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.

More on the Taxonomic Affinities of Isolated Leaf-Shaped Teeth from the Triassic

In the conclusions section of the recent paper by Kammerer et al., there is a worthwhile discussion regarding the taxonomic assignment of isolated Triassic teeth.  In the past some isolated leaf-shaped, denticulated teeth were considered apomorphic and used to erect discrete ornithischian dinosaur taxa (e.g., Hunt and Lucas, 1994; Heckert, 2004). Parker et al. (2005) argued that at least in Revueltosaurus callenderi, the teeth were apomorphic allowing assignment of non-dental material to the taxon. Irmis et al. (2007) discussed this in more detail, arguing the teeth of other purported ornithischians were not assignable to dinosaurs based solely on morphology and in fact could not be assigned to a more inclusive taxonomic level than Archosauromorpha.

However, in this recent paper Kammerer et al. note that many of these Triassic tooth taxa are very similar to the teeth of the traversodontid cynodonts Dadadon isaloi and Arctotraversodon plemmyridon. They especially note that the lower incisors of D. isaloi are very similar to the holotype teeth of Tecovasaurus murryi and the fourth upper incisor of D. isaloi has a similar morphology to Lucianosaurus wildi. Thus the characters that have been used to diagnose at least several of these 'tooth taxa' converge on other forms and are not autapomorphic. Although it would be tempting to use the teeth of Tecovasaurus and Lucianosaurus to suggest the further presence of cynodonts in the Triassic of the American southwest, we cannot discount the similarities of these teeth to archosaurian forms as well and therefore as noted by Kammerer et al., these isolated teeth can presently only be assigned to the level of Amniota  rather than Archosauriformes.

REFERENCES

Heckert, A.B. 2004. Late Triassic microvertebrates from the lower Chinle Group (Otischalkian-Adamanian: Carnian), southwestern U. S. A. New Mexico Museum of Natural History and Science Bulletin 27:1-170.

Hunt, A. P., and S.G. Lucas. 1994. Ornithischian dinosaurs from the Upper Triassic of the United States. pp. 227–241 in In the Shadows of the Dinosaurs: Early Mesozoic Tetrapods (ed. N. C. Fraser & H.-D. Sues). Cambridge University Press.
Irmis, R. B., Parker, W. G., Nesbitt, S. J., and J. Liu. 2007. Early ornithischian dinosaurs: the Triassic record. Historical Biology 19:3-22.

Kammerer, C. F., Flynn, J. J., Ranivoharimanana, L., and A. R. Wyss. 2012. Ontogeny in the Malagasy traversodontid Dadadon isaloi and a reconsideration of its phylogenetic relationships. Fieldiana Life and Earth Sciences 5:112-125.

Parker, W.G., Irmis, R.B., Nesbitt, S.J., Martz, J.W., and L.S. Browne. 2005. The Late Triassic pseudosuchian Revueltosaurus callenderi and its implications for the diversity of early ornithischian dinosaurs. Proceedings of the Royal Society B 272:963-969.
 

 

Introducing Protome batalaria, a New Phytosaur from the Chinle Formation of Petrified Forest National Park, Arizona

In the Fall of 2004 Michelle Stocker and I were out at the Battleship NW fossil locality in Petrified Forest National Park with several researchers from Northern Arizona University. They were working on completing the geological map of the area and had noted that they could not get the current stratigraphic scheme we were using (introduced in 2002) to work out on the map.  The stratigraphic position of this quarry was an important issue behind this work as I had just collected a good skeleton of the aetosaur Calyptosuchus wellesi here just above a prominent sandstone that previous workers had correlated to the "Sonsela Sandstone Bed". If this bed correlation was correct then the specimen would be from the Revueltian biozone. This was problematic because Calyptosuchus is considered an index taxon of the Adamanian.  As we hemmed and hawed back and forth and discussed various possible correlations to work out these problems, Michelle noted some scraps of bone in unconsolidated sand at top of this bed and very near to where we were standing. She was very surprised, as was I, when she reached down and pulled up part of the skull roof of a phytosaur.

After the NAU researchers moved on to complete their work, we examined Michelle's new "quarry" much closer.  By literally sifting our fingers through the loose sand we easily collected numerous parts of the skull including large portions of the rostrum and skull roof. We also uncovered a ramus of the mandible, but this was actually in-situ in the bedrock just underneath the loose sand. We were able to jacket this element, but it was wintertime and I distinctly remember how frozen our hands were after each application of a plaster bandage.  Luckily the truck was very nearby, so after each application we would run to the running truck to stick our hands under the heater.

Back in the lab we were able to piece back together much of the skull and it later became part of the focus of Michelle's Masters Thesis. Prior to this Randall Irmis and I mentioned (and figured) this specimen in a 2005 paper where we referred it to "Leptosuchus" adamanensis based on the overall morphology of the squamosals following work by Long and Murry. However, Michelle's detailed phylogenetic analysis in her thesis suggested something different, specifically the specimen did not form a clade with Smilosuchus adamanensis and instead was something else.

In her new paper in the Journal of Vertebrate Paleontology Michelle has described this specimen as a new taxon, which she names Protome batalaria. The name reflects the condition of the specimen, "face of an animal" and where it was found "warship" (for the Battleship Quarry). It can be diagnosed by a unique combination of characters as well as three autapomorphies of the braincase and lower jaw. Her phylogenetic analysis recovers it as a non-pseudopalatine leptosuchomorph.

Important discussion in her paper revolves around the importance of the use of apomorphies to describe and classify specimens. In this particular case past workers (myself) had focused on the generally morphology of the squamosal and robustness of the specimen to make a taxonomic assignment and ignored other discrete apomorphies of the material, which a phylogenetic analysis later determined to be of significance.  Thus the longtime practice of assigning isolated phytosaur squamosals to taxa based on general similarity and utilizing these for Late Triassic biochronology is called into question. This general squamosal morphology used to assign (fragmentary and complete) specimens to Rutiodon or Leptosuchus instead just appears to be a shared character of non-pseudopalatine leptosuchomorphs, a paraphyletic assemblage.

As recommended by Michelle it is now necessary to go back to collections such as those from the Petrified Forest and look carefully at all of the specimens assigned to "Leptosuchus" and sort them out using apomorphies. Hopefully this will provide a clear distribution pattern and biochronological signal for these specimens, testing their importance in phytosaur biochronology and biogeography.  Overall this new paper provides a great description and discussion that Michelle should be proud of and will be landmark (along with her 2010 paper) for sorting out the labyrinth that is phytosaur taxonomy.

By the way, the stratigraphic problem mentioned at the beginning of this post was finally figured out by Jeff Martz and I in 2009 when we discovered that the bed in question was definitely not the "Sonsela Sandstone Bed", but rather an isolated sandstone lens in the older Lot's Wife Beds and  Adamanian in age.

Stocker, M. R. 2012. A new phytosaur (Archosauriformes, Phytosauria) from the Lot’s Wife beds (Sonsela Member) within the Chinle Formation (Upper Triassic) of Petrified Forest National Park, Arizona. Journal of Vertebrate Paleontology 32(3): 573-586 DOI:10.1080/02724634.2012.649815

Abstract - A new phytosaur taxon from Petrified Forest National Park, Arizona, is here described based on cranial material from a single individual. This specimen previously was included in an extensive phylogenetic analysis, and it was found to possess a combination of character states that differs from all known phytosaur taxa in addition to two autapomorphies within the braincase and an autapomorphy of the mandible. The new taxon adds to the taxonomic diversity recognized from the Sonsela Member of the Chinle Formation. The continued increase in phytosaur diversity emphasizes the need to more accurately characterize and identify taxa within a phylogenetic systematic context in order to produce a more refined signal for biostratigraphic correlations, biochronologic inferences, and faunal dynamics during the Late Triassic.

Reevaluation of Therapsid Fossils from Antarctica

Huttenlocker, A. K., and C. A. Sidor. 2012. Taxonomic Revision of Therocephalians (Therapsida: Theriodontia) from the Lower Triassic of Antarctica. American Museum Novitates Number 3738 :1-19.

Abstract - We reevaluate the taxonomic status of therocephalian fossils recovered from the lower Fremouw Formation (Lower Triassic) of the central Transantarctic Mountains, Antarctica. The material, which includes mostly fragmentary juvenile specimens, is reidentified using an apomorphy-based approach. We recognize the presence of three higher-level taxa: Eutherocephalia, Akidnognathidae, and Baurioidea. The only genus-level identification is for a partial lower jaw and pterygoid tentatively attributed to the baurioid, Ericiolacerta parva. An indeterminate theriodont partial skull is reassigned to the therocephalian family Akidnognathidae. The holotypes of Pedaeosaurus parvus and Rhigosaurus glacialis are represented by indeterminate juvenile baurioids and, in the absence of clear autapomorphies, are considered nomina dubia. The results of the taxonomic revision indicate that the therocephalian fauna of Antarctica lacks endemic genera and thus corresponds to that of the Triassic Lystrosaurus Assemblage Zone fauna of South Africa's Karoo Basin. More generally, we consider the southern Gondwanan basins of South Africa and Antarctica to sample a broadly distributed Lower Triassic tetrapod fauna, although the latter basin documents the first occurrence of several taxa (e.g., Kombuisia, Palacrodon). More precise (i.e., species-level) identifications are needed to better constrain the biogeographic signal for therocephalians, but the presence of juveniles strongly suggests that this group of therapsids, like dicynodonts, were year-round high-latitude inhabitants during Early Triassic times.

David Peter's Take on Revueltosaurus

David Peters has a new post up on his blog that has been getting some attention including on Facebook.  I'll address it shortly but first I'd like to apologize for the long delay in getting the full description of this taxon out in publication, especially since everyone has now seen Jeff Martz's amazing reconstruction. Originally I suggested he submit it for the Lanzandorf prize because I thought the paper would actually be submitted by that point. The main text has been near completion for some time now and very recently revised.  The hang-up is in completing the figures and because I keep taking on other tasks and responsibilities keeping me from focusing on the project. 

David Peters post with the suggestion that Revueltosaurus may be a paracrocodylomorph is actually fairly insightful given that he has not seen the material first hand and is relying solely on preliminary descriptions and Jeff's reconstruction.  Revueltosaurus is an amazing critter because it possesses character states found in a variety of suchian taxa, including paracrocodylomorphs; however, it has many characters only shared with aetosaurs which results in the position found by Nesbitt (2011). Sterling's coding was based on a thorough examination of all presently known material and although I don't agree with 100% of his codings I don't think the phylogenetic position of Revueltosaurus will change with the publication of the full description and revised phylogenetic analysis.

I'd ask everyone to please be a bit more patient and we'll get the paper out. I realize that it is an important taxon and as a result a lot of people want/need to see the material.

New Ginormous Carnosaur from the Triassic of North America

It is absolutely amazing what has been arriving in my inbox lately, this one caught me by complete surprise.

Howard, M., Howard, S., Fine, L., Howard, C., and J. DeRita. 2010. Chinleraptor dockumensis a megacooldudinid carnosaur (Family Dromaeosauridae) from the Late Triassic (Ungualia biozone) of Texas, the largest (and thus coolest) raptor ever. Upublishyerself 1:1-2.
Abstract - Herein we describe a new taxon of carnivorous dinosaur, Chinleraptor dockumensis, known solely from a gigantic pedal ungual from the Upper Triassic of the southwestern United States. This taxon can be diagnosed by the claw-like shape of its unguals and by its extremely large size. Comparisons with another large claw-bearing dromaeosaur from the southwest U.S., Utahraptor, demonstrates an extreme size difference between the two. Hence we proclaim C. documensis to have the biggest claws of them all. This is further supported by the fact that despite the lack of associated field notes the mudstone matrix suggests that the specimen is from Texas and it is common knowledge that everything is big in Texas. Moreover we reject the recent cladotaxonomic hypotheses of theropod dinosaur relationships and assign C. dockamensis to the Infraorder Carnosauria because of its large size; however, it also has even larger claws than any known carnosaur group and therefore we assign this taxon to a new dromaeosaurid subfamily, which we name Megacooldudinae. A bivariate plot of the size of known specimens of Chinleoraptor versus cumulative sample size percentage demonstrates that all known specimens of C. dockumenses were all equally huge. Therefore we interpret these data to determine that all died at the exact age of 2 years, 3 months, and 27 days, demonstrating the superiority of utilizing size to calculate the precise age at time of death instead of more subjective and thus unreliable techniques such as bone histology. Therefore, despite its enormous size C. decumensis clearly did not live to reproductive age and we predict that no more specimens of its kind exist. Finally, the large claw shaped hole resulting from the collection of this fossil clearly was made by the depression of a pedal element into substrate and therefore represents a new ichnotaxon we name and describe here as Ungualia impressisorium. The co-occurrence of Unguaallia and Chinlerattor in the Dockum is a clear indicator of a Late Triassic age for that highly misunderstood (by others) unit.


Pedal unguals of Utahraptor ostrommaysorum and Chinloraptor dockumi at same scale. Large scale bar equals 10 cm.

Graph showing that all known specimens of Chinlearaptor are "freakin ginormous" at 849 days old.


P.S. Any similarities in this post to real events or published, dearly loved, yet clearly erroneous hypotheses are purely coincidental.

P.P.S. apologies to M. C.

Reptile Assemblage from the Middle Triassic Moenkopi Formation of New Mexico

A very well-written and detailed paper demonstrating the importance of apomophy based identifications when assigning scrappy material to taxa for accurate determination of faunal assemblages. Further demonstrates the abundance of archosaurs, including primitive poposauroids and a possible shuvosaurid, in the Early to Middle Triassic rocks of the American Southwest.

Schoch, R. R., Nesbitt, S. J., Mueller, J. M., Lucas, S. G., and J. A. Boy, J. A. 2009, The reptile assemblage from the Moenkopi Formation (Middle Triassic) of New Mexico. Neues Jahrbuch für Geologie und Paläontologie Abhandlungen, DOI: 10.1127/0077-7749/2009/0030; Stuttgart.

Abstract: Focused collecting and excavation in the Moenkopi Formation (Anton Chico Member)of north-central New Mexico yielded a large quantity of tetrapod bones. Most of the finds were collected from intraformational conglomerates, and consist of isolated bones or bone fragments. The most abundant large members of the assemblage, the archosaurs, include at least three taxa: (1) a primitive suchian or archosauriform, (2) a primitive poposauroid (Arizonasaurus babbitti), and (3) a taxon similar to shuvosaurids. Less abundant remains are tentatively referred to archosauromorphs with rhynchosaur affinities. An analysis of the tetrapod Lagerstätten reveals that primary deposits formed in lakes that were located on floodplains. In these lakes, autochthonous conchostracans, actinopterygians, coelacanths, and temnospondyls were evidently preserved. Fluvial reworking of lacustrine deposits resulted in a secondary deposition of bones, teeth, coprolites, and wood in channel-borne conglomerates. However, the large amount of elements from terrestrial tetrapods indicates that these conglomerates acquired bones from additional primary deposits (?channels, paleosols?) that are still unknown.