Monday, July 16, 2012

Phytosaurs - Some Are Real and Some Are Just Dinosaurs

Phytosaurs may not be crown group archosaurs (according to Nesbitt 2011), but they are definitely important in archosaur evolutionary history as well as Triassic ecology. Stocker's new paper increases the known diversity of phytosaurs with the description of the new species Protome batalaria and reinforces the importance of apomorphy-based identifications. Some recent accounts of partial skeletons have suggested that phytosaurs may have survived into the Early Jurassic, but Barrett and Xu re-affirm their end-Triassic demise and urge caution in identifying poorly preserved, partial remains, which tend to belong to dinosaurs.

Stocker, M. R. 2012. "A new phytosaur (Archosauriformes, Phytosauria) from the Lot’s Wife beds (Sonsela Member) within the Chinle Formation (Upper Triassic) of Petrified Forest National Park, Arizona." Journal of Vertebrate Paleontology 32(3): 573-586
A new phytosaur taxon from Petrified Forest National Park, Arizona, is here described based on cranial material from a single individual. This specimen previously was included in an extensive phylogenetic analysis, and it was found to possess a combination of character states that differs from all known phytosaur taxa in addition to two autapomorphies within the braincase and an autapomorphy of the mandible. The new taxon adds to the taxonomic diversity recognized from the Sonsela Member of the Chinle Formation. The continued increase in phytosaur diversity emphasizes the need to more accurately characterize and identify taxa within a phylogenetic systematic context in order to produce a more refined signal for biostratigraphic correlations, biochronologic inferences, and faunal dynamics during the Late Triassic.

Barrett, P. M., and X. Xu. 2012. "The enigmatic reptile Pachysuchus imperfectus Young, 1951 from the lower Lufeng Formation (Lower Jurassic) of Yunnan, China." Vertebrata PalAsiatica 50:151-159. [Free download here]
Phytosaurs are generally considered to have become extinct at the end of the Triassic Period, but several records have suggested that they survived into the basal Jurassic in Europe and Asia. The Asian record consists of Pachysuchus imperfectus from the lower Lufeng Formation (?Hettangian-Sinemurian) of Yunnan, China. However, this specimen differs from phytosaurs in numerous aspects and is more likely a poorly preserved, indeterminate sauropodomorph dinosaur skull. The referred specimens of this species are also regarded as indeterminate, thereby removing the post-Triassic record of phytosaurs from Asia. The European records of Jurassic phytosaurs are also shown to be doubtful, suggesting that this clade was restricted to the Late Triassic. 

Saturday, July 14, 2012

Recent Papers on Triassic Archosaurs (and Archosauriforms) and Other News

Several papers regarding Triassic archosaurs have come out recently. The first is a re-evaluation of Proterochamspia, including genera (specifically Proterochamspa) within the clade and a look at its evolutionary history. The second is an interesting look at bipedality and cursoriality in archosaurs. And finally, we have Smok, a new archosaur from Poland. The paper does not commit to which archosaur branch this new animal belongs to (since this is a topic of the author's in-progess PhD), but I would bet money that it's NOT a dinosaur.

In other news, there is a new paleo blog out there looking at the coevolution between plants and animals - Antediluvian Salad. Check it out! And while you are checking things out, head over to the Pictures tab of The Forgotten Archosaurs for some great shots of work going on in Petrified Forest National Park this summer, including the Revueltosaurus Quarry and other PEFO paleo field work.

Dilkes, D., and A. Arcucci. 2012. "Proterochampsa barrionuevoi (Archosauriformes: Proterochampsia) from the Late Triassic (Carnian) of Argentina and a phylogenetic analysis of Proterochampsia." Palaeontology (online)
Restudy of skulls and available postcrania of the proterochampsian archosauriform Proterochampsa barrionuevoi from the Ischigualasto Formation (Upper Triassic, Carnian) in the San Juan Province, Argentina, confirms that the genus is diagnosed by autapomorphies that include dermal sculpturing consisting of prominent ridges and nodular protuberances, a large hook-like lateral projection on the quadratojugal, an antorbital fossa restricted to a depression along the maxilla, lateral expansion of the premaxilla anterior to the premaxilla–maxilla contact, absence of a supratemporal fossa, exclusion of jugal from suborbital fenestra, basal tubera of parabasisphenoid facing ventrally and reaching laterally beyond the basipterygoid process, and a ventral lamina on the angular. Proterochampsa nodosa is a valid species distinguished from P. barrionuevoi by fewer cranial ridges with larger protuberances, relatively smaller supratemporal fenestrae and width of frontals between orbits less than that of the nasals. A phylogenetic analysis supports the monophyly of Proterochampsia consisting of Proterochampsa, Chanaresuchus bonapartei, Gualosuchus reigi, Tropidosuchus romeri and Cerritosaurus binsfeldi. A temporal separation between the two basal proterochampsians with earliest records in the Late Triassic (Proterochampsa and Cerritosaurus) and Chanaresuchus, Gualosuchus and Tropidosuchus in the Middle Triassic indicates hidden proterochampsian diversity in the Middle Triassic.

Kubo, T., and M. O. Kubo. 2012. "Associated evolution of bipedality and cursoriality among Triassic archosaurs: a phylogenetically controlled evaluation." Paleobiology 38: 474–485. (online)
Bipedalism evolved more than twice among archosaurs, and it is a characteristic of basal dinosaurs and a prerequisite for avian flight. Nevertheless, the reasons for the evolution of bipedalism among archosaurs have barely been investigated. Comparative analysis using phylogenetically independent contrasts showed a significant correlation between bipedality (relative length of forelimb) and cursoriality (relative length of metatarsal III) among Triassic archosaurs. This result indicates that, among Triassic archosaurs, bipeds could run faster than quadrupeds. Bipedalism is probably an adaptation for cursoriality among archosaurs, which may explain why bipedalism evolved convergently in the crocodilian and bird lineages. This result also indicates that the means of acquiring cursoriality may differ between archosaurs and mammals.

Niedźwiedzki, G., T. Sulej, and J. Dzik. 2012. "A large predatory archosaur from the Late Triassic of Poland." Acta Palaeontologica Polonica 57 (2): 267-276. (online)
We describe a new large predatory archosaur, Smok wawelski gen. et sp. nov., from the latest Triassic (latest Norian–early Rhaetian; approximately 205–200 Ma) of Lisowice (Lipie Śląskie clay−pit) in southern Poland. The length of the reconstructed skeleton is 5–6 m and that of the skull 50–60 cm, making S. wawelski larger than any other known predatory archosaur from the Late Triassic and Early Jurassic of central Europe (including theropod dinosaurs and “rauisuchian” crurotarsans). The holotype braincase is associated with skull, pelvic and isolated limb−bones found in close proximity (within 30 m), and we regard them as belonging to the same individual. Large, apparently tridactyl tracks that occur in the same rock unit may have been left by animals of the same species. The highly autapomorphic braincase shows large attachment areas for hypertrophied protractor pterygoideus muscles on the lateral surface and a wide, funnel−like region between the basal tubera and basipterygoid processes on the ventral surface. The skeleton (cranial and postcranial) possesses some features similar to those in theropod dinosaurs and others to those in large crocodile−line archosaurs (“rauisuchians”), rendering phylogenetic placement of S. wawelski difficult at this time.

Sunday, July 8, 2012

Revueltosaurus Quarry- The Evolution of A Jacket

In field paleontology, one of the most important things you do once you find bone is create a proper field jacket. Jeff Martz recently created a nice little cartoon that describes the typical steps involved in jacketing bone once it's found (above), although he does leave out a very important final step - carrying the jacket out of the field. Here I'll show you what these steps look like in real life - an example from the Revueltosaurus Quarry - as we go from finding bone to bringing it home.

Step 1 was complete in 2004, when Bill Parker and his interns discovered this site while prospecting. In anticipation of finding more bone, we've been excavating (Step 2) since the beginning of the summer. A little over two weeks ago (June 22nd, 2012), we removed the first two big jackets from the Revueltosaurus Quarry here at PEFO. One weighed around 100 lbs, the other over 300 lbs. The 300 lb jacket contained what is likely an entire individual revueltosaur.

Slowly outlining where the bone is. It's hard to see, but the bone is a faint orange color in the middle of the photo.
We first encountered bone in the general area on June 2nd when Frankee Sena pulled out a big chunk of overburden with bone on it. Since it came from a hole, we all had to start bringing things down to that level in the surrounding area.  I found a few isolated vertebrae, but then on June 4th, we found the jackpot. The bone just wouldn't stop. This is the point when, even though we just spent days (if not weeks) hoping to find bones, we started cursing each new bone that we found. It's starts to get overwhelming. And in the back of our minds, as we watched the area of bone expand, we were all thinking "this is going to be a really heavy jacket".
Jacketing some parts of the block as Bill continues to define the edges.
We managed to define a few edges (Step 3) before the end of the day, so I started to jacket (Step 4) part of the block. It's important to protect the bone as best you can when excavating, so if you can start to jacket something, you should. First I put down a separator (toilet paper) then started adding plaster (small plaster medical bandages).

The block continued to expand, until we were finally able to define all the edges (Step 3) by June 12. By June 15, we had a complete, jacketed block. We also had the second block starting to take shape right beside it. Bill managed to recruit some help to haul these two jackets out of the quarry and up out of the badlands, so by June 21, we were ready to flip them both (Step 5). A testament to good jacketing, both blocks flipped perfectly, with no signs flexing.

With the smaller jacket flipped, Bruce chisels out some excess rock.
After flipping them, we cleaned some rock off the bottom (to lighten the jacket a bit) and plastered the underside. And on Friday, June 22, the Youth Conservation Corp (YCC) kids arrived to help us carry them out. This post is dedicated to them (and the two park rangers, Lauren and Desmond, who were in charge of wrangling all those teenagers). It took about 2 hours to carry those jackets almost a mile, up and down badlands, including a very steep hill at the end. And all without one word of complaint. Way to go YCC!