Field of Science

New Vertebrate Locality from the Lower Triassic of Brazil

The taxonomic diversity of these Gondwanan sites is incredible. I'd love to find even fragmentary procolophonids and synapsids in the Chinle.

Dias-da-Silva, S., and Á. A. S. da-Rosa. 2011. Granja Palmeiras, a new fossiliferous site for the Lower Triassic of southern Brazil. Revista Brasileira de Paleontologia 14(2):157-168 doi:10.4072/rbp.2011.2.04

Abstract - A new fossiliferous locality, Granja Palmeiras, is described for the Sanga do Cabral Formation (Lower Triassic of Southern Brazil, Rosário do Sul Group, Paraná Basin). It consists on orange and reddish fine sandstones, with sandy and calcareous concretions and intercalated fossiliferous intraformational conglomerates. Its fossils are fragmentary and badly preserved. Nevertheless, among the 46 specimens collected so far, putative actinopterygians,temnospondyls, procolophonoids, archosauromorphs, and non-mammalian cynodonts were identified. Besides, several non-diagnostic appendicular elements are ascribed to Tetrapoda indet. The fossiliferous content found in Granja Palmeiras can provide a valuable new framework for future correlation with other Lower Triassic South American units as well as other continental tetrapod- bearing deposits from Gondwana.

RESUMO – Uma nova localidade fossilífera, Granja Palmeiras, é descrita para a Formação Sanga do Cabral (Triássico Inferior do sul do Brasil, Grupo Rosário do Sul, bacia do Paraná). Consiste em arenitos finos alaranjados e avermelhados, com concreções carbonáticas e arenosas, e conglomerados intraformacionais intercalados. Os fósseis se apresentam fragmentários e em mal estado de preservação. Mesmo assim, dentre os 46 espécimes coletados até o momento foram identificados restos de actinopterígios, temnospôndilos, procolofonóides, arcossauromorfos e prováveis cinodontes não-mamalianos. Além destes, vários elementos apendiculares não diagnósticos são atribuídos a Tetrapoda indet. O conteúdo fossilífero registrado na Granja Palmeiras pode fornecer informações valiosas para a correlação com outras unidades do Triássico Inferior sul-americano, bem como com outras localidades gondwânicas de outras regiões do globo.

Revisiting Our Summer of Fieldwork at PEFO

It's been a pretty slow week for Triassic-themed papers and events, and I'm pretty swamped trying to complete a couple of manuscripts as well as getting ready for upcoming meetings in Argentina and Las Vegas.

Luckily Susan Drymala is back up and blogging at the Forgotten Archosaurs and has an excellent new post on the beginning of our 2011 summer fieldwork. Please go check it out.

CAMP Magnetostratigraphy Revisited

New paper in which the results suggest that either the SA5.r magnetozone from St. Audrie's Bay is not recorded in North American and Moroccan CAMP deposits or that the SA5.r is not reliable or useful for global-scale correlations. This has implications on the timing of the CAMP eruptions in relation to the Triassic-Jurassic boundary as well as correlations into non-marine sequences. This paper also provides a new paleo pole hypothesis for CAMP deposits in Morocco, which is more similar than past poles recovered for that unit to those determined for the North American sequence.

Font, E., Youbi, N., Fernandes, S., El Hachimi, H., Kratinova, Z., and Y. Hamim. 2011. Revisiting the magnetostratigraphy of the Central Atlantic Magmatic Province (CAMP) in Morocco. Earth and Planetary Science Letters, corrected proof. doi:10.1016/j.epsl.2011.07.007

Abstract - The origin of the Triassic–Jurassic (Tr–J) mass extinction is still a matter of debate: proponents of the idea that continental flood basalts of the Central Atlantic Magmatic Province (CAMP) are responsible for the crisis are opposed by those who favor an extraterrestrial origin linked to the impact of meteorite. Principal limitations reside in the difficulty to date and correlate CAMP lavas with the marine realm turnover. One argument widely used to suggest that CAMP lavas pre-dated the Tr–J boundary in Morocco is based on the presence of two brief magnetic reversals in the intermediate units of the Tiourjdal and Oued Lahr sections (Morocco) that were correlated to the E23r chron from the Newark basin and to the SA5n.2r/3r and SA5r chrons of the Saint Audrie Bay [Knight, K.B., Nomade, S., Renne, P.R., Marzoli, A., Betrand, H., Youbi, N., 2004. The Central Atlantic Magmatic Province at the Triassic–Jurassic boundary: paleomagnetic and 40Ar/30Ar evidence from Morocco for brief, episodic volcanism. Earth and Planetary Science Letters 228, 143–160]. However the primary origin for these negative (reverse) magnetic components is questionable since no field or reversal test was provided to constrain the primary character of the remanence as well as because the small number of samples. Here we have conducted a detailed paleomagnetic and magnetic mineralogy study of the interbedded limestones of the Tiourjdal section and of other CAMP lavas sections where the intermediate unit is complete, namely the Tizi El Hajaj, Jbel Imzar and Aït Ourir sections, to better constrain the origin and stratigraphic location of these negative magnetic components. We show that the interbedded limestones of the Tiourjdal section were entirely remagnetized by chemical processes via acid and oxidizing hydrothermal fluids generated by eruptions of CAMP lavas. In addition, magnetostratigraphic data of the Tizi El Hajaj, Jbel Imzar and Aït Ourir sections show that the entire intermediate unit encompassed a positive (normal) magnetic interval. A good quality paleomagnetic pole for the CAMP lava in Morocco is then provided (Plat = 60.0°; Plong = 241.6°; A95 = 2.6; N = 99) that is now in better agreement with its trans-Atlantic counterpart.

More Thoughts on Smok

Brian Switek has a really good post titled "The Dinosaur That Wasn't" over at Dinosaur Tracking.

New Isotopic Dates for Strata in the Late Triassic Chinle Formation, Petrified Forest National Park


I'm thrilled that this is finally out, along with the recent Irmis et al. paper. This new paper by Ramazani et all provides high-precision isotopic dates for a variety of stratigraphicl levels of the Chinle Formation in Petrified Forest National Park. Furthermore it provides the first dates for the Mesa Redondo and Owl Rock Members which essentially contrain the entire park section. The Mesa Redondo date is particularly important because it comes close to representing the base of the Chinle Formation in Arizona (see stratigraphic discussion in Irmis et al., 2011). The stratigraphic sequence and scheme used for this study is based upon independent work conducted by Dr. David Fastovsky of the University of Rhode Island and some of his students, as well as work done by a group from Baylor University.  Thus it doesn't match the current park stratigraphic nomenclature introduced by Martz and Parker (2010) and Parker and Martz (2011). Still the two are close and if anyone has any questions where these new dates fit into our scheme please contact me.

Some important points made by the paper:

- Chinle deposition in Petrified Forest ranged from about 225 - 208 million years ago or a duration of 17 million years.

- There is not enough stratal thickness in the Sonsela Member to account for the elapsed amount of time, so there must be many hiatuses in this unit.

- Despite the purported presence of numnerous hiatuses in the Sonsela none of them are large-scale, and there is little evidence for a sizable regional unconformity (i.e., the TR-4). [Note that this is also supported by other stratigraphic and biostratigraphic data].

- These authors argue that the basal Chinle date demonstrates overlap between the Chinle and Ischigualasto formations, suggesting that the rise of early dinosaurs was not diachronous (but see Irmis et al., 2011).


Ramezani, J., Hoke, G. D., Fastovsky, D. E., Bowring, S. A., Therrien, F., Dworkin, S. I., Atchley, S. C., and L. C. Nordt. 2011. High-precision U-Pb zircon geochronology of the Late Triassic Chinle Formation, Petrified Forest National Park (Arizona, USA): Temporal constraints on the early evolution of dinosaurs. Geological Society of America Bulletin. First published online August 19, 2011, doi: 10.1130/B30433.1 

Abstract - The Triassic successions of the Colorado Plateau preserve an important record of vertebrate evolution and climate change, but correlations to a global Triassic framework are hampered by a lack of geochronological control. Tuffaceous sandstones and siltstones were collected from the Upper Triassic Chinle Formation exposed in the Petrified Forest National Park, Arizona, USA, within a refined stratigraphic context of 31 detailed measured sections. U-Pb analyses by the isotope dilution–thermal ionization mass spectrometry (ID-TIMS) method constrain maximum depositional ages for nine tuffaceous beds and provide new insights into the depositional history of the Chinle fluvial system. The base of the Blue Mesa Member of the Chinle Formation is placed at ca. 225 Ma, and the top of the Petrified Forest Member is placed at 208 Ma or younger, bracketing an ∼280-m-thick section that spans nearly the entire Norian Stage of the Late Triassic. Estimated sediment accumulation rates throughout the section reflect extensive hiatuses and/or sediment removal by channel erosion. The new geochronology for the Chinle Formation underscores the potential pitfalls of correlation of fluvial units based solely on lithostratigraphic criteria. A mid-Norian age (ca. 219–213 Ma) for the distinctive Sonsela conglomeratic sandstone bed constrains the Adamanian-Revueltian land vertebrate faunachron boundary. Our new data permit a significant time overlap between the lower Chinle sequence and the dinosauromorph-rich Ischigualasto Formation of northwestern Argentina. Near-contemporaneity of the trans-American deposits and their faunal similarities imply that early dinosaur evolution occurred rapidly across the Americas.

How I May Be In advertantly Warping My Student Interns Minds....

Here is a picture of the last two pages in 2011 summer paleo intern Susan Drymala's field notebook.


I know I told her she should take good notes, but I didn't know she was writing EVERYTHING down ;).

Diodorus scytobrachion, A New Silesaurid from the Late Triassic of Morocco


I've had this paper in the queue for a bit as I still don't like the idea of online publishing of new taxon names at the "accepted manuscript" stage, but the knowledge of this proposed new taxon is increasingly widespead so I'll post the abstract and link here now. Silesaurids are amazingly cosmopolitan in their distribution and must have been significant members of various Triassic ecosystems, most likely filling the role later occupied by ornithischians.


I'm a big fan of the creative taxonomic name as well.


Kammerer, C. F., Nesbitt, S. J., and N. H. Shubin. In press. The first basal dinosauriform (Silesauridae) from the Late Triassic of Morocco. Acta Palaeontologica Polonica. doi: 10.4202/app.2011.0015


Abstract - Disarticulated material from the Late Triassic Timezgadiouine Formation in the Argana Basin of Morocco represents a new taxon of silesaurid dinosauromorph,
Diodorus scytobrachion gen. et sp. nov. D. scytobrachion can be distinguished from other silesaurids by the presence of anteriorly-canted teeth that decrease in size towards the anterior end of the dentary and a distinct lateral ridge running parallel to the dentary alveolar margin. In a phylogenetic analysis, D. scytobrachion is recovered as the sister taxon to the Brazilian Sacisaurus agudoensis, nested deep within Silesauridae. This new taxon provides further evidence of a near-cosmopolitan range for basal dinosauriforms in the Late Triassic and further demonstrates the disparity of dental morphologies within Silesauridae.

Smok wawelski, a New Late Triassic Archosaur from Poland

Interesting critter if all the material belongs to the same animal (and I can't see any reason right now why it wouldn't). The broadly expanded basisphenoid appears to be particularily autapomorphic. Taxonomically I'm going to put my bet on a fairly derived paracrocodylomorph, especially because the supratemporal fossa incises the posterior margin of the frontal; however, the presence of a postfrontal suggests it is not a crocodylomorph. I'll refrain from plugging this taxon into the Nesbitt (2011) matrix as the authors clearly state that the phylogenetic relationships are part of Grzegorz Niedźwiedzki's PhD project.

I do have a question regarding the specific name. If the specific name intends "from Wawel Hill" should the correct name be Smok wawelensis or maybe S. wawelhillensis? As I have stated before I don't think it is the best idea for new taxon names to be published online in accepted manuscript form because the authors may decide to change the name or modify it before final publication.

Niedźwiedzki, G., Sulej, T., and J. Dzik. in press A large predatory archosaur from the Late Triassic of Poland. Acta Palaeontologica Polonica. doi:10.4202/app.2010.0045

Abstract - 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.


High-resolution U-Pb ages from the Chinle Formation with a Stratigraphic Revision of the Chinle and Support for the Diachronous Rise of Dinosaurs

This is the full paper providing two new radioisotopic ages for Chinle Formation strata in New Mexico. One for the purported base of the Blue Mesa Member (thus a basal Chinle age constraint) from Six Mile Canyon in New Mexico, and the other from the younger Hayden Quarry, which has produced a number of new dinosauromorphs including the type specimens of Dromomeron romeri and Tawa hallae (Irmis et al., 2007; Nesbitt et al., 2009). Although the Blue Mesa date has been widely cited these have previously only appeared in abstract form (Irmis & Mundil, 2008, 2010).

Jeff's and my contribution to this paper is mainly a revised hypothesis of stratigraphic relationships of units in the lower part of the Chinle Formation based on several years of detailed fieldwork in Arizona, Utah, and New Mexico. Our revised correlations demonstrate that the date from Six Mile Canyon is more likely from strata from the uppermost part of the Blue Mesa Member (Chinle Formation) type section in Petrified Forest National Park (PEFO), and not from the base of the unit as previously supposed. Therefore this date is from stratigraphically younger rocks than previously believed. We also argue that the lower part of the Blue Mesa Member type section at PEFO is equivalent to the Bluewater Creek Member in New Mexico and northeastern Arizona, and that the Bluewater Creek is not directly equivalent to the Mesa Redondo Member. Instead we argue that the Mesa Redondo Member is mainly a lateral equivalent of the Shinarump Member. These are novel hypotheses that we have much supporting data for and we hope to have a full manuscript detailing these revised correlations prepared in the near future.

Irmis, R. B., Mundil, R., Martz, J. W., and W. G. Parker. 2011. High-resolution U-Pb ages from the Upper Triassic Chinle Formation (New Mexico, USA) support a diachronous rise of dinosaurs. Earth and Planetary Science Letters [advance online publication]. doi:10.1016/j.epsl.2011.07.015

Abstract - Though the Late Triassic preserves major paleoenvironmental fluctuations and is key for understanding the evolution of Mesozoic and modern terrestrial ecosystems, comparisons of Late Triassic non-marine sedimentary and fossil records are difficult because global correlations lack precise radioisotopic ages, and have instead been based upon unconstrained biostratigraphic ranges of palynomorph and vertebrate fossils. The Chinle Formation in southwestern North America preserves a major Late Triassic record of paleoenvironmental and biotic change, including significant early dinosaur fossils. Previous high-resolution radioisotopic age constraints for the formation are limited to a single U-Pb zircon age from the upper third of the formation. The extraction of a geologically meaningful age is challenging from these redeposited units and preference is given to considering the youngest age of a deposit as a maximum age and closest approximation of the depositional age. Because calculating a weighted mean age (or median age) from a group of ages from such deposits is often not adequate, the precision of our two new CA-TIMS single crystal zircon U-Pb ages from the Chinle Formation of New Mexico is limited to ca 0.3% (or ± 0.7 Ma) of the youngest crystal age. Our 206Pb/238U age of ~ 218 Ma from the Blue Mesa Member in Six Mile Canyon, western New Mexico, demonstrates that strata, palynomorphs, and vertebrate fossils previously considered to be late Carnian in age are actually middle Norian in age. Our new age of ~212 Ma from the Hayden Quarry within the Petrified Forest Member at Ghost Ranch, northern New Mexico, provides the first maximum age for important vertebrate assemblages from this area that record the rise of dinosaurs, and demonstrates that basal dinosauromorphs (‘dinosaur precursors’) co-existed with dinosaurs for at least 18 Ma. These new radioisotopic data allow a new correlation of the Chinle Formation to the Late Triassic timescale, suggesting that most if not all of the lower Chinle is Norian in age. This new correlation has global implications as it allows us to make more precise comparisons with early dinosaur assemblages from the Ischigualasto Formation of Argentina, indicating that Chinle dinosaur assemblages are significantly younger than those from South America. The revised age of the Chinle Formation also demonstrates that dinosaurs were much rarer in North America at a time when they were abundant in South
America, supporting hypotheses of paleolatitudinal variation during the
rise of dinosaurs.

REFERENCES

Irmis, R., Mundil, R., 2008. New age constraints from the Chinle Formation revise global comparisons of Late Triassic vertebrate assemblages. J. Vertebr. Paleontol. 28, 95A(Suppl.).

Irmis, R.B., Mundil, R., 2010. New U–Pb zircon ages from the Chinle Formation (western US) revise understanding of Late Triassic terrestrial vertebrate evolution. Geol. Soc. Am. Abstracts Prog. 42, 393.

Irmis, R.B., Nesbitt, S.J., Padian, K., Smith, N.D., Turner, A.H., Woody, D., Downs, A., 2007. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science 317, 358-361.

Nesbitt, S.J., Smith, N.D., Irmis, R.B., Turner, A.H., Downs, A., Norell, M.A., 2009. A complete skeleton of a Late Triassic saurischian and the early evolution of dinosaurs. Science 326, 1530–1533.

Viviparity and Possible Maternal Care in Mesozoic Marine Reptiles

Not Triassic but too potentially cool to pass up....

O'Keefe, F. R., and L. M. Chiappe. 2011. Viviparity and K-Selected Life History in a Mesozoic Marine Plesiosaur (Reptilia, Sauropterygia). Science 333:870-873. DOI: 10.1126/science.1205689

Abstract - Viviparity is known in several clades of Mesozoic aquatic reptiles, but evidence for it is lacking in the Plesiosauria. Here, we report a Late Cretaceous plesiosaur fossil consisting of a fetus preserved within an adult of the same taxon. We interpret this occurrence as a gravid female and unborn young and hence as definitive evidence for plesiosaur viviparity. Quantitative analysis indicates that plesiosaurs gave birth to large, probably single progeny. The combination of viviparity, large offspring size, and small brood number differs markedly from the pattern seen in other marine reptiles but does resemble the K-selected strategy of all extant marine mammals and a few extant lizards. Plesiosaurs may have shared other life history traits with these clades, such as sociality and maternal care.

The Bristol Dinosaur Project Featuring Thecodontosaurus

Benton, M. J., Schouten. R., Drewitt, E. J. A., and P. Viegas. in press. The Bristol dinosaur project. Proceedings of the Geologist's Association. doi:10.1016/j.pgeola.2011.07.004

Abstract - Dinosaurs have been fascinating to the widest public since the 1840s, and that interest has grown step-wise ever since. Public interest has been harnessed over the years especially by museums in blockbuster exhibitions, and in the form of best-selling books and films. Here we describe a major educational initiative, the Bristol Dinosaur Project, which has run for ten years and has reached tens of thousands of children and adults, supported by substantial funding. The Bristol Dinosaur Project focuses on the fourth dinosaur ever named in the world, Thecodontosaurus, discovered in Bristol in 1834, and named in 1836. The dinosaur is not in itself spectacular, being only 1–2 m long, but its evolutionary role as one of the first plant-eating dinosaurs in the world justifies our current research, and provides a strong theme for the public presentation. Further, the fact that the dinosaur is found as disarticulated bones in ancient tropical cave systems, allows us to develop numerous key themes with all age groups: the geological time scale, continental drift, reconstruction of ancient environments, modern landscape analogues, the rock cycle, evolution, biomechanics, and critical assessment of geological and palaeontological evidence. These themes are of key importance for socio-economic and intellectual reasons, and yet are often poorly understood.

Middle Triassic Tetrapod from the Dead Sea Region of the Middle East

Schoch, R. R. 2011. A trematosauroid temnospondyl from the Middle Triassic of Jordan. Fossil Record 14:119–127 DOI: 10.1002/mmng.201100002

Abstract - A well-preserved mandible from the Lower Anisian Mukheiris Formation from near the Dead Sea (Jordan) proves the presence of tetrapods in the region. It is identified as a stereospondyl lower jaw sharing synapomorphies with the Trematosauroidea. It has the following combination of features: (1)Meckelian fenestra almost one-third the length of the ramus, (2) postglenoid area posterodorsally rising and robust, as long as glenoid facet, (3) preglenoid process substantially higher than medial margin of adductor chamber, (4) all teeth anteriorly and posteriorly carinate, and (5) symphysis without additional tooth rows, with a pair of unequal fangs as part of the dentary arcade, which contains unusually large teeth. The Jordan specimen shares most character-states with South African Microposaurus (size of teeth, bicarinate structure) and the Russian Inflectosaurus (preglenoid process, PGA). Phylogenetic analysis finds it to nest with Microposaurus, whereas Inflectosaurus forms an unresolved polytomy with other trematosauroids.

Evolution of the Dinosauriform Respiratory Apparatus: New Evidence from the Postcranial Axial Skeleton

Schachner, E. R., Farmer, C. G., McDonald, A. T., and P. Dodson. 2011. Evolution of the dinosauriform respiratory apparatus: new evidence from the postcranial axial skeleton. The Anatomical Record Early View. DOI: 10.1002/ar.21439

Abstract -
Examination of the thoracic rib and vertebral anatomy of extant archosaurs indicates a relationship between the postcranial axial skeleton and pulmonary anatomy. Lung ventilation in extant crocodilians is primarily achieved with a hepatic piston pump and costal rotation. The tubercula and capitula of the ribs lie on the horizontal plane, forming a smooth thoracic ‘‘ceiling’’ facilitating movement of the viscera. Although the parietal pleura is anchored to the dorsal thoracic wall, the dorsal visceral pleura exhibits a greater freedom of movement. The air sac system and lungs of birds are associated with bicapitate ribs with a ventrally positioned capitular articulation, generating a rigid and furrowed rib cage that minimizes dorsoventral changes in volume in the dorsal thorax. The thin walled bronchi are kept from collapsing by fusion of the lung to the thorax on all sides. Data from this study suggest a progression from a dorsally rigid, heterogeneously partitioned, multichambered lung in basal dinosauriform archosaurs towards the small entirely rigid avian-style lung that was likely present in saurischian dinosaurs, consistent with a constant volume cavum pulmonale, thin walled parabronchi, and distinct air sacs. There is no vertebral evidence for a crocodilian hepatic piston pump in any of the taxa reviewed. The evidence for both a rigid lung and unidirectional airflow in dinosauriformes raises the possibility that these animals had a highly efficient lung relative to other Mesozoic vertebrates, which may have contributed to their successful radiation during this time period.