Field of Science

A New Placodont from the Late Triassic of China

Wang, W., Li, C., Scheyer, T. M., and Zhao, L. 2019. A new species of Cyamodus (Placodontia, Sauropterygia) from the early Late Triassic of south-west China. Journal of Systematic Palaeontology. Link.

Abstract -
The Triassic eastern Tethyan faunas have continued to yield numerous specimens of marine reptile taxa in recent years. Nevertheless, compared with other sauropterygian clades, the diversity of placodonts in these faunas is low, and remains of this group are relatively rare in the fossil assemblages. Here, we report a new cyamodontoid specimen (ZMNH M8820) from the early Late Triassic of Guizhou, south-west China. This specimen is a nearly complete skeleton lacking only the forelimbs. It is distinct from other known Chinese placodonts as it features a large skull with remarkably enlarged supratemporal fenestrae and a small and less regularly arranged carapace. Interestingly, this new specimen resembles the European Cyamodus more than any Chinese cyamodontoid genera, particularly when considering the dentition and other cranial morphology. However, it differs from known Cyamodus species in some cranial features (e.g. epipterygoid fully ossified, posttemporal fenestra large, dentition derived) and the absence of a separate pelvic shield. Furthermore, based on an updated data matrix of placodonts, our phylogenetic results support the affinity of this new Chinese specimen with European Cyamodus species, and a new species, Cyamodus orientalis sp. nov., is erected here. This new material represents the first reported Cyamodus specimen in the world that preserves a three-dimensional skull with an associated postcranial skeleton and it extends the distribution of this genus into the early Carnian of the eastern Tethys. The existence of Cyamodus, a nearshore taxon, in south-west China at this time reveals greater similarity and more rapid intercommunication than previously known between western and eastern Tethyan vertebrate faunas, although the palaeobiogeographical origin and migration history of Cyamodontidae – and of other clades of placodont reptiles – are still obscure due to the scarcity of material from the northern and southern margins of the Palaeotethys.

Platypus-like Hupehsuchian from Early Triassic of China

Cheng, L., Motani, R.,  Jiang, D., Yan, C., Tintori, A. and O. Rieppel. 2019. Early Triassic marine reptile representing the oldest record of unusually small eyes in reptiles indicating non-visual prey detection. Scientific Reports 9, number 152. DOI: 10.1038/s41598-018-37754-6

Abstract - The end-Permian mass extinction (EPME) led to reorganization of marine predatory communities, through introduction of air-breathing top predators, such as marine reptiles. We report two new specimens of one such marine reptile, Eretmorhipis carrolldongi, from the Lower Triassic of Hubei, China, revealing superficial convergence with the modern duckbilled platypus (Ornithorhynchus anatinus), a monotreme mammal. Apparent similarities include exceptionally small eyes relative to the body, snout ending with crura with a large internasal space, housing a bone reminiscent of os paradoxum, a mysterious bone of platypus, and external grooves along the crura. The specimens also have a rigid body with triangular bony blades protruding from the back. The small eyes likely played reduced roles during foraging in this animal, as with extant amniotes (group containing mammals and reptiles) with similarly small eyes. Mechanoreceptors on the bill of the animal were probably used for prey detection instead. The specimens represent the oldest record of amniotes with extremely reduced visual capacity, utilizing non-visual cues for prey detection. The discovery reveals that the ecological diversity of marine predators was already high in the late Early Triassic, and challenges the traditional view that the ecological diversification of marine reptiles was delayed following the EPME.

Histological Evidence of Trauma in Dicynodont Tusks

Whitney, M. R., Ting Tse, Y., and C. A. Sidor. 2019. Histological evidence of trauma in tusks of southern African dicynodonts. Palaeontologia Africana 53: 75-80. PDF.

Abstract -
Dicynodonts were a clade of globally-distributed therapsids known for their abundance in the fossil record and for surviving the Permo-Triassic mass extinction. The group had distinctive dental adaptations including a beak and, in many species, paired maxillary tusks. The function of these tusks has long been of interest, yet remains poorly understood.We report here on two instances of unusual morphology in tusk dentine from specimens of: 1) Lystrosaurus from the Karoo Basin of South Africa and, 2) an unidentified dicynodontoid from the Luangwa Basin of Zambia. In both, the cross-sectional shape of the tusk root is lobed and infolded, which histological features suggest is a result of abnormal dentine deposition. We infer that this abnormal morphology is likely the consequence of trauma given its reparative nature and structural similarities to trauma-related morphologies reported in the tusks of modern elephants. This study demonstrates that histological sampling of dicynodont tusks can shed light on the biology of this important clade of therapsids.

Examining Functional Convergence Between Triassic Phytosaurs and Slender-Snouted Crocodylians

A new preprint in PeerJ.

Lemanis R., Jones A.S., Butler R.J., Anderson P.S.L., and E.J. Rayfield. 2019. Comparative biomechanical analysis demonstrates functional convergence between slender-snouted crocodilians and phytosaurs. PeerJ Preprints 7:e27476v1https://doi.org/10.7287/peerj.preprints.27476v1

Abstract - Morphological similarities between the extinct Triassic archosauriform clade Phytosauria and extant crocodilians have formed the basis of long-proposed hypotheses of evolutionary convergence. These hypotheses have informed the reconstructions of phytosaur ecology and biology, including feeding preferences, body mass, soft tissue systems, mating behaviours, and environmental preferences. However, phytosaurs possess numerous cranial apomorphies that distinguish them from modern crocodilians and potentially limit ecomorphological comparisons. Here, we present the first computational mechanical comparison of phytosaur cranial strength to several extant crocodilian taxa using two biomechanical approaches: beam theory and finite element analysis. We demonstrate mechanical convergence between the slender-snouted phytosaur Ebrachosuchus neukami and modern slender-snouted crocodilians. We provide evidence that the phytosaurian premaxillary palate is functionally equivalent to the crocodilian secondary palate. The premaxillary palate is associated with greater resistance to biting induced stress, lower strain energy, higher resistance to bending and torsion, as well as increased performance under tension. In all tests, Ebrachosuchus performed worse than all tested crocodilians, showing higher stress under equivalent loading conditions. These findings have implications for the proposed feeding ecology of slender-snouted phytosaurs and corroborate previous broad assessments of phytosaur ecology based on morphological comparisons to crocodilians; however, we urge caution in overextending those assessments given the current paucity of comparative functional data.

Why are Temnospondyl Skulls Bumpy?

Today Bryan Gee at Temno Talk Blog discusses and evaluates the various hypotheses of why temnospondyl skulls (and other bones) have heavily ornamented, irregular surfaces.

If you missed the link here it is again.

Triassic Park is Temporarily Closed: What Happens at Petrified Forest During a Government Shutdown

[Disclaimer: I am a furloughed Federal employee and this is a personal blog. It is not my intent to take a political side or to make a a political statement here. I am simply explaining what a shutdown is for those who might not understand and its effects on a specific park and program].

On December 22, 2018 funding appropriations for the U.S. National Park Service ended. What does this mean? It means that Congress and the President have not allocated funding to allow the Service to pay its bills and keep functioning. There is a little known law on the books called The Antideficiency Act passed in 1884 that prevents "the incurring of obligations or the making of expenditures in excess of amounts available in appropriations of funds". In other words, U.S. Government agencies cannot spend more money each year than they are appropriated by Congress.

One of the President's and the Congress' main jobs is to develop a budget each year for the functioning of the Federal Government. If they fail to develop, and pass by law, a Federal budget then the Antideficiency Act kicks in after the last day of lawful appropriations expires. This time that occurred at 12:01 EST on December 22, 2018. The Act requires that the Federal Government initiate a shutdown, which includes the furlough of pre-determined "non-essential" staff and the limitation of services.

What is meant by 'non-essential" staff? Basically positions and employees that do not have a health-safety, law enforcement, or cybersecurity role. In National Parks a handful of "essential" staff are kept on the guard the park entrances, and keep up some basic maintenance duties such as water and other utility monitoring. Computer and network monitoring is also provided for. Unfortunately scientific work is not considered essential. It's also important to note that although essential staff are required to work, there is no funding so they do not receive pay for their work time during a shutdown.

Since 1976 there have been 22 funding lapses and shutdowns, three in 2018 including the present one. The current one is now a day short of being the longest in history, 22 days. This shutdown is also different because unlike other shutdowns the National Parks have been kept 'open'. The closure of parks during the 17 day 2013 shutdown was not well received by the public and was considered a black eye for the Obama Administration. The current administration did not want to face this and ordered the parks to stay open, but with the greatly reduced "essential" staff. This has led to resource damage, overflowing toilets, etc... situations now being remedied by volunteers and other actions being taken.

At Petrified Forest National Park in Arizona the park is closed at night and parks with limited hours are allowed to close those areas normally closed for a portion of the day. Because of the vast amounts of petrified wood and how easily it can be removed the main portion of the park is closed to protect these resources. However, as a service to visitors and travelers on Interstate 40 the restaurant and gas station at the north end of the park, run by a permitted concessionaire, remain open.

This has caused a lot of confusion with the public because they see on the news where parks are "open", but don't always realize that only limited services can be offered because there are no staff. So visitor centers and bathrooms are closed at most parks and this is generally unexpected. I highly recommend that anyone planning on visiting a National Park in a shutdown time do some research first to see what is available For example at Petrified Forest the visitor centers are not open, but there are bathroom services. There are also some exhibits and some petrified wood outside of the restaurant. The Grand Canyon is open because it is such a large economic draw for the State of Arizona, that the state is providing the funding to keep some of the basic services operating and some of the park open. Again do some research before visiting and don't expect full services.

The thing that is most significant to regular readers of this blog is that the paleontology program at the Petrified Forest (and other units) is a non-essential service and is temporarily closed. Thus park scientists are unable to go to work. This means fossils threatened by erosion don't get collected and preserved, collected fossils don't get prepared or curated, and research does not get done. Fortunately wintertime is not a major collecting season for us so the first point is not critical. However, planning for the summer field season is usually done now and cannot happen and we fall behind in recruiting student interns and working with other researchers. Even more important the NPS scientists cannot apply for external funding sources (e.g., NSF), so we rely on internal grant funding. This year grant proposals were due in January 11, but this year none will be submitted by the deadline. What this means for future grant funding is uncertain.

Another thing to realize is that a lot of research in National Parks is done by permitted outside institutions and with a shutdown that work cannot be done, permits and fieldwork are cancelled or postponed. This is not only paleontology but also ecology, archaeology, etc... The park maintains several air quality monitoring stations that require weekly upkeep and data collection. Weeks of non-collection cause sizeable gaps in data that can render a whole year of data unusable. Fortunately this year there was no outside paleontology research work scheduled for this time, although in the 2013 shutdown several research groups were affected. Since that time we try to warn groups not to schedule trips that correspond to funding end periods.

Again my purpose here is not to pass judgment on political reasons for this or any other shutdown. I know that a lot of paleontology enthusiasts don't necessarily understand how government shutdowns work and what effects they can have on our scientific work.  I hope I have sufficiently explained the process. Those of us who have chosen civil service understand that our work can be temporarily disrupted by funding lapses. Regardless when the park reopens we will get back to our duties of caring for the park fossils and researching their significance for the public and the scientific community. I'm confident that our law enforcement who have to work during the shutdown are doing a great job protecting park resources and explaining this situation to any park visitors. They deserve a lot of thanks.


Extinction and the Rise of Dinosaurs - What Will the Microvertebrates Tell Us?

Brian Switek has a great year end article (based mainly on the recent Allen et al., study in Palaeontology) regarding the loss of most pseudosuchian groups in the end-Triassic extinction and discussion on why the dinosaurs were mostly unaffected.

According to their findings body size was not a factor; however, there are not too many data regarding Middle Triassic - Early Jurassic microfaunas. My intern, colleague and Virginia Tech grad student Ben Kligman is adding to this information. Ben started a couple of years ago at Petrified Forest National Park looking at a new microsite in the Blue Mesa Member of the park. This unit and roughly the same horizon had been the subject of several previous microvertebrate studies that despite being nearly two decades apart had generated roughly the same results, a lot of teeth and scales that could only be assigned to broad taxonomic levels. Thus, I was not enthusiastic about this at first. However, Ben tackled this new site with gusto and developing a new sampling technique with the help of PEFOs lead preparator and curator Matt Smith, very quickly built a sample of over 100 different morphotypes. Even more important this new technique allowed preservation of relatively complete jaw elements.

<i>Palacrodon browni</i> from the Chinle Formation of Arizona.
From Kligman et al 2018. Acta Palaeotologica Polonica 63(1).


Ben already has several publications about new these finds (Kligman et al., 2017; Kligman et al., 2018) and several more in the works. Furthermore, this research won the Student Poster Prize at the 2018 Society of Vertebrate Paleontology meeting. Ben is now sampling a wider stratigraphic range of sites and his work will help us further understand the effects of the end-Triassic extinction.

New Blog TemnoTalk: A Blog About All Things Temnospondyl

Introducing a new blog by my friend and colleague Bryan Gee from the University of Toronto. Since his first find of half of a metoposaur skull in Petrified Forest National Park quite a few years back now Bryan has been obsessed with the fossil record of temnospondyls, a group with constituents that are not always well studied (e.g., Late Triassic North American metoposaurids).

Bryan embarked on a series of discoveries at the Petrified Forest that kindled a badly needed interest in these forms and has resulted in quite a few recent publications (Gee et al., 2017; Gee and Parker, 2017; Gee and Parker, 2018) and an upcoming paper reexamining the anatomy and taxonomy of the metoposaurid <i>Anaschisma</i>.  Bryan is one of the most prolific writers I have ever seen and has published a number of papers now as a graduate student (see his Google Scholar page here). I look forward to his blogging and I've added the link to the Chinleana blogroll.

New Osteological and Phylogenetic Review of the Triassic Loricatan Prestosuchus chiniquensis from Brazil

Roberto-Da-Silva, L., Müller , R. T., Gallo de França, M. A., Cabreira, S. F., and Dias-Da-Silva, S. 2018. An impressive skeleton of the giant top predator Prestosuchus chiniquensis (Pseudosuchia: Loricata) from the Triassic of Southern Brazil, with phylogenetic remarks. Historical Biology (Early Online).

Abstract - In the present contribution, we aim to present the osteology of ‘ULBRA-PVT-281’, which comprises the best-preserved skeleton of Prestosuchus chiniquensis ever found. ULBRA-PVT-281 combines the morphology of two classic specimens referred to P. chiniquensis, UFRGS-PV-0156-T and UFRGSPV- 0152-T, reunited in a single operational taxonomic unit (OTU) in previous phylogenetic studies. Therefore, the new specimen reinforces the combination of both specimens. We performed a phylogenetic analysis, combining the information of these three specimens plus braincase data from a fourth specimen, UFRGS-PV-0629-T, into a new P. chiniquensis terminal taxon. Moreover, our analysis also included some new taxa potentially related to P. chiniquensis. As a result, we found a topology slightly distinct from previous studies, where Ticinosuchus ferox is the basalmost member of Loricata, which also includes the new combined P. chiniquensis. Our results place P. chiniquensis, Luperosuchus fractus, and Saurosuchus galilei distributed in a pectinate paraphyletic pattern towards Crocodylomorpha. On the other hand, a constrained analysis forcing the monophyly of these taxa demands just a single extra step. Therefore, both scenarios are plausible and agree with the placement of P. chiniquensis within Loricata, whereas T. ferox nests in Loricata only in the unconstrained analysis.

Ichnofossil Assemblages and Paleosols of the Upper Triassic Chinle Formation, South-Eastern Utah

Adding to our understanding of the understudied Chinle Formation fossils of Utah.

Fischer, S. J. and S. T. Hasiotis 2018. Ichnofossil assemblages and palaeosols of the Upper Triassic Chinle Formation, south-eastern Utah (USA): Implications for depositional controls and palaeoclimate. 
Annales Societatis Geologorum Poloniae 88(2): 127–162.

Abstract - The Upper Triassic Chinle Formation in the Stevens Canyon area in south-eastern Utah represents fluvial, palustrine, and lacustrine strata deposited in a continental back-arc basin on the western edge of Pangea. Previous investigations interpreted a megamonsoonal climate with increasing aridity for the Colorado Plateau towards the end of the Triassic. In this study, we systematically integrate ichnological and pedological features of the Chinle Formation into ichnopedofacies to interpret palaeoenvironmental and palaeoclimatic variations in the north-eastern part of the Chinle Basin. Seventeen ichnofossil morphotypes and six palaeosol orders are combined into twelve ichnopedofacies, whose development was controlled by autocyclic and allocyclic processes and hydrology. Ichnopedofacies are used to estimate palaeoprecipitation in conjunction with appropriate modern analogue latitudinal and geographic settings. In the north-east Chinle Basin, annual precipitation was ~1100–1300 mm in the Petrified Forest Member. Precipitation levels were >1300 mm/yr at the base of the lower Owl Rock Member, decreased to ~700–1100 mm/yr, and then to ~400–700 mm/yr. Two drying upward cycles from ~1100 mm/yr to ~700 mm/yr occurred in the middle and upper part of the Owl Rock Member. In the overlying Church Rock Member, precipitation decreased from ~400 mm/yr at the base of the unit to ~25–325 mm/yr at the end of Chinle Formation deposition. Ichnopedofacies indicate monsoonal conditions persisted until the end of the Triassic with decreasing precipitation that resulted from the northward migration of Pangea. Ichnopedofacies in the northeast Chinle Basin indicate both long-term drying of climate and short-term, wet-dry fluctuations.

Expanding the Late Triassic Record of the Dinosaur Precursor Dromomeron romeri: A New Record from the Chinle Formation of Arizona.

A new open access paper from my co-worker, friend, and colleague Adam Marsh documenting a new record of the dinosaur precursor Dromomeron romeri from the Chinle Formation Arizona. This further demonstrates the importance of museum collections and apomorphy based identification work to identify stratigraphic, chronologic, and bibliographical extensions, improving our understanding of early dinosaur distributions.  


Marsh, A. D. 2018. A new record of Dromomeron romeri Irmis et al., 2007 (Lagerpetidae) from the Chinle Formation of Arizona, U.S.A. PaleoBios, 35. Retrieved from https://escholarship.org/uc/item/8w5755sg

Abstract -
The relatively recent discovery and contextualization of silesaurid and lagerpetid dinosauromorphs has led to a revolution in understanding the early evolutionary history of the dinosaurian lineage. Lagerpetids are known from North America and South America in Middle and Upper Triassic rocks, especially the Chinle Formation of New Mexico and the Dockum Group of Texas. Until now, only a single specimen of Dromomeron gregorii was known from the Upper Triassic Chinle Formation of Arizona. However, a new lagerpetid astragalus specimen (MNA V7237) from the Owl Rock Member of the Chinle Formation found on Ward Terrace in the Navajo Nation of Arizona is referred to Dromomeron romeri. MNA V7237 represents the youngest radioisotopically-dated record of Lagerpetidae, indicating that D. romeri persisted throughout the entire Norian (Otischalkian into the Apachean) in North America.


Fuyuanichthys wangi A New Ginklymodian Fish from the Middle Triassic of China

Xu, G., Ma, X., and Y. Ren. 2018. Fuyuanichthys wangi gen. et sp. nov. from the Middle Triassic (Ladinian) of China highlights the early diversification of ginglymodian fishes. PeerJ 6:e6054 https://doi.org/10.7717/peerj.6054

Abstract - A series of well-preserved fossil assemblages from the Middle Triassic marine rock succession in Southwest China provide unique evidences for studying the early evolution of holostean fishes, including Halecomorphi (e.g., bownfin) and Ginglymodi (e.g., gars). Ginglymodi have the earliest record in the early Middle Triassic (Anisian, ∼244 Ma) of China, represented by Kyphosichthys and Sangiorgioichthys sui from Yunnan and S. yangjuanensis from Guizhou. Here, we report the discovery of a new ginglymodian, Fuyuanichthys wangi gen. et sp. nov., based on 22 well-preserved specimens from the lower part of the Zhuganpo member of the Falang Formation in eastern Yunnan and western Guizhou, which documents the first discovery of convincing ginglymodians from the late Middle Triassic (Ladinian, ∼240 Ma) Xingyi biota in China. Fuyuanichthys possesses a unique combination of features that easily distinguishes it from other ginglymodians, such as presence of a median gular and short and edentulous maxillae, and absence of a supramaxilla and supraorbitals. As one of the smallest known ginglymodians with a maximum standard length of ∼75 mm, the new finding further supports that the Middle Triassic Ginglymodi have a relatively small range of body sizes compared with the Halecomorphi from the same ecosystems in China. Results of a phylogenetic analysis recover Fuyuanichthys as a sister taxon to Kyphosichthys at the ginglymodian stem, and provide new insights into the early evolution of this clade.




New Specimen of Prolacerta broomi from the Early Triassic of Antarctica

Spiekman, S. N. F. 2018. A new specimen of Prolacerta broomi from the lower Fremouw Formation (Early Triassic) of Antarctica, its biogeographical implications and a taxonomic revision. Scientific Reports 8, Article number: 17996. https://www.nature.com/articles/s41598-018-36499-6

Abstract - Prolacerta broomi is an Early Triassic archosauromorph of particular importance to the early evolution of archosaurs. It is well known from many specimens from South Africa and a few relatively small specimens from Antarctica. Here, a new articulated specimen from the Fremouw Formation of Antarctica is described in detail. It represents the largest specimen of Prolacerta described to date with a nearly fully articulated and complete postcranium in addition to four skull elements. The study of this specimen and the re-evaluation of other Prolacerta specimens from both Antarctica and South Africa reveal several important new insights into its morphology, most notably regarding the premaxilla, manus, and pelvic girdle. Although well-preserved skull material from Antarctica is still lacking for Prolacerta, a detailed comparison of Prolacerta specimens from Antarctica and South Africa corroborates previous findings that there are no characters clearly distinguishing the specimens from these different regions and therefore the Antarctic material is assigned to Prolacerta broomi. The biogeographical implications of these new findings are discussed. Finally, some osteological characters for Prolacerta are revised and an updated diagnosis and phylogenetic analysis are provided.

UWBM 95529 

Further Investigating the Biogeographic Origins of Dinosauria

New paper out in Palaeontology.

Marsola, J. C., Ferreira, G. S., Langer, M. C., Button, D. J., and R. J. Butler. 2018. Increases in sampling support the southern Gondwanan hypothesis for the origins of dinosaurs. Palaeontology. Early Online. https://doi.org/10.1111/pala.12411

Abstract - Dinosaurs were ubiquitous in terrestrial ecosystems through most of the Mesozoic and are still diversely represented in the modern fauna in the form of birds. Recent efforts to better understand the origins of the group have resulted in the discovery of many new species of early dinosaur and their closest relatives (dinosauromorphs). In addition, recent re‐examinations of early dinosaur phylogeny have highlighted uncertainties regarding the interrelationships of the main dinosaur lineages (Sauropodomorpha, Theropoda and Ornithischia), and questioned the traditional hypothesis that the group originated in South Gondwana and gradually dispersed over Pangaea. Here, we use an historical approach to examine the impact of new fossil discoveries and changing phylogenetic hypotheses on biogeographical scenarios for dinosaur origins over 20 years of research time, and analyse the results in the light of different fossil record sampling regimes. Our results consistently optimize South Gondwana as the ancestral area for Dinosauria, as well as for more inclusive clades including Dinosauromorpha, and show that this hypothesis is robust to increased taxonomic and geographic sampling and divergent phylogenetic results. Our results do not find any support for the recently proposed Laurasian origin of dinosaurs and suggest that a southern Gondwanan origin is by far the most plausible given our current knowledge of the diversity of early dinosaurs and non‐dinosaurian dinosauromorphs.

An interesting new study out today that uses phylogeny based biogeographical analyses to test the hypothesis of Baron et al. (2017a,b) that stem-dinosaurs originated in Laurasia. Their results reject that hypothesis in favor of the long standing hypothesis of a Gondwanan origin. I couldn't access the supplemental data in Dryad because the article isn't officially out. I'm not suggesting that the conclusions are wrong, but do have a few questions/comments about the data and how specimen sampling issues from Western North America could affect a rerun of the analysis. 

1) Some of the separation of taxa into biogeographical bins is confusing. For example most of the Chinle Formation taxa Chindesaurus, Tawa,  and Eucoelophysis are shown in green depicting the 'Equatorial Belt' as the ancestral zone, yet taxa from the same formation and localities therein such as Dromomeron gregorii and D. romeri are shown in yellow from the 'Euroamerica' zone. Why are they separated?

2) I am not aware of any Rhaetian occurrences of Eucoelophysis baldwini. This taxon occurs in a couple of quarries from around Ghost Ranch, New Mexico and one of them, the Hayden Quarry, is solidly dated in the middle-late Norian at about 212 Ma (Irmis et al., 2011). There is a purported occurrence (Rinehart et al., 2009) of Eucoelophysis from the Coelophysis Quarry at Ghost Ranch that is most likely Rhaetian in age; however, this occurrence is based on the rejected hypothesis that Eucoelophysis remains a neotheropod dinosaur with the holotype representing a highly weathered individual (Rinehart et al., 2009). This referred specimen is simply another specimen of Coelophysis. Thus all presently known occurrences of Eucoelophysis are Norian in age.

3) Recent fieldwork in the Chinle Formation, especially at Petrified Forest National Park, has recovered a significant amount of early dinosaur material. This includes the earliest known dated neotheropod specimen and early occurrences of dinosauriforms. This material is presently under study. Combined with already published accounts of silesaurids and coelophysids (e.g., Padian, 1986; Parker et al., 2006), these show a robust record of dinosauromorphs in the early-middle Norian of Arizona. Thus a specimen based study using autapomorphy-based identifications would pull Equatorial Laurasian silesaurids and neotheropods down into the early-middle Norian. Also important is a recently mentioned occurrence of Dromomeron gregorii from the Otischalkian Boren Quarry in the Dockum Group of Texas which is older than any of the Chinle Formation occurrences and pulls these occurrences down even further (Lessner et al., 2018).

4) Many of the specimens mentioned above are of interest because they originate from some of the lowest fossil bearing beds in the Chinle Formation, the Blue Mesa Member. To date no diagnostic vertebrate fossils from the Chinle Formation are known from below the middle of the Blue Mesa Member, thus the vertebrate faunas of the lower Chinle (lower Blue Mesa, Mesa Redondo, Shinarump) are unknown. This is significant because these units represent the earliest Norian based on the 'long-Norian' hypothesis (227-208 Ma). Coupled with the Moenkopi/Chinle unconformity much of the well-sampled Triassic of the western U.S. is apparently lacking the Carnian and earliest Norian. This is a bias that should not be ignored. Possible Carnian rocks elsewhere such as the base of the Dockum Group in Texas and units in Wyoming need to be better sampled.  

It's difficult to say how these details would affect these early dinosaur biogeographical studies, but there are data out there that should be included in future analyses.

REFERENCES

Baron, M. G., Norman, D. B. and Barrett, P. M. 2017a. A new hypothesis of dinosaur relationships and early dinosaur evolution. Nature, 543, 501–506.

Baron, M. G., Norman, D. B. and Barrett, P. M. 2017b. Baron et al. reply. Nature, 551, E4–E5.

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, U.S.A.) support a diachronous rise of dinosaurs. Earth and Planetary Science Letters 309:258-267.

Lessner, E. J., Parker, W. G., Marsh, A. D., Nesbitt, S. J., Irmis, R. B. and B. Mueller. 2018. New insights into Late Triassic dinosauromorph-bearing assemblages from Texas using apomorphy-based identifications. PaleoBios, 35.ucmp_paleobios_39960.

Padian, K.. 1986. On the type material of Coelophysis Cope (Saurischia: Theropoda), and a new specimen from the Petrified Forest of Arizona (Late Triassic: Chinle Formation), p. 45-60. In K. Padian (ed.), The beginning of the Age of Dinosaurs: Faunal change across the Triassic-Jurassic boundary. Cambridge University Press, Cambridge.

Parker, W. G., Irmis, R. B., and S. J. Nesbitt. 2006. Review of the Late Triassic dinosaur record from Petrified Forest National Park, Arizona. Museum of Northern Arizona Bulletin 62:160-161.

Rinehart, L. F., Lucas, S. G., Heckert, A. B., Spielmann, J. A., and M. D. Celeskey. 2009. The paleobiology of Coelophysis bauri (Cope) from the Upper Triassic (Apachean) Whitaker Quarry, New Mexico, with detailed analysis of a single quarry block. New Mexico Museum of Natural History and Science Bulletin 45.