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II CLPV talk summaries: Day 2

Bom dia DMLers!

First, let me send a special shout out to Adam Yates; we missed you! III CLPV is in Argentina in 2008, so start making plans (that goes for the rest of you too!).

I must confess that I missed the second banquet. I was exhausted and I had to take care of some work-related emails, so I won?t be able to provide the skinny on the second social event. By all reports it was also fantastic, and I was a fool (albeit a rested fool?) to have missed it. The morning session was a symposium on Early Dinosaur Evolution, and it had some of the most exciting talks of the conference. On to the talks:

Day II: Thursday the 11th.

Regina Fechner examined the functional morphology of Lagerpeton. She presented a very good morphological overview of the known remains, and then made comparisons to facultatively bipedal lizards, from which she concluded that Lagerpeton was likely not very erect in its stance, and that when it engaged in bipedal locomotion it likely relied on lateral undulation to increase hind-leg stride, again as in extant lizards that are facultative bipeds. If I may editorialize for a moment; I?m not prepared to say she is wrong, but I was unconvinced by her justifications for using lizard mycology and locomotion as the primary model. The short iliac shelf was emphasized, in conjunction with the presumed sprawling stance (which she inferred from the non-perforated acetabulum). I have not seen the Lagerpeton material, and she may be correct, but as an erect-stanced biped with a non-perforated acetabulum, I wasn?t sure I bought off on that. Also, other presumably erect dinosaurimorphs had short iliac blades (Dilophosaurus, some prosauropods, Herrerasaurus, etc). Hopefully she will publish some clarifications in the proceedings volume.

Michael Benton went next with a more general talk about dinosaur origins. He emphasized his disagreement with the Romer-based model of the absolute competitive superiority of dinosaurs (competition with a capital ?C?, as he clarified to me later), instead emphasizing that changing environmental factors probably opened the door to dinosaur radiations. He also reaffirmed his belief in a monophyletic ornithodira, with Scleromochalus as the most primitive known member. I want to add some comments from a discussion we had today, because I was pleased to find out that he and I are much more in agreement on this issue than I?d realized. My objection to the ?non-competitive? model is that unlike the K/T event, where the non-avian dinosaurs were literally removed from existence and could no longer compete with mammals (allowing our subsequent radiation), the Triassic faunal turnover did not happen as catastrophically (at least in a temporal sense), and not all of the groups died out (at least not right away). That is, there may well have been a series of environmental factors that were knocking out species of dicynodonts, rynchosaurs, etc, but over time dinosaurs proved they were more survivable, and better able to radiate into those niches once available. In addition, once they occupied a niche (i.e. large herbivore), they neither relinquished it nor shared it, a feat earlier large bodied Triassic groups had proven unable to accomplish. And, it turns out, Benton agrees with competitive superiority in this more restricted sense of the term.

Sterling Nesbitt gave one of my favorite talks of the conference. He showed that Shuvosaurus is not an ornithomimid (no real surprise there), but is rather a derived suchian. And he demonstrated this pretty convincingly, since he has a number of specimens with post crania conveniently attached to skulls. For those of you who haven?t seen this thing, it is insanely cool. It?s like a crocodile-line archosaurs trying its best to be a prosauropod, complete with long flexible neck. Even weirder, it is probably an obligate biped. Likewise, he showed that Revueltosaurus teeth are not those of a Triassic ornithopod, but rather come attached to a suchian skull. His point being that there is some exceptional homoplasy in Late Triassic archosaurs, and that identifying things as dinosaurs is tenuous from isolated remains. Coauthor and fellow speaker Randall Irmis returns to this point a few talks later?

But first Paul Sereno gave a talk that had two main points. One is that he is helping to create an online database for sharing and analyzing data matrices used in phylogenetic analyses. He showed images of software that could show what percentage of different matrices used the same characters, if they used disagreeing character states, and (literally) dozens of other useful tools for trying to mine useful comparative data from cladistic data sets. I don?t know when it will be released (although apparently there will be a paper forthcoming?wait for it!), but having just spent the last six months doing phylogenetic analyses of two different groups of animals, I?m pretty excited about the possibilities. The second part of his talk mostly consisted of showing new, better photos of Eoraptor after further preparation. They got it CT scanned again, and apparently this time it clarified some internal data. Sereno still feels that both Herrerasaurus and Eoraptor are basal theropods, not basal saurischians as has been (cough?frequently) suggested.

Randall Irmis was up next, and picked up where Sterling left off; they feel that a lot of North American Triassic dinosaurs aren?t and made a pretty convincing argument for it. A (non-comprehensive) list includes Eucoelophysis, which they feel pretty strongly is a silesaurid. Which makes the name EU-coelophysis ironic, to say the least. Gojirosaurus they feel is a chimera (Ken, want to comment?), made up of theropod material and Shuvosaurus (or shuvosaur-like suchian) material. Not surprisingly they conclude that Protoavis is a chimera, including ?coelophysoid material and non-dinosaur material?. Finally, they think Technosaurus is a silesaurid as well.

Watch silesaurids, it seems to be raining them lately?

Max Langer gave a talk that was ostensibly on the first ornithischian body fossils from the Triassic of Brazil. When the first slide came up, however, it was obvious that he has a bone-bed of silesaurid-like material as well. He has a minimum of twelve animals (he has 12 right femurs and no left femurs in the quarry?), of differing ontogenetic ages. He made a good case that there is more than one taxa in the bone bed, although I wouldn?t yet rule out sexual dimorphism. None of the specimens are articulated. He did note the similarity to Silesaurus, but rather than concluding that his new animal(s) are not dinosaurs, he inferred that Silesaurus is itself a basal ornithischian. I personally have some doubts about that, but with all the new silesaurid material coming out, we?ll hopefully have a better handle on this and it?s bearing on ornithischian origins (if any) in the near future.

Oliver Rahut finished off the talks before the coffee break with his analysis of saurischian diversity throughout the Mesozoic. He analyzed Saurischia as a whole (with and without birds), and sauropods and theropods independently (the latter with and without birds). He found weak support consistent with sauropods (mostly) reaching peak diversity in the Jurassic and then declining, while theropods continue to increase in diversity throughout the Mesozoic (not surprisingly this was more pronounced when birds were included). He cautioned, however, that the data is very susceptible to sampling bias, and in many cases one or two new specimens could upset the apparent diversity curves entirely. His implied conclusion was that we need far more data before we can safely infer macro evolutionary patterns of this sort. I would heartily agree.

After the coffee break (and two more cups of that wonderful Brazilian cup o? joe), Jonas Bittencourt gave a talk (in Portuguese) on diagnosing Staurikosaurus. Happily his slides were in English, so I caught the main gist of it. He discussed the problems with older diagnoses, which largely included plesiomorphic characters, rendering Staurikosaurus more or less without any diagnosable autapomorphies. They confirmed that one suggested novel character, a strong bevel on the anterior portion of the distal end of the pubis. He also provided new characters from the pelvis and hind limbs. He did not find any useful diagnostic characters in the vertebral column, and concluded that axial evolution was more conservative during the early theropod radiation than appendicular evolution was.

Martin Ezcurra gave a good talk on the morphology and relationships of Zupaysaurus. He provided compelling data that Zupaysaurus is a coelophysoid, not a basal tetanuran. He also demonstrated that Zupaysaurus is definitely not crested, as previous reports have suggested. Instead the skull underwent oblique crushing, leaving part of the left lacrimals visible about the right lacrimals, giving the appearance of a crest. Sorry to artists who have already drawn Zupaysaurus! Also, due to the very similar distortion of the skull of Coelophysis kayentakatae, he urged caution in interpreting it as crested without further analysis to rule out the possibility of the ?crest? being a taphonomic artifact.

Diego Pol presented data from new specimens of Mussaurus. He found incomplete adult and subadult specimens, and based on them was able to refer other specimens that had been described as Plateosaurus sp. To Mussaurus. Good thing too, as his phylogenetic analysis found that Mussaurus is quite a bit closer to true sauropods than Plateosaurus is. He found a paraphyletic prosauropoda. Interestingly, looking at the ontogenetic series of Mussaurus, he found that ontogenetic trends usually paralleled phyletic trends in phenotype; that is, Mussaurus had a primitive ?prosauropod? set of frontals and parietals as a juvenile, but they alter (quite extensively) during ontogeny and end up looking very sauropod-ish. Sauropodomorph evolution seems to be crying out for a heterochrony-based approach to understanding the early morphological diversification of the group.

Claudia Mariscano gave an overview of the abundant dinosaurimorphs footprints her team has found in Argentina. She feels that the inherent difficulties in taxonomic identity (i.e. correlating with body fossils) in intractable at this point, but does feel that the ichnofossil record argues persuasively for an early evolution and radiation of dinosaurs than the body fossil record shows.

Jeff Wilson gave the last talk of the morning, and demonstrated some interesting techniques for integrating functional data from ichnofossils with body fossils to extract timing information for the origin certain functional traits. He scored synapomorphies from ichnotaxa into a matrix with sauropodmorph body fossils, and then used stratocladistics to see how the resulting tree affected the timing of certain morphological traits. He concluded that the ichnofossils argued that a digitigrade forelimbs evolved earlier than the body fossils indicated (since I?ve always interpreted the prosauropod manus as digitigrade, this wasn?t a surprise to me). He also concluded that quadrupedality was more common basally than is often inferred, and that the heal pad evolved further down the sauropodomorph tree than is usually thought. That last one I found really intriguing, as it had never occurred to me to put heal pads on prosauropod hind feet, but some of the tracks did look convincing. I don?t know how susceptible Jeff?s analysis technique is to the incompleteness of the fossil record, but that seems pretty relevant. If Claudia is right that dinosaurs diversified much earlier than though, than it?s at least possible that the tracks Jeff are finding record that more derived sauropodomorphs were common earlier than commonly realized. I don?t know what kind of sensitivity analysis could be done to test this, but it certainly would be nice to be able to combine comparative data sets like this if it proves effective!

After lunch the talks were not on dinosaurs, and most were in Portuguese, so I did not finish the afternoon (and have little useful to report from the time I was there). I?ll try to get day three posted as soon as possible.

Scott Hartman Science Director Wyoming Dinosaur Center 110 Carter Ranch Rd. Thermopolis, WY 82443 (408) 483-9284