Field of Science

Views From the Petrified Forest

Obviously I am somewhat biased but I do think that the Petrified Forest National Park is one of the best and most beautiful places in the world. Even after eight years I am awestruck every day that I spend in the park. Here is a short series of photos for readers who have never had a chance to visit. All photos are courtesy of the National Park Service. Photos 1, 3, and 5 were taken by T. Scott Williams.

The "sled log" in the Blue Forest (Blue Mesa and Sonsela Members, Chinle Formation) .

Sonsela Member hoodoos in the "Devil's Playground" area of the park.

Pedestal petrified logs in the Sonsela Member at Blue Mesa.

Looking down on the Rainbow Forest badlands from cliffs of the Flattops Sandstone #1.

Reddish badlands of the Petrified Forest Member capped by volcanics of the Pliocene Bidahochi Formation.

Polonosuchus silesiacus, a New Name for the 'Rauisuchian' Archosaur Teratosaurus silesiacus from the Upper Triassic of Poland

Brusatte, S.L., Butler, R.J., Sulej, T., and G. Niedźwiedzki. 2009. The taxonomy and anatomy of rauisuchian archosaurs from the Late Triassic of Germany and Poland. Acta Palaeontologica Polonica 54: 221–230.−221.pdf

Abstract - The German Late Triassic archosaur Teratosaurus suevicus is a historically important taxon, being the first described rauisuchian. Unfortunately the holotype is a single element, a maxilla, which is poorly preserved and incomplete. We redescribe this maxilla and identify a single potential autapomorphy. The fragmentary type specimen complicates attempts to refer additional material to this taxon, and other unassociated archosaur and rauisuchian specimens from the Mittlerer Stubensandstein of Germany cannot be referred to T. suevicus with any degree of confidence. The stratigraphically older T. silesiacus, from the upper Carnian of Poland, is represented by a much more complete and better preserved specimen. Comparison of the maxillae of T. suevicus and T. silesiacus reveals that the two are distinct taxa, contra recent suggestions, but also that they do not share any synapomorphies or a unique combination of characters relative to Postosuchus kirkpatricki and other rauisuchians. Thus, the Polish material must be transferred to a new genus, Polonosuchus gen. nov. Both Polonosuchus and Teratosaurus are very similar to Postosuchus kirkpatricki, and the three taxa are likely closely related.

Chinle Formation "Bible" Still Available From the USGS

Many papers have been written on the stratigraphy of the Chinle Formation; however, the 1972 USGS professional paper by John Stewart and colleagues still ranks as the best overview of the formation and is crucial for any detailed study of the unit. This is especially true for the basic straigraphic nomenclature, unit descriptions, and key correlations across the Colorado Plateau region.

Bound paper copies of this important work are available for only $12.50 USD from the USGS store. What a great price for a 690 page document complete with maps, fence diagrams, and other fold out plates.
The photo is of the Upper Triassic Chinle Formation capping dark brown cliffs of Middle Triassic Moenkopi Formation in Capitol Reef National Park and is courtesy of the USGS.


Stewart, J.H., Poole, F.G. and Wilson, R.F. 1972. Stratigraphy and origin of the Chinle Formation and related Upper Triassic strata in the Colorado Plateau region: U.S. Geological Survey Professional Paper, 690, 336 p.

New Look

Well I've decided to rearrange things a bit on the ole blog. I've added new blog links, moved around and retitled some blog sections, and added a photo to my header. I also removed the very cumbersome 'labels' list.

The photo is of what is one of the least studied units of the Chinle Formation, the Mesa Redondo Member. Restricted to the Little Colorado Valley of eastern Arizona, the Mesa Redondo was named and described by 'Spade' Cooley (probably the hippest name for a geologist ever!) in 1958. It occurs between the Shinarump and Blue Mesa Members and is probably laterally equivalent to (but lithologically distinct from) the Bluewater Creek, Monitor Butte, and Cameron Members. Very little is known about the Mesa Redondo as it has never been studied nor have any fossils been recovered from it. Nonetheless, it has become one of my favorite members as the type area is just awesomely scenic and the lithology of the member is so different from the rest of the Chinle Formation.


Cooley, M.E. 1958. The Mesa Redondo member of the Chinle Formation, Apache and Navajo Counties, Arizona. Plateau 31:7-15.

Here we go again: redux.

Yesterday I commented on the status of taxonomic names published in online only journals and received from great comments. In my post I linked to a similar article by Carl Zimmer on his blog "The Loom". Read here to see the follow-up after he contacted the ICZN. In a nutshell until the ICZN rules change or another code is adopted these names are not valid. Another possibility (as suggested by Brian Axsmith) is for PLoS One to follow what Palaeontologia Electronica does... deposit print copies in at least five libraries and openly state where the copies are located. This makes the name valid according to the ICZN.

By the way...some were worried that because the online article is not recognized by the ICZN, then the first print medium (e.g., newspapers, magazines) that "publish" the name would gain priority. However, ICZN rules also state (and unfortunately I don't have my copy nearby as I am typing this) that the article in which the name first appears must intend to actually erect a new taxonomic name. The authors of newspaper and popular magazine do not have this intent and therefore do not "officially" erect the name except as a nomen nudem. Nomina nuda have no status and thus are still available for the authors of the official publication.

Postscript: Check out this comment on The Loom from Peter Binfeld, the managing editor of PLos One. Way to go guys, but unfortunately this is just one case. For more discussion see this post on DinoGoss.

I've missed Mike Taylor's comment on Rioarribasimius....can anyone tell me where it was made?

Here We Go Again: Darwinius, the ICZN, and the Online Publication of Taxonomic Names

I brought this up back in February regarding the new stegosaur Miragaia longicollum; about how regardless of the claims made by journals, unless the guidelines put forth by the International Committee of Zoological Nomenclature (ICZN) regarding publication are adhered to (i.e., hard copy placed in at least five libraries that are explicitly identified in the document) published names in online only publications are simply not valid. Now a similar case is coming under heavy discussion.

The newly described primate Darwinius masillae (Franzen et al., 2009) has been receiving tons of press heralded as being a 'missing link' in primate evolution (however see this article in Laelaps), however, it is not only the phylogentic position and its interpretation that is being hotly debated. Now the validity of the taxonomic name is being called into question because the name was published in the online-only journal PLoS One. Carl Zimmer's blog The Loom has a great discussion of this. Check it out.

Hopefully the ICZN will soon amend the code as advocated by Harris (2004) to deal with the increasing trend of online only journals and the early online releases (ahead of print versions) now popular with many journals.

This is becoming a serious problem.


Franzen, J., Gingerich, P., Habersetzer, J., Hurum, J., von Koenigswald, W., & Smith, B. (2009). Complete Primate Skeleton from the Middle Eocene of Messel in Germany: Morphology and Paleobiology PLoS ONE, 4 (5) DOI: 10.1371/journal.pone.0005723

Harris, J.D. 2004. 'Published Works' in the electronic age: recommended amendments to Articles 8 and 9 of the Code. Bulletin of Zoological Nomenclature 61:138-148.

The Ex-Ornithischian Revueltosaurus callenderi

Lukas Panzarin guessed correctly. The reconstruction below is of the Late Triassic pseudosuchian Revueltosaurus callenderi courtesy of Jeff Martz. The new reconstruction is based on new material of this taxon from the Chinle Formation of Petrified Forest National Park.

For those readers not familiar with Revueltosaurus, it was named in 1989 by Adrian Hunt based on isolated teeth from near Revuelto Creek in east-central New Mexico (Bull Canyon Formation of the Dockum Group). The teeth are highly distinctive, leaf-shaped with denticles, and very similar to the teeth of basal ornithischians. Based on these similarities Hunt (1989) tentatively referred Revueltosaurus to the Ornithischia. Below are teeth of Revueltosaurus from Petrified Forest National Park.

However, although no non-dental material of Revueltosaurus was yet known Hunt and Lucas (1994) did consider it to be a bona-fide Ornithischian. Furthermore, these authors erected several other "Ornithischian" taxa from North America based solely on teeth. Heckert (2002) fully redescribed the holotype material and also erected a second species, Revueltosaurus hunti, also based on isolated teeth. As a result, the entire Late Triassic ornithischian record from Narth America and Europe was based solely on isolated teeth. Below is a reconstruction of a hypothesized basal ornithischian.

In 2004 I discovered skeletal material of R. callenderi from the Petrified Forest Member (Chinle Formation) of Petrified Forest National Park. This amazing site (named the Revueltosaurus Quarry) has provided hundreds of bones of numerous individuals of R. callenderi. This was the first recognized non-dental material of this taxon. Below are Randy Irmis, Lori Browne, and Jeff Martz initially excavating the site in 2004.

In 2005 we published a preliminary description of this material. Interestingly the recovered skeletons were not of an ornithischian, or even a dinosaur, but rather from a crocodile-line archosaur (Pseudosuchia). Amazingly, the ornithischian-like dentition was simply a convergence. We argued that none of the North American and European teeth could be unambiguously considered to represent ornithischians. Thus, the entire Late Triassic record of ornithischians from these continents was essentially erased. Below is a cladogram showing the revised position of Revueltosaurus.

A few authors (e.g., Heckert, 2005) have argued against this interpretation, insisting that some of these teeth do represent ornithischians; however, there are no clear characters of these teeth that support this interpretation (Irmis et al, 2007).

In 2006 the Revueltosaurus Quarry yielded a superbly preserved almost complete skeleton of R. callenderi, which I featured at a recent Society of Vertebrate Paleontology meeting. A full description of this specimen (and thus the taxon) is almost complete. One really neat character (I think) apparent in Jeff's reconstruction is the large size of the skull in relation to the postcranial skeleton. The skull is quite a bit longer than the femur, and this is a bit odd considering the skull "accomplishes" this without elongating the forward portion of the skull as in champsosaurids, phytosaurs, and crocodiles.

I have jokingly refered to Revueltosaurus as the "duck-billed platypus" of the Triassic because of its ornithichian-like dentition, aetosaur-like armor carapace, and other characteristics found only in rauisuchians and crocodylomorphs.

Indeed Revueltosaurus belongs to a previously unrecognized clade of archosaur, which hopefully will elucidate phylogentic relationships within Pseudosuchia.

By the way...the PDF of Parker et al (2005) is freely available from the link in the reference below.


Heckert, A. B. 2002 A revision of the Upper Triassic ornithischian dinosaur Revueltosaurus, with a description of a new species. New Mexico Museum of Natural History and Science Bulletin 21:253–267.

Heckert, A.B. 2005. Krzyzanowskisaurus, a new name for a probable ornithischian dinosaur from the Upper Triassic Chinle Group, Arizona and New Mexico, USA. New Mexico Museum of Natural History and Science Bulletin 29: 77-83.

Hunt, A. P. 1989. A new ?ornithischian dinosaur from the Bull Canyon Formation (Upper Triassic) of east-central New Mexico. pp. 355–358 in Dawn of the age of dinosaurs in the American Southwest (ed. S. G. Lucas & A. P. Hunt). New Mexico Museum of Natural History, Albuquerque, NM.

Hunt, A. P., and S.G. Lucas. 1994. Ornithischian dinosaurs from the Upper Triassic of the United States. pp. 227–241 in In the Shadows of the Dinosaurs: Early Mesozoic Tetrapods (ed. N. C. Fraser & H.-D. Sues). Cambridge University Press.

Irmis, R.B., Parker, W.G., Nesbitt, S.J., and Liu, J. 2006. Early ornithischian dinosaurs: the Triassic record. Historical Biology 19:3-22.

Parker, W.G., Irmis, R.B., Nesbitt, S.J., Martz, J.W., and L.S. Browne. 2005. The Late Triassic pseudosuchian Revueltosaurus callenderi and its implications for the diversity of early ornithischian dinosaurs. Proceedings of the Royal Society B 272:963-969. doi:10.1098/rspb.2004.3047

Triassic Critter Reconstructions

Here is one of my favorite Triassic critter reconstructions done recently by Jeff Martz. Any ideas on what it is?

Note: Anyone who has already seen this please refrain from answering for a bit. Thanks.

Photos from the CPCP Field Trip

Here are some photos from last weekends' Colorado Plateau Coring Project field trip to Chinle Formation exposures in Six Mile Canyon near Fort Wingate, New Mexico, USA. These photos and captions are all courtesy of Randy Irmis.

Don't forget to enjoy the Chinle outcrops in the background :).

Sterling Nesbitt perplexed by the mysteries of the Chinle

Ron Blakey for scale

Twins (Sterling Nesbitt and Jessica Whiteside)

Mike Benton and Dennis Kent

King Olsen of Chinle (Paul Olsen)

Jeff Martz in his natural environment

Giggles McNesbitt

Studious Bill Parker

Latest Literature

A few new Triassic-ish papers....

Maidment, S.C.R., and L.B. Porro. 2009. Homology of the palpebral and origin of supraorbital ossifications in ornithischian dinosaurs. Lethaia, 10.1111/j.1502-3931.2009.00172.x.

Abstract - The palpebral is a small ossification that projects across the orbit in some ornithischian dinosaurs and its presence is considered a synapomorphy of the clade. By contrast, other ornithischians lack the palpebral but possess accessory ossifications, commonly termed supraorbitals, which form the dorsal margin of the orbit. The homology of the ornithischian palpebral to one or more of the supraorbitals is widely accepted in the literature, but this homology has never been explicitly tested and no hypotheses have been proposed regarding the function of the palpebral or why it was incorporated into the orbital margin. As homology is synonymous with synapomorphy, incorrect homology statements can lead to incorrect hypotheses of relationships being obtained during cladistic analysis. The primary and secondary homologies of the ornithischian palpebral and the anterior supraorbital of more derived members of the major ornithischian clades are tested and we demonstrate that these homology hypotheses can be accepted. Osteological correlates indicate that the palpebral supported a layer of connective tissue that roofed the orbit; ossification of this connective tissue resulted in the incorporation of the palpebral into the skull roof and gave rise to additional supraorbital elements, which are neomorphic ossifications. Large-scale structural changes in the ornithischian skull, including dermal ossifications associated with display or defence and the development of complex feeding mechanisms, may have led to the incorporation of the palpebral into the skull roof.

Nicolas, M., and B.S. Rubidge. 2009. Changes in Permo-Triassic terrestrial tetrapod ecological representation in the Beaufort Group (Karoo Supergroup) of South Africa. Lethaia, 10.1111/j.1502-3931.2009.00171.x.

Abstract - For more than a century, large collections of fossils from the Beaufort Group have been built up at various museums in South Africa and have been handled as separate databases in the individual museums. Because of the unique time-extensive record of continental vertebrate biodiversity represented by the fossils of the Beaufort Group, a single standardized database has been compiled for the fossils collected from the Beaufort Group housed in South African museums. This unique data set has enabled the determination of terrestrial tetrapod ecological representation from the Middle Permian to Middle Triassic Beaufort Group of South Africa.

Korte, C., Hesselbo, S.P., Jenkyns, H.C., Rickaby, R.E.M., and C. Spotyl. 2009. Palaeoenvironmental significance of carbon- and oxygen-isotope stratigraphy of marine Triassic–Jurassic boundary sections in SW Britain. Journal of the Geological Society, London 166:431–445. doi: 10.1144/0016-76492007-177.

Abstract - Carbon-isotope stratigraphy is a useful tool for stratigraphic correlation, especially for strata deposited during major perturbations of the carbon cycle that affected the marine, terrestrial and atmospheric reservoirs. For the Triassic–Jurassic boundary, effectively defined by a first-order mass extinction, major fluctuations in carbon-isotope values have been well documented, but these datasets have generally been derived from bulk-rock samples. Hence, the extent to which features of the isotopic curve reflect diagenetic alteration or changing proportions of constituent materials is unconstrained. Here, carbon- and oxygen-isotope
data are presented from well-preserved oyster shells (Liostrea) comprising low-magnesium calcite, a mineral species relatively resistant to diagenetic alteration. Samples were obtained from Lavernock Point, Glamorgan, Wales, a coastal section close to a candidate stratotype for the base of the Jurassic at St Audrie’s Bay, Somerset, England. The carbon-isotope signature from St Audrie’s Bay, previously defined on the basis of analysis of bulk organic matter, is confirmed by our new data. Major features are (1) the upper part of an ‘initial’ negative isotope excursion in the lowest part of the section, followed by (2) a pronounced positive excursion, and (3) an extended ‘main’ negative isotope excursion in the highest part of the section. The data
confirm that the carbon-isotope stratigraphy previously documented from bulk organic matter in SW England records the chemical composition of the contemporaneous seawater. Bulk carbonates sampled over the same interval near Lyme Regis, England, show similar trends to those from oyster calcite in the lower part of the study section, but there are more 13C-depleted values up-section. These lower values probably result from an admixture of primary and diagenetic carbonate. Palaeotemperatures calculated from oxygen-isotope values from Lavernock Point oyster shells are relatively cool at the beginning of the positive carbon-isotope
excursion, and increased by up to 10 8C during the main negative carbon-isotope excursion. The new results are compatible with the view that positive carbon-isotope excursions correspond to times of low atmospheric carbon dioxide content, whereas negative carbon-isotope excursions correspond to times of high atmospheric carbon dioxide content, as is also found to be the case during the Early Jurassic (Toarcian) Oceanic Anoxic Event. The Mg/Ca and Sr/Ca ratios and 18O of investigated Liostrea hisingeri show no correlation, supporting data from modern bivalves that indicate that incorporation of Mg and Sr is controlled mainly by factors other than temperature.

Colorado Plateau Coring Project

I've just returned from the New Mexico Museum of Natural History and Science in Albuquerque where I attended the 2nd workshop for the Colorado Plateau Drilling Project. This is a proposed project to core Triassic and Jurassic rocks of the Colorado Plateau (western U.S.A.) to obtain detailed stratigraphic data including paleomagnetism, palynology, isotopic dates, etc... This project is similar to what was done in the past for the Triassic and Jurassic rocks of the Newark Supergroup (eastern U.S.A.) which has became a global standard for Triassic and early Jurassic paleomagnetism. You can read about the first workshop here.

It was great to spend a few days with friends and colleagues as well as meet many new researchers from around the globe. There were some excellent talks and good field trips. Plus we got the stay one evening at the famous Route 66 El Rancho Hotel in Gallup, NM. I also was able to see the IMAX movie "Dinosaurs Alive" which features my friends Sterling Nesbitt, Randy Irmis, Alan Turner, and Nate Smith working at Ghost Ranch, New Mexico. Jeff Martz and I also appear in the film very briefly.

Jeff Martz has more on the meeting and his cool reconstruction of Typothorax here .

Dinosaur Diversity and the Rock Record

Barrett, P.M., McGowan, A.J., and V. Page. 2009. Dinosaur diversity and the rock record. Procedings of the Royal Society B published online 29 April 2009. doi: 10.1098/rspb.2009.0352

Abstract - Palaeobiodiversity analysis underpins macroevolutionary investigations, allowing identification of mass extinctions and adaptive radiations. However, recent large-scale studies on marine invertebrates indicate that geological factors play a central role in moulding the shape of diversity curves and imply that many features of such curves represent sampling artefacts, rather than genuine evolutionary events. In order to test whether similar biases affect diversity estimates for terrestrial taxa, we compiled genus-richness estimates for three Mesozoic dinosaur clades (Ornithischia, Sauropodomorpha and Theropoda). Linear models of expected genus richness were constructed for each clade, using the number of dinosaur-bearing formations available through time as a proxy for the amount of fossiliferous rock outcrop. Modelled diversity estimates were then compared with observed patterns. Strong statistically robust correlations demonstrate that almost all aspects of ornithischian and theropod diversity curves can be explained by geological megabiases, whereas the sauropodomorph record diverges from modelled predictions and may be a stronger contender for identifying evolutionary signals. In contrast to other recent studies, we identify a marked decline in dinosaur genus richness during the closing stages of the Cretaceous Period, indicating that the clade decreased in diversity for several million years prior to the final extinction of non-avian dinosaurs at the Cretaceous-Palaeocene boundary.

Skeletal Pneumaticity in Early Pterosaurs

Butler, R.J., Barrett, P.M., and D.J. Gower. 2009. Postcranial skeletal pneumaticity and air-sacs in the earliest pterosaurs. Biology Letters, published online. doi:10.1098/rsbl.2009.0139

Abstract - Patterns of postcranial skeletal pneumatization (PSP) indicate that pterosaurs possessed components of a bird-like respiratory system, including a series of ventilatory air-sacs. However, the presence of PSP in the oldest known pterosaurs has not been unambiguously demonstrated by previous studies. Here we provide the first unequivocal documentation of PSP in Late Triassic and earliest Jurassic pterosaurs. This demonstrates that PSP and, by inference, air-sacs were probably present in the common ancestor of almost all known pterosaurs, and has broader implications for the evolution of respiratory systems in bird-line archosaurs, including dinosaurs.

Standing Against Bad Behavior

Janet Stemwedel at Adventures in Ethics and Science has an excellent discussion on the roles and relationships between senior and junior scientists regarding "standing against bad behavior and standing with the members of the community who are harmed by it".

Regardless of how one feels about the specific case that is mentioned, this is an important read for all on the importance of "develop[ing] standards that help the whole community work together to build a reliable body of knowledge and a group of responsible practitioners". As Stemwedel argues this should be the ultimate goal of all scientific fields including vertebrate paleontology.

Read the full post at:

Phytosaur Skull Excavation IV

The last post in this series showed us jacketing our phytosaur skull (see below). The next step after the plaster dries is to flip the block. This is a small jacket and in a sandstone so we are not expecting any problems.Ha! The block flipped cleanly and is ready to be transported out. The one (only) good thing about not having much of the skull present is that it is simple to get it back to the truck (especially when you cannot drive to the site, which is common at the Petrified Forest). I'm not quite sure what Jeff is doing here. I think that he was trying to lighten the jacket a bit.

Nothing left to do but to fill the quarry hole back in. Get to it Jeff! (It's good to be the boss)

Good news! Not all is lost. While we were excavating this specimen, the landowners located another skull about a mile away at approximately the same stratigraphic horizon. This on definitely looks to be upside down and hopefully more complete! We should get to this once our interns arrive in about a month. Stay tuned!

Congratulations Sterling!

You gotta love graduation time. I'd like to recognize my good friend and colleague Sterling Nesbitt who is now officially Dr. Nesbitt. His mighty tome (dissertation) of over 600 pages pretty much covers most aspects of early archosaur history and phylogeny. Excellent work. Sterling is moving on to a post-doc position at the University of Austin at Texas where he will be working with Dr. Julia Clarke.P.S. Congrats also to Sterling and his fiancee Michelle Stocker on their recent engagement!

Nesbitt, S.J. 2009. The Early Evolution of Archosaurs: Relationships and the Origin of Major Clades. Columbia University.