Silesaurid-Herrerasaurid-Neotheropod Assemblage from the Late Triassic of Poland

This is currently free from the Palaeontology Online website.

Niedźwiedzki, G., Brusatte, S. L., Sulej, T., and R. J. Butler. 2014. Basal dinosauriform and theropod dinosaurs from the mid–late Norian (Late Triassic) of Poland: implications for Triassic dinosaur evolution and distribution. Palaeontology 57(6): 1121–1142 DOI: 10.1111/pala.12107
 
Abstract - The rise of dinosaurs during the Triassic is a widely studied evolutionary radiation, but there are still many unanswered questions about early dinosaur evolution and biogeography that are hampered by an unevenly sampled Late Triassic fossil record. Although very common in western North America and parts of South America, dinosaur (and more basal dinosauriform) remains are relatively rare in the Upper Triassic deposits of Europe, making any new discoveries critically important. One of the most diverse dinosauriform assemblages from Europe comes from the Poręba site in Poland, a recently described locality with exposures of the Zbąszynek Beds, which have a palynomorph assemblage characteristic for the mid–late Norian in the biostratigraphic schemes of the Germanic Basin. Using a synapomorphy-based approach, we evaluate several isolated dinosauriform specimens from Poręba. This assemblage includes a silesaurid, a herrerasaurid and remains of another type of theropod (potentially a neotheropod). The Poręba herrerasaurid is the first record of this rare group of primitive dinosaurs from Europe and one of the youngest records worldwide, whereas the silesaurid is the youngest record of a silesaurid from Europe. These findings indicate that silesaurids persisted alongside true dinosaurs into the mid–late Norian of Europe and that silesaurid–herrerasaurid–neotheropod assemblages (which are also known from the Norian of North America, at low latitudes) were more widespread geographically and latitudinally than previously thought. Silesaurid–herrerasaurid–neotheropod assemblages may have been a common ecological structuring of dinosaurs during their early evolution, and their widespread distribution may indicate weak palaeolatitudinal controls on early dinosaur biogeography during the latest Triassic.

Large Body Size in Non-dinosaurian Dinosauromorphs - Evidence from a Large Silesaurid from Late Triassic of Tanzania

Barrett, P. M., Nesbitt, S. J., and B. R. Peecook. 2014. A large-bodied silesaurid from the Lifua Member of the Manda beds (Middle Triassic) of Tanzania and its implications for body-size evolution in Dinosauromorpha. Gondwana Research (accepted manuscript). http://dx.doi.org/10.1016/j.gr.2013.12.015

Abstract - Many dinosaur lineages were characterised by wide ranges of body-size, ranging from taxa that were <1 m in length to the largest of all terrestrial vertebrates. On the other hand, the closest relatives of dinosaurs, the non-dinosaurian dinosauromorphs, such as Marasuchus and lagerpetids, were small-bodied animals with little variation in body-size. Here, we describe a partial femur of an unexpectedly large-bodied silesaurid (non-dinosaurian dinosauriform) from the Lifua Member of the Manda beds (?late Anisian) from southwestern Tanzania. This specimen (NHMUK R16303) is estimated to have had a femoral length of approximately 345 mm, which exceeds that of many Triassic and Lower Jurassic dinosaurs, and is either a large individual of the contemporary Asilisaurus kongwe or represents a new and otherwise unknown silesaurid taxon. In either case, it shows that body-size increases were more prevalent among early dinosauromorphs than realised previously. Moreover, silesaurid size increase occurred in parallel with that in early dinosaurs, alongside the convergent acquisition of other features related to locomotion and herbivory. However, Late Triassic faunas including large-bodied sauropodomorph and theropod dinosaurs lack similarly-sized non-dinosaurian dinosauromorphs, whereas the Lifua Member fauna includes both a large silesaurid and the early ?dinosaur Nyasasaurus, which overlapped in size.

Osteology of Eoraptor lunensis

Finally this is published. Now if I can just get the Revueltosaurus monograph out all will be right in the Triassic world, right?

Sereno, P. C., Martínez, R. N.,  and  O. A. Alcober. 2013. Osteology of Eoraptor lunensis (Dinosauria, Sauropodomorpha). Journal of Vertebrate Paleontology Memoir 12:83-179.

Abstract - We describe the basal sauropodomorph Eoraptor lunensis, based on the nearly complete holotypic skeleton and referred specimens, all of which were discovered in the Cancha de Bochas Member of the Ischigualasto Formation in northwestern Argentina. The lightly built skull has a slightly enlarged external naris and a spacious antorbital fossa with a prominent, everted dorsal margin and internal wall lacking any pneumatic extensions into surrounding bones. The tall quadrate is lapped along its anterior margin by the long, slender ventral process of the squamosal, and the lower jaw has a mid-mandibular joint between a tongue-shaped splenial process and a trough in the angular. All but the posterior-most maxillary and dentary crowns have a basal constriction, and the marginal denticles are larger and oriented more vertically than in typical theropod serrations. Rows of rudimentary palatal teeth are present on the pterygoid. Vertebral centra are hollow, although not demonstrably pneumatized,and all long bones have hollow shafts. The radius and ulna are more robust, the manus proportionately shorter, and the manual unguals less recurved than in the contemporaneous basal theropod Eodromaeus murphi. An outstanding feature of the manus of Eoraptor is the twisted shaft of the first phalanx of the pollex, which deflects medially the tip of the ungual as in basal sauropodomorphs. The long bones of the hind limb have more robust shafts than those of Eodromaeus, although in both genera the tibia remains slightly longer than the femur.

Resumen - Describimos el sauropodomorfo basal Eoraptor lunensis basados en el esqueleto prácticamente completo del holotipo y especímenes referidos, todos ellos descubiertos en el Miembro Cancha de Bochas de la Formaci ón Ischigualasto, en el noroeste de Argentina. El grácil cráneo tiene las narinas externas ligeramente agrandadas, una amplia fosa antorbital con un margen dorsal prominente y evertido, y ausencia de extensiones neumáticas en los huesos circundantes. El alto cuadrado presenta todo su margen anterior solapado por el delgado proceso ventral del escamoso y la mandíbula tiene una junta medial entre un proceso linguoide del esplenial y un canal en el angular. Todas las coronas dentarias y maxilares, menos las más posteriores, tienen una constricci ón basal y los dentículos marginales son largos y orientados más verticalmente que en el aserrado típico de los terópodos. El pterigoideo tiene filas de dientes palatales rudimentarios. Los centros de las vértebras son huecos, aunque no demostrablemente neumatizados, y todos los huesos largos tienen las di íafisis huecas. El radio y la ulna son más robustos, la mano proporcionalmente corta y los ungueales manuales menos recurvados que en el contemporáneo terópodo basal Eodromaeus murphi. Una característica sobresaliente de la mano de Eoraptor es la rotaci ón de la primera falange del pulgar, que desvía medialmente la punta del ungueal como en los sauropodomorfos basales. Los huesos largos de las piernas tienen di áfisis más robustas que aquellas de Eodromaeus, aunque en ambos géneros la tibia es ligeramente más larga que el fémur.

Evolution of Bipedality and Herbivory Among Triassic Dinosauromorphs

Note that this paper is in Japanese with an English version of the abstract.

Kubo, T. 2011. Evolution of bipedality and herbivory among Triassic dinosauromorphs. Memoir of the Fukui Prefectural Dinosaur Museum 10:55－62．

Abstract - Discoveries of Triassic non-dinosaur dinosauromorphs since 2000 revealed that they were more widely spread chronologically and geographically than previously thought. A member of silesaurids, the sister clade of dinosaurs, Silesaurus was a quadrupedal and herbivorous animal that differs considerably from the condition previously assumed for the ancestor of dinosaurs that are bipedal and carnivorous. Currently, stance and diet of the common ancestor of dinosaurs are not clear. To redeem this situation, Ancestral State Reconstruction methods were conducted to infer how quadrupedality and herbivory were evolved among dinosauromorphs. The results of analyses indicate that quadrupedal stance evolved only among silesaurids. Herbivorous diet was readily evolved from carnivorous diet among Dinosauromorpha and the ancestral state reconstruction using likelihood methods indicated that the possibility of the common ancestor of dinosaurs being herbivore is more than 60%.

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.

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.

A Late Triassic Vertebrate Paleontology Extravaganza - ‘Late Triassic Terrestrial Biotas and the Rise of Dinosaurs’ Special Issue

It's out. The special volume in Earth and Environmental Science Transactions of the Royal Society of Edinburgh on Late Triassic Terrestrial Biotas and the Rise of Dinosaurs. These papers stem from the Society of Vertebrate Paleontology Symposium at the 2009 annual meeting in Bristol, U. K.  I've included a list of the papers and their abstracts below. There is an amazing amount of information here on Late Triassic vertebrates and early dinosaurs.  It will take me awhile to get through the papers, but for now I'd like to say it is an honor to be included in this volume.  I think Randy, Richard, Max, and the staff of EESTRSE did an excellent job in the production of this volume and I hope everyone who has an interest in Late Triassic terrestrial biotas enjoys the volume and finds the papers interesting and useful.

Issue cover featuring artwork by Jeff Martz.

Table of Contents - Volume 101 - Special Issue 3-4 (Late Triassic Terrestrial Biotas and the Rise of Dinosaurs)

1) Butler, R. J., Irmis, R. B., and M. C. Langer. Preface to ‘Late Triassic Terrestrial Biotas and the Rise of Dinosaurs’ Special Issue.

Abstract - The early Mesozoic records an important transition in the history of the Earth’s terrestrial ecosystems. As they recovered from the largest known mass extinction (the end-Permian event), organisms in these ecosystems transitioned to new forms that eventually evolved into the classic Mesozoic biotas, and laid the foundations for many groups still flourishing today (Fraser 2006; Irmis & Whiteside 2010; Sues & Fraser 2010). All of this was set against a backdrop of dynamic climatic and physical events that shaped these biotas. This early Mesozoic terrestrial transition reached its culmination in many ways during the Late Triassic, when ecosystems had largely recovered from the end-Permian extinction, but had not yet been affected by the end-Triassic mass extinction (Fraser & Sues this volume). Thus, we see a combination of taxa, with some groups that would not survive the end of the Triassic living alongside early representatives of lineages that flourished later in the Mesozoic (e.g., Fraser 2006; Irmis et al. 2007; Brusatte et al. 2008; Sues & Fraser 2010, this volume) and in some cases are still diverse today. Just one example of this transition, recorded during the Late Triassic, is the origin and diversification of non-avian dinosaurs, the iconic representatives of Mesozoic terrestrial ecosystems (Brusatte et al. 2010; Langer et al. 2010). Although small and rare components of their respective biotas when they first evolved ∼231 Ma, dinosaurs were abundant and had a near-worldwide distribution by the beginning of the Jurassic Period (∼201·3 Ma).

2) Fraser, N. C., and H. D. Sues. The beginning of the ‘Age of Dinosaurs’: a brief overview of terrestrial biotic changes during the Triassic.

Abstract - The first appearance of dinosaurs during the early Late Triassic coincided with marked faunal changes in terrestrial ecosystems. Most of the major groups of extant tetrapods (or their proximate sister-taxa), including mammaliaforms, crocodyliform archosaurs, lepidosaurs and turtles, also first appeared in the fossil record during the Late Triassic. On the other hand, a number of Palaeozoic ‘holdovers’, such as procolophonid parareptiles, dicynodont therapsids and many groups of temnospondyls, vanished near or at the end of the Triassic. The tempo and mode of this faunal turnover have long been debated, but there has been growing acceptance of a rather sudden event, although the precise dating of such an event remains controversial. However, new discoveries have cast doubt on this assumption. The persistence of non-dinosaurian dinosauromorphs alongside dinosaurs well into Norian times hints at a more protracted turnover. New data on Triassic insect assemblages indicate that turnover among insects may also have been more protracted and possibly not co-incident with the faunal changes among tetrapods. Future work directed toward improved absolute age assessments for major faunal assemblages will be critical for a better understanding of the transition from therapsid-dominated to dinosaur-dominated communities during the early Mesozoic.

3) Olsen, P. E., Kent, D. V., and J. H. Whiteside. Implications of the Newark Supergroup-based astrochronology and geomagnetic polarity time scale (Newark-APTS) for the tempo and mode of the early diversification of the Dinosauria.

Abstract - The Newark-APTS established a high-resolution framework for the Late Triassic and Early Jurassic. Palaeomagnetic polarity correlations to marine sections show that stage-level correlations of continental sequences were off by as much as 10 million years. New U–Pb ages show the new correlations and the Newark basin astrochronology to be accurate. Correlation of Newark-APTS to the Chinle Formation/Dockum Group, Glen Canyon Group, Fleming Fjord Formation and Ischigualasto Formation led to the following conclusions: (1) there are no unequivocal Carnian-age dinosaurs; (2) the Norian Age was characterised by a slowly increasing saurischian diversity but no unequivocal ornithischians; (3) there was profound Norian and Rhaetian continental provinciality; (4) the classic Chinle-, Germanic- and Los Colorados-type assemblages may have persisted to the close of the Rhaetian; (5) the distinct genus-level biotic transition traditionally correlated with the marine Carnian–Norian is in fact mid-Norian in age and within published error of the Manicouagan impact; (6) the end-Triassic marine and continental extinctions as seen in eastern North America were contemporaneous; and (7) compared to Triassic communities, Hettangian and Sinemurian age terrestrial communities were nearly globally homogenous and of low diversity. Consequently, the complex emerging picture of dinosaur diversification demands biostratigraphically-independent geochronologies in each of the faunally-important regions.

4) Parker, W. G., and J. W. Martz. The Late Triassic (Norian) Adamanian–Revueltian tetrapod faunal transition in the Chinle Formation of Petrified Forest National Park, Arizona.

Abstract - Recent stratigraphic revisions of the Upper Triassic Chinle Formation of Petrified Forest National Park, in conjunction with precise and accurate documentation of fossil tetrapod occurrences, clarified the local biostratigraphy, with regional and global implications. A significant overlap between Adamanian and Revueltian faunas is rejected, as is the validity of the Lamyan sub-land vertebrate faunachron. The Adamanian–Revueltian boundary can be precisely placed within the lower Jim Camp Wash beds of the Sonsela Member and thus does not occur at the hypothesised Tr-4 unconformity. This mid-Norian faunal turnover, may coincide with a floral turnover, based on palynology studies and also on sedimentological evidence of increasing aridity. Available age constraints bracketing the turnover horizon are consistent with the age of the Manicouagan impact event. The rise of dinosaurs in western North America did not correspond to the Adamanian–Revueltian transition, and overall dinosauromorph diversity seems to have remained at a constant level across it. The paucity of detailed Late Triassic vertebrate biostratigraphic data and radioisotopic dates makes it currently impossible to either support or reject the existence of globally synchronous Late Triassic extinctions for tetrapods.

5) Sulej, T., Bronowicz, R., Tałanda, M., and G. Niedźwiedzki. A new dicynodont–archosaur assemblage from the Late Triassic (Carnian) of Poland.

Abstract - This paper reports a new assemblage from the Late Triassic (mid–late Carnian) at Woźniki near Częstochowa (Poland). The Woźniki vertebrate assemblage is similar to that of Lisowice–Lipie Śląskie, a new locality bearing vertebrates from latest Triassic (latest Norian–early Rhaetian) strata of southern Poland, in the presence of dicynodonts, shark spines, plagiosaurs and a cyclotosaur, but conchostracans and bivalves are similar to those from the Krasiejów site (late Carnian). The most complete specimen from Woźniki belongs to a dicynodont, and consists of cranial and postcranial bones of a single individual. It demonstrates that large dicynodonts were part of the Late Triassic vertebrate assemblage in Central Europe. Numerous tetrapod tracks and traces are associated with skeletal fossils at Woźniki.

6) Nesbitt, S. J., Liu, J., and C. Li. A sail-backed suchian from the Heshanggou Formation (Early Triassic: Olenekian) of China.

Abstract - The two major lineages of extant archosaurs, crocodylians and avians, diverged in the Triassic, but the details and timing of this event are incompletely understood. Fragmentary and phylogenetically uninformative specimens, in addition to poor temporal constraints on rock units from the Early and Middle Triassic, typify obstacles in identifying early archosaurs. This paper re-describes the partial skeleton of the only known specimen of Xilousuchus sapingensis Wu, 1981 from the Early Triassic Heshanggou Formation in north-central China. Originally assigned to the non-archosaurian archosauriform clade Proterosuchidae, an extensive phylogenetic analysis posits X. sapingensis as a crown-group archosaur within Suchia, thus making this taxon the unequivocally oldest known member of Archosauria. The age and phylogenetic position of X. sapingensis indicate that many archosaurs, including all major clades of non-archosaurian archosauriforms, the avianline, ornithosuchids, aetosaurs and paracrocodylomorph lineages, must have diverged by the end of the Early Triassic. X. sapingensis is part of a possible clade of sail-backed poposauroids that were common components of archosaur assemblages during the Early to Middle Triassic.

7) Benton, M. J., and A. D. Walker. Saltopus, a dinosauriform from the Upper Triassic of Scotland.

Abstract - Saltopus elginensis, reported in 1910 from the yellow sandstones of the Lossiemouth Sandstone Formation (Late Triassic) of Morayshire, NE Scotland, has long been controversial. It was described first as a theropod dinosaur, but others disagreed. Reanalysis of the type, and only, specimen using casts from the natural rock moulds, as well as X-rays and CT scans, has revealed new anatomical data not available to previous researchers. Saltopus was a small, 800–1000 mm-long biped, whose tail made up more than half its length. It is an avemetatarsalian because it has elongated and tightly bunched metatarsals, the tibia is longer than the femur, the calcaneal tuber is rudimentary or absent, and metatarsal II is equal to or longer than metatarsal IV; a unique assemblage of characters diagnosing this clade. Saltopus is a dinosauromorph on the basis of the reduced fingers IV and V, the saddle-shaped dorsal margin of the iliac blade, and the articulation of sacral rib 1 close to the front of the iliac blade. Saltopus is a dinosauriform on the basis of the trochanteric shelf and lesser trochanter on the proximal end of the femur, the waisted sacral ribs, and perhaps the rod-like and straight pubis. However, it lacks all apomorphies of Dinosauria, retaining for example the primitive condition of two sacral vertebrae. Cladistic analyses place Saltopus within Dinosauromorpha and Dinosauriformes, and between the basal dinosauriform Pseudolagosuchus and the derived clade consisting of Silesauridae and Dinosauria, so making it one of a radiation of small pre-dinosaurian bipedal archosaurs in the Triassic found so far in North and South America and in Europe.

8) Langer, M. C., Bittencourt, J. S., and C. L. Schultz. A reassessment of the basal dinosaur Guaibasaurus candelariensis, from the Late Triassic Caturrita Formation of south Brazil.

Abstract - The dinosaur record of the Santa Maria beds of Rio Grande do Sul (Mid–Late Triassic; south Brazil) includes the herrerasaur Staurikosaurus pricei, and two basal members of the sauropodomorph lineage: Saturnalia tupiniquim and Unaysaurus tolentinoi. The most enigmatic of the saurischian taxa is, however, Guaibasaurus candelariensis, previously regarded as either a basal theropod or a basal sauropodomorph. This study provides a detailed anatomical revision of all specimens originally referred to G. candelariensis by Bonaparte and co-authors, including its type-series and a more recently excavated partial postcranium. Although coming from different sites, these specimens share a unique combination of traits, and at least one possible autapomorphic feature of the pelvis, which support the inclusivity and uniqueness of the species. G. candelariensis was a medium-sized (nearly 2 m long) biped with an intriguing mix of plesiomorphic and derived (eusaurischian/theropod) features. Phylogenetic studies reveal weak support for the nesting of G. candelariensis within Theropoda, but this affinity is bolstered by various traits it shares with neotheropods. The Norian age of G. candelariensis corroborates previous studies that suggest the continuous radiation of more basal dinosauromorphs until the end of the Triassic, after the appearance of the three main dinosaur clades.

9) Novas, F. E., Ezcurra, M. D., Chatterjee, S., and T. S. Kutty. New dinosaur species from the Upper Triassic Upper Maleri and Lower Dharmaram formations of Central India.

Abstract - The beginning of dinosaur evolution is currently known based on a handful of highly informative Gondwanan outcrops of Ischigualastian age (late Carnian–early Norian). The richest Triassic dinosaur records of the southern continents are those of South America and South Africa, with taxonomically diverse faunas, whereas faunas from India and central Africa are more poorly known. Here, the known diversity of Gondwanan Triassic dinosaurs is increased with new specimens from central India, which allow a more comprehensive characterisation of these dinosaur assemblages. Five dinosauriform specimens are reported from the probable late Norian–earliest Rhaetian Upper Maleri Formation, including two new sauropodomorph species, the non-plateosaurian Nambalia roychowdhurii and the plateosaurian Jaklapallisaurus asymmetrica, a guaibasaurid and two basal dinosauriforms. The Lower Dharmaram Formation, probably latest Norian–Rhaetian in age, includes basal sauropodomorph and neotheropod remains, providing the second record of a Triassic Gondwanan neotheropod. The currently available evidence suggests that the oldest known Gondwanan dinosaur assemblages (Ischigualastian) were not homogeneous, but more diverse in South America than in India. In addition, the Upper Maleri and Lower Dharmaram dinosaur assemblages resemble purported coeval South American and European beds in the presence of basal sauropodomorphs. Accordingly, the current available evidence of the Triassic beds of the Pranhita–Godavari Basin suggests that dinosaurs increased in diversity and abundance during the late Norian to Rhaetian in this region of Gondwana.

10) Porro, L. B., Butler, R. J., Barrett, P. M., Moore-Fay, S., and R. L. Abel. New heterodontosaurid specimens from the Lower Jurassic of southern Africa and the early ornithischian dinosaur radiation.

Abstract - Heterodontosaurids are poorly understood early ornithischian dinosaurs with extensive geographic and stratigraphic ranges. The group is best known from the Lower Jurassic upper ‘Stormberg Group’ (upper Elliot and Clarens formations) of southern Africa, previously represented by at least three distinct species and ten described specimens. This paper describes four additional heterodontosaurid specimens from southern Africa. A partial skull of a large individual of Heterodontosaurus tucki (NM QR 1788) is approximately 70 longer than that of the type specimen of Heterodontosaurus, and provides new information on allometric changes in mandibular morphology during growth in this taxon. It is the largest known heterodontosaurid cranial specimen, representing an individual approximately 1·75 metres in length, and perhaps 10 kg in body mass. NHMUK R14161 is a partial skull that appears to differ from all other heterodontosaurids on the basis of the proportions of the dentaries, and may represent an unnamed new taxon. Two additional partial skulls (NHMUK RU C68, NHMUK RU69) are referred to cf. Lycorhinus. At least four, and possibly five or more, heterodontosaurid species are present in the upper ‘Stormberg’. This high diversity may have been achieved by dietary niche partitioning, and suggests an adaptive radiation of small-bodied ornithischians following the end Triassic extinctions.

11) Brusatte, S. L., Benton, M. J., Lloyd, G. T., Ruta, M., and S. C. Wang. Macroevolutionary patterns in the evolutionary radiation of archosaurs (Tetrapoda: Diapsida).

Abstract - The rise of archosaurs during the Triassic and Early Jurassic has been treated as a classic example of an evolutionary radiation in the fossil record. This paper reviews published studies and provides new data on archosaur lineage origination, diversity and lineage evolution, morphological disparity, rates of morphological character change, and faunal abundance during the Triassic–Early Jurassic. The fundamental archosaur lineages originated early in the Triassic, in concert with the highest rates of character change. Disparity and diversity peaked later, during the Norian, but the most significant increase in disparity occurred before maximum diversity. Archosaurs were rare components of Early–Middle Triassic faunas, but were more abundant in the Late Triassic and pre-eminent globally by the Early Jurassic. The archosaur radiation was a drawn-out event and major components such as diversity and abundance were discordant from each other. Crurotarsans (crocodile-line archosaurs) were more disparate, diverse, and abundant than avemetatarsalians (bird-line archosaurs, including dinosaurs) during the Late Triassic, but these roles were reversed in the Early Jurassic. There is no strong evidence that dinosaurs outcompeted or gradually eclipsed crurotarsans during the Late Triassic. Instead, crurotarsan diversity decreased precipitously by the end-Triassic extinction, which helped usher in the age of dinosaurian dominance. 



12) Barrett, P. M., Butler, R. J., and S. J. Nesbitt. The roles of herbivory and omnivory in early dinosaur evolution.

Abstract - Herbivorous and omnivorous dinosaurs were rare during the Carnian stage of the Late Triassic. By contrast, the succeeding Norian stage witnessed the rapid diversification of sauropodomorphs and the rise of the clade to ecological dominance. Ornithischians, by contrast, remained relatively rare components of dinosaur assemblages until much later in the Mesozoic. The causes underlying the differential success of ornithischians and sauropodomorphs remain unclear, but might be related to trophic specialisation. Sauropodomorphs replaced an established herbivore guild consisting of rhynchosaurs, aetosaurs and basal synapsids, but this faunal turnover appears to have been opportunistic and cannot be easily attributed to either competitive interactions or responses to floral change. Consideration of diversity patterns and relative abundance suggests that the ability to eat plants might have been a major factor promoting sauropodomorph success, but that it was less important in the early evolution of Ornithischia. On the basis of current evidence it is difficult to determine the diet of the ancestral dinosaur and scenarios in which omnivory or carnivory represent the basal condition appear equally likely.

13) Irmis, R. B. Evaluating hypotheses for the early diversification of dinosaurs.

Abstract - Many hypotheses have been proposed for the rise of dinosaurs, but their early diversification remains poorly understood. This paper examines the occurrences, species diversity and abundance of early dinosaurs at both regional and global scales to determine patterns of their early evolutionary history. Four main patterns are clear: (1) sauropodomorph dinosaurs became abundant during the late Norian–Rhaetian of Gondwana and Europe; (2) Triassic dinosaurs of North America have low species diversity and abundance until the beginning of the Jurassic; (3) sauropodomorphs and ornithischians are absent in the Triassic of North America; and (4) ornithischian dinosaurs maintain low species diversity, relative abundance and small body size until the Early Jurassic. No one hypothesis fully explains these data. There is no evidence for a Carnian–Norian extinction event, but sauropodomorphs did become abundant during the Norian in some assemblages. No clear connection exists between palaeoenvironment and early dinosaur diversity, but environmental stress at the Triassic–Jurassic boundary is consistent with changes in North American dinosaur assemblages. Elevated growth rates in dinosaurs are consistent with the gradual phyletic increase in body size. This study demonstrates that early dinosaur diversification was a complex process that was geographically diachronous and probably had several causes.

Arcusaurus pereirabdalorum, A New Basal Sauropodomorph From The Early Jurassic Of South Africa

Yates, A. M., Bonnan, M. F., and J. Neveling. 2011. A new basal sauropodomorph dinosaur from the Early Jurassic of South Africa. Journal of Vertebrate Paleontology 31:610-625. DOI: 10.1080/02724634.2011.560626

Abstract - A new basal sauropodomorph dinosaur, Arcusaurus pereirabdalorum, sp. nov., is named and described on the basis of a partial, disarticulated but associated skull and dispersed cranial and postcranial elements from at least two individuals. Arcusaurus is part of a distinctive local fauna from the upper Elliot Formation (Lower Jurassic) in the Senekal District, Free State, South Africa. It can be diagnosed by various details of the premaxilla, nasal, and dentary in the skull and the shape of the distal caudal vertebrae. The taxon displays an unusual mix of characteristics. It lacks several synapomorphies of Plateosauria (Plateosaurus + Massospondylus and all descendants of their most recent common ancestor) but does display other derived characteristics that are otherwise known only from less inclusive clades within Plateosauria. In a cladistic analysis a position outside Plateosauria as the sister group of the clade of Efraasia + more-derived sauropodomorphs is supported; however, this position was not found to be a significantly better explanation of the data as a relatively derived position within Plateosauria. If the basal position for Arcusaurus is accepted, then a divergence from other sauropodomorphs in the middle Norian and a ghost lineage up to 35 Ma is implied. No other non-plateosaurian sauropodomorphs are known from the Jurassic, making Arcusaurus a potentially relictual taxon in the Early Jurassic.

Another North American Triassic Dinosaur that Wasn't

Holbrook, Arizona is a small little city of barely 5,000 people along Interstate 40 in Northeastern Arizona and is where I call home because it is the closest city to the Petrified Forest National Park. It's a neat little place, an old Route 66 town (this sign is visible from my home) with an even older bloody wild west history.

The local paper, the Holbrook Tribune, has a weekly feature where they reprint news snippets from the last 10, 25, 50, and 75 years. This one caught my eye in last Friday's edition.

"25 Years Ago - The oldest articulated dinosaur was named after Holbrook, according to Petrified Forest National Park Superintendent Ed Gastellum. Known affectionately as "Gertie," its official name was Holbrookosauras Smallii, honoring the community of Holbrook and Brian [sic] Small, the discoverer of the remains at the Petrified Forest."

Twenty five years ago, 1986, marked nearly a year since the specimen was collected in the most spectacular manner. I had always thought that the first unofficial name applied to the specimen was the nomen nudum "Chindesaurus bryansmalli" by Murry and Long (1989) but it looks like "Holbrookosauras smallii" beat it by several years. 

Obviously the valid name for this specimen today is Chindesaurus bryansmalli Long and Murry 1995. The name Chindesaurus is derived from Chinde (Navajo for ghost or spirit) Point in Petrified Forest National Park, near where the specimen was collected.

So it appears that for some reason the City of Holbrook lost out on their dinosaur name.  Fortunately, they did just get a style of new Oakley brand sunglasses designed by professional snowboarder Shaun White named for the town so all is not lost, and there are still tons of fossils waiting to be discovered out there in the Chinle Formation, including the elusive Triassic dinosaurs; so their day still may come. Next time we will get the spelling right though ;).

New Triassic Dinosaur Papers from the Proceedings of the Third Gondwanan Dinosaur Symposium

Most of you are probably aware that the Proceedings of the Third Gondwanan Dinosaur Symposium have just been published in the journal Anais da Academia Brasileira de Ciências. There are numerous papers here, three of which pertain to the Triassic.  You can view and download all of the papers from the following link:
http://www.scielo.br/scielo.php?script=sci_issuetoc&pid=0001-376520110001&ln

I have listed the relevent Triassic dinosaur papers below.

Bittencourt, J. S., and M. C. Langer. 2011. Mesozoic dinosaurs from Brazil and their biogeographic implications. Anais da Academia Brasileira de Ciências 83:23-60.

Abstract - The record of dinosaur body-fossils in the Brazilian Mesozoic is restricted to the Triassic of Rio Grande do Sul and Cretaceous of various parts of the country. This includes 21 named species, two of which were regarded as nomina dubia, and 19 consensually assigned to Dinosauria. Additional eight supraspecific taxa have been identified based on fragmentary specimens and numerous dinosaur footprints known in Brazil. In fact, most Brazilian specimens related to dinosaurs are composed of isolated teeth and vertebrae. Despite the increase of fieldwork during the last decade, there are still no dinosaur body-fossils of Jurassic age and the evidence of ornithischians in Brazil is very limited. Dinosaur faunas from this country are generally correlated with those from other parts of Gondwana throughout the Mesozoic. During the Late Triassic, there is a close correspondence to Argentina and other south-Pangaea areas. Mid-Cretaceous faunas of northeastern Brazil resemble those of coeval deposits of North Africa and Argentina. Southern hemisphere spinosaurids are restricted to Africa and Brazil, whereas abelisaurids are still unknown in the Early Cretaceous of the latter. Late Cretaceous dinosaur assemblages of south-central Brazil are endemic only to genus or, more conspicuously, to species level, sharing closely related taxa with Argentina, Madagascar, Indo-Pakistan and, to a lesser degree, continental Africa.

and two new papers on Staurikosaurus, one of which was previously mentioned here.

Grillo, O. N., and S. A. K. Azevedo. 2011. Pelvic and hind limb musculature of Staurikosaurus pricei (Dinosauria: Saurischia). Anais da Academia Brasileira de Ciências 83:73-98.

Abstract - The study of pelvic and hind limb bones and muscles in basal dinosaurs is important for understanding the early evolution of bipedal locomotion in the group. The use of data from both extant and extinct taxa placed into a phylogenetic context allowed to make well-supported inferences concerning most of the hind limb musculature of the basal saurischian Staurikosaurus pricei Colbert, 1970 (Santa Maria Formation, Late Triassic of Rio Grande do Sul, Brazil). Two large concavities in the lateral surface of the ilium represent the origin of the muscles iliotrochantericus caudalis plus iliofemoralis externus (in the anterior concavity) and iliofibularis (in the posterior concavity). Muscle ambiens has only one head and originates from the pubic tubercle. The origin of puboischiofemoralis internus 1 possibly corresponds to a fossa in the ventral margin of the preacetabular iliac process. This could represent an intermediate stage prior to the origin of a true preacetabular fossa. Muscles caudofemorales longus et brevis were likely well developed, and Staurikosaurus is unique in bearing a posteriorly projected surface for the origin of caudofemoralis brevis.

Anatomy of the Basal Sauropodomorph Pantydraco caducus from the Upper Triassic of the UK

Just received this.....

Galton, P. M., and D. Kermack. 2010. The anatomy of Pantydraco caducus, a very basal sauropodomorph dinosaur from the Rhaetian (Upper Triassic) of South Wales, UK. Revue de Paléobiologie, Genève 29 (2) : 341-404.

Abstract - Apart from characters of the dentary (proportional shortness, also Saturnalia tupiniquim) and vertebrae of proximal third of tail (posterior position of antero-posteriorly short neural spine on arch, absence of ventral furrowing on centra ; both also Efraasia minor), the bones of very basal sauropodomorphs from the Rhaetian (Upper Triassic) fissure fill in Clifton near Bristol (including holotypes of Thecodontosaurus antiquus, Asylosaurus yalensis ; taxon with robust humerus) share no diagnostic characters with those of Pantydraco caducus from the Rhaetian of South Wales. This taxon is diagnosed by four autapomorphies : median fusion of the nasals, prominent medial tubercle from posterior part of surangular, epipophyses of cervical vertebrae 3-5 form flat plates that overhang the posterior margins of the postzygapophyseal facets but do not form raised ridges on the dorsal surface of the postzygapophysis, and the fossae, possibly pneumatic, prominent on the neurocentral suture of cervical vertebrae 6-8 and shallow on the lateral part of centrum 9. The dentary is deep and short, with maximum height of more than 20 % of length (also Saturnalia tupiniquim, Thecodontosaurus antiquus), occupying less than 40 % of total mandibular length (also Saturnalia tupiniquim). The ilium is tall with a long anterior process (also Anchisaurus polyzelus) and a short postacetabular process with the plesiomorphic absence of a brevis shelf. Other plesiomorphic characters include the lack of a buccal emargination on the dentary (also Saturnalia tupiniquim); teeth all recurved in lateral view; neck short with mid-cervical centra less than three times as long as wide (also Riojasaurus incertus, “Gyposaurus” sinensis) ; and humerus with a uniquely small tubercle medial to head and an antero-posteriorly low (also Asylosaurus yalensis) asymmetrical deltopectoral crest with the apex at 40 % of humeral length. At least three different sized individuals are preserved and the new skeletal reconstruction, with the posterior region scaled up to match the larger holotype, indicates a more bipedal animal than the more quadrupedal pose based on the incorrect premise that the two main blocks represent one individual. The specimens represent juveniles as indicated by the proportionally large skull with large orbits and short, high snout, slender postorbital bone, separation of most of bones of braincase, large metotic fissure and fenestra ovalis, low maxillary and dentary tooth counts, open neurocentral sutures of cervical vertebrae, and incomplete ossification of distal ends of the femur and metatarsals. The diversity of basal sauropodomorphs from the Rhaetian of Wales and England adjacent to the Severn Estuary is high with five taxa (Pantydraco caducus, three from Clifton, large basal sauropod Camelotia borealis from Somerset).

Sanjuansaurus gordilloi a new Herrerasaurid from Argentina

Here is a new herrerasaurid from the the Ischigualasto Formation of Argentina. Looks much more similar to Herrerasaurus than to Staurikosaurus or Chindesaurus, although the latter taxon was not included in the phylogenetic analysis.  This analysis finds Herrerasauridae to be the sister taxon to Eoraptor + (Guaibasaurus + Neotheropoda), so we are back to the position of herrerasaurids still being dinosaurs but as basal saurischians rather than theropods.  Comparison is provided in the text to Tawa hallae, but it is not included in the phylogenetic analysis.  Too bad.  However, I'm pretty certain that based on the current material coding Sanjuansaurus into the analysis of Nesbitt et al. (2009) would not change the position of herrerasaurids as basal theropods as recovered in that analysis. So whether or not herrerasaurids are theropods or not appears to be entirely dependent on the base matrix one uses. Thus, unfortunately, the analysis in this paper does not appear to offer anything particularly game-changing or significant in that regards. Also unfortunate is that there is no discussion of these differing hypotheses in the paper.

The further recognition of the increased diversity of basal saurischian dinosaurs in the latest Carnian is interesting and provides more circumstantial support for the earlier diversification of Archosauria in the Early Triassic as hypothesized by Nesbitt (2009) based on body fossils and more recently by Brusatte et al. (2010) based on footprint evidence. 

Alcober O.A., and R. N. Martinez. 2010. A new herrerasaurid (Dinosauria, Saurischia) from the Upper Triassic Ischigualasto Formation of northwestern Argentina. ZooKeys 63 : 55 – 81 . doi: 10.3897/zookeys.63.550

Abstract - Herrerasauridae comprises a basal clade of dinosaurs best known from the Upper Triassic of Argentina and Brazil, which have yielded remains of Herrerasaurus ischigualastensis and Staurikosaurus pricei, respectively. Systematic opinion regarding the position of Herrerasauridae at the base of Dinosauria has varied. Here we describe a new herrerasaurid, Sanjuansaurus gordilloi gen. n., sp. n., based on a partial skeleton from Carnian-age strata of the the Upper Triassic Ischigualasto Formation of northwestern Argentina. The new taxon is diagnosed by numerous features, including long, band-shaped and posterolaterally oriented transverse process on the posterior cervical vertebrae; neural spines of the sixth to eighth dorsal vertebrae, at least, bearing acute anterior and posterior processes; scapula and coracoid with everted lateral margins of the glenoid; and short pubis (63% of the femoral length). Phylogenetic analysis placed Sanjuansaurus within a monophyletic Herrerasauridae, at the base of Theropoda and including Herrerasaurus and Staurikosaurus. The presence of Sanjuansaurus at the base of the Ischigualasto Formation, along with other dinosaurs such as Herrerasaurus, Eoraptor, Panphagia, and Chromogisaurus suggests that saurischian dinosaurs in southwestern Pangea were already widely diversified by the late Carnian rather than increasing in diversity across the Carnian-Norian boundary.


Holotype specimen of Sanjuansaurus gordilloi (PVSJ 605)

REFERENCES
Brusatte, S. L., Niedźwiedzki, G., and R. J. Butler. 2010. Footprints pull origin and diversification of dinosaur stem lineage deep into Early Triassic. Proceedings of the Royal Society B. doi: 10.1098/rspb.2010.1746


Nesbitt, S. J. 2009. The antiquity of Archosauria and the origin of Late Triassic archosaur assemblages. Journal of Vertebrate Paleontology 29:155A.

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

New Late Triassic Sauropodomorph, Chromogisaurus novasi from Argentina

Ezcurra, M. D. 2010. A new early dinosaur (Saurischia: Sauropodomorpha) from the Late Triassic of Argentina: a reassessment of dinosaur origin and phylogeny. Journal of Systematic Palaeontology 8: 371-425.

Abstract - It was traditionally thought that the oldest known dinosaur assemblages were not diverse, and that their early diversification and numerical dominance over other tetrapods occurred during the latest Triassic. However, new evidence gathered from the lower levels of the Ischigualasto Fm. of Argentina challenges this view. New dinosaur remains are described from this stratigraphical unit, including the new species Chromogisaurus novasi. This taxon is distinguished from other basal dinosauriforms by the presence of proximal caudals without median notch separating the postzygapophyses, femoral lateral surface with deep and large fossa immediately below the trochanteric shelf, and metatarsal II with strongly dorsoventrally asymmetric distal condyles. A phylogenetic analysis found Chromogisaurus to lie at the base of Sauropodomorpha, as a member of Guaibasauridae, an early branch of basal sauropodomorphs composed of Guaibasaurus, Agnosphitys, Panphagia, Saturnalia and Chromogisaurus. Such an affinity is for the first time suggested for Guaibasaurus, whereas Panphagia is not recovered as the most basal sauropodomorph. Furthermore, Chromogisaurus is consistently located as more closely related to Saturnalia than to any other dinosaur. Thus, the Saturnalia + Chromogisaurus clade is named here as the new subfamily Saturnaliinae. In addition, Eoraptor is found to be the sister-taxon of Neotheropoda, and herrerasaurids to be non-eusaurischian saurischians. The new evidence presented here demonstrates that dinosaurs first appeared in the fossil record as a diverse group, although they were a numerically minor component of faunas in which they occur. Accordingly, the early increase of dinosaur diversity and their numerical dominance over other terrestrial tetrapods were diachronous processes, with the latter preceded by a period of low abundance but high diversity.

Besides the information provided in the abstract here are a couple of other tidbits:

1) Diagnosis: the holotype material is very fragmentary, but Chromogisaurus novasi is diagnosed by "the following combination of characteristics (autapomorphies∗): proximal caudals without median notch separating the postzygapophyses; ilium with strongly posteriorly developed postacetabular process; incipiently perforated acetabulum; a femoral lateral surface with deep and large fossa immediately below the trochanteric shelf;∗ and a metatarsal II with strongly dorsoventrally asymmetric distal condyles" (Ezcurra, 2010:374).

2) Etymology:  The generic name is a combination of the Greek "chroma" (color) and "gi" (ground or land) for the Painted Valley where the specimen was collected.

3) Clades: This paper provides definitions for the newly recovered clades Guaibasauridae and Saturnaliinae.

4) Chindesaurus: The paper contains discussion on the phylogenetic position of Chindesaurus bryansmalli from the Chinle Formation.  This study (378 characters) finds Chindesaurus as eithr a basal theropod or as a non-eusaurischian saurischian.

5) Photos: There is a nice comparative figure (photos) of the skulls of Herrerasaurus, Eoraptor, and Zupaysaurus.

I'm looking forward to reading the rest of this....

Chindesaurus bryansmalli = "Gertie" the Dinosaur

In 1985 the holotype specimen of the basal theropod Chindesaurus bryansmalli was excavated in Petrified Forest National Park.  At the time it was (erroneously) billed in the media as the world's "earliest dinosaur".  The excavation was widely covered in the press with dozens of media passes distributed.  The block was ceremoniously lifted out of the Painted Desert by helicopter, with noted paleontologists such as Samuel Welles and Edwin Colbert aboard the "historic" flight. A party was held in honor of this event at the nearby Painted Desert Inn, complete with food and dinosaur ice sculptures from the Fred Harvey Company and of course a far too common summer power outage.  Park Rangers circled the building will vehicles, turned on their headlights, and the party continued.

At the time Chindesaurus was thought to represent a "prosauropod" based on it's primitive looking astragalus, but is now considered a herrerasaurid.  The specimen was affectionately given the nickname "Gertie" by the excavators and even today this is how the specimen is often referred to by many park staff.  In fact, when I first tried to find the specimen's catalogue record in 2001, it had been catalogued using this nickname rather than under Chindesaurus! Unfortunately, this name was far overused in 1980s and 90s park interpretive products and thus has been immortalized on the internet, as is readily apparent if one does an internet search for "Gertie" and "Petrified Forest".  Nonetheless, this specimen was very popular when first recovered, and casts of the skeleton are still on exhibit at the Rainbow Forest Museum. For those of you who are not familiar, the name stems from one of the earliest animated films ever made (1914), which featured a dinosaur named "Gertie" who would respond to commands by the animator and perform for audiences.  This short is still considered to be one of the most important animated films ever made. 

The Origin and Early Radiation of Dinosaurs

Finally this is out, although presently only as an accepted manuscript in Earth Science Reviews.  I was one of the reviewers for this paper and felt that it constitutes a very well written overview of early dinosaur work to the present, including many of the recent cool finds from the Chinle Formation of course.  I was reviewing this manuscript last year about the time another early dinosaur review paper came out by Max Langer and colleagues (not sure why this paper is so delayed) and feel that these papers are nice complements to each other.

[Note: after writing this I noticed that Brusatte et al. added a similarily worded paragraph to the end of the introduction.  I also noticed that they use the word "compliment" when they mean "complement".  See the difference here ;)].

Brusatte, S. L., Nesbitt, S. J., Irmis, R. B., Butler, R. J., Benton, M. J., and M. A. Norell. 2010. The origin and early radiation of dinosaurs. Earth Science Reviews. Early online. doi: 10.1016/j.earscirev.2010.04.001

Abstract - Dinosaurs were remarkably successful during the Mesozoic and one subgroup, birds, remain an important component of modern ecosystems. Although the extinction of non-avian dinosaurs at the end of the Cretaceous has been the subject of intense debate, comparatively little attention has been given to the origin and early evolution of dinosaurs during the Late Triassic and Early Jurassic, one of the most important evolutionary radiations in earth history. Our understanding of this keystone event has dramatically changed over the past 25 years, thanks to an influx of new fossil discoveries, reinterpretations of long-ignored specimens, and quantitative macroevolutionary analyses that synthesize anatomical and geological data. Here we provide an overview of the first 50 million years of dinosaur history, with a focus on the large-scale patterns that characterize the ascent of dinosaurs from a small, almost marginal group of reptiles in the Late Triassic to the pre-eminent terrestrial vertebrates of the Jurassic and Cretaceous. We provide both a biological and geological background for early dinosaur history. Dinosaurs are deeply nested among the archosaurian reptiles, diagnosed by only a small number of characters, and are subdivided into a number of major lineages. The first unequivocal dinosaurs are known from the late Carnian of South America, but the presence of their sister group in the Middle Triassic implies that dinosaurs possibly originated much earlier. The three major dinosaur lineages, theropods, sauropodomorphs, and ornithischians, are all known from the Triassic, when continents were joined into the supercontinent Pangaea and global climates were hot and arid. Although many researchers have long suggested that dinosaurs outcompeted other reptile groups during the Triassic, we argue that the ascent of dinosaurs was more of a matter of contingency and opportunism. Dinosaurs were overshadowed in most Late Triassic ecosystems by crocodile-line archosaurs and showed no signs of outcompeting their rivals. Instead, the rise of dinosaurs was a two-stage process, as dinosaurs expanded in taxonomic diversity, morphological disparity, and absolute faunal abundance only after the extinction of most crocodile-line reptiles and other groups.

A New Late Triassic Theropod, Tawa hallae, and its Implications for Early Dinosaur Evolution

A new Late Triassic basal theropod, Tawa hallae, is described by Nesbitt et al. (2009) in a new paper out today in Science. Tawa is known from two relatively complete skeletons and other isolated material from the Hayden Quarry at Ghost Ranch New Mexico [another link]. The Hayden Quarry is in the Petrified Forest Member of the Chinle Formation.

This quarry is an absolutely spectacular site that is proving to be the most diverse locality in the Chinle Formation, even more than the famed Coelophysis Quarry (which is close geographically but higher stratigraphically). Other taxa found at this site include Dromomeron romeri, Chindesaurus bryansmalli, Eucoelophysis baldwini, a coelophysoid theropod, and a shuvosaurid as well as various aetosaurs, crocodylomorphs, rauisuchians, phytosaurs, drepanosaurs, metoposaurs, and fish (Irmis et al. 2007).

Key points of the paper:

• Tawa possesses a mix of “coelophysoid” (Neotheropoda) and herrerasaurid characters that help clarify basal saurischian relationships.

- Herrerasaurids (Herrerasaurus, Chindesaurus, Staurikosaurus) and Eoraptor are unambiguously nested within Theropoda.

- Tawa is the sister taxon to Neotheropoda (see phylogenetic reconstruction artwork and tree below).

- Coelophysoidea is found to be paraphyletic, with the hypothesis that this clade had been serving as a “phylogenetic vacuum cleaner”, picking up deep theropod synapomorphies and ceratosaur/tetanuran reversals and treating them as coelophysoid synapomorphies.

• The presence of cervical pleurocoels in Tawa supports the hypothesis that cervical air sacs predate the origin of Neotheropoda and may be ancestral for Saurischia.

• The age of the Hayden Quarry (~215-213) and comparison with the Ischigualasto fauna supports the hypothesis of the diachronous evolution of Triassic dinosaur faunas.

• The presence of Dromomeron, Chindesaurus, Tawa, and a basal neotheropod in the Hayden Quarry suggests that the North American theropod fauna was not endemic, an was the result of several dispersals of taxa from South America.

• This prevalence of dispersal among early dinosaurs and other Triassic reptile groups indicates that physical barriers did not prevent these groups from moving around Pangaea - specifically into North America. Thus the question is why didn't sauropodomorphs and ornithischians make it to North America during the Triassic? Nesbitt et al. hypothesize that they were excluded by climate.

Dentary of Tawa hallae


Reconstruction of the head of Tawa hallae.


Articulated manus of Tawa hallae


In-situ articulated limbs of Tawa hallae


Associated dentary and maxilla of Tawa hallae



Block containing skull and other bones.

Thanks to Randy Irmis and Sterling Nesbitt for providing the photos and reconstructions used here. The reconstructions are by Jorge Gonzalez.

Links to some early news articles [here] [here] [here]

Link to National Science Foundation special report with lots of additional information on Tawa, its discovery, and its finders.

REFERENCES

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

New Paper on the Origin and Early Evolution of Dinosaurs

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.

My Favorite Kind of News Story

Mesalands Community College professor (and phytosaur expert) Axel Hungerbuehler is finding some great Late Triassic material in the Redonda Formation (Dockum Group) of New Mexico. Obviously I always get excited about the discovery of new aetosaur material.... oh yeah, there is some dinosaur material as well (which, of course, got the headline). Other related stories can be found here and here.

Students discover possible dinosaur fossil

By Thomas Garcia, Freedom New Mexico
January 13, 2009 - 9:21PM

A Mesalands Community College paleontology class has found a fossil that could be of a new form of Triassic reptile at an eastern New Mexico dig site. “I think that we have found a new form of aetosaurs,” said Axel Hungerbuehler, professor of Paleontology at Mesalands Community College.

The aetosaur, or eagle lizard, fossils were among numerous fossils excavated at a site in the Redonda formation in Quay County. Aetosaurs, a heavily armored plant-eater that lived in the Triassic period an estimated 200 Million years ago, are identified by the armor plating on their back and sides. Each of the plates has a distinct pattern and shape, Hungerbuehler said.

“The analysis of the armor plates found at the dig site indicates that we have found a new form of aetosaur,” Hungerbuehler said. In addition to the plates, they have identified bones of the internal skeleton of an aetosaur, including parts of the hip and several leg bones.

So far, however, no complete articulated skeletons have been excavated from the site, Hungerbuehler said.

Several more dinosaur-like elements, including another hip bone (pubis) and several hollow limb bones, were also recovered, Hungerbuehler said.

“These bones are not from the same individual dinosaur that was found in 2007,” Hungerbuehler said. “They could be fossils of a similar type of dinosaur.”

In 2007 a field class found a hip bone (ilium) of an un-named primitive dinosaur that was collected at the Redonda Formation site.

“We have not done enough examination of the fossil to determine if it is a new and previously undiscovered type of primitive dinosaur,” Hungerbuehler said. “A definite identification will be done once these fossils have been freed from their rocky host and they can be carefully cleaned.”

This all started during the summer of 2006, when three field classes and several volunteers of Mesalands Community College’s Dinosaur Museum started excavating bones of reptiles at the current dig site.

Hungerbuehler said an abundance of fossils were found in red and green siltstones, and sandstones of the Upper Triassic estimated to be 200 million years old. To date, about 250 field numbers have been recorded.

At the site they have found that bones occur in two different settings.

• In coarser layers of sandstones, bones are evenly distributed and show signs like breaking and abrasion, indicating they have been washed together by water currents.

• In red, fine-grained siltstones, undamaged bones have been found in spots of dense concentrations.

These probably represent skeletons that fell apart at the spot. Many of the bones still await preparation.

Items identified from the records kept in the field and the bones already freed from the rock in Mesalands Community College’s Dinosaur Museum Lab include:

• Phytosaurs — semiaquatic crocodile-like reptiles - two phytosaur skulls and parts of a large lower jaw were recovered, plus numerous bones of the body.

• Large carnivorous reptile, A large reptile, perhaps, a rauisuchian (Rau’s crocodiles) which includes the largest predators in the Late Triassic, is represented by the tip of a lower jaw. The element is currently under study by students at Mesalands to confirm the identity

Dromomeron, the Hayden Quarry, and Cool Jobs!

These have been out for awhile, but I just became aware of them a little bit ago. Anyhow for those of you who are interested and haven't seen these, here are my Triassic colleagues Randy Irmis, Sterling Nesbitt, and Alex Downs discussing The Skinny on Naming a New Dinosaur, Fossil Hunters Roll the Bones for Clues, and Cool Jobs: Fossil Hunters. These clips are from the Discovery Channel and I found them here. Enjoy!