II CLPV talk summaries: Day 2

[dinoboygraphics@aol.com]

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

www.skeletaldrawing.com