycephalosaurus and Stenopelix follows Butler et al. 2011. Placement of Zhuchengceratops inexpectus follows Xu et al. 2010, with Zhuchengceratops and Udanoceratops arbitrarily placed as sister taxa (based on biogeography).

Topology of Psittacosauridae follows Sereno 2010, figure 2.23E. P. gobiensis is placed arbitrarily as sister to P. sibiricus. Psittacosaurus ordosensis is synonymized with P. sinensis, following a tentative suggestion from this paper. Psittacosaurus xinjiangensis is placed following the polytomy in Averianov et al. 2006, with its resolution arbitrary.

Pachycephalosauria

Topology within Pachycephalosauria follows Longrich et al. 2010. In recognition of the probably synonymy of Pachycephalosaurus, Stygimoloch, and Dracorex, the latter two animals were removed from the matrix and the matrix was rerun in PAUP otherwise following the specifications of Longrich et al. 60 equally parsimonious trees resulted; in order to more completely resolve relationships within the clade, the 50% majority rule tree was used for the topology within Pachycephalosauria. ?Sphaerotholus brevis was arbitrarily placed at the base of the clade including all other Sphaerotholus species, and Texacephale was arbitrarily placed at the base of the clade including Stegoceras+Gravitholus+Colepiocephale.

Ankylosauria

Topology within Ankylosauria updated following Burns et al. 2011, Figure 8 (50% majority rule consensus tree).

The placement of Cedarpelta as an ankylosaurid follows Lü et al. 2007 and an unpublished analysis by Nick Gardner (http://whyihatetheropods.blogspot.com/2008/12/cedarpelta-as-ankylosaurid.html). Ultimately, no postcrania for this taxon are included, so its placement is not terribly critical. Cedarpelta and Gobisaurus placed as sister taxa following this same analysis.

Dyoplosaurus is recognized as a unique taxon (Arbour 2009), and is arbitrarily placed as sister to Euoplocephalus.
Aletopelta is tentatively given as an ankylosaurid, based on text in Ford and Kirkland 2001.

The polytomy between Tianzhenosaurus, Nodocephalosaurus, and Ankylosaurus was resolved arbitrarily.

Niobrarasaurus and Nodosaurus are arbitrarily given as sister taxa, because of their general similarity. Furthermore, Coombs (1990), in The Dinosauria, suggested that Nodosaurus is close to Sauropelta and Silvisaurus (p. 478, caption for Figure 22.14, “Nodosaurus probably fits just above or just below node 8.” [i.e., either between Sauropelta and Silvisaurus, or Silvisaurus and Panoplosaurus], so this opinion is followed here. Based on geography alone, they are given as sister to Sauropelta.

Placement of Crichtonsaurus was semi-arbitrary; the tree of Lu et al. with this taxon cannot be easily reconciled with the Burns et al. phylogeny. Noting that both phylogenies recover Pinacosaurus “above” Gobisaurus; Crichtonosaurus was placed between the two. Crichtonsaurus‘s placement “above” Minmi was arbitrary, based on the later geological occurrence of Crichtonsaurus.

Polacanthus foxii is arbitrarily given the basal position within Nodosauridae occupied by Hylaeosaurus, for Coombs 1990, Fig. 22.14.
Zhejiangosaurus is completely arbitrarily placed as more derived than Polacanthus.
Because of great uncertainty in phylogenetic position, and because no phylogenetic analysis has adequately addressed the taxa, I recommend removing Aletopelta, Niobrarasaurus, Nodosaurus, Polacanthus, and Zhejiangosaurus from the analysis.

The topology of nodosaurids (including the placement of Hungarosaurus and Struthiosaurus) follows Ösi 2005, Figure 15. The monophyly of Edmontonia follows Burns et al. 2011.

Basal iguanodonts

Topology of basal iguanodonts follows McDonald 2011, Figures 1 and 2.

Genus of “Camptosaurus” aphanoecetes changed to Uteodon, per McDonald 2011

Muttaburrasaurus placed in Rhabdodontidae following McDonald et al. 2010. Its resolution at the base of the clade is arbitrary, but based on the fact that it occurs much earlier in the fossil record than other rhabdodontids.

Monophyly of Zallovosaurus+Dryosaurus+Dysalotosaurus+Elrhazosaurus+Kangnasaurus+Valdosaurus follows McDonald et al. 2010. Resolution within that clade is arbitrary. Dysalotosaurus is made its own genus, following recent work.

“Dollodon bampingi” and M. atherfieldensis are synonymized following McDonald 2010.

Resolution of Cumnoria and Uteodon is arbitrary relative to their polytomy.

Resolution of Cedrorestes, Dakotadon, Lanzhousaurus, and Iguanacolossus relative to their polytomy is arbitrary. Lanzhousaurus as being part of less inclusive clade follows Figure 2 of McDonald.

Position of Tethyshadros, Nanyangosaurus, and Tanius adjusted in light of McDonald figures 1 and 2. Position of Telmatosaurus as part of clade excluding Lophorothon also follows this analysis.

Levnesovia and Nanyangosaurus arbitrarily made sister taxa; also made part of clade excluding Tethyshadros, following Figure 2 of McDonald. Probactrosaurus and Eolambia were arbitrarily made sister taxa to resolve a polytomy.

Altirhinus and Equijubus were arbitrarily made sister taxa, and arbitrarily placed as part of clade excluding Jinzhousaurus+Penelopognathus in order to resolve polytomy.

Iguanodon placed outside of more derived iguanodonts+Mantellisaurus. Position of Ouranosaurus is arbitrarily resolved.

Lambeosaurinae

Topology of Lambeosaurinae modified following Evans 2010 (Hypacrosaurus paper), Figure 16A (parsimony trees, strict consensus).. Pararhabdodon+Koutalisaurus+Tsintaosaurus retained from “old” Prieto-Marquez phylogeny, because the first two taxa are not on the Evans phylogeny. Nipponosaurus was deleted, because it is an obvious juvenile and many characters cannot be scored effectively. Amurosaurus+Sahaliyania retained from previous version of phylogeny, because latter taxon is not on Evans phylogeny. Polytomy of Corythosaurus and Olorotitan resolved following Bayesian tree (Fig. 16B). Lambeosaurus laticaudatus and Velafrons are arbitrarily resolved. Velafrons placed as closer to corythosaurins follows the original Gates et al. 2007 description of the taxon (Velafrons is not in the Evans phylogeny).

Filling in the Blanks

During the extended gestation/hibernation/dormancy of the ODP, a few new papers with relevant data have slipped into circulation, some with ornithischians preserving limb bones, as well as new or updated phylogenetic analyses. So, if you’re looking for a final chance at data entry, here are a few possibilities:

Open Access

Currie PJ, Badamgarav D, Koppelhus EB, Sissons R, Vickaryous. Hands, feet and behaviour in Pinacosaurus (Dinosauria: Ankylosauridae). Acta Palaeontologica Polonica in press. doi:10.4202/app.2010.0055 [link]

McDonald AT, Kirkland JI, DeBlieux DD, Madsen SK, Cavin J, et al. (2010) New basal iguanodonts from the Cedar Mountain Formation of Utah and the evolution of thumb-spiked dinosaurs. PLoS ONE 5(11): e14075. doi:10.1371/journal.pone.0014075 [link]

Closed Access

Bell, P. R. and Evans, D. C., 2010. Revision of the status of Saurolophus (Hadrosauridae) from California, USA. Canadian Journal of Earth Sciences, 47, 1417-1426.

Butler RJ, Liyong J, Jun C, Godefroit P (2011) The postcranial osteology and phylogenetic position of the small ornithischian dinosaur Changchunsaurus parvus from the Quantou Formation (Cretaceous: Aptian–Cenomanian) of Jilin Province, north-eastern China. Palaeontology 54:667-683. [link]

Cuthbertson, R. S. and Holmes, R. B., 2010. The first complete description of the holotype of Brachylophosaurus canadensis Sternberg, 1953 (Dinosauria: Hadrosauridae) with comments on intraspecific variation. Zoological Journal of the Linnean Society, 159, 373-397.

Ezcurra, M. D., 2010. A new early dinosaur (Saurischia: Sauropodomorpha) from the Late Triassic of Argentina: a reassessment of dinosaur origin and phylogeny. Journal of Systematic Palaeontology, 8, 371-425.

Langer, M. C., Bittencourt, J. S. and Schultz, C. L., 2011. A reassessment of the basal dinosaur Guaibasaurus candelariensis, from the Late Triassic Caturrita Formation of south Brazil. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 101, 301-332.

Lee, Yuong-Nam; Ryan, Michael J.; and Kobayashi, Yoshitsugo (2011). “The first ceratopsian dinosaur from South Korea”. Naturwissenschaften 98 (1): 39–49.

McDonald, A. T., Barrett, P. M. and Chapman, S. D., 2010. A new basal iguanodont (Dinosauria: Ornithischia) from the Wealden (Lower Cretaceous) of England. Zootaxa, 2569, 1-43.

Makovicky, P. J., Kilbourne, B. M., Sadleir, R. W. and Norell, M. A., 2011. A new basal ornithopod (Dinosauria, Ornithischia) from the Late Cretaceous of Mongolia. Journal of Vertebrate Paleontology, 31, 626-640.

Martinez, R. N., Sereno, P. C., Alcober, O. A., Colombi, C. E., Renne, P. R., Montanez, I. P. and Currie, B. S., 2011. A basal dinosaur from the dawn of the dinosaur era in southwestern Pangaea. Science, 331, 206-210.

Pol, D.; Rauhut, O.W.M.; and Becerra, M. (2011). “A Middle Jurassic heterodontosaurid dinosaur from Patagonia and the evolution of heterodontosaurids”. Naturwissenschaften 98 (5): 369–379. [phylogeny only - no useful postcrania] [link to free PDF]

Prieto-Marquez A. Cranial and appendicular ontogeny of Bactrosaurus johnsoni, a hadrosauroid dinosaur from the Late Cretaceous of northern China. Palaeontology (in press). DOI: 10.1111/j.1475-4983.2011.01053.x [link]

Prieto-Marquez, A. and Salinas, G. C., 2010. A re-evaluation of Secernosaurus koerneri and Kritosaurus australis (Dinosauria, Hadrosauridae) from the Late Cretaceous of Argentina. Journal of Vertebrate Paleontology, 30, 813-837. [no measurements; phylogeny only]

Wang X, Pan R, Butler RJ, Barrett PM. 2011 (for 2010). The postcranial skeleton of the iguanodontian ornithopod Jinzhousaurus yangi from the Lower Cretaceous Yixian Formation of western Liaoning, China. Earth and Environmental Science Transactions of the Royal Society of Edinburgh 101: 135-159.

Note: Most of these citations were gathered from Graeme Lloyd’s excellent compendium of dinosaur phylogenies. I’ve tracked down the links in a few cases, but otherwise you should be able to find them using a quick search on-line. Not all of the papers necessarily have usable data; the list here is a quick-and-dirty overview. I may have missed some important new contributions, too. Please feel free to flag them in the comments, and I’ll add them to the list.

Wondering what to do in order to contribute data, or just need a refresher? Check out this how-to guide.

Disparity Notebook

Local disparity guru and paleontologist Randy Irmis (that’s Randall B. Irmis, Ph.D., if you go by his web page) recently posted a nice long list of recommended readings on the issue of disparity – what it is, how to calculate it, etc. As a reminder, disparity is the measure of how different species are from each other in terms of shape, size, or other discrete features (not the same as diversity, which just counts how many different species exist – once again, see Randy’s eloquent post on the topics). It just so happens that documenting disparity in ornithischian dinosaurs is at the top of our list for the ODP. Hence, I decided to buckle down and read through an important recent paper on the topic (one that Randy happened to highlight in his list, too).

In the interest of getting this post out in a timely manner, I’m mainly going to be posting my unpolished notes, taken a few weeks ago in the comfort of my bed (nothing like a little light bedtime reading). I’ve made a few adjustments here and there, but otherwise you can consider this a peek into my stream of consciousness while reading the literature. Because I was mainly interested in how the work could be applied to the ODP, I didn’t really bother with summarizing the specific analyses done by the authors. Thus, without further preface:

The Citation:
Brusatte, S. L., Montanari, S., Yi, H.-Y, and Norell, M. A. 2011. Phylogenetic corrections for morphological disparity analysis: new methodology and case studies. Paleobiology 37: 1-22. [unfortunately, not openly available as a PDF] [link to abstract]

The Main Gist:
The fossil record just isn’t complete – and that’s particularly true for many of the early members of important ornithischian clades (like thyreophorans and marginocephalians). However, it’d be nice to interpolate some of these missing data in order to produce a more complete picture of the changes in a clade’s disparity over time and in morphospace (the multi-dimensional plot of the shape of an animal’s bones, in this case). Brusatte and colleagues, building on the work of many other authors, have formalized a method to fill in some of these gaps by producing a plausible reconstruction of missing ancestors.

An early thyreophoran, Scelidosaurus; image by Nobu Tamura, used under a Creative Commons License

My Notes
[as presented here, it's a mix of to-do tasks for the ODP, a cookbook for the analysis, and how Brusatte et al.'s method will be applied; caveat emptor]

The questions: What is the morphospace occupied by ornithischian dinosaurs over time? How does the morphospace change? How does the morphospace occupied by specific clades differ?

The tasks:

• Assemble data matrix (taxon/measurement matrix)
• Reconstruct ancestoral measurements following Brusatte et al. 2011
• Calculate Euclidean distance matrix (“quantifies the pairwise dissimilarity between taxa”) – this presumably calculates dissimilarity for each taxon/measurement pair
• Apply principal coordinates analysis (PCoA) to each analysis (better handles missing data than does PCA [principal components analysis]). Can be done in R.
• PCoA produces scores for each taxon along n=#taxa axes. Can be done in R.
• Examine slope of scree plot to determine where break occurs; only examine these “interesting” axes. I think this scree plot can be done in R.
• Calculate disparity indices from the PCoAs, using different bins (categories). Can be done in R. Categories might include: 1) clade; 2) time; 3) locomotor category; 4) combination of clade/locomotor category.
• Indices include: sum of range of values along axis 1, 2, … n (i.e., range 1+range2+range3. . .); product of range of values along axis 1, 2, n (range 1 * range 2 * range 3. . .) normalized to the nth root; and same sum and products for variance in each bin.
• Rinse and repeat using ancestral values as calculated following Brusatte et al. 2011.

Ideal results:

• Disparity indices that can be compared statistically (using bootstrap values) for various categories. E.g., a disparity value for Ceratopsia, Ornithopoda, Thyreophora, etc. disparity  value for quadrupeds vs. bipeds.
• Graphs showing point clouds for various clades along various axes (e.g., PC1 vs. PC2)
• Graphs showing trends for disparity over time, with different groups. E.g., trend line showing disparity in ornithischians as a whole, along with trend line showing disparity in thyreophorans, ceratopsians, etc. Potential sample size issues here, particularly for clades with few members or few members early in their history
• Narrative text and / or table showing what factors are loaded on which axes

Summertime, open ignorance, and finishing the project

Hi, all. Thanks for your patience this spring. Sorry we’ve let things lie fallow for so long. Many thanks to everyone for keeping things ticking over while we were AWOL.

Like Andy said in the last post, it’s time to wrestle this thing to the ground and stick a knife through its heart (I may be paraphrasing a bit). Andy, Mike, and I have cleared some protected time in our summer schedules to finish the analyses and write the paper. The next two weeks may be a bit quiet on our end as we all work to get other things tied up and off our desks–and as Andy moves his residence!–but we should be ready to hit it hard by the second week of June.

There is a lot of work to be done, and there are lots of ways to contribute to the paper for everyone who wants to be involved, right now and continuing through the summer. I’ll give some suggestions in a minute. But first, an admission.

We don’t really know what we’re doing here. That’s obvious with the social side of the project, because nothing like this has been attempted before, at least not on this scale or with this degree of openness. But it’s also true on the scientific side. None of us (Andy, Mike, or I) has ever written a paper on this topic. There are some specific analyses that we need for the paper that we’ve never run before. So we are very much learning as we go–this is the open ignorance I alluded to in the title. This isn’t by accident. We could have chosen to do something simpler and less ambitious–perhaps repeat a project that we’d already done before with only the names of the critters changed. But we wanted to learn from the project–from you, the contributors, and alongside you–and to grow as scientists from having participated in it. And we want the final product to be a truly collaborative effort, and not to simply walk everyone through a series of moves that we already know by heart.

And it is working. We have been amazed at the level of enthusiasm and commitment that you have brought to the project, and our only regret is that we have not reciprocated with the sustained level of effort that you, and the project, deserve. So we’re committing ourselves to getting this done, starting now.

How can you contribute? Here are some suggestions:

• Update the database. New taxa continue to be described, new descriptions of established taxa continue to be published, and older publications continue to become available. So if you have been wanting to do some (more) good old-fashioned ODP gruntwork, there’s still a little time.
• Suggest relevant references, or read up on the ones that are already suggested. It might be a good idea to gather those references together so they can be made available to anyone who is working on the project. We’ll probably do a post specifically on this in the near future, but there’s no reason not to be pulling things together in the meantime.
• Look at the outline of the paper, suggest improvements, and–if you are so inclined–start writing those bits that can be written right now. For now, feel free to post chunks in comments or send them to us. Jay Fitzsimmons’s paragraph on citizen science and the ODP is a good model to follow. We’ll definitely be posting more on the actual writing of the paper soon, but, as with boning up on the relevant references, there’s no reason to hold off if this is something you’re interested in working on.
• Analyze data. Obviously there are limits to what we can do until we really finalize the database once and for all, but this is a good time for exploring the data and for test-driving analyses to be done on the finalized database. We have enough data that overall trends are not likely to change much, so anything that looks interesting now will probably still be interesting in the final version.
• Work on a time-calibrated phylogeny for the dataset. This is a big one, again probably deserving of a post of its own. We’ll also need to update the “master tree” to include the most current phylogenetic trees for the included taxa. If you’re into trees, timelines, or both, the mothership is calling you home.
• Figure out how to do disparity analyses. This is one of those things that we project organizers have never done before. We’re reading up on it right now, but if you know anything about it, let us know. Even when we get up to speed, we’ll still need your input. Like Project Mayhem, you can determine your own level of involvement.
• Other stuff? The project is probably at its maximum breadth in terms of types of work to be done. Up until now we’ve focused mainly on building the database and outlining where we want to go, and in a few weeks we’ll have the database finalized and our efforts will narrow as we focus on running the analyses and writing the paper. So whether you’re brand new and want to get involved for the first time, or an old hand who wants to do something different, there is something around here that needs doing. Have a look at the tasks list, go back through the last few posts, and see what appeals to you. If in doubt, give us a shout.

That’s all for now. Stay tuned for more posts very soon. But don’t just stay tuned–keep posting ideas, data, references, bits of text, and whatever else you want to contribute. We’ll do likewise.

Outlining the Paper

Pisanosaurus, by FunkMonk

After all of this work and data accumulation, it’s probably just about time to do the darned analyses and write the darned paper. We’ve had quite a bit of discussion over the last year or so on what this might look like. To that end, I want to outline one possibility and then solicit input from everyone. Again, this is very much a work in progress, so please comment as appropriate.

Working Title: Trends and Variation in Limb Proportions of Ornithischian Dinosaurs [please think up a more exciting, succinct, and descriptive title]

Outline of Contents

1. Introduction
   What are ornithischian dinosaurs?
   What do we already know about their modes of locomotion and limb proportions? How are they unusual compared to other dinosaurs?
   What have other workers done with analyzing dinosaurian limb proportions?
   What is the main point of this study? [to document, describe, and interpret ornithischian limb morphology, and how it relates to function]
2. Materials and Methods
   Jay Fitzsimmon’s very nice paragraph on citizen science and the ODP goes here.
   How specimens were selected.
   Where we got the measurements.
   How we winnowed down the data.
   How we assembled the phylogeny
   Statistical analyses performed on the data [PCA to describe overall patterns; regressions accounting for phylogeny to describe various allometric patterns {we probably only want to look at patterns that are comparable with theropods or other analyses of interest}; analyses looking at trends within clades; analysis of disparity; analysis comparing characters using phylogenetically independent contrasts]
3. Results
   Principal components analysis – done on uncorrected data, how do we describe the limb proportions in various ornithischians. Believe it or not, this hasn’t really been done!
   Regressions accounting for phylogeny to describe allometric patterns – we might want to look at a few regressions, such as forelimb vs. hindlimb length, femur vs. tibia+MTIII, humerus vs. radius+MCIII
   Analysis documenting trends in clades –  include pretty colored images a la Padian et al’s charts of dinosaurian growth rates
   Analysis of disparity – how disparate are various groups? How rapidly did the bauplans for the various groups develop?
4. Discussion & Conclusions
   What do these results mean?
   We’ll have more to fill in when we get some “final” results!

A Recommendation:

We all will have an urge to make this paper as absolutely comprehensive as possible – in the past we have talked about many, many different kinds of analyses, hypotheses, etc. But, I think we also want to avoid getting bogged down in needless detail or bloated and waylaid by side tangents of marginal importance. (some of what I outlined above may very well fall into this category!) So, let’s keep that in mind. . .(but don’t be afraid to make suggestions, either!)

Forelimb Proportions, Ternary Style

An important part of our manuscript will simply be a description of limb proportions in ornithischian dinosaurs. For this, ternary plots really have no parallel. These graphs simultaneously plot three variables in two dimensions on an equilateral triangle. And wouldn’t you know it – we can consider each dinosaur limb to have three major bones! In the case of the forelimb, these are the humerus, radius, and metacarpal III (see this post for an explanation of why we would look at the radius rather than the ulna).

In the figure below, I’ve generated a quick and dirty ternary plot for ornithischian dinosaur forelimb proportions. You’ll note that ornithischians occupy a very small chunk of morphospace! Hadrosaurs (and one or two non-hadrosaurid ornithopods; likely ones very close phylogenetically, such as Tethyshadros) have their own special brand of metacarpal lengths (this has been discussed before). It’s an absolute shame that stegosaurs and pachycephalosaurs simply aren’t represented!

Comments or thoughts are very welcome – and if you want to generate other versions of the plot, all data are freely available (see below). In fact, we encourage you to play with the data. Drop a note in the comments if there’s an image you’d like to post here, too!

Ornithischian Limb Proportions (A=ankylosaurs; C=ceratopsians; H=hadrosaurs; O=non-hadrosaur ornithopods)

What Species Are Included?

• Any species for which the three major bones of the forelimb (humerus, radius, and MC III) were known. For taxa with multiple individuals, only the largest was used. Known juveniles are excluded, to my knowledge.
  

How Was It Plotted?

• The following text provides the sequence of commands that I typed into the terminal, to produce the plot. I created this plot using R 2.10.1, running on Ubuntu 10.04. The file “forelimb_tern.csv” can be downloaded here. It is taken from the “Fore Hind 1″ tab in the spreadsheet posted the other day.
• These commands read the data file, plot a ternary plot, and export said plot to a PDF. [Important: Your web browser may "cleverly" reformat the quote marks into 'smart quotes'; so, reformat back before pasting into your terminal]
• After I had the PDF, I manipulated it in GIMP and Inkscape, in order to produce the graphic seen above.
• This is surely the most inelegant way to accomplish the task; I received some odd errors when trying to add a legend, and never figured out how to plot just the portion of the graph with the data. If anyone figures this out, I’d love to hear it! We will almost certainly produce a nicer version of this plot for the final manuscript.

R
library(vcd)
ornith=read.csv(“forelimb_tern.csv”)
attach(ornith)
colors <- c(“black”,”red”,”green”,”blue”)
pch <- substr(levels(taxon), 1, 1)
pdf(“test.pdf”)
ternaryplot(
ornith[,2:4],
pch = as.character(taxon),
col = colors[as.numeric(taxon)],
main = “Ornithischian Limb Bone Proportions”
)
dev.off()

Relevant References for the ODP

Olde Timey Restoration of Scelidosaurus, after Marsh

In response to a recent query on this blog, ODPer Christian Foth contributed a list of papers potentially relevant to the ODP, specifically limb posture and evolution in ornithischian dinosaurs. It’s important to recognize work that others did before and see how it relates to ours. Furthermore, a good reference list is essential for the upcoming manuscript.

What can you do?

If you think of another paper that might be added to the list (within reason, of course), drop a line in the comments section. If you are interested in providing a summary of a certain paper as a guest blog post (either here or at your own blog), that would be great, too. As always, one need not be a Ph.D’ed scientist to apply! We’re just looking for a short summary.

For my part, I added the Middleton and Gatesy reference – although it deals with theropods, I think some of the background info and analytical methods are quite relevant. Hmm. . .that might be a good one to blog about.

Reference List in Progress

Alexander R. 1985. Mechanics of posture and gait of some large dinosaurs. Zoological Journal of the Linnean Society 83: 1-25.
Bakker RT. 1968. The superiority of dinosaurs. Discovery 3 (2): 11-22.
Biewener (1983). Allometry of quadrupedal locomotion: the scaling of duty factor, bone curvature and limb orientation to body size. J. Exp. Biol. 105: 147-171.
Bonnan MF & P Senter. 2007. Were the basal sauropodomorph dinosaurs Plateosaurus and Massospondylus habitual quadropeds. Special Papers in Palaeontology 77: 139–155
Bonnan, MF, & AM Yates. 2007. A new description of the forelimb of the basal sauropodomorph Melanorosaurus: implications for the evolution of pronation, manus shape and quadrupedalism in sauropod dinosaurs. pp. 157-168 in: Paul M. Barrett and David J. Batten (eds.), Special Papers in Palaeontology 77: Evolution and Palaeobiology of Early Sauropodomorph Dinosaurs. The Palaeontological Association, U.K.
Bultynck P (1992) An assessment of posture and gait in Iguanodon bernissartensis Boulenger, 1881. Bulletin de l’Institut Royal des Sciences Naturelles de Belgique: Sciences de la Terre 63: 5-11.
Carrano MT. 2000. Homoplasy and the evolution of dinosaur locomotion. Paleobiology 26 (3): 489-512.
Carrano MT (2001) Implications of limb bone scaling, curvature and eccentricity in mammals and non-avian dinosaurs. Journal of Zoology 254: 41-55.
Dilkes DW. 2000. Appendicular myology of the hadrosaurian dinosaur Maiasaura peeblesorum from the Late Cretaceous (Campanian) of Montana. Transactions of the Royal Society of Edinburgh, Earth Sciences 90: 87-125.
Dilkes DW. 2001. An ontogenetic perspective on locomotion in the Late Cretaceous dinosaur Maiasaura peeblesorum (Ornithischia: Hadrosauridae). Canadian Journal of Earth Sciences 38: 1205-1227.
Dodson, P & JO Farlow. 1997. The forelimb carriage of ceratopsid dinosaurs. DinoFest International Proceedings 393-398.
Galton PM. 1970. The posture of hadrosaurian dinosaurs. Journal of Paleontology 44 (3): 464-473.
Garstka WR & DA Burnham. 1997. Posture and stance of Triceratops. Evidence of digitigrade manus and cantilever vertebral column. DinoFest International Proceedings 385-391.
Heinrich DE, Bruff CB & DB Weishampel. 1993. Femoral ontogeny and locomotor biomechanics of Dryosaurus lettowvorbecki (Dinosauria, Iguanodontia). Zoological Journal of the Linnean Society 108: 179-196.
Hutchinson JR. 2004. Biomechanical modeling and sensitivity analysis of bipedal running ability. I. Extant taxa. Journal of Morphology 262: 421-440.
Johnson RE, Ostrom JH (1995) The forelimb of Torosaurus and an analysis of the posture and gait of ceratopsian dinosaurs. In: Thomason JJ, editor. Functional Morphology in Vertebrate Paleontology. New York: Cambridge University Press. pp. 205-218.
Kilbourne BM & PJ Makovicky. 2010. Limb bone allometry during postnatal ontogeny in non-avian dinosaurs. Journal of Anatomy 217: 135-152.
Kubo T & MJ Benton. 2007. Evolution of hindlimb posture in archosaurs: limb streeses in extinct vertebrates. Palaeontology 50 (6): 1519-1529.
Lee DV & SG Meek 2005. Directionally compliant legs influence the intrinsic pitch behaviour of a trotting quadroped. Proceedings of the Royal Society B 272(1563): 567–572.
Mallinson. 2010. CAD assessment of the posture and range of motion of Kentrosaurus aethiopicus Hennig 1915. Swiss J Geosci 103: 211-233.
McMahon, T (1975) Allometry and biomechanics: Limb bones in adult Ungulates. Am. Nat. 109:547-563.
Middleton KM & S Gatesy. 2000. Theropod forelimb design and evolution. Z J Linn Soc 128: 149-187
Organ CL. 2006. Biomechnics of ossified tendons in ornithopod dinosaurs. Paleobiology 31 (4): 652-665.
Papantoniou V, Avlakiotis P & R Alexander. 1999. Control of a robit dinosaur. Phil.Trans. R. Soc. Lond. B 354: 863-868.
Paul GS & P Christiansen. 2000. Forelimb posture in neoceratopsian dinosaurs: implications for gait and locomotion. Paleobiology, 26 (3): 450–465.
Romer AS. 1923. The ilium in dinosaurs and birds. Bulletin American Museum of Natural Histroy 48: 141-145.
Raichlen DA. 2006. Effects of limb mass distribution on mechanical power outputs during quadrupedalism. The Journal of Experimental Biology 209: 633-644
Romer AS. 1927. The pelvic musculature of ornithischian dinosaurs. Acta Zoologica 8: 225-275.
Sellers WI & PL Manning. 2007. Estimating dinosaur maximum running speeds using evolutionary robotics. Proceedings of Royal Society B 274: 2711-2716.
Senter P. 2007. Analysis of forelimb function in basal ceratopsians. Journal of Zoology 273: 305-314.
Sternberg CM. 1965. New restoration of hadrosaurian dinosaur. National Museum of Canada, Natural History Papers 1-5.
Taylor CR. 1978. Why change gaits? Recruitment of muscles and muscle fibers as a function of speed and gait. American Zoologist 18: 153.161.
Tereshchenko VS. 1994. A reconstruction of the erect posture of Protoceratops. Paleontological Journal 28 (1): 104-119.
Tereshchenko VS. 1996. A reconstruction of the locomotion of Protoceratops. Paleontological Journal 30 (2): 232-245.
Tereshchenko VS. 2008. Adaptive features of protoceratopoids (Ornithischia: Neoceratposia). Paleontological Journal 42 (3): 273-286.
Thompson S & R Holmes. Forelimb stance and step cycle in Chasmosaurus irvenenesis (Dinosauria: Neoceratopsia). Palaeontologica Electronica 10 (1): 5A.
Thulborn RA. 1982. Speeds and gaits of dinosaurs. Palaeogeography, Palaeoclimatology, Palaeoecology, 38: 227-256.
Thulborn RA. 1984. Preferred gaits of bipedal dinosaurs. Alcheringa 8 (3): 243-252.
Yates, Adam M., Matthew F. Bonnan, Johann Neveling, A. Chinsamy and Marc G. Blackbeard. 2009. A new transitional sauropodomorph dinosaur from the Early Jurassic of South Africa and the evolution of sauropod feeding and quadrupedalism. Proceedings of the Royal Society B, published online. doi:10.1098/rspb.2009.1440

 

• Alexander R. 1985. Meachanics of posture and gait of some large dinosaurs. Zoological Journal of the Linnean Society 83: 1-25.

• Bakker RT. 1968. The superiority of dinosaurs. Discovery 3 (2): 11-22.

• Bonnan MF & P Senter. 2007. Were the basal sauropodomorph dinosaurs Plateosaurus and Massospondylus habitual quadropeds. Special Papers in Palaeontology 77: 139–155

• Carrano MT. 2000. Homoplasy and the evolution of dinosaur locomotion. Paleobiology 26 (3): 489-512.

• Dilkes DW. 2000. Apendicular myology of the hadrosaurian dinosaur Maiasaura peeblesorum from the Late Cretaceous (Campanian) of Montana. Transactions of the Royal Society of Edinburgh, Earth Sciences 90: 87-125.

• Dilkes DW. 2001. An ontogenetic perspective on locomotion in the Late Cretaceous dinosaur Maiasaura peeblesorum (Ornithischia: Hadrosauridae). Canadian Journal of Earth Sciences 38: 1205-1227.

• Dodson, P & JO Farlow. 1997. The forelimb carriage of ceratopsid dinosaurs. DinoFest International Proceedings 393-398.

• Galton PM. 1970. The posture of hadrosaurian dinosaurs. Journal of Paleontology 44 (3): 464-473.

• Garstka WR & DA Burnham. 1997. Psoture and stance of Triceratops. Evidence of digitigrade manus and cantilever vertebral column. DinoFest International Proceedings 385-391.

• Heinrich DE, Bruff CB & DB Weishampel. 1993. Femoral ontogeny and locomotor biomechanics of Dryosaurus lettowvorbecki (Dinosauria, Iguanodontia). Zoological Journal of the Linnean Society 108: 179-196.

• Hutchinson JR. 2004. Biomechanical modeling and sensitivity analysis of bipedal running ability. I. Extant taxa. Journal of Morphology 262: 421-440.

• Kilbourne BM & PJ Maklovicky. 2010. Limb bone allometry during postnatal ontogeny in non-avian dinosaurs. Journal of Anatomy 217: 135-152.

• Kubo T & MJ Benton. 2007. Evolution of hindlimb posture in archosaurs: limb streeses in extinct vertebrates. Palaeontology 50 (6): 1519-1529.

• Lee DV & SG Meek 2005. Directionally compliant legs influence the intrinsic pitch behaviour of a trotting quadroped. Proceedings of the Royal Society B 272(1563): 567–572.

• Mallinson. 2010. CAD assessment of the posture and range of motion of Kentrosaurus aethiopicus Hennig 1915. Swiss J Geosci 103: 211-233.

• Organ CL. 2006. Biomechnics of ossified tendons in ornithopod dinosaurs. Paleobiology 31 (4): 652-665.

• Papantoniou V, Avlakiotis P & R Alexander. 1999. Control of a robit dinosaur. Phil.Trans. R. Soc. Lond. B 354: 863-868.

• Paul GS & P Christiansen. 2000. Forelimb posture in neoceratopsian dinosaurs: implications for gait and locomotion. Paleobiology, 26 (3): 450–465.

• Romer AS. 1923. The ilium in dinosaurs and birds. Bulletin American Museum of Natural Histroy 48: 141-145.

• Raichlen DA. 2006. Effects of limb mass distribution on mechanical power outputs during quadrupedalism. The Journal of Experimental Biology 209: 633-644

• Romer AS. 1927. The pelvic musculature of ornithischian dinosaurs. Acta Zoologica 8: 225-275.

• Sellers WI & PL Manning. 2007. Estimating dinosaur maximum running speeds using evolutionary robotics. Proceedings of Royal Society B 274: 2711-2716.

• Senter P. 2007. Analysis of forelimb function in basal ceratopsians. Journal of Zoology 273: 305-314.

• Sternberg CM. 1965. New restoration of hadrosaurian dinosaur. National Museum of Canada, Natural History Papers 1-5.

• Taylor CR. 1978. Why change gaits? Recruitment of muscles and muscle fibers as a function of speed and gait. American Zoologist 18: 153.161.

• Tereshchenko VS. 1994. A reconstruction of the erect posture of Protoceratops. Paleontological Journal 28 (1): 104-119.

• Tereshchenko VS. 1996. A reconstruction of the locomotion of Protoceratops. Paleontological Journal 30 (2): 232-245.

• Tereshchenko VS. 2008. Adaptive features of protoceratopoids (Ornithischia: Neoceratposia). Paleontological Journal 42 (3): 273-286.

• Thompson S & R Holmes. Forelimb stance and step cycle in Chasmosaurus irvenenesis (Dinosauria: Neoceratopsia). Palaeontologica Electronica 10 (1): 5A.

• Thulborn RA. 1982. Speeds and gaits of dinosaurs. Palaeogeography, Palaeoclimatology, Palaeoecology, 38: 227-256.

• Thulborn RA. 1984. Preferred gaits of bipedal dinosaurs. Alcheringa 8 (3): 243-252.