The Robo-aetosaur Paratypothorax andressorum

On his recent post on the Staatliches Museum für Naturkunde Stuttgart Dave Hone featured a photo of a rare thing, an aetosaur mount. What Dave found so interesting about this mount; however, is that the missing portions of the skeleton have been filled in with burnished metal (see below).

The "robo-aetosaur" as Dave affectionately calls it, is the holotype specimen of Paratypothorax andressorum Long and Ballew 1985, and if I am not mistaken the actual osteoderms are used in the mount and are completely removable for study (Randy, Sterling, or Jeff will have to correct me on this if I am wrong).

The photo below is one of the dorsal paramedian plates of the left side of the holotype. Paratypothorax is a typothoracisine aetosaur and a member of the clade Paratypothoracisini (Parker, 2007). Members of this clade are characterized by paramedian plates that are much wider than long, have a distinct radial patterning, sharp anteromedial and anterolateral projections, a smooth anterior bar, and a medially offset dorsal eminence or boss.

Paratypothorax is also known from Greenland and the western United States. The best skeleton from the Chinle Formation was collected from Petrified Forest National Park by the Field Museum in 1982. The Petrified Forest specimen was described by Hunt and Lucas (1992) and again by Lucas et al. (2006) who assign it to Paratypothorax andressorum; however, this ID has not been accepted by all workers (e.g., Long and Murry, 1995) who suggest that it may be a new taxon.

Surprisingly the holotype specimen, which consists solely of armor, has never been completely described. Just as strange, even though the Petrified Forest specimen was not considered to be the same taxon as the German material by Robert Long and Karen Ballew, the species name given to the German material (collected in the 1800s and originally believed to be a phytosaur) was named for Chris Andress (the chief ranger at Petrified Forest) and his family (Long and Ballew, 1985).

Thanks to Dave Hone who sent me his photos of the Paratypothorax mount and secured permission to post the photos.

REFERENCES

Hunt, A.P. and S.G. Lucas. 1992. The first occurrence of the aetosaur Paratypothorax andressi (Reptilia, Aetosauria) in the western United States and its biochronological significance. Paläontologische Zeitschrift 66:147-157. DOI:10.1007/BF02989485.

Long, R. A., and K. L. Ballew. 1985. Aetosaur dermal armor from the late Triassic of southwestern North America, with special reference to material from the Chinle Formation of Petrified Forest National Park. Museum of Northern Arizona Bulletin 47:45-68.

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.

Lucas, S.G., Heckert, A.B., and L.F. Rinehart. 2006. The Triassic aetosaur Paratypothorax. New Mexico Museum of Natural History and Science Bulletin 37:575-580

Parker, W. G. 2007. Reassessment of the aetosaur “Desmatosuchus” chamaensis with a reanalysis of the phylogeny of the Aetosauria (Archosauria: Pseudosuchia). Journal of Systematic Palaeontology 5:41–68.

Phytosaur Skull Excavation II

On Wednesday we returned to our phytosaur skull excavation which I first featured on April 14th. Since that time there had been a late spring storm with some precipitation, but the site was covered and fine. The photo below shows the site as uncovered and us continuing the trench around the specimen.

Several pieces of float on the surface were portions of the upper jaw (maxilla) and Jeff set to work piecing it back together. The alveoli (tooth sockets) are clearly visible in the picture below.

Strangely when this piece of maxilla was fit back onto the in-situ specimen the alveoli were facing downwards (see photo below). This was troublesome as the ventral portion of the skull was exposed on the surface. We wondered if we could actually have part of the lower jaw; however, the fragment is definitely not from the lower jaw. Maybe the skull was distorted and the maxilla has disarticulated and flipped around? Extreme distortion of phytosaur skulls is actually common, they often deform plastically and can be flattened, skewed, and even twisted. One specimen from the Chinle has the snout folded tightly like an accordion.

Still, nothing to do except keep on trenching and get ready for the plaster jacketing. So far we have been able to do all the work with pick, shovel, and cold chisels. There appears to be a mud layer in the sandstone just beneath the skull that makes the digging easier.

However, we were starting to get clues that maybe all was not well with this skull. We had a hypothesis and to test this we trenched across the front where the snout should be and found...nothing (see photo below, snout should have been under Jeff's left leg). So far we have the rear portion of the skull, braincase, and palate exposed and an "upside down" maxilla. It quickly became apparent what had happened here, but I will leave that for you to guess at and will reveal in the next post in this series.

New Paper on the Triassic Dinosaur Staurikosaurus pricei

Bittencourt, J.S., and A.W.A. Kellner. 2009. The anatomy and phylogenetic position of the Triassic dinosaur Staurikosaurus pricei Colbert, 1970. Zootaxa 2079:1-56.

Abstract: We redescribe the holotype of the saurischian dinosaur Staurikosaurus pricei Colbert, 1970 from Late Triassic Santa Maria Formation (southern Brazil), following additional preparation that revealed new anatomical features. A revised diagnosis is proposed and the published synapomorphies for Dinosauria and less inclusive clades (e.g. Saurischia) are evaluated for this species. Some characters previously identified as present in the holotype, including the intramandibular joint, hyposphene-hypantrum articulations in dorsal vertebrae, and a cranial trochanter and trochanteric shelf on the femur, cannot be confirmed due to poor preservation or are absent in the available material. In addition, postcranial characters support a close relationship between S. pricei and Herrerasaurus ischigualastensis Reig, 1963 (Late Triassic, Argentina), forming the clade Herrerasauridae. Several pelvic and vertebral characters support the placement of S. pricei as a saurischian dinosaur. Within Saurischia, characters observed in the holotype, including the anatomy of the dentition and caudal vertebrae, support theropod affinities. However, the absence of some characters observed in the clades Theropoda and Sauropodomorpha suggests that S. pricei is not a member of Eusaurischia. Most morphological characters discussed in previous phylogenetic studies cannot be assessed for S. pricei because of the incompleteness of the holotype and only known specimen. The phylogenetic position of S. pricei is constrained by that of its sister taxon H. ischigualastensis, which is known from much more complete material.

Thank You

As some readers may be aware my mother passed away at the beginning of March. I'd like to thank everyone who sent cards and messages. Today I received the following card from a cadre of fellow bloggers. Thank you for your thoughtfulness...

Upcoming Paper on the Basal Ornithischian Dinosaurs Lesothosaurus and Stormbergia

Please note that this is an accepted (in press) publication, has not yet undergone the proofing stage, and thus may still undergo some minor changes before final publication.

Knoll, F., Padian, K., and A. de Ricqles. 2009. Ontogenetic change and adult body size of the early ornithischian dinosaur Lesothosaurus diagnosticus: Implications for basal ornithischian taxonomy. Gondwana Research. Available online 15 April 2009, doi:10.1016/j.gr.2009.03.010.

Abstract: Questions about the taxonomic status, diversity, and pace of evolution of basal ornithischian dinosaurs persist in part because some historically important taxa have been based on incomplete material of uncertain ontogenetic status. We examined the morphology of critical “fabrosaurid” specimens and analyzed the bone tissues of small and large individuals. We conclude that the case for the existence of a non-heterodontosaurid ornithischian distinct from Lesothosaurus diagnosticus in the upper Elliot Formation of southern Africa is not conclusive and we suggest that this species and Stormbergia dangershoeki may actually represent ontogenetic stages of one taxon that reached maturity in approximately four years.

Amazing Convergence: Crustacean vs. Aetosaur

Wow! Check out this blog post at Amphidrome on an amazing (I think) extant gammaroid crustacean from Siberia. I will be damned if the anterior portion of the carapace on Acanthogammarus is not a dead ringer for the cervical armor of the Triassic aetosaur Desmatosuchus spurensis (see Parker, 2008)! Especially check out the last photo on the post (and reproduced below) and compare to the postcard photo of the Petrified Forest mount. Note that the proposed purpose for these structures in the crustacean is defensive, whereas I have argued recently that such spines in aetosaurs may also be used for species recognition and display (Parker, 2007).

Very cool crustacean. Where can I get one? ;)

top photo is from here.

REFERENCES

Parker, W.G. 2007. Reassessment of the aetosaur ‘Desmatosuchus’ chamaensis with a reanalysis of the phylogeny of the Aetosauria (Archosauria: Pseudosuchua). Journal of Systematic Palaeontology 5: 41-68. doi:10.1017/S1477201906001994

Parker, W.G. 2008. Description of new material of the aetosaur Desmatosuchus spurensis (Archosauria: Suchia) from the Chinle Formation of Arizona and a revision of the genus Desmatosuchus. PaleoBios 28:1–40.

Phytosaur Skull Excavation

Awhile back some of our park neighbors alerted us to a specimen weathering out in outcrops of the Sonsela Member of the Chinle Formation. Matt Brown checked it out and identified it as a phytosaur skull. Last week we braved an incoming storm to document the site and check out the specimen. In this photo Jeff Martz is taking notes on the site. This specimen is important because of its stratigraphic position, just below what we believe is the Jasper Forest bed, and based on this should represent a "Leptosuchus".

As you can see the specimen is weathering out along its entire length. The matrix is a muddy, poorly sorted sandstone, crystalline and very hard in some places, and easily friable in others. This will make for a challenging excavation.

Although at first glance the specimen looks like just a scatter of weathered fragments, closer examination (below) shows that it is a phytosaur skull. The specimen is lying with its ventral surface exposed. Unfortunately much of the ventral surface has fragmented and much is missing; however, the upper portion of the skull, including the all important squamosals, should be present. We believe that the rostrum may be gone but cannot say for sure without further excavation.

The bottom photo shows where we left off on our first day (2 hours) at the site. We have picked up much of the float outside of the skull perimeter and consolidated loose pieces that are nearly in place. About six or seven centimeters down the matrix gets really hard. Looks to be a three or four day job.

I will be posting our progress with this specimen regularily mainly because the landowners, who have generously donated the specimen, will be away and thus can follow the excavation here. Of course I hope that my readers will also find this of interest.

New Issue of Albertiana Out - Triassic Stratigraphy Newsletter/Journal

From its official webpage, "Albertiana is the newsletter of the Subcommision on Triassic stratigraphy". This subcommision is responsible for establishing a standard, global stratigraphic scale for the Triassic system. Albertiana is published twice a year (usually) and features reports on conferences, news items, special reports, bibliographies, etc.. all dealing with the Triassic. The website includes free access to recent and current issues. The newest issue was just released and you can access it here.

While you are at it check out the subcommision on Triassic stratigraphy webpage here.

I've Been Waiting For This For A Long Time

Walker, J., & Geissman, J. (2009). 2009 GSA Geologic Time Scale GSA Today, 19 (4) DOI: 10.1130/1052-5173-19.4-5.60

The Geological Society of America has just released its updated geological timescale for 2009 (here and here). A significant revision of this timescale is the Triassic section based on recent studies by Furin et al. (2006) and Kent and Olsen (2008). Most notably is the incorporation of the "long Norian" stage. In the previously published version of the timescale, the Carnian/Norian boundary was dated at 216.5 Ma. Now this boundary is dated at 228 Ma, which in the previous version was the date for the Ladinian/Carnian boundary (Middle/Late Triassic boundary).

The beginning of the Late Triassic is now dated at 235 Ma (previously a strong Middle Triassic date). Incredibly the majority of the Triassic now consists of the Late Triassic. In fact just the Norian stage (24 my) of the Late Triassic is longer than the combined Early (6 my) and the Middle (17 my) Triassic Epochs! The base of the Triassic is still at 251 Ma (defined by a GSSP); however, the age of the Triassic/Jurassic boundary has changed from 199.6 Ma to 201.6 Ma.

As it is now "official" the "long Norian" will have significant implications for the age of the Chinle Formation and other supposed "Carnian" fossil assemblages worldwide as suggested recently by studies such as that of Furin et al. (2006) and Irmis and Mundil (2008). As more GSSPs are established for the Triassic these dates should stabilize.

REFERENCES

Furin, S., Preto, N., Rigo, M., Roghi, G., Gianolla, P., Crowley, J.L., and Bowring, S.A., 2006, High-precision U-Pb zircon age from the Triassic of Italy: Implications for the Triassic time scale and the Carnian origin of calcareous nannoplankton and dinosaurs: Geology, v. 34, p. 1009–1012, doi: 10.1130/G22967A.1.

Irmis, R. B., and R. Mundil. 2008. New age constraints from the Chinle Formation resolve global comparisons of Late Triassic vertebrate assemblages. Journal of Vertebrate Paleontology 28:95A.

Kent, D.V., and Olsen, P.E.,2008, Early Jurassic magnetostratigraphy and paleolatitudes from the Hartford continental rift basin (eastern North America): Testing for polarity bias and abrupt polar wander in association with the central Atlantic magmatic province: Journal of Geophysical Research, v. 113, B06105, doi: 10.1029/2007JB005407.

More Free PDF Access - Vertebrata Palasiatica

For those of you not subscribed to the Dinosaur Mailing List or the Vertebrate Paleontology List, note that the Chinese journal Vertebrata Palasiatica is now available freely on-line. I do not know how long it will be open for, but here is the URL:

http://www.ivpp.ac.cn/en/about_ivpp/about_IVPP_vpa.html

Free PDFs of Paläontologische Zeitschrift

Springer-Link is currently offering free access to PDFs of Paläontologische Zeitschrift from 1957 to the present. This journal features Geology and Paleontology papers in German and English. This series includes many Late Triassic dinosaur and pseudosuchian papers such as this, this, this and this. The PDF quality is not the greatest but is still better than the blacked out figures in my interlibrary loan copies.

Happy downloading.

Historic USGS Photos of the Chinle Formation

Caption: View Petrified Forest, Lithodendron Wash, Apache and Navajo counties, Arizona. Fort Defiance quadrangle. Chinle formation. August, 1913.

The above photo shows scattered petrified logs from a portion of Petrified Forest National Park known as the Black Forest. This photo was taken by the famous American geologist Herbert E. Gregory during the course of research, which resulted in his 1917 report that first named the Chinle Formation (Gregory, 1917).

This photo is available at the U.S. Geological Survey online photographic library and is one of 223 photos of the Chinle Formation. Some of these photos have previously been published in USGS publications; however, many of them are still unpublished. Over 100 photos are from Gregory's important Chinle work from the early to mid 1900s. Old photos are an indispensible resource when conducting stratigraphic work as it allows the stratigrapher to view key outcrops which were important to the original studies. Before the advent of point and shoot and digital cameras a lot of work went into taking and developing photos and therefore sites were only photographed when they were of some importance.

Jeff Martz has already discussed (scroll down past the giraffe and donkey part) the importance of photographing key stratographic sections, labelling them, and publishing them in order to allow future researchers to replicate and test your work. We are currently dealing with the frustrating task of trying to relocate key Chinle sections (type sections) in order to match them with our current work. Unfortunately the original publications provide only vague directions to and descriptions of these outcrops and more recent workers who claim to have relocated the sites (and measured sections there) have published data not only with geographical errors but also with measured sections that do not even come close to matching the original descriptions (more on some of these in future posts, maybe they thought no one else would ever check?).

To close, here is another classic H.E. Gregory photo. "Division C" was later formally named the Petrified Forest Member (Gregory, 1950).


Caption: Chinle formation, Division C, Chinle Valley, near Round Rock. June, 1913.

REFERENCES

Gregory,H. E. 1917. GeologyoftheNavajo Country -a reconaissance of parts of Arizona, New Mexico. and Utah: U.S. Geological Survey Professional Paper 93, 161 p.

Gregory, H.E. 1950. Geology and geography of the Zion [National] Park region, Utah and Arizona: U.S. Geological Survey Professional Paper, 220, 200 p.

Phytosaur Skull Preparation II

I last featured this phytosaur skull undergoing preparation on February 24th and since that time more work has been done. Some of the right side of the skull has now been exposed. Preparation has been slow due to a plethora of other projects combined with a really tough sandstone matrix. Separation is poor in places and in parts the bone is impregnated with hematite, a common condition of bone encased in Chinle sandstones.

The ventral portion of the right side of the skull projects laterally a little too far suggesting that some dorsoventral crushing of the skull has occurred. So far we have exposed the lateral surface of the posterior projection of the squamosal (it is still a pseudopalatine), both frontals, the right jugal and much of the right maxilla. This picture shows the right side of the skull as currently exposed. Anterior (forward) is to the right, posterior (back) is to the left.




Preparation continues and we will follow it here until it is complete.

Whoa! New Feathered Pseudosuchian from the Upper Triassic of Texas

This paper just came out today and its appearance is timely given that it is right on the heels of the feathered heterodontosaur paper. The reconstruction is particularily striking!

Fry, P.J., Bender, B.R., and L. Turanga. 2009. A new feathered aetosaurian pseudosuchian from the Rottenhillian (?Carnian/?Norian?) of Texas. Naturama 55:235-236.

Abstract – The Rotten Hill Quarry from the Upper Triassic of Texas is reknown for its non-distinctive, somewhat important, and thus monograph worthy vertebrate faunal assemblage that includes indeterminate metoposaurs and phytosaurs, and tiny vertebrates which have been assigned to numerous different taxa based on their perceived stratigraphic position and a whole wack of plesiomorphies. Here we describe a new aetosaurian pseudosuchian, Thecopullipectosuchus alienus, which possesses the first preserved integument known for this clade. This integument consists of numerous structures, which have been interpreted to represent proto-feathers in ornithischians and saurischians. Despite being known from only a single mostly complete paramedian plate, it is apparent that the tube-like structures emanate from pitting in the dermal armor, solving the mystery of the purpose of these structures. It is hypothesized here that the differences in dermal armor ornamentation in aetosaurs reflects the distribution of proto-feathers, which is diagnostic to taxa. Furthermore although the ornamentation of the dorsal armor in Thecopullipectosuchus is identical to Typothorax, it is not referable to that taxon due to the integument and the distinct “flarked” nature of the plates rather than being flexed or arched as in Typothorax. Despite only being known from a single locality, Thecopullipectosuchus is erected here as an index taxon of the Rottenhillian sub-lvf. Another aetosaur from this locality, Sierritasuchus, despite being autapomorphic, is considered here to be a junior synonym of Desmatosuchus simply to further strengthen our biostratigraphic hypothesis and because we strongly dislike the people who named it. The presence of proto-feathers in a pseudosuchian archosaur pushes the first occurrence of these structures back almost to the base of Archosauria and conclusively demonstrates that dinosaurs really are pseudosuchian wanna-bees as previously suspected.
P.S. Any similarities in this post to real events or published, dearly loved, yet clearly erroneous hypotheses are purely coincidental.