Field of Science

New Triassic themed blog and another earliest dinosaur claim

I just recently became aware of this relatively new blog "The Life of Madygen" which has featured several posts on Triassic paleontology. Check it out. One recent post discusses purported sauropodomorph dinosaur footprints from Middle Triassic rocks near Bernberg Germany (also see this related article and my earlier post). If indeed attributable to dinosaurs, this find would represent the earliest occurrence of dinosaurs in the world; a claim which would need some accompanying body fossils to it back up, given the wide variety of Triassic critters that could hypothetically create a "dinosaur" track. One of the more outspoken critics of the claim seems to be Dr. Hartmut Haubold, an archosaur track specialist, who stated "It's ridiculous, it's as if someone found a 10-million-year-old stone and claimed it was a hand axe made by humans." "Dinosaurs didn't come into existence until a good 15 million years later" than these tracks. Haubold believes the trackmaker is Cheirotherium, which has been attributed to crocodile-line archosaurs such as "rauisuchians" (who do have body fossils preserved in Middle Triassic deposits).

Whereas I consider tracks to provide important information regarding the fossil record, especially information about the "living animal" that bones alone cannot preserve, I feel that claims such as these should only be made in concert with other lines of evidence, especially body fossils. I am reminded of a talk I saw a few years ago where it was stated that based on track evidence, the most common animal in the Late Triassic fauna of North America were sauropods. I found this claim quite perplexing given that not even a single bone of a sauropodomorph has ever been found in rocks of this age.

Dr. John A. Wilson (1914-2008)

With much sadness I heard of the passing of Dr. John A. Wilson earlier this week (photo courtesy of the National Park Service). Dr. Wilson was a charter member of the Society of Vertebrate Paleontology and founded the Vertebrate Paleontology Lab at the University of Texas in Austin, supervising and influencing numerous students for over sixty years. Whereas his main field of study was Tertiary mammals, he studied under Ermine Cowles Case at the University of Michigan and published several papers on Triassic vertebrates (Wilson 1941; 1948) as well as a paper describing topotypes of the aetosaur Desmatosuchus spurensis (Wilson, 1950). Although I never had the opportunity to meet Dr. Wilson in person, I wrote to him back in 2002 regarding his relationship with Case (who originally described Desmatosuchus, the topic of my graduate work). Dr. Wilson kindly responded with a handwritten letter containing much information about Case. I'd like to share a portion of that letter here:

"I was the first of two graduate students that Dr. Case had at Univ. Michigan. In the fall of my freshman year I went to his office at the museum to introduce myself and to tell him I wanted to major in VP. His first words to me were: "Son, you are a damn fool, where do you expect to get a job?" I replied that I didn't know, but maybe something will open up. We talked a while and then he said "when do you want to go to work?" I swallowed and said "now!" He pulled a piece of amphibian bone from the Permian of N. Texas and put me to work cleaning it."

From the influence that Dr. Wilson had on his friends, students, and colleagues, the Society of Vertebrate Paleontology, and the profession of paleontology, it is clear that much opened up for this remarkable man.

REFERENCES

Wilson, J. A. 1941. An interpretation of the skull of Buettneria, with special reference to the cartilages and soft parts. Contributions from the University of Michigan Museum of Paleontology 6:71-111.

Wilson, J. A. 1948. A small amphibian from the Triassic of Howard County, Texas. Journal of Paleontology 22:359-361.

Wilson, J. A. 1950. Cope's types of fossil reptiles in the collection of the Bureau of Economic Geology , University of Texas. Journal of Paleontology 24:113-115.

Mystery Fossil #2 is.....

...the astragalus of the basal saurichian Chindesaurus bryansmalli. Kudos to Adam and Jaime who got it right. This element is from the holotype specimen, and one of the autapomorphies of the taxon as proposed by Long and Murry (1995) was an astragalus that is "glutealiform" in ventral view, which probably ranks as one of my favorite descriptive terms of all time. Unfortunately (if you are a fan of this character), we (Sterling Nesbitt, Randy Irmis, and myself) determined that the element is actually broken and worn and actually was similar to the astragalus of other basal saurischians including Saturnalia and Herrerasaurus (Nesbitt et al, 2007).

The SVP meeting was very well attended with a fabulous program of oral and poster presentations. It is always great to catch up with colleagues (and to meet lots of new people), although unfortunately I did have to miss the bloggers lunch. I was at the open SVP Executive Committee meeting and hopefully my absence at the lunch was understood. There were some excellent (and important ) Triassic talks which I may feature here in the near future. As directly blogging on the content of posters and talks is discouraged by the SVP, I will focus on the published abstracts and my take on their implications. Stay tuned.

REFERENCES

Long, R.A., and P.A. Murry. 1995. Late Triassic (Carnian and Norian) tetrapods from the Southwestern United States. New Mexico Museum of Natural History and Science Bulletin 4:1–254.

Nesbitt, S.J., Irmis, R.B., and W.G. Parker. 2007. A critical re-evaluation of the Late Triassic dinosaur taxa of North America. Journal of Systematic Palaeontology 5:209-243.

SVP Meeting and Mystery Fossil #2

I am off to attend the annual meeting of the Society of Vertebrate Paleontology in Cleveland. There are lots of interesting abstracts (especially Triassic) and I am hoping it will be a very good meeting.


Because I will not be posting for over a week I've included another mystery fossil for anyone still checking these pages. I'll give you a couple of hints, you are looking the element in distal (ventral) view, the specimen is an archosaurian bone from the Chinle Formation, the specimen is part of the holotype of an animal whose generic name roughly translate as "ghost reptile", and another clue can be found by reading over the comments from Triassic Mystery Fossil #1.



New "Proto-Turtle" from the Late Triassic of New Mexico

Chinlechelys tenertesta ("delicate shelled turtle from the Chinle") is a newly described stem turtle from the Upper Triassic of New Mexico (Joyce et al., 2008). Based on fragmentary but diagnostic material, the implications of this find are the subject of several recent news articles (here and here for examples). Most importantly the find gives clues to the evolution of the turtle shell and demonstrates that early turtles possessed a carapace of rows of dermal armor. A figure from the paper and news reports (courtesy of the Royal Society) shows a hypothesized gradual evolution of the shell.


Furthermore this specimen demonstrates that the ribs are independent ossifications from the osteoderms, contrasting embryological evidence. Thus this specimen is considered by one researcher to be "one of the most important turtle fossils ever found."

There are a couple of other aspects of this paper that I would like to address. First off, I feel that the genus name is misleading as the specimen is from the Bull Canyon Formation which is actually from the Dockum Group and not from the Chinle Formation. Lucas (1993) and Lucas and Anderson (1994) did place the Dockum (as a formation) in an expanded Chinle Group (and later papers by Lucas and colleagues abandon the name completely), however, this is still controversial and not accepted by all Triassic workers as the older name Dockum would have priority under the North American Stratigraphic Code (e.g., Lehman, 1994; Dubiel, 1994; Carpenter, 1997).

The second point which I find interesting is the interpretation of a terrestrial habitat for Chinlechelys based the depositional setting for the locality as interpreted by Newell (1993). Below is the faunal list for this locality as provided by Hunt (2001) which shows a fair mix of aquatic taxa, although this would not necessarily argue against a terrestrial setting, especially with the presence of aetosaurs, "rauisuchians", Revueltosaurus, and poposaurs.

Bull Canyon fauna from NMMNH loc 1 (from Hunt, 2001)

?Colobodontidae indet.
Actinopterygii indet.
Ceratodontoidei indet.
Quayia zideki (Coelocanthidae)
Apachesaurus gregorii (Metoposauridae)
Lepidosauria indet.
Rhynchosauridae indet.
Parasuchia indet.
Typothorax coccinarum (Aetosauria)
Rauisuchidae indet.
Shuvosaurus inexpectatus (Poposauridae)
Revueltosaurus callenderi (Pseudosuchia)
Sphenosuchia indet. ?theropoda indet.

What is striking is that except for the indeterminate rhynchosaur and leidosaur this fauna is extremely similar to sites in Petrified Forest National Park where Revueltosaurus callenderi is common (Parker and Irmis, 2005). Indeed the site that provided Chinlechelys is also the type locality of R. callenderi. Thus, it is these types of units (terrestrial and Revueltosaurus bearing) which may represent the proper environment and age to provide more "proto-turtle" material.

REFERENCES

Carpenter, K. 1997. A giant coelophysoid (Ceratosauria) theropod from the Upper Triassic of New Mexico, USA. Neues Jahrbuch für Geologie und Paläontologie, Monatschefte 205(2):189-208.


Dubiel, R. F. 1994. Triassic deposystems, paleogeography, and paleoclimate of the Western Interior; pp. 133-168 in M. V. Caputo, J. A. Peterson, and K. J. Franczyk (eds.), Mesozoic Systems of the Rocky Mountain Region, USA. Rocky Mountain Section Society of Economic Paleontologists and Mineralogists (Society for Sedimentary Geology), Denver, Colorado.


Hunt, A. P. 2001. The vertebrate fauna, biostratigraphy, and biochronology of the type Revueltian land-vertebrate faunachron, Bull Canyon Formation (Upper Triassic), East-central New Mexico; pp. 123-152 in in S. G. Lucas and D. S. Ulmer-Scholle (eds.), Geology of the Llano Estacado: New Mexico Geological Society Guidebook, 52nd Field Conference.

Joyce, W. G., Lucas, S. G., Scheyer, T. M., Heckert, A. B., and A. P. Hunt. 2008. A thin-shelled reptile from the Late Triassic of North America and the origin of the turtle shell. Proceedings of the Royal Society B, published early on-line, doi: 10.1098/rspb.2008.1196.


Lehman, T. M. 1994a. The saga of the Dockum Group and the case of the Texas/New Mexico boundary fault. New Mexico Bureau of Mines and Mineral Resources Bulletin 150:37-51.


Lucas, S. G. 1993b. The Chinle Group: Revised Stratigraphy and Biochronology of Upper Triassic Nonmarine Strata in the Western United States; pp. 27-50 in M. Morales (ed.), Aspects of Mesozoic Geology and Paleontology of the Colorado Plateau: Museum of Northern Arizona Bulletin 59.


Lucas, S. G., and O.J. Anderson. 1994. The Camp Springs Member, base of the Late Triassic Dockum Formation in West Texas. West Texas Geological Society Bulletin 34(2):5-15.


Newell, A. J. 1993. Depositional environment of the Late Triassic Bull Canyon Formation (New Mexico): Implications for ‘Dockum Formation’ Paleogeography; pp. 359-368 in S. G. Lucas and M. Morales. 1993. The Nonmarine Triassic: New Mexico Museum of Natural History & Science Bulletin 3.


Parker, W. G., and R. B. Irmis. 2005. Advances in Late Triassic vertebrate paleontology based on new material from Petrified Forest National Park, Arizona; pp. 45-58 in A. B. Heckert and S. G. Lucas (eds.), New Mexico Museum of Natural History and Science Bulletin 29.

Late Triassic Mystery Fossil #1 is...


...the posterior portion of the right squamosal bone of a phytosaur. Because of the robust nature of these elements they are often preserved even when the rest of the skull is not. In fact, they are a very common fossil in the Chinle Formation. This is actually fortunate because the morphology of the posterior process of the squamosal is diagnostic and therefore the entire skull does not need to be recovered to determine the presence of a taxon. The specimen to the upper left belongs to Pseudopalatus pristinus and is characterized by being extremely thickened and knoblike (down in the photo is posterior), with many surfaces for muscle attachment. Phytosaur evolution is characterized by changes in the "post temporal" arcade, including depression and narrowing of the supratemporal fenestrae as well as a posterior elongation and mediolateral widening of the squamosal process. The common preservation and recovery of isolated squamosals in concert with their diagnostic nature make them excellent biostratigraphic index fossils and thus they should be collected whenever found. The picture below shows a complete upper portion of a skull of P. pristinus with the position of the squamosal fragment above (from a different individual) outlined.

Late Triassic Mystery Fossil #1

One of the key skills needed to work on Late Triassic fossils is the ability to readily identify fragmentary specimens (because that is all that you usually get!). I've seen this on a few other blogs and have found it entertaining, so from time to time I will present a mystery fossil specimen from the Late Triassic for reader identification. I'll start with a fairly easy one. I would ask some of my colleagues who specialize in the Late Triassic and read this blog to please refrain from providing an ID immediately ;).