Chinleana

New Paper on the Origin and Early Evolution of Dinosaurs

2009-11-06T20:51:00.004-07:00

Langer, M.C., Ezcurra, M.D., Bittencourt, J.S., and F.E. Novas. 2009. The origin and early evolution of dinosaurs. Biological Reviews 84:1-56. doi:10.1111/j.1469-185X.2009.00094.x

ABSTRACT-The oldest unequivocal records of Dinosauria were unearthed from Late Triassic rocks(approximately 230 Ma)accumulated over extensional rift basins in southwestern Pangea. The better known of these are Herrerasaurus ischigualastensis, Pisanosaurus mertii, Eoraptor lunensis, and Panphagia protos from the Ischigualasto Formation, Argentina, and Staurikosaurus pricei and Saturnalia tupiniquim from the Santa Maria Formation, Brazil. No uncontroversial dinosaur body fossils are known from older strata, but the Middle Triassic origin of the lineage may be inferred from both the footprint record and its sister-group relation to Ladinian basal dinosauromorphs. These include the typical Marasuchus lilloensis, more basal forms such as Lagerpeton and Dromomeron, as well as silesaurids: a possibly monophyletic group composed of Mid-Late Triassic forms that may represent immediate sister taxa to dinosaurs. The first phylogenetic definition to fit the current understanding of Dinosauria as a node-based taxon solely composed of mutually exclusive Saurischia and Ornithischia was given as ‘‘all descendants of the most recent common ancestor of birds and Triceratops’’. Recent cladistic analyses of early dinosaurs agree that Pisanosaurus mertii is a basal ornithischian; that Herrerasaurus ischigualastensis and Staurikosaurus pricei belong in a monophyletic Herrerasauridae; that herrerasaurids, Eoraptor lunensis, and Guaibasaurus candelariensis are saurischians; that Saurischia includes two main groups, Sauropodomorpha and Theropoda; and that Saturnalia tupiniquim is a basal member of the sauropodomorph lineage. On the contrary, several aspects of basal dinosaur phylogeny remain controversial, including the position of herrerasaurids, E. lunensis, and G. candelariensis as basal theropods or basal saurischians, and the affinity and/or validity of more fragmentary taxa such as Agnosphitys cromhallensis, Alwalkeria maleriensis, Chindesaurus bryansmalli, Saltopus elginensis, and Spondylosoma absconditum. The identification of dinosaur apomorphies is jeopardized by the incompleteness of skeletal remains attributed to most basal dinosauromorphs, the skulls and forelimbs of which are particularly poorly known. Nonetheless, Dinosauria can be diagnosed by a suite of derived traits, most of which are related to the anatomy of the pelvic girdle and limb. Some of these are connected to the acquisition of a fully erect bipedal gait, which has been traditionally suggested to represent a key adaptation that allowed, or even promoted, dinosaur radiation during Late Triassic times. Yet, contrary to the classical ‘‘competitive’’ models, dinosaurs did not gradually replace other terrestrial tetrapods over the Late Triassic. In fact, the radiation of the group comprises at least three landmark moments, separated by controversial (Carnian Norian, Triassic-Jurassic) extinction events. These are mainly characterized by early diversification in Carnian times, a Norian increase in diversity and (especially) abundance, and the occupation of new niches from the Early Jurassic onwards. Dinosaurs arose from fully bipedal ancestors, the diet of which may have been carnivorous or omnivorous. Whereas the oldest dinosaurs were geographically restricted to south Pangea, including rare ornithischians and more abundant basal members of the saurischian lineage, the group achieved a nearly global distribution by the latest Triassic, especially with the radiation of saurischian groups such as ‘‘prosauropods’’ and coelophysoids.

More Free PDFs

2009-11-05T16:08:00.003-07:00

Paläontologische Zeitschrift, now published by Springer, is offering open access for the month of November only.

http://www.springerlink.com/content/0031-0220?sa_campaign=email/PROM/PSE11800_V1

The New Mexico Museum of New Mexico and Science is also offering free PDFs of many of its published bulletins. Obviously there are lots of free Triassic PDFs here but the one that I highly recommend is Bulletin #4 (Long and Murry, 1995 - Late Triassic Carnian and Norian Tetrapods from the Southwestern United States). Although becoming dated it is still one of the quintessential references for anyone interested in Late Triassic vertebrates of the American southwest (and one of the most cited Triassic references ever). This has been out of print for awhile and those who have copies know that they were poorly bound and thus most existing copies are in tatters. Here is your chance to get the volume in its entirety.

http://econtent.unm.edu/cdm4/document.php?CISOROOT=/bulletins&CISOPTR=659&REC=6

BTW...you'll have to turn off your pop-up blocker to get the bulletin.

Tyrannosauroid from the Bathonian (Middle Jurassic) of England

2009-11-04T19:58:00.004-07:00

Important new Jurassic paper for those of you not subscribed to the VRTPALEO listserve...

RAUHUT, O.W.M., A.C. MILNER, and S. MOORE-FAY. 2009. Cranial osteology and phylogenetic position of the theropod dinosaur Proceratosaurus bradleyi(Woodward, 1910) from the Middle Jurassic of England. Zoological Journal of the Linnean Society Early View doi: 10.1111/j.1096-3642.2009.00591.x

ABSTRACT
The cranial osteology of the small theropod dinosaur Proceratosaurus from the Bathonian of Minchinhampton, England, is described in detail, based on new preparation and computed tomography (CT) scan images of the type, and only known, specimen. Proceratosaurus is an unusual theropod with markedly enlarged external nares and a cranial crest starting at the premaxillary-nasal junction. The skull is highly pneumatic, with pneumatized nasals, jugals, and maxillae, as well as a highly pneumatic braincase, featuring basisphenoid, anterior tympanic, basipterygoid, and carotid recesses. The dentition is unusual, with small premaxillary teeth and much larger lateral teeth, with a pronounced size difference of the serrations between the mesial and distal carina. The first dentary tooth is somewhat procumbent and flexed anteriorly. Phylogenetic analysis places Proceratosaurus in the Tyrannosauroidea, in a monophyletic clade Proceratosauridae, together with the Oxfordian Chinese taxon Guanlong. The Bathonian age of Proceratosaurus extends the origin of all clades of basal coelurosaurs back into the Middle Jurassic, and provides evidence for an early, Laurasia-wide, dispersal of the Tyrannosauroidea during the late Middle to Late Jurassic.

Enigmatic Triassic Fossils - Agnosphitys cromhallensis

2009-11-03T20:16:00.004-07:00

Alton Dooley over at Updates from the VPL has some excellent photos of the holotype material of Agnosphitys cromhallensis from the Upper Triassic fissure fills of England. The name, 'unknown begetter', reflects upon the unclear phylogentic relationships of this taxon. The original describers, Fraser et al. (2002), considered it to be a dinosauromorph more derived than Eoraptor and Herrerasaurus, but just outside of Dinosauria. It is known from an isolated left ilium, a left maxilla, a right humerus and a left astragalus. There is also a referred tooth. The association of this material was questioned with Langer (2004) considering it a nomen dubium.

The ilium possesses a distinct brevis shelf and 'open' ventral portion of the acetabulum (so it was slightly perforated), yet only has scars for two sacrals. The subrectangular deltopectoral crest on the humerus is typical for dinosauromorphs and the astragalus is very similar to that of basal saurischians (Nesbitt et al., 2007). Thus these specimens contain a melange of basal and derived characters making its phylogenetic placement uncertain (Fraser et al., 2002). This is also a very small animal as the humerus length is under 35mm. Unfortunately, more material needs to be found to elucidate the relationships of this animal, but what is present is not only very well preserved but extremely interesting.

REFERENCES

Fraser, N. C., Padian, K., Walkden, G. M., and Davis, A. L. M. 2002. Basal dinosauriform remains from Britain and the diagnosis of the Dinosauria. Palaeontology 45:79–95.

Langer, M.C. 2004. Basal Saurischia. In: Weishampel, D.B., Dodson, P., & Osmolska, H. (Eds.). The Dinosauria (2nd Edition). Berkeley: University of California Press. Pp. 25–46.

Nesbitt, S. J., Irmis, R. B. & Parker, W. G. 2007. A critical re-evaluation of the Late Triassic dinosaur taxa of North America. Journal of Systematic Palaeontology 5, 209-243.

Why I Use Pseudosuchia Instead of Crurotarsi for the Crocodile-line Archosaurs

2009-11-01T19:29:00.006-07:00

This issue was briefly mentioned on the Vertebrate Paleontology List-server about a week ago and I feel like discussing this a bit further. A quick perusal of archosaurian literature will show that there is a dichotomy in the nomenclature when referring to the lineage of Archosauria that leads to the crocodylians. Some workers will refer to this clade as Pseudosuchia and others as Crurotarsi, with the latter seeming to be the most popular. However, I along with some of my closest Triassic collaborators prefer Pseudosuchia over Crurotarsi, and often when I review papers I will suggest that workers using Crurotarsi switch. Why? Well for me it comes down to two issues, priority and stability.

This problem has been reviewed by several workers, such as Brochu (1997) and most recently Senter (2005). Gauthier and Padian (1985) defined Pseudosuchia as "crocodiles and all archosaurs closer to crocodiles than to birds"; however, Pseudosuchia has a much longer history dating back to the late 1800s, and although it has always had the intent of containing non-dinosaurian archosaurs, the membership of this clade has changed through the years and at some points even included some of what are now considered to be non-dinosaurian ornithodirans (the bird-line clade).

Several authors disliked Gauthier and Padian's (1985) redefining of what they considered to be an "ill-defined and misused" name. Furthermore, the name is in a sense contradictory as Pseudosuchia means "false-crocodiles" yet includes crocodiles as members. Accordingly Benton and Clark (1988) suggested a new name, "Crocodylotarsi", and although they did not explicitly define this clade they inferred that it was the same as Pseudosuchia. Sereno and Arcucci (1990) proposed a third name, Crurotarsi, which Sereno (1991) defined as "Parasuchia, Ornithosuchidae, Prestosuchus, Suchia, and all decendents of their common ancestor".

However, just because a group once contained members that have since been recognized as belonging to other groups does not warrant abandonment. Indeed if this were the case very few names would be valid, including Dinosauria. Likewise, contradictory names also are not grounds for dismissal, for example the name phytosaur means 'plant-reptile' although they surely ate everything but. Despite this we are still stuck with the contradictory name. Furthermore, there is no confusion among modern workers as to the meaning of Pseudosuchia, so statements to the contrary are moot. When I say something is a pseudosuchian, those familiar with archosaurs clearly understand what I mean.

Crocodylotarsi has been used by some workers but has since fallen out of usage with most modern workers using either Pseudosuchia or Crurotarsi. As all three groups currently have the same membership it has been argued by some that Pseudosuchia should be used as it has precedence. I agree in principle that the first defined name should have priority and this is the reason that I use Pseudosuchia instead of Crocodylotarsi. However, as noted by Brochu (1997) and Senter (2005) the definitions of Pseudosuchia and Crurotarsi are not the same.

Pseudosuchia is stem-based and thus is flexible to future changes, as any archosaur that is not an ornithodiran is included in this group. Crurotarsi, however, is defined as a node-based taxon and thus has an explicit membership, most notably phytosaurs (parasuchians), ornithosuchids, Prestosuchus, aetosaurs, "rauisuchians", and crocodylomorphs. This definition is much less flexible. In fact let's just suppose that the basal most group of crurotarsans, the phytosaurs, fell outside of the crown-clade Archosauria, and were instead considered to be derived archosauriforms. What would happen to Pseudosuchia and Crurotarsi? The content of Pseudosuchia would be pretty much the same except that phytosaurs would no longer be constituents. In contrast, because the base of Crurotarsi is specified by phytosaurs, Crurotarsi would now include phytosaurs plus all of Archosauria. Thus dinosaurs (including birds) would be Crurotarsans by definition. As you can see this definition is much less stable, another reason why I prefer and highly recommend that all workers use Pseudosuchia over Crurotarsi. Admit it, having to say "non-phytosaurian and non-ornithiodiran crurotarsan" is pretty clunky!

Actually, if this ever did happen ;), in my eyes Crurotarsi might actually now be a useful name when discussing phytosaurs, as you could now simply say that phytosaurs are the basalmost crurotarsans and still be correct. This is probably just slightly more explicit than simply saying they are derived archosauriforms.

For much more detail on this issue read Brochu (1997) and Senter (2005). You can also check out this page for a different opinion.

REFERENCES

Benton, M.J., and J.M. Clark. 1988. Archosaur phylogeny and the relationships of the Crocodylia. Pp. 295–338 in M.J. Benton (ed.). The Phylogeny and Classifi cation of the Tetrapods, Volume 1: Amphibians, Reptiles, Birds. Clarendon Press, Oxford.

Brochu, C.J. 1997. Synonymy, Redundancy, and the name of the crocodile stem group. Journal of Vertebrate Paleontology 17:448-449.

Gauthier, J., and K. Padian. 1985. Phylogenetic, functional, and aerodynamic analyses of the origin of birds and their flight. Pp. 185–197 in M.K. Hecht, J.H. Ostrom, G. Viohl, and P.
Wellnhofer (eds.). The Beginnings of Birds. Freunde des Jura- Museums, Eichstätt.

Senter, P. 2005. Phylogenetic taxonomy and the names of the major archosaurian (Reptilia) clades. PaleoBios 25:1–7.
Sereno, P.C. 1991. Basal archosaurs: phylogenetic relationships and functional implications. Society of Vertebrate Paleontology Memoir 2:1–53.

Sereno, P.C., and A.B. Arcucci. 1990. The monophyly of crurotarsal archosaurs and the origin of bird and crocodile ankle joints. Neues Jahrbuch für Geologie und Paläontologie Abhandlungen
180:21–52.

Phytosaur Taxonomy Flowchart

2009-10-29T16:09:00.005-07:00

I remember sitting down one evening back in 2001 and putting this together. It proceeds through time from left to right. This is why nobody wants to research phytosaur taxonomy!

Rhaetian Magneto-biostratigraphy from the Southern Alps (Italy): Constraints on Triassic Chronology

2009-10-28T08:00:00.000-07:00

This is fairly significant as it argues for quite a long Rhaetian Stage of the latest Triassic. If this is correct it means that a sizable portion of the upper part of the Chinle Formation could actually be Rhaetian in age. Not bad considering not too long ago workers were arguing if the Rhaetian was really even applicable outside of the marine realm.

Muttoni, G., Kent, D.V., Jadoul, F., Olsen, P.E., Rigo, M., Galli, M.T., and A. Nicora. 2009. Rhaetian magneto-biostratigraphy from the Southern Alps (Italy): Constraints on Triassic chronology. Palaeogeography, Palaeoclimatology, Palaeoecology. doi: 10.1016/j.palaeo.2009.10.014.

ABSTRACT: New Late Triassic-earliest Jurassic magneto-biostratigraphic data have been obtained from three overlapping sections in the Southern Alps, Italy (Costa Imagna, Brumano, Italcementi Quarry), comprised of ~ 520 m of shallow marine carbonates outcropping in stratigraphic continuity. Characteristic magnetic components of presumed depositional age record a sequence of 9 normal and reverse polarity magnetozones (as defined by at least three stratigraphically superposed samples) linked by conodont and palynofloral evidence from this study and the literature to Rhaetian to Triassic–Jurassic boundary age. This represents a significantly larger number of polarity zones than previously recognized in more condensed
Rhaetian sections from the literature, and by inference represents more time. These data are placed in a broader Late Triassic temporal framework by means of correlations to published magneto-biostratigraphic data from the Tethyan marine Pizzo Mondello section and the Newark astronomical polarity time scale (APTS). This framework is consistent with a position of the
Norian–Rhaetian boundary (as defined at Brumano and Pizzo Mondello by the first appearance of Misikella posthernsteini) within Newark magnetozones E17r–E19r in the ~ 207–210 Ma time interval, in basic agreement with the position originally estimated in the Newark using pollen biostratigraphy (E18 at 208–209 Ma). This framework is also consistent with the position of
the Triassic–Jurassic boundary interval (placed at Italcementi Quarry at the acme of Kraeuselisporites reissingeri coincident with a negative carbon isotope excursion) correlative to just above Newark magnetozone E23r and just below the oldest CAMP lavas dated at ~ 202 Ma. Hence, we estimate the duration of the Rhaetian to be ~ 5.5–8.5 Myr (or even longer if the
Triassic–Jurassic boundary is instead placed above the negative carbon isotope excursion as at Kuhjoch, which is the designated GSSP for the base of the Hettangian), and encompassing 9 magnetozones. This duration contrasts with a duration of ~ 2 Myr and only ~ 4 magnetozones in several alternative published magneto-biostratigraphic schemes.

Just In Case You Missed This One

2009-10-27T15:02:00.003-07:00

This came out about three weeks ago in PLoS ONE. Pretty cool study showing how different types of dinosaurs would negotiate a particularily difficult terrain.

Wilson, J. A., Marsicano, C. A., and R. M. H. Smith. 2009. Dynamic Locomotor Capabilities Revealed by Early Dinosaur Trackmakers from Southern Africa. PLoS ONE 4(10): e7331. doi:10.1371/journal.pone.0007331.

ABSTRACT

Background

A new investigation of the sedimentology and ichnology of the Early Jurassic Moyeni tracksite in Lesotho, southern Africa has yielded new insights into the behavior and locomotor dynamics of early dinosaurs.

Methodology/Principal Findings

The tracksite is an ancient point bar preserving a heterogeneous substrate of varied consistency and inclination that includes a ripple-marked riverbed, a bar slope, and a stable algal-matted bar top surface. Several basal ornithischian dinosaurs and a single theropod dinosaur crossed its surface within days or perhaps weeks of one another, but responded to substrate heterogeneity differently. Whereas the theropod trackmaker accommodated sloping and slippery surfaces by gripping the substrate with its pedal claws, the basal ornithischian trackmakers adjusted to the terrain by changing between quadrupedal and bipedal stance, wide and narrow gauge limb support (abduction range = 31°), and plantigrade and digitigrade foot posture.

Conclusions/Significance

The locomotor adjustments coincide with changes in substrate consistency along the trackway and appear to reflect ‘real time’ responses to a complex terrain. It is proposed that these responses foreshadow important locomotor transformations characterizing the later evolution of the two main dinosaur lineages. Ornithischians, which shifted from bipedal to quadrupedal posture at least three times in their evolutionary history, are shown to have been capable of adopting both postures early in their evolutionary history. The substrate-gripping behavior demonstrated by the early theropod, in turn, is consistent with the hypothesized function of pedal claws in bird ancestors.

Proof! Dinosaurs and People Co-existed!

2009-10-24T12:47:00.006-07:00

Now I've seen it with my own two eyes, a place where dinosaurs and humans co-habitate. Here is a close-up of part of the village.

Notice the crude stone construction and lack of straight lines and 90 degree angles.

Here is one of the dinosaurs, a large 'brontosaur' with some kind of transport device on its back. Actually the dinosaur is the transport device.

Here is one of the 'human' inhabitants. Notice the primitive feature of on three digit on the pes...and a seriously large snozolla.

Here is a human powered mechanical transport.

Some kind of primitive service station. Fossils using fossil fuels. Ironic!

Watch out for the active volcano (presumably Mesozoic) and the large pterosaur! I wonder what the pterosaurs eat here?

Ah Ha! Question answered. Better watch the kids in the open.

Or maybe this is more appropriate? What a menu. I can't believe the humans in this place eat dinosaur meat. What more proof do you need for their co-existance?

They have giant snakes too! This place is not the safest little town.

At least some slightly modern technology.

For those of you who have not seen one of these places, it is a Bedrock Village, one of two small little theme parks built in the U.S. in the 1960s and based on the TV show, The Flintstones. This one in in Valle, Arizona, about 25 miles south of the Grand Canyon. The is another in South Dakota. The one in Arizona is a bit hokey, but my kids really enjoyed it, especially climbing through the giant snake, which is actually a tunnel. The show was primetime TV in the early 1960s and reruns through my childhood, a staple of Saturday morning cartoons. I wonder if they are still on the air?

I remember hearing somewhere that The Flintstones represent a large percentage Americans' only experience with 'prehistoric life' and of course it shows co-habitation of humans and dinosaurs mixed with 'stone age' versions of modern technology, which many bought into. They should have put a disclaimer at the end of each show that it is pure fiction and does not depict accurate events in life history.

End of Blogpost Disclaimer: If you have gotten this far and still believe that dinosaurs and humans did indeed co-exist you need to do yourself a big favor. Go down to your local Community College and take a Historical Geology class (and read this post). Please do pay attention, you won't regret it. Yabba-Dabba-Doo.

Fruitadens Paper Available Online From Royal Society Publishing

2009-10-22T13:44:00.003-07:00

In case you are not aware, the full text and PDF files of the paper on Fruitadens, the new diminutive heterodontosaurid from North America, are available for download here. Don't forget the supplemental data files.

New Diminutive Heterodontosaur from North America

2009-10-20T22:08:00.000-07:00

Good to see this out. Available online today is a new paper describing a new heterodontosaurid, Fruitadens haagarorum, from the Late Jurassic on Colorado, U.S.A.

There are lots of cool things about this critter:

1) Small size. Specimens of Fruitadens have a maximum body length of about 75 cm, making it the smallest known ornithischian. Histological work was done to determine the relative age of the specimens. It is estimated that the largest individual was about 4-5 years old at death, but had already slowed down its growth as is seen in sub-adult and adult non-avian dinosaurs.

2) Age. The specimen is Late Jurassic, making it one of the youngest known heterodontosaurids. Only Echinodon from the Early Cretaceous of England is younger. Interestingly both Echinodon and Fruitadens have small adult sizes, but it is possible to differentiate the two.

3) Plesiomorphic dentition. Fruitadens differs from older heterodontosaurs in possessing less sophisticated craniodental adaptations, thus was probably more of a generalist feeder. The authors believe that this adaptation, as well as small size, allowed the group to survive into the Late Triassic and Early Cretaceous. Also cool is that it seems to have regularly undergone tooth replacement, which is unknown in most other heterodontosaurs.

4) Theropod-like femur. One feature of Fruitadens that I find interesting is that the femur closely resembles that of theropods like Dilophosaurus and is very unlike that of ornithischians. Richard Butler assures me that the material represents a single taxon so this is an interesting characteristic. I often like to play devil's advocate and claim that there are no Triassic ornithischians (not even Pisanosaurus) despite a wealth of saurischians, and although I've been assured over and over by dinosaur workers that the saurischian line could not have given rise to the ornithischians, I always find synapomorphies like this (basal ornithischian with saurischian-like characters) of great interest. Hey, someones got to keep stirring the pot or we'll get too complacent.

4) Biogeography. Fruitadens is from the Upper Jurassic Morrison Formation of Colorado. This is the first described heterodontosaurid from North America. As it is from the Brushy Basin Member it was a contemporary of the classic dinosaurs such as Allosaurus, Camarasaurus, Stegosaurus, and Diplodocus.

Overall another great find. They just keep coming. Read more here and here.

Butler, R. J., Galton, P. M., Porro, L. B., Chiappe, L. M., Henderson, D. M., and G. M. Erickson. 2009. Lower limits of ornithischian dinosaur body size inferred from a new Upper Jurassic heterodontosaurid from North America. Proceedings of the Royal Society B. doi:10.1098/rspb.2009.1494.

Abstract-The extremes of dinosaur body size have long fascinated scientists. The smallest (<1>Fruitadens haagarorum, from the Late Jurassic of western North America that rivals the smallest theropods in size. The largest specimens of Fruitadens represent young adults in their fifth year of development and are estimated at just 65–75 cm in total body length and 0.5–0.75 kg body mass. They are thus the smallest known ornithischians. Fruitadens is a late-surviving member of the basal dinosaur clade Heterodontosauridae, and is the first member of this clade to be described from North America. The craniodental anatomy and diminutive body size of Fruitadens suggest that this taxon was an ecological generalist with an omnivorous diet, thus providing new insights into morphological and palaeoecological diversity within Dinosauria. Late-surviving (Late Jurassic and Early Cretaceous) heterodontosaurids are smaller and less ecologically specialized than Early (Late Triassic and Early Jurassic) heterodontosaurids, and this ecological generalization may account in part for the remarkable 100-million-year-long longevity of the clade.

Finally! Aetosaurs in National Geographic Magazine

2009-10-20T09:29:00.005-07:00

The most recent issue of National Geographic has an article titled 'When Crocs Ruled' which mainly focuses on the long evolutionary history of the crocodile lineage and the threats extant crocodylians face today. One highlight of the article is the large two page spread of the Desmatosuchus mount from Petrified Forest National Park. It's a nice photo that almost makes me forget about the erroneous armor reconstruction (Unfortuntely, we'll need to remold and cast the whole thing to fix). I'm not as forgiving with the term "croc forerunner" in the title, because as we know aetosaurs were never crocodiles and their lineage did not give rise to the group. Still, I'm thrilled to see an aetosaur displayed prominently in National Geographic (but why not the cover?)

There is also a time line with some great reconstructions that gives props to Triassic forms such as Effigia, Postosuchus, and Proterosuchus. It also gives a good representation of crocodylomorph diversification through the later Mesozoic and Tertiary, something that often gets overshadowed by the dinosaurs, birds, and mammals.

There is also a secondary article by Paul Sereno titled "Strange Crocs of the Sahara", which again tries to demonstrate the great diversity in forms. Although I don't really care for terms such as 'RatCroc', 'DogCroc', and 'DuckCroc' they do seem to get the point across.

Latest Literature - Distribution of Supernumerary Carinae in Archosauriforms

2009-10-17T09:50:00.002-07:00

Beatty, B.L., and A.B. Heckert. 2009. A large archosauriform tooth with multiple supernumerary carinae from the Upper Triassic of New Mexico (USA), with comments on carina development and anomalies in the Archosauria. Historical Biology 21:57-65. DOI: 10.1080/08912960903154511.

Abstract-Here we report a tooth of a large archosauriform from the Upper Triassic of New Mexico, USA that displays developmental anomalies of carina formation. This tooth has two supernumerary carinae, both on the lingual side of the tooth. Previously, carina anomalies of this sort were primarily known from theropod dinosaurs, but always from the labial surface. Integrating this specimen into a reassessment of the published accounts of carina anomalies in other fossil diapsids reveals that supernumerary carinae are more widespread throughout Archosauriformes than previously reported. Our interpretation of this developmental anomaly highlights the present lack of understanding of tooth development in archosaurs, particularly carina formation, and suggests that crown morphology development in archosauriforms may be constrained differently than it is in mammals. This developmental constraint may explain the differences observed between the complexity found in mammal and archosauriform cusp morphology.

More Triassic Repeat Photography - Ned Colbert (AMNH) at the Petrified Forest in 1946

2009-10-13T15:39:00.005-07:00

In 1946 the American Museum of Natural History initiated fieldwork in the Chinle Formation of Arizona. Led by Edwin (Ned) Colbert, the goal of the expedition was to add to our knowledge of Triassic vertebrates and expand the museum's collection of Chinle Formation fossils. The previous year Colbert had travelled to the Petrified Forest with Charles L. Camp to check out Camp's old localities from the 1920s. This lead to a full blown, successful field season in 1946 (several amazing stories from this work can be found in one of Colbert's autobiographies - Digging into the Past). Set to return in 1947, Colbert never made it because on the way to the Petrified Forest he stumbled upon the huge deposit of vertebrates at the Coelophysis Quarry at Ghost Ranch, New Mexico. As a side note: he did return to the park briefly in 1947 to take part in the first ever Society of Vertebrate Paleontology field conference (see Camp et al., 1947; Nesbitt and Parker, 2005).

Fantastically, Colbert shot many rolls of Kodachrome (color) slide film of his Triassic work in 1946 and 1947. The 1946 set was purchased by the Petrified Forest shortly afterwards and some of these are still in the collections to this day. Since 2001 I have been actively trying to relocate two of the sites, the first a large bed of fresh water clams that AMNH staff proclaimed the greatest deposit of Triassic freshwater clams (Unionids) ever! Actually dozens of these sites occur throughout the park but when first discovered this was a big deal.

1946 shot of AMNH jeep parked near clam bed.

2009 photo of same site

The second site was where Colbert and crew collected the skull of a pseudopalatine phytosaur. This site was particularly intriguing as in the photo the outcrop being excavated looks very much like strata of the Blue Mesa Member. If this site really is in the Blue Mesa Member, this would represent a very low occurrence of a pseudopalatine phytosaur.

1946 photo of phytosaur skull excavation.

2009 photo of same site.

The park also has a very old map where Charles Camp's localities as well as those of National Park staff had been plotted. Colbert's 1946 sites were added to this map. Unfortunately, numerous visits to where these two sites were plotted failed to match up the photographs. By 2009 I had eliminated all possibilities except for one area of badlands south of a place called Billing's Gap. This past summer the interns and I were finally able to precisely relocate these sites. Interestingly both were situated very close to each other geographically and over 1.5 miles away from where they had been mapped! Also of interest was that the sites were in the upper portion of the Sonsela Member, thus no low occurrence of a pseudopalatine.

How fortunate we are that past researchers such as Colbert photographed their work (and he did it in color in 1946!). Even with dots on a map (and GPS coordinates) photos are indispensable for relocating sites and determining stratigraphic position of historic specimens. Nowadays with digital photography, there is no excuse for researchers not to photodocument every single site where fossils are collected.

For those interested in historic documentation of paleontology I encourage you to please check out the 2005 article I did with Sterling Nesbitt for a SVP field trip that year. It includes many previously unpublished photos from the 1947 field conference which was attended by notable VP'ers such as Romer, Gregory, Simpson, Colbert, etc... You can order the entire volume (with papers on the vertebrate faunas and plants of the Moenkopi and Chinle Formations from the Arizona Museum of Natural History.

REFERENCES

Camp, C.L., Colbert, E.H., McKee, E.D., and S.P. Welles. 1947. A guide to the continental Triassic of Northern Arizona. Plateau 20:1-8.

Nesbitt, S.J., and W.G. Parker. 2005. The 1947 Society of Vertebrate Paleontology Triassic fieldtrip, then and now, and its significance to Triassic vertebrate paleontology. Mesa Southwest Museum Bulletin 9:1-12.

Limusaurus and Bird Digit Identity

2009-10-08T20:15:00.003-07:00

For those of you who may have missed this or are not subscribed to the Dinosaur Mailing List, this is a comment left for my recent post on Limusaurus, the strange new beaked ceratosaur from China. One of the purported significances of this specimen is that it shed light on the debate on dinosaur digit homologies. As you can see below, this new article is a response to that claim.

A. Vargas has left a new comment on your post "Limusaurus inextricabilis, a Bizarre Beaked Cerato...":

Vargas, AO, Wagner GP, and Gauthier, JA. Limusaurus and bird digit identity.

hdl.handle.net/10101/npre.2009.3828.1

Here is our response to the Limusaurus paper. It was recently rejected by nature, not for any technical reason but because it was considered not to be of sufficient interest/importance.
We have uploaded it at the nature precedings citable archive, because we think it is important there is a quick and citable reply that unlike Xu’s proposal, is consistent with the view of the larger community of theropod paleontologists, namely, that tetanuran digits still are I, II, III. We are preparing a longer paper on this topic.

The First Morphological Evidence for Turtles as Archosauromorphs

2009-10-06T10:14:00.004-07:00

Bhullar, B.S., and G.S. Bever. 2009. An archosaur-like laterosphenoid in early turtles (Reptilia:Pantestudines). Breviora 518:1-11. doi: 10.3099/0006-9698-518.1.1

Abstract: Turtles are placed with increasing consistency by molecular phylogenetic studies within Diapsida as sister to Archosauria, but published gross morphology–based phylogenetic analyses do not recover this position. Here, we present a previously unrecognized unique morphological character offering support for this hypothesis: the presence in stem turtles of a laterosphenoid ossification identical to that in Archosauriformes. The laterosphenoid is a tripartite chondrocranial ossification, consisting of an ossified pila antotica, pila metoptica, and taenia medialis + planum supraseptale. It forms the anterior border of the exit for the trigeminal nerve (V) and partially encloses the exits for cranial nerves III, IV, and II. This ossification is unique to turtles and Archosauriformes within Vertebrata. It has been mistakenly dismissed as anatomically dissimilar in these two groups in the past, so we provide a complete description and detailed analysis of correspondence between turtles and Archosauriformes in each of its embryologically distinct components. A preliminary phylogenetic analysis suggests other potential synapomorphies of turtles and archosaurs, including a row or rows of mid-dorsal dermal ossifications.

Thanks to Randall Irmis for bringing this to my attention.

I Think the Jet Lag is Mostly Gone

2009-10-04T21:31:00.004-07:00

I've been back from England for a few days but really have not had the energy to do too much with my evenings except try to get my sleep schedule back to Arizona time rather than London/Bristol, an 8 hour difference.

This year's SVP meeting was excellent and I totally enjoyed my time in Bristol and in London. While many attendees returned to the states after the meeting I went on to London for three days of work in the sub-basement of the Natural History Museum. I stayed at a neat little bed and breakfast in Parsons Green about six underground stops from the museum, which saved me some cash, and actually enjoyed my commute everyday. After eight hours of non-stop work in the museum, we would take the underground to various places in the city and check out sites such as the Tower of London, Buckingham Palace, Piccadilly Circus, and of course Westminster Abbey. Unfortunately I did not get to go into many of these places due to arriving after hours, but it was still cool to see the outsides. The last day Jeff Martz skipped the museum and went out to see to Victorian dinosaurs at Crystal Palace Park and caught a second copy of William Smith's map of England (we had seen another copy in Bristol), which of course represents the beginnings of geological mapping, stratigraphy, and biostratigraphy. Nightly we would stop at a little pub near our B&B for internet and a pint of Young's Bitter.

The museum was excellent although I admit I spent the majority of my time in the basement and did not really get to see much else. I was mainly studying specimens of the aetosaur Stagonolepis robertsoni which is mostly represented by natural molds in sandstone from the Elgin area of Scotland, and a series of old casts made from these molds. Without these casts it would be almost impossible to study this material and I was pleasantly surprised about how much information is available from them. I also was able to see some phytosaur material collected from Germany in the 1860s and originally described by Hermann von Meyer.

Although my research took up almost all of my time and attention I did sneak a peak at some of the amazing dinosaur material in the collections. It was an honor to look upon some of Gideon Mantell's Iguanodon specimens, and browse through specimens studied by Owen, Huxley, Seeley, Lydekker, and others, and to reminisce about the beginnings of dinosaur paleontology (which all started there). However, as is typical for museum study, there never seems to be enough time to complete your primary research, never mind look at other things in great detail. It is absolutely amazing how many fossils are out there and how many are in venerable institutions such as the Natural History Museum in London. I don't think that even the staff who work there are able to see everything during their careers.

Success in Bristol

2009-09-27T14:42:00.005-07:00

Despite running concurrent to the best student presentations (Romer Prize), the Preparators and Bird/Dinosaur sessions, the Triassic symposium managed to draw large crowds for each talk. In fact I heard we had better crowds than the bird/dinosaur talks. This would have simply been unheard of six or more years ago and is a testament to all the great research going on in Triassic paleontology right now.

I am no longer in Bristol, and instead am sitting in a pub in central London downing a pint of bitter and watching football (soccer) on the telly. This years SVP meeting was excellent and held in a great place with 1100 great colleagues. Tomorrow Jeff and I are off to the Natural History Museum to look at the holotype of Stagonolepis robertsoni.

The 69th Annual Meeting of the Society of Vertebrate Paleontology

2009-09-21T06:00:00.000-07:00

This week I will be attending the annual meeting of the Society of Vertebrate Paleontology. Jeff Martz and I have been invited to present a paper on our recent biostratigraphic work in the Petrified Forest as part of a special symposium "Late Triassic Terrestrial Biotas and the Rise of Dinosaurs". This year the meeting is being held in Bristol, England and as I have never been to the U.K. (or Europe) before this should be a real treat. I will be following up the meeting with a few days of research at the Natural History Museum in London. I must remember to look the opposite way before crossing streets or this will be a very short trip!

Cynodonts and More Cynodonts

2009-09-19T21:50:00.004-07:00

The current issue of the Journal of Vertebrate Paleontology has two articles on Gondwanan cynodonts that are important for Middle Triassic biostratigraphy.

Abdala, F., and R.M.H. Smith. 2009. A Middle Triassic Cynodont Fauna from Namibia and Its Implications for the Biogeography of Gondwana. Journal of Vertebrate Paleontology 29:837-851. doi: 10.1671/039.029.0303

Abstract - The upper Omingonde Formation of Namibia contains a diverse vertebrate fauna represented by amphibians, dicynodonts, archosaurs, therocephalians, and cynodonts, which is generally considered to be of Anisian age. Four cynodont taxa (Cynognathus, Diademodon, Trirachodon, and Titanogomphodon) are currently known from this fauna. Here we document four additional cynodonts, all of which were recovered from the highest levels of the formation: Luangwa, an indeterminate traversodontid, Aleodon, and Chiniquodon. These discoveries allow us to recognize the Omingonde Formation as preserving the most diverse fauna of Middle Triassic cynodonts in the world. Furthermore, we recognize that the formation is a biostratigraphic link among Middle Triassic faunas from South Africa, Tanzania, Zambia, Argentina, Brazil, and Antarctica. Aleodon is recorded here for the first time in Anisian faunas of southern Africa, and the unexpected record of Chiniquodon poses a biostratigraphic enigma because this taxon is known only from Ladinian—Carnian faunas of South America. We explore some possible scenarios related to the radiation of traversodontid cynodonts in Gondwana during the Anisian.

Martinelli, A.G., de la Fuente, M., and F. Abdala. 2009. Diademodon tetragonus Seeley, 1894 (Therapsida: Cynodontia) in the Triassic of South America and Its Biostratigraphic Implications. Journal of Vertebrate Paleontology 29:852-862. doi: 10.1671/039.029.0315

Abstract - We report for the first time the presence of the cynodont Diademodon tetragonus Seeley, 1894 in the South American Triassic. The specimen, represented by a fragmented skull and lower jaws, was found in levels of the Rio Seco de la Quebrada Formation (Puesto Viejo Group), Mendoza Province, Argentina. It is assigned to D. tetragonus based on its overall skull shape (narrow and elongated snout with a concave outline in dorsal view), the morphology of the jugal that forms most of the dorsoventral depth of the zygoma and shows a well-excavated external auditory meatus, and a postcanine series including circular outlined anterior teeth, ovoid gomphodont teeth in the middle, and posterior sectorial teeth. The association of this taxon with the cynodonts Cynognathus crateronotus and Pascualgnathus polanskii, along with comparisons to African Triassic assemblages, suggest an Early to Late Anisian age for the Río Seco de la Quebrada Formation. These levels are most likely correlated to the subzones B and C of the South African Cynognathus Assemblage Zone, where both Cynognathus and Diademodon are known. This discovery represents the fourth report of shared cynodont genera between allegedly Lower to Middle Triassic African and South American terrestrial faunas.

Cute! Raptorex kriegsteini New Miniature Tyrannosaur from the Early Cretaceous of China

2009-09-17T12:00:00.011-07:00

This isn't Triassic, but it has been a slow month and this is pretty cool. Out today in Science is an article describing a new miniature tyrannosaur from the Early Cretaceous of China. Sereno et al. have named the specimen Raptorex kriegsteini after the parents of the benefactor who purchased the specimen from a private seller at the Tucson Gem and Mineral Show. This is a good story about how an illegally collected specimen is donated by a benefactor to science, studied and published for the scientific community and the public, and now will be returned back to China from where it was removed.

http://scienceblogs.com/notrocketscience/2009/09/raptorex_tiny_king_of_thieves_shows_how_tyrannosaurus_body_p.php

The reconstruction is from here. Todd Marshall does amazing work.

One thing I did notice is that the species name is improperly constructed. Because the specimen is named for Mr. and Mrs. Kriegstein, by ICZN convention the name should be R. kriegsteinorum. This seems to occur more often then it should, especially with multiple authors, reviewers, and editors.

REFERENCE

Sereno, P.C., Tan, L., Brusatte, S., Kriegstein, H.J., Zhao, X., and K. Cloward. 2009. Tyrannosaurid body design first evolved at small body size. Science 325. doi: 10.1126/science.1177428

Supplemental Material

Did Tetrapods Undergo a Postural Shift after the End-Permian Extinction?

2009-09-15T12:41:00.005-07:00

Kubo, T. and M. J. Benton. 2009. Tetrapod postural shift estimated from Permian and Triassic trackways. Palaeontology 52:1029-1037. doi: 10.1111/j.1475-4983.2009.00897.x

Abstract- The end-Permian mass extinction, 252 million years (myr) ago, marks a major shift in the posture of tetrapods. Before the mass extinction, terrestrial tetrapods were sprawlers, walking with their limbs extended to the sides; after the event, most large tetrapods had adopted an erect posture with their limbs tucked under the body. This shift had been suspected from the study of skeletal fossils, but had been documented as a long process that occupied some 15–20 myr of the Triassic. This study reads posture directly from fossil tracks, using a clear criterion for sprawling vs erect posture. The track record is richer than the skeletal record, especially for the Early and Middle Triassic intervals, the critical 20 myr during which period the postural shift occurred. The shift to erect posture was completed within the 6 myr of the Early Triassic and affected both lineages of medium to large tetrapods of the time, the diapsids and synapsids.

Enigmatic Triassic Taxa - Kraterokheirodon colberti

2009-09-10T20:05:00.001-07:00

When you watch 'Walking With Dinosaurs' the Triassic portion (which supposedly represents the Chinle Formation of Arizona) contains numerous scenes featuring a group of cynodonts. In reality this presence of cynodont therapsids in the Chinle Formation was based on two teeth. The first (AMNH 4947) was found at St. Johns Arizona in 1946 by Guy Hazen of the USGS and presented to Ned Colbert that summer and reposited at the American Museum of Natural History. The second tooth (PEFO 9984) was found in 1984 on a geology field trip through Petrified Forest National Park. Preliminarily assigned to traversodont cynodonts (e.g., Long and Murry, 1995) these teeth were under study by Colbert until his passing in 2001.

The location of these specimens was unknown until 2002 when Randall Irmis was helping sort out Colbert's office at the Museum of Northern Arizona and found the original and a cast of PEFO 9984 and a cast of AMNH 4947 (unfortunately the original specimen has yet to be rediscovered).

In 2005 Randy and I published a paper describing these teeth as a new taxon, Kraterokheirodon colberti. The name, created by Randy, means "cupped hand tooth", which describes the morphology of the occlusal surfaces (cusps) of the teeth (six in all), and also honors Ned Colbert. [photo below is of PEFO 9984 in what we believe is a posterior view, the crown is to the left].

The morphology of these teeth is unique "differing from all other known vertebrate teeth in possessing a convexly arched transverse ridge of six cusps." The problem is that they are so unique that determining a taxonomic assignment for this taxon is almost impossible at this time. The thecodont implantation suggests tetrapod affinities, but assignment to a less inclusive clade is ambiguous. [photo below is of PEFO 9984 in occusal view].

One thing is clear, these teeth belong to a very large tetrapod with a long stratigraphic range. The AMNH tooth is from the Monitor Butte Member near the base of the Chinle, whereas the PEFO tooth is from the middle of the Petrified Forest Member. What is even more of a mystery is how such a large animal could escape detection in the well known Chinle faunal assemblage. The largest tetrapods found in these assemblages are phytosaurs and rauisuchians, two groups in which the dentition is very well known and extremely different than that of Kraterokheirodon.

Even though Revueltosaurus was only known from teeth for over 15 years, this was simply due to not finding teeth directly associated with other bones as non-dental material had been collected as early as the 1920s. To date, my colleagues and I have no candidate specimens to associate with the teeth of Kraterokheirodon. No potential postcrania, zip. As with Acallosuchus rectori, our only hope is to keep sampling the horizons in which these teeth occur in hopes of finally solving the mystery as we did with Revueltosaurus (Parker et al., 2005).

REFERENCES

Irmis, R. B., and W. G. Parker. 2005. Unusual tetrapod teeth from the Upper Triassic
Chinle Formation, Arizona, USA. Canadian Journal of Earth Science 42: 1339–1345.
doi: 10.1139/E05-031

Long, R. A., and P. A. Murry. 1995. Late Triassic (Carnian and Norian) tetrapods from the southwestern United States. New Mexico Museum of Natural History and Science Bulletin 4:1-254.

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

These Guys Might Be Crazy

2009-09-08T20:49:00.008-07:00

...or maybe not.... or maybe so.

Nonetheless I've got to give Matt Wedel, Mike Taylor, and Andy Farke kudos for a very interesting, definitely novel, and potentially insane idea. They appear to be looking for (apparently thousands of) potential co-authors in a new project to build a large database of measurements for ornithischian dinosaur bones to attempt to solve a variety of research questions. This database will be open access and available to all researchers providing measurement data for potentially every known ornithischian dinosaur bone. Amazing...or maybe foolish. Is this a pipe dream or absolute brilliance that will revolutionize the field of vertebrate paleontology? It's too early to say and the only way to find out for sure is to get involved. Too bad there aren't any Triassic ornithischians in North America, guess I'm out ;).

You can read all about this and get started here, here, here, and read some commentary here.

Discovery of an Entire Fossil Cycad from the Late Triassic of China

2009-09-07T21:31:00.007-07:00

One of the frustrating things about fossil plants is that when the die they tend to break down rapidly and fall apart. Thus finding an entire plant is rare and therefore the leaves, stems, and reproductive structures are often found separately and provided different taxonomic names. Even at Petrified Forest National Park we do not know for certain what foliage belongs with our main types of fossil wood, although we do have isolated preserved foliage. A recent article in Chinese Science Bulletin (Springer) documents an entire cycad from the Late Triassic of China. This well preserved specimen includes the leaves, pinnae, stem, and a male cone as well as preserving their arrangement. An amazing and important find, unfortunately the article is just a note and not a full description and discussion. According to the article this is forthcoming.

You can download the PDF here for free until the end of November 2009 courtesy of Springer. The image above is from the article.

Wang, X., Li., N., Wang, Y. D., and S. Zheng. 2009. The discovery of whole-plant fossil cycad from the Upper Triassic in western Liaoning and its significance.
Chinese Science Bulletin 54: 3116―3119. doi: 10.1007/s11434-009-0384-z

Abstract - A recently discovered megafossil of whole plant cycad is briefly reported here. The specimen is collected from the Yangcaogou Formation (Upper Triassic) in Changheying, Beipiao, Liaoning. The whole plant is preserved intact on a sandstone slab, 89 cm long and 130 cm wide, including leaves up to 82 cm long and a male cone physically attached to the stem apex. Analysis on the morphology, arrangement and venation of leaf and pinna, male cone and its relationship with other parts indicates that the fossil is closely related to living Zamiaceae in Cycadales. This cycad fossil is hitherto most completely preserved cycad specimen including both vegetative and reproductive organs. Its discovery contributes much to our understanding of the morphology and evolution of cycads, palaeoclimate as well as palaeoenvironment.

Thanks to Randy Irmis for sending this on.