What can I say, the Triassic is hot right now especially dinosaur origins and the Late Triassic of the American Southwest (of course temnospondyls and marine reptiles always seem to be happening). On Monday I pointed out that over 60 presentations at this years annual SVP meeting dealt with the Triassic. Now the abstracts for the 2009 annual meeting of the Geological Society of America are available online. Again quite a few Triassic presentations. The hot topics for that meeting appear to be the Triassic/Jurassic transition, and U-Pb dates for the Chinle Formation. There is quite a debate growing between those who accept the recent hypothesis of a long Norian (with all of the Chinle being Norian in age) and those who favor the traditional Carnian-Norian split of the Chinle. You can read some of my thoughts on this here and here.
There are actually quite a few places out there where you can experience the Triassic. I've already briefly covered Ghost Ranch, New Mexico and of course the Petrified Forest National Park in Arizona. Another great place is Dinosaur State Park (DSP) in Rocky Hill Connecticut. Now before somebody shouts it out I am aware that the main feature, the track bed, is Early Jurassic in age; however, when I visited as a kid in the 1970s they still thought it was Triassic (I've just dated myself I think). Anyhow, DSP also has a Triassic mural and obviously the Triassic-Jurassic transition is an important topic for them.
As I stated above the main feature is a sandstone surface covered (and I mean covered) with dinosaur footprints. The site was discovered in the mid-1960s by a highway construction project and the park was opened in 1968. A large dome protects the trackways. Over 500 tracks are exposed and at least three times that many are buried for preservation.
This place is a great resource and I know that it made a lasting impression on me as a child (I am originally from Connecticut).
You can read more about Dinosaur State Park here and here.
Wow! The Society of Vertebrate Paleontology made the abstract book for their annual meeting available on-line today to members and registrants. I spent a bit of time glancing through the hundreds of abstracts and could not help but notice the large number of Triassic-themed talks. Of course it helps that there will be a Triassic themed symposium this year (Late Triassic Terrestrial Biotas and the Rise of Dinosaurs); however, not counting the 15 presentations associated with this event I counted no less than 48 ADDITIONAL presentations on Triassic fossils. Read again....more than 60 Triassic-themed presentations. The coverage ranges from fish and amphibians to marine reptiles and therapsids; however, there are numerous presentations on archosauromorph groups including pseudosuchians and early dinosaurs.
Unfortunately I cannot give details of the presentations here (there is an embargo until the meeting); however, I'm glad that I am attending this year (Bristol, UK) because it is going to be an absolute blast to attend the majority of these presentations and to chat with all of my Triassic (and other) colleagues.
Well another summer field season has come and gone at the Petrified Forest. The student interns left at the end of last week and hopefully they enjoyed themselves and learned a lot. Jeff and I will continue fieldwork through the end of the year, but I wanted to share a few scenic photos from this past summer to emphasize once again what a beautiful field area we have.
The Blue Mesa/Sonsela Member contact at "Phytosaur Basin" in the Blue Forest.
Prospecting some of the Blue Mesa Member badlands in the Blue Forest.
Great exposures of the Sonsela Member at "the Pennisula".
Jeff in the Blue Mesa badlands.
A spectacular sandstone outcrop in the Painted Desert.
Arguably one of the most important finds in the history of Triassic paleontology was the discovery of fossil bones assignable to Lystrosaurus from the Early Triassic of Antarctica in 1969 by a team including famed paleontologist Edwin "Ned" Colbert. The finding of this non-marine animal on four different continents helped support the theory of continental drift.
Below is some old footage (from the 1970s I believe) taken in his office at the Museum of Northern Arizona of Ned discussing this find and its importance. You can feel his excitement in reliving his initial finds, especially when he starts picking up the various fossils. Enjoy!
I think that I will try to stay with aetosaurs for a little bit (and put Julia's law to a test). First I would like to provide an explanation of the osteoderm nomenclature that workers use for these animals. The terminology we use stems from the seminal paper by Long and Ballew in 1985, which was the first comprehensive work to utilize osteoderm morphology in aetosaur taxonomy (I discussed this in more detail in a post last February). Thus, aetosaur plate nomenclature generally differs from that of other armored animals such as crocodiles and alligators and may not even make sense to some of you.
Figure A shows a (an old) reconstruction of Desmatosuchus spurensis in dorsal (top) view. Aetosaurs are characterized by an extensive carapace of generally rectangular osteoderms (plates) that cover the entire back of the animal. Furthermore in most taxa the belly and the underside of the tail are also covered, as well as irregular shaped, small osteoderms that cover the limbs and possibly the flanks. This armor makes aetosaurs interesting to study, because there is lots of armor to look at, but a nightmare to excavate and prepare as you usually find them in a huge, jumbled mass of plates and the other bones.
The dorsal surface armor is arranged in four columns straddling the midline of the animal. The two inner columns are termed the paramedian columns (left and right), whereas the outer two columns are termed lateral columns (left and right). In addition there are numerous transverse rows, each consisting of a total of four plates (one from each column). Because generally each row overlies a vertebra, the rows are distinguished (divided into regions) by what type of vertebra they cover. Thus, we have cervical (neck), dorsal (back), and caudal (tail) rows. Sometimes we even separate out the sacral (or pelvic) rows. The belly plates are called "ventral plates" and in some aetosaurs there are additional rows under the tail, which mirror the ones covering the top of the tail. The nomenclature of the tail plates can get cumbersome as you have dorsal caudal lateral plates and ventral caudal lateral plates. Dorsal and cervical plates are only those that occur on the upper surface, so you do not have dorsal cervicals, ventral cervicals, ventral dorsals, or dorsal dorsals...whew!
Figure B shows a dorsal paramedian (so it is covering a dorsal [thoracic for you mammal workers] vertebra) of the aetosaurine Calyptosuchuswellesi. Anterior is up. All aetosaurs have a wide smooth transverse area on the anterodorsal portion of the plate for articulation under a more anterior plate. If this area is raised in relation to the rest of the plate it is termed an "anterior bar" (ab); if it is depressed then it is an "anterior lamina" (al). In aetosaurine aetosaurs there are several projections off of the anterior bar, an "anterolateral projection" (alp), which projects laterally (Fig. B), and often an "anteromedial projection", which projects anteriorly (not shown). The medial edge (me) is straight for articulation with the corresponding paramedian from the other side, whereas the lateral edge (le) is usually sigmoidal for articulation with the lateral plate. Finally there is almost always a boss or eminence on the dorsal surface of the plate and this is usually termed the "dorsal eminence" (de). Some taxa possess a strong transverse thickening on the ventral plate surface termed the "ventral strut" (not shown). Figure C is a dorsal lateral plate of the desmatosuchine Desmatosuchus spurensis. Lateral plates have a medial edge that is often sigmoidal for articulation for the paramedian plate. There is no articulation on the lateral surface. There is still the anterior, transverse articular surface and in Desmatosuchus it is depressed so it is an "anterior lamina". The dorsal eminence is often very pronounced (e.g., spikes) in the lateral plates, and this eminence marks an area of strong flexion, which divides the plate into dorsal (df) and lateral flanges (lf). In addition Desmatosuchus possesses a rounded projection of the lateral flange termed the "ventrolateral projection". Some other taxa have simple straight edges. The upper surfaces of all aetosaur plates possess some kind of ornamentation of grooves, pits, and/or ridges. This ornamentation is usually diagnostic of clades and heavily used in aetosaur taxonomy; however, I argue for dividing aetosaurs into clades based on the overall morphology of the lateral armor (Parker, 2007). I will discuss this and the taxonomic utility of the armor ornamentation in future posts. For those of you who followed and were keeping score the paramedian plate in Figure B is from the right side, as is the lateral plate in Figure C.
Figure B is taken from Long and Ballew (1985). Figures A and C are from Parker (2003).
Long, R. A., and K. L. Ballew. 1985. Aetosaur dermal armor from the Late Triassic of southwestern North America, with special reference to material from the Chinle Formation of Petrified Forest National Park. Museum of Northern Arizona Bulletin 47:45-68.
Parker, W. G. 2003. Description of a new specimen of Desmatosuchus haplocerus from the Late Triassic of Northern Arizona. Unpublished M. S. thesis, Northern Arizona University, Flagstaff, 315 p.
Parker, W. G. 2007. Reassessment of the aetosaur “Desmatosuchus” chamaensis with a reanalysis of the phylogeny of the Aetosauria (Archosauria: Pseudosuchia). Journal of Systematic Palaeontology 5:41–68.
By now almost everyone probably knows that aetosaurs are my favorite Triassic critter and the animal in which I choose to specialize (although I deal from time to time with phytosaurs and other Triassic beasties, as well as early dinosaurs). What amazed me when I first started researching aetosaurs (I was not really familiar with them prior to 1997) was who had worked on them. Here is a short (and certainly not complete) list of prominent researchers who have worked on and/or collected aetosaur specimens. Although many of the earliest workers thought they were dealing with fish, crocodylians, or phytosaurs they laid the foundation for our modern studies. How many other fossil animals can claim this pedigree?
Louis Agassiz. Named Stagonolepis in 1844. First description of an aetosaur.
Thomas Huxley. Provided first detailed descriptons of Stagonolepis and determined its reptilian affinities.
Note that I have left out many recent workers, not because they have not made important contributions to aetosaurs, but because it would be premature to judge how they will be remembered by their peers in regards to those named above.
Below is a photo of an aetosaur femur collected from the Chinle Formation of Utah by Barnum Brown in the late 1800s. Photo courtesy of the USMN.
During a recent trip to the "Little Painted Desert" County Park north of Winslow Arizona (the "standing on the corner" place) Jeff took this photo of a thick section of the Petrified Forest Member capped by the Owl Rock Member. The small figure in the center of the photo is me! The Chinle Formation is hundreds of meters thick here, ranging from the middle of the Sonsela Member to the base of the Owl Rock Member.
Lithosphere is a new peer-reviewed journal published by the Geological Society of America. Awhile back I was contacted by the editors who really liked the photo of an outcrop of the Mesa Redondo Member of the Chinle Formation in Arizona that I use as the title background for Chinleana. They asked for permission to use it for the cover of the August issue of Lithosphere and here it is:
Abstract-The function of the jaw apparatus and the possible dietary habits of the aetosaur Neoaetosauroides engaeus from the Triassic of South America were analyzed in comparison with Northern Hemisphere aetosaurs Desmatosuchus haplocerus and Stagonolepis robertsoni and the living short-snouted crocodile Alligator mississippiensis. The adductor and depressor jaw musculature of these was reconstructed on the basis of dental and skeletal comparisons with living closest relatives’ extant phylogenetic bracket (EPB), followed by the analysis of the moment arms of these muscles to infer feeding habits. The aetosaurian skull design indicates that the total leverage of the inferred jaw musculature provides force rather than speed. However, within aetosaurs, the high ratios of muscle moment arms to bite moments indicate stronger bites in the northern Hemisphere forms, and faster ones in Neoaetosauroides. These differences indicate more developed crushing, chopping, and slicing capacities, especially at the back of the tooth series for D. haplocerus and S. robertsoni; whereas it opens a window to consider different abilities in which speed is involved for N. engaeus. There are differences among aetosaurs in dental characteristics, position of the supratemporal fenestra, location of the jaw joint relative to the tooth row, and shape of the lower jaw. Neoaetosauroides does not show evidence of dental serrations and wear facets, probably consistent with a relatively soft and non abrasive diet, for example soft leaves and/or larvae and insects without hard structures. It might be possible that Neoaetosauroides represents a tendency towards insectivorous feeding habits, exploiting a food source that was widespread in continental environments throughout the Triassic.
More evidence is presented in this paper that aetosaurs may have been insectivorous or omnivorous, rather than solely herbivorous, an idea that was first raised by Bryan Small back in 2002 for Desmatosuchus spurensis. Note that I consider Episcoposaurus (=Desmatosuchus) haplocerus to be a nomen dubium, thus this material is actually referable to the original type species of Desmatosuchus, D. spurensis (Case, 1920; Parker, 2008).
Case, E. C , 1920. Preliminary description of a new suborder of phytosaurian reptiles with a description of a new species of Phytosaurus. Journal of Geology 28:524-535.
Parker, W.G. 2008. Description of new material of the aetosaur Desmatosuchus spurensis (Archosauria: Suchia) from the Chinle Formation of Arizona and a revision of the genus Desmatosuchus. PaleoBios 28: 1-40.
Small, B.J. 2002. Cranial anatomy of Desmatosuchus haplocerus (Reptilia: Archosauria: Stagonolepididae). Zoological Journal of the Linnean Society 136: 97-111.