Thursday, May 27, 2010

Rinehart et al. 2009's Coelophysis monograph- A review

It's funny how the most complete specimens are often the most poorly described.  Coelophysis is known from more individuals than any Mesozoic theropod except Confuciusornis, but it was only in 1989 that we even got an attempt at a detailed osteology (Colbert, 1989).  Alas, Colbert's paper suffers from simplistic description and schematic illustrations that are restored in a Chatterjee-esque manner and oftentimes misrepresent the anatomy (Downs, 2000).  If you want to know what Ghost Ranch Coelophysis' anatomy actually is, you have to try to interpret the unlabeled photographs in Colbert's paper, which don't feature most of the postcrania up close.  So imagine my joy to see a new Coelophysis monograph was published.  Not just an article, but an entire NMMNH Bulletin devoted to the taxon!  Alas, it was too good to be true.

I should preface this by saying that even ignoring my criticisms below, this volume was mostly not designed to be the kind of study I was looking forward to.  Benson's recent megalosaur papers are a good example of my ideal- in depth osteology highlighting characters used in cladistic analyses and differences from related taxa, photographs and detailed illustrations of material that clearly indicate morphological and taphonomic features, and a phylogenetic analysis to top it off.  Rinehart et al.'s monograph is mostly history, geology, accompanying fauna, and paleobiology though.  On most of these topics I have little to say- I'm not an expert on stratigraphy, non-dinosaurian animals, population biology, or optics (though Rinehart et al.'s analysis of the sclerotic ring is certainly interesting).  I can't really blame them for this, it's just not what I was expecting.  Guess I should have noticed it's titled "The Paleobiology of Coelophysis bauri..." and not the Osteology of Coelophysis bauri. heh

One amusing part is in the history section, where the authors describe the ICZN petition to use Coelophysis bauri for the Ghost Ranch material instead of Hunt and Lucas' replacement name Rioarribasaurus colberti.  "This step would validate C. bauri, invalidate R. colberti, and confirm Colbert's identification of the Whitaker quarry theropod as C. bauri through legislation rather than scientific consensus.  Although it violated the principle of priority and was proposed without the necessary revisionary work called for by the International Code of Zoological Nomenclature, the comission approved the petition of Colbert et al. (1992).  Thus the Ghost Ranch dinosaur is now "legally" called Coelophysis bauri."  Still a tad sore about the whole thing? ;)

In the faunal section, they follow their 2007 paper in sinking Effigia into Shuvosaurus as S. okeeffeae.  I really can't determine why they would do such a thing.  Everyone agrees genera are subjective, so it doesn't increase taxonomic accuracy.  They attribute Effigia to their Apachean age and Shuvosaurus to Revueltian age, so it's not to help their problematic faunachrons.  They even include cranial reconstructions of the two, which look more dissimilar than Gorgosaurus vs. Tyrannosaurus.

One very odd part is their description of a supposed specimen of Eucoelophysis in one of the blocks.  This skeleton is articulated and is only missing most cervicals, the skull, mid and distal caudals, and the forelimbs except for a humerus.  You would think this would be rather important, since otherwise the genus is only known from some hindlimb elements, unfigured dorsals, partial ilium and dentary fragment, and it was originally described as a coelophysid but later claimed to be a non-dinosaurian dinosauriform like Silesaurus. But the phylogenetic controversy is never discussed (it's merely said to be a dinosauromorph) or even mentioned in relation to any of the characters listed.  Not that you'll find many characters listed, since the description is appallingly short.  Want to know about the vertebrae?  The cervicals have pleurocoels, there are 13 or 14 dorsals, the sacrum has four vertebrae of which the last two are not fused, and... that's it.  Maybe you're interested in the presence of hyposphenes, the depth of the pleurocoels, the vertebral laminae, the form of the transverse processes, the details of the sacral vertebrae and their articulation with the ilium?  Well too bad.  Maybe we could examine the humerus to see if it has a dinosaur-like elongate deltopectoral crest?  Sorry, the humerus' position warranted a sentence, but we get no actual description.  How about the ilium?  That's pretty different in coelophysoids and silesaurs.  All we're told is that it has a well developed supracetabular shelf and deep brevis fossa ("posteroventral arch"), both of which are present in both taxa.  Care how long the preacetabular process is, how open the acetabulum is, if the supracetabular crest is continuous with the brevis fossa edge, if the brevis fossa is posteriorly expanded, etc.?  You won't find that information here.  The photo of the specimen is too small to see anything but its basic position, and the pelvic closeup doesn't help much (the preacetabular process appears to be of intermediate length, but it's said to be complete, yet also fragmented... hmm).  Besides those, we get a stereophoto of the femur in proximal and anterolateral views.  Honestly, I wouldn't be surprised if this is just another Coelophysis specimen.  Other coelophysoids have been described as having four sacrals when they had five (Dilophosaurus, Liliensternus), the supposedly less distally rounded scapula with a broader shaft is never illustrated, nor are the supposedly more robust distal tarsals.  As for the femoral differences, the proximal sulcus looks much less prominent than in Eucoelophysis (which is claimed to be due to lighting conditions and angle) but similar to Coelophysis specimens such as UCMP 129618 and NMMNH 29046.  They themselves note the femoral head is more rounded and medially projected than in Eucoelophysis, but say it's "probably due to the weathered condition of the holotype."  As for the dorsolateral trochanter, with how the rest of the femur is fragmented, it could be damage for all I know.  What would have been especially useful and easy to do is add this specimen to Ezcurra's (2006) matrix which includes both Coelophysis and the Eucoelophysis holotype.  This would have provided a wealth of anatomical information, and would be quite illuminating.  As it is, the description is more frustrating than anything.

And that sets the stage for the section I was looking forward to- the osteology.  As Rinehart et al. state, "significant redundancy of elements allows a thorough description of each element of the postcranium and description of intraspecific variation within various functional complexes."  If only that were taken advantage of.  For a start, don't think you're getting a description of the skull or forelimb, because those are being worked on by other people.  You can also cross the pes off your list, since it gets all of five sentences.  Basically you could substitute my above complaints for Eucoelophysis and they'd work almost as well here, though at least the photos are more numerous and larger.  Unfortunately, because the material is fragmented and the same color as the matrix, features on the photos are often unclear.  This could be resolved with detailed illustrations indicating where breakage had occured and showing the shape of the bone surface, but instead we get basic outlines with very few contour lines.  So the coracoids are all irregular ovalish blobs, one with the glenoid indicated and another with a contour line representing who knows what.  It's odd these drawings are often so large, since the included detail would have been just as visible at a fraction of the size.  Figure 73 just consists of the outlines of 4-5 bones, with the only internal detail being the glenoid on two of them.  Yet it takes up an entire page.  Perhaps the most annoying part of the description though is the lack of phylogenetic context and comparisons.  Nearly everything they say could be applied to Megapnosaurus or "M." kayentakatae equally well, or even Liliensternus.  But not quite everything I bet.  But since other taxa are literally never mentioned, the significance of any feature is unknown.  Having a huge sample of different sizes of one species of Coelophysis also sounds like an ideal opportunity to compare them to other fragmentary specimens like Padian's (1986) UCMP 129618, Podokesaurus, or the original Cope material.  But no such luck.  It's not that these authors are incapable of good osteological study either, as Spielmann et al.'s (2007) paper on Snyder Quarry coelophysoids shows.  That had clear photos from numerous angles, detailed descriptions, and a decent comparison to UCMP 129618 and Ghost Ranch material, along with characters used in phylogenetic analyses that apply to the remains at hand.

If you want to know the history of the Ghost Ranch Quarry, the visual acuity of Coelophysis, the position of its vent, or if you just want a ton of biometric information on a population of theropods, this is a fine volume.  If you want a good osteology of Coelophysis though, it looks like we'll have to wait.  Hopefully Reisz's cranial study and Nesbitt's forelimb study will improve matters.

References- Padian, 1986. On the type material of Coelophysis Cope (Saurischia: Theropoda) and a new specimen from the Petrified Forest of Arizona (Late Triassic: Chinle Formation). in Padian (ed.). The Beginning of the Age of Dinosaurs: Faunal Change Across the Triassic-Jurassic boundary. Cambridge University Press, Cambridge, England. 45-60.

Colbert, 1989. The Triassic dinosaur Coelophysis. Museum of Northern Arizona Bulletin. 57, 1-174.

Downs, 2000. Coelophysis bauri and Syntarsus rhodesiensis compared, with comments on the perparation and preservation of fossils from the Ghost Ranch Coelophysis quarry. in Lucas and Heckert (eds.). Dinosaurs of New Mexico. New Mexico Museum of Natural History and Science Bulletin 17, 33-37.

Ezcurra, 2006. A review of the systematic position of the dinosauriform archosaur Eucoelophysis baldwini Sullivan & Lucas, 1999 from the Upper Triassic of New Mexico, USA. Geodiversitas. 28(4), 649-684.

Spielmann, Lucas, Rinehart, Hunt, Heckert and Sullivan, 2007. Oldest records of the Late Triassic dinosaur Coelophysis bauri. in Lucas and Spielmann (eds.). The Global Triassic. New Mexico Museum of Natural History and Science Bulletin 41, 384-401.

Rinehart, Lucas, Heckert, Spielmann and Celeskey, 2009. The paleobiology of Coelophysis bauri (Cope) from the Upper Triassic (Apachean) Whitaker Quarry, New Mexico, with detailed analysis of a single quarry block. New Mexico Museum of Natural History and Science Bulletin 45, 260 pp.

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