Back in August I briefly discussed the find of a large theropod and dicynodont from a quarry in Lisowice in southern Poland. This find is significant because it represents the latest stratigraphical unambiguous occurrence of a dicynodont in the Late Triassic, as well as the possible earliest occurrence of a tetnuran theropod. The peer-reviewed article detailing this find is now out in Acta Palaeontologica Polonica.
I still need to read through the paper to comment some more but in the meantime here is the abstract:
It is generally accepted that during the Triassic the composition of tetrapod faunas underwent a series of fundamental transformations, mainly as a result of diversification of
archosaurs and decline of therapsids (Benton 1994, 2004, 2006). The last herbivorous basal synapsids, dicynodonts, disappeared from the record in the early Norian of the
Americas, about 220 Ma (Langer et al. 2007), being unknown from the Late Triassic of Europe. Here, we report a partially articulated skeleton and isolated bones of a giant
rhino−size dicynodont in the Upper Triassic fluvial sediments at Lisowice (Lipie Śląskie clay−pit) in southern Poland. Paleobotanical data indicate an early Rhaetian age for
the fauna (Dzik et al. 2008; Niedźwiedzki and Sulej 2008). The dicynodont bones are associated with bones of carnivorous dinosaurs, pterosaurs, as well as capitosaur and plagiosaur amphibians. Dicynodonts were represented in the Germanic Basin throughout the Late Triassic, as proven by findings of smaller dicynodonts in older deposits in the same area, associated there with temnospondyl amphibians. It appears, thus, that the fossil record of tetrapod succession in the Late Triassic was strongly controlled by ecological factors and biased by uneven representation of particular environments. The Lisowice assemblage proves that faunas dominated by dicynodonts did not entirely disappear at least until the end of the Triassic.
REFERENCE
Dzik, J., Sulej, T., and G. Niedźwiedzki. 2008. A dicynodont−theropod association in the latest Triassic of Poland. Acta Palaeontologica Polonica 53:733–738.
Rethinking Turtle Origins - Odontochelys
What an exciting time it must be to work on basal turtles. Hot on the heels of Chinlechelys and Eileanchelys comes a new basal turtle, Odontochelys semitestacea, from the Norian (~220 Ma) of China. The article and commentary came out today in the journal Nature and you can also read about it here and here.
Odontochelys predates other earliest known turtles by at least 5 million years and is from marine rocks suggesting a marine origin for turtles. The complete fossil (see these photos from the Nature News website), known from four specimens, possesses a ventral plastron but not a dorsal carapace suggesting that the plastron formed first (but see argument by Reisz and Head, 2008).
Finally, as also hinted at by the name, Odontochelys is the first known turtle to possess teeth.
Whereas, the marine origin is surprising given the terrestrial nature of other Triassic turtles overturning what was thought to be a stable hypothesis, the teeth are a nice find, but not so surprising given that turtles must have originated from a toothed reptilian ancestor.
As to the ventral carapace forming first, Reisz and Head (2008) argue against the interpretation provided by Li et al. (2008); however, based on a statement made by Li that "here, in our hands, there is an ideal missing link for turtle evolution. It has no osteoderms on its back, but only ossified neural [central] plates and expanded ribs." I wonder if what we are looking at is a preservational artifact. Maybe the plastron fully ossifies earlier on in ontogeny. Not being a turtle specialist or seeing the specimens I may be completely wrong, but that is the explanation that first popped into my head.
Sounds like there is a lot more exploration and work to be done on basal turtles.
REFERENCES
Chun Li, Xiao-Chun Wu, Olivier Rieppel, Li-Ting Wang, Li-Jun Zhao (2008). An ancestral turtle from the Late Triassic of southwestern China Nature, 456 (7221), 497-501 DOI: 10.1038/nature07533
Robert R. Reisz, Jason J. Head (2008). Palaeontology: Turtle origins out to sea Nature, 456 (7221), 450-451 DOI: 10.1038/456450a
Whereas, the marine origin is surprising given the terrestrial nature of other Triassic turtles overturning what was thought to be a stable hypothesis, the teeth are a nice find, but not so surprising given that turtles must have originated from a toothed reptilian ancestor.
As to the ventral carapace forming first, Reisz and Head (2008) argue against the interpretation provided by Li et al. (2008); however, based on a statement made by Li that "here, in our hands, there is an ideal missing link for turtle evolution. It has no osteoderms on its back, but only ossified neural [central] plates and expanded ribs." I wonder if what we are looking at is a preservational artifact. Maybe the plastron fully ossifies earlier on in ontogeny. Not being a turtle specialist or seeing the specimens I may be completely wrong, but that is the explanation that first popped into my head.
Sounds like there is a lot more exploration and work to be done on basal turtles.
REFERENCES
Chun Li, Xiao-Chun Wu, Olivier Rieppel, Li-Ting Wang, Li-Jun Zhao (2008). An ancestral turtle from the Late Triassic of southwestern China Nature, 456 (7221), 497-501 DOI: 10.1038/nature07533
Robert R. Reisz, Jason J. Head (2008). Palaeontology: Turtle origins out to sea Nature, 456 (7221), 450-451 DOI: 10.1038/456450a
Pseudopalatus jablonskiae
rutgerjansma answered both quickly and correctly. Mystery fossil #3 is the holotype skull of the phytosaur Pseudopalatus jablonskiae named by myself and Randall Irmis in 2006. This skull was collected from the Sonsela Member of the Chinle Formation in Petrified Forest National Park. It was lying palate side up in a path used by archaeologists to access a ruined pueblo on a cliff top. Fortunately, Pat Jablonsky (a long time volunteer at the Denver Museum of Natural History, who was working as a ranger in the park at the time) recognized the specimen in the path and brought it to my attention. Unfortunately, it was pretty badly eroded (and trampled) and only the skull roof was still in-situ. The upper portion of the brain case was able to be reassembled by collecting the float. Preparation showed that it was a pseudopalatine phytosaur; however, it differed from other known pseudopalatines in possessing very anteroposteriorly short squamosal processes (seen in the photo below projecting from the back of the skull). In addition, the squamosal tips were not pointed and 'knob-like' as in other pseudopalatines, but more like the older Leptosuchus. This was supported by a character of the braincase, the entrance of an anterior projection of the squamosal into the lateral wall, another character of Leptosuchus (Camp, 1930). Finally, there is a small fossa around the supratemporal fenestra that is only seen in this specimen (autapomorphy). These characters and discussion with Axel Hungerbuehler (probably THE expert on phytosaurs) made us realize that this specimen was unique. Unfortunately, unique was definitely the right word here, because this incomplete skull is the only known specimen of P. jabloskiae.
However, earlier this summer a trip back to the quarry resulted in the discovery of the lower portion of the braincase of the holotype specimen. It had rolled away from the exposed skull and been buried, surfacing only this year. Subsequently another trip was made to the site to try to find more of the holotype and another, this time complete, skull of a phytosaur was found about 40 meters away and at the same horizon. This specimen has not been prepared yet but preliminary work during the excavation suggests that it may belong to P. jablonskiae. If so this would provide a description of the rest of the skull and further support the taxonomic validity of the species.
One more note. In our 2006 paper we state that P. jablonskiae is from just above the base of the Sonsela Member and therefore represents the lowest occurrence of Pseudopalatus in Petrified Forest National Park. However, reexamination of the Sonsela Member this summer by Jeff Martz figured out that the type locality for P. jablonskiae is higher in the Sonsela than previously believed, and that it occurs just above other localities that have provided specimens of another species of Pseudopalatus, P. pristinus. Thus, the newly recovered skull becomes even more important to test whether or not P. jablonskiae is restricted to a narrow horizon or represents a species that co-existed with P. pristinus.
The full description of P. jablonskiae can be found at Randall Irmis' CV page.
REFERENCES
Camp, C. L. 1930. A study of the phytosaurs with description of
new material from western North America. Memoirs of the University
of California, 10:1-174.
Parker, W. G., and R. B. Irmis. 2006. A new species of the Late Triassic phytosaur Pseudopalatus (Archosauria: Pseudosuchia) from Petrified Forest National Park, Arizona. Museum of Northern Arizona Bulletin 62:126-143.
However, earlier this summer a trip back to the quarry resulted in the discovery of the lower portion of the braincase of the holotype specimen. It had rolled away from the exposed skull and been buried, surfacing only this year. Subsequently another trip was made to the site to try to find more of the holotype and another, this time complete, skull of a phytosaur was found about 40 meters away and at the same horizon. This specimen has not been prepared yet but preliminary work during the excavation suggests that it may belong to P. jablonskiae. If so this would provide a description of the rest of the skull and further support the taxonomic validity of the species.One more note. In our 2006 paper we state that P. jablonskiae is from just above the base of the Sonsela Member and therefore represents the lowest occurrence of Pseudopalatus in Petrified Forest National Park. However, reexamination of the Sonsela Member this summer by Jeff Martz figured out that the type locality for P. jablonskiae is higher in the Sonsela than previously believed, and that it occurs just above other localities that have provided specimens of another species of Pseudopalatus, P. pristinus. Thus, the newly recovered skull becomes even more important to test whether or not P. jablonskiae is restricted to a narrow horizon or represents a species that co-existed with P. pristinus.
The full description of P. jablonskiae can be found at Randall Irmis' CV page.
REFERENCES
Camp, C. L. 1930. A study of the phytosaurs with description of
new material from western North America. Memoirs of the University
of California, 10:1-174.
Parker, W. G., and R. B. Irmis. 2006. A new species of the Late Triassic phytosaur Pseudopalatus (Archosauria: Pseudosuchia) from Petrified Forest National Park, Arizona. Museum of Northern Arizona Bulletin 62:126-143.
Late Triassic Mystery Fossil #3
Man I am busy (but aren't we all?), family, two jobs, research, upcoming holidays, and now studying for the GRE (I last took it 11 years ago!). Not too sure what I am thinking at times. Anyhow, I have not done one of these for awhile so here is Late Triassic mystery fossil #3. It comes from the Chinle Formation and is shown here in dorsal view. Hopefully I will post on this fossil and its relatives soon. I also know that there are a few new Triassic papers coming down the pipe soon, so there will be lot to cover in the next couple of months....but for now it is back to the quantitative section study guide.
New Paleontology Blog - Paleo Errata
I'd like to point out a new blog written by one of my colleagues, Dr. Jeff Martz, called Paleo Errata and found here: http://paleoerrata.blogspot.com/
I agree with Jeff that blogs are an excellent way to communicate and share ideas on a variety of topics, especially geology and paleontology. Like Jeff, I wholly support the sharing of information and open communication between researchers and hope that some day we all can do so freely without the fear of being betrayed. Developing professional relationships with colleagues including the sharing of unpublished information not only makes science fun, it is integral to doing good science. So much is going on "behind the scenes" and "in progress" that not being privy to such information inhibits our ability to formulate and test up to date hypotheses. Of course this involves a fair amount of trust that must be earned as well as given. There is plenty of material for everyone to work on and/or collaborate on without needing to rip each other off.
Jeff has offered to provide his unpublished ideas on various subjects on his blog and I would like to do the same from time to time here as well. Let's make an effort to open things up.
I just need everyone to promise not to...... ;)
I agree with Jeff that blogs are an excellent way to communicate and share ideas on a variety of topics, especially geology and paleontology. Like Jeff, I wholly support the sharing of information and open communication between researchers and hope that some day we all can do so freely without the fear of being betrayed. Developing professional relationships with colleagues including the sharing of unpublished information not only makes science fun, it is integral to doing good science. So much is going on "behind the scenes" and "in progress" that not being privy to such information inhibits our ability to formulate and test up to date hypotheses. Of course this involves a fair amount of trust that must be earned as well as given. There is plenty of material for everyone to work on and/or collaborate on without needing to rip each other off.
Jeff has offered to provide his unpublished ideas on various subjects on his blog and I would like to do the same from time to time here as well. Let's make an effort to open things up.
I just need everyone to promise not to...... ;)
Enigmatic Taxa I - Acallosuchus rectori
From time to time I'd like to introduce readers to some of the more 'interesting' Triassic critters. To start things off I will cover one of the more poorly known taxa, a mystery fossil in its own right, Acallosuchus rectori from the Chinle Formation of Arizona.
In his fieldnotes from May 22, 1923 Charles Camp discusses the discovery of what he described as the skull of "a small dinosaur or pterodactyl" from a quarry in what is today Petrified Forest National Park. His notes further state that he "plastered this and took it out but plaster broke off block and it had to be removed in pieces. Skull ab
out 6 inches long. Part of rostrum broken" (Long and Murry, 1995). Accompanying this description is a field sketch of this "skull" (figure to the left taken from Irmis, 2005). According to Long and Murry (1995) when they rediscovered the specimen (in a cigar box) in the early 1980s the specimen bore almost no resemblance to Camp's field sketch. Still, what was preserved, although barely identifiable, is autopomorphic thus they felt justified to erecting a new taxon based on this material.
Previously the specimen was considered to represent a possible protrochampsid by Murry and Long (1989) who assigned a fragmentary postcranial skeleton (from probably the same locality) to their new taxon. However, by 1995 they had separated the material, naming the postcranial material Vancleavea campi, and the "skull" Acallosuchus rectori (Rector's ugly crocodile). We now know, based on new material (e.g., Hunt et al., 2002; Parker and Barton, 2008), what the skull of Vancleavea looks like and that this separation was indeed correct. Unfortunately, the skull is only known from a partial "mandible", and two other skull fragments which were interpreted as a portion of the frontal and postorbital, and a portion of the "postorbitojugal" bar by Long and Murry (1995).
Furthermore, Camp's sketch is unlike any known "reptile" skull, but as presented it would suggest that the element that Long and Murry (1995) identify as a dentary would actually be a maxilla. The large triangular opening would be an antorbital fenestra, above that a nasal and anteriorly (to the right on the drawing) possibly a premaxilla. The posterior opening could be an orbit, surrounded by a jugal/lacrimal bone anteriorly, and a postorbital dorsally? Unfortunately, the sketch does not provide clarification and was not labelled.
One of the autapomorphies of Acallosuchus is the presence of what Long and Murry (1995) described as osteoderms covering the surfaces of the skull. Irmis (2005) who further commented on this specimen and described these "osteoderms" as subtriangular knobs and noted that these knobs "are often arranged in rows running the length of the bone, and are themselves sculptured with longitudinal furrows. Other areas of bone not covered by these eminences are sculptured with additional grooves" (see photo below [from Irmis, 2005] of the dentary [occusal view] and another skull fragment [? view] showing these unique "knobs").
As discussed by Long and Murry (1995) and further commented on by Irmis (2005) the phylogenetic placement of this taxon is highly ambiguous. Long and Murry (1995) considered Acallosuchus to be a "neodiapsid" based on the presence of the "postorbitojugal bar"; however, even this identification is not unambiguous (Irmis, 2005) and will remain so without the discovery of more and better material.
One final note. Long and Murry (1995:193) named the species from ex-superintendent of Petrified Forest National Park Roger Rector, and his wife Betty, therefore the correct specific name would be A. rectororum; however, the current version of the ICZN does not require such emendations to be made, thus the name will stand as A. rectori. On a similar note I cannot believe that when such emendations were required that no none noticed that the 'rauisuchian' Postosuchus kirkpatricki was named by Chatterjee (1985) for the Kirkpatrick family and thus should probably have been P. kirkpatrickorum as well.
REFERENCES
Chatterjee, S. 1985. Postosuchus, a new thecodontian reptile from the Triassic of Texas and the origin of tyrannosaurs. Philosophical Transactions of the Royal Society of London B, 309:395-460.
Hunt, A. P., A. B. Heckert, S. G. Lucas, and A. Downs. 2002. The distribution of the enigmatic reptile Vancleavea in the Upper Triassic Chinle Group of the western United States. New Mexico Museum of Natural History & Science Bulletin, 21:269-273.
Irmis, R. B. 2005. The vertebrate fauna of the Upper Triassic Chinle Formation of Arizona. Mesa Southwest Museum Bulletin 9:63-88.
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.
Murry, P. A., and R. A. Long. 1989. Geology and paleontology of the Chinle Formation, Petrified Forest National Park and vicinity, Arizona and a discussion of vertebrate fossils of the southwestern Upper Triassic, p. 29-64. In S.G. Lucas and A.P. Hunt (eds.), Dawn of the Age of Dinosaurs in the American Southwest. New Mexico Museum of Natural History, Albuquerque, New Mexico.
Parker, W. G., and B. J. Barton. 2008. New information on the Upper Triassic archosauriform Vancleavea campi based on new material from the Chinle Formation of Arizona. Palaeontologia Electronica 11.3.14A.
In his fieldnotes from May 22, 1923 Charles Camp discusses the discovery of what he described as the skull of "a small dinosaur or pterodactyl" from a quarry in what is today Petrified Forest National Park. His notes further state that he "plastered this and took it out but plaster broke off block and it had to be removed in pieces. Skull ab
out 6 inches long. Part of rostrum broken" (Long and Murry, 1995). Accompanying this description is a field sketch of this "skull" (figure to the left taken from Irmis, 2005). According to Long and Murry (1995) when they rediscovered the specimen (in a cigar box) in the early 1980s the specimen bore almost no resemblance to Camp's field sketch. Still, what was preserved, although barely identifiable, is autopomorphic thus they felt justified to erecting a new taxon based on this material.Previously the specimen was considered to represent a possible protrochampsid by Murry and Long (1989) who assigned a fragmentary postcranial skeleton (from probably the same locality) to their new taxon. However, by 1995 they had separated the material, naming the postcranial material Vancleavea campi, and the "skull" Acallosuchus rectori (Rector's ugly crocodile). We now know, based on new material (e.g., Hunt et al., 2002; Parker and Barton, 2008), what the skull of Vancleavea looks like and that this separation was indeed correct. Unfortunately, the skull is only known from a partial "mandible", and two other skull fragments which were interpreted as a portion of the frontal and postorbital, and a portion of the "postorbitojugal" bar by Long and Murry (1995).
Furthermore, Camp's sketch is unlike any known "reptile" skull, but as presented it would suggest that the element that Long and Murry (1995) identify as a dentary would actually be a maxilla. The large triangular opening would be an antorbital fenestra, above that a nasal and anteriorly (to the right on the drawing) possibly a premaxilla. The posterior opening could be an orbit, surrounded by a jugal/lacrimal bone anteriorly, and a postorbital dorsally? Unfortunately, the sketch does not provide clarification and was not labelled.
One of the autapomorphies of Acallosuchus is the presence of what Long and Murry (1995) described as osteoderms covering the surfaces of the skull. Irmis (2005) who further commented on this specimen and described these "osteoderms" as subtriangular knobs and noted that these knobs "are often arranged in rows running the length of the bone, and are themselves sculptured with longitudinal furrows. Other areas of bone not covered by these eminences are sculptured with additional grooves" (see photo below [from Irmis, 2005] of the dentary [occusal view] and another skull fragment [? view] showing these unique "knobs").
As discussed by Long and Murry (1995) and further commented on by Irmis (2005) the phylogenetic placement of this taxon is highly ambiguous. Long and Murry (1995) considered Acallosuchus to be a "neodiapsid" based on the presence of the "postorbitojugal bar"; however, even this identification is not unambiguous (Irmis, 2005) and will remain so without the discovery of more and better material.One final note. Long and Murry (1995:193) named the species from ex-superintendent of Petrified Forest National Park Roger Rector, and his wife Betty, therefore the correct specific name would be A. rectororum; however, the current version of the ICZN does not require such emendations to be made, thus the name will stand as A. rectori. On a similar note I cannot believe that when such emendations were required that no none noticed that the 'rauisuchian' Postosuchus kirkpatricki was named by Chatterjee (1985) for the Kirkpatrick family and thus should probably have been P. kirkpatrickorum as well.
REFERENCES
Chatterjee, S. 1985. Postosuchus, a new thecodontian reptile from the Triassic of Texas and the origin of tyrannosaurs. Philosophical Transactions of the Royal Society of London B, 309:395-460.
Hunt, A. P., A. B. Heckert, S. G. Lucas, and A. Downs. 2002. The distribution of the enigmatic reptile Vancleavea in the Upper Triassic Chinle Group of the western United States. New Mexico Museum of Natural History & Science Bulletin, 21:269-273.
Irmis, R. B. 2005. The vertebrate fauna of the Upper Triassic Chinle Formation of Arizona. Mesa Southwest Museum Bulletin 9:63-88.
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.
Murry, P. A., and R. A. Long. 1989. Geology and paleontology of the Chinle Formation, Petrified Forest National Park and vicinity, Arizona and a discussion of vertebrate fossils of the southwestern Upper Triassic, p. 29-64. In S.G. Lucas and A.P. Hunt (eds.), Dawn of the Age of Dinosaurs in the American Southwest. New Mexico Museum of Natural History, Albuquerque, New Mexico.
Parker, W. G., and B. J. Barton. 2008. New information on the Upper Triassic archosauriform Vancleavea campi based on new material from the Chinle Formation of Arizona. Palaeontologia Electronica 11.3.14A.
Royal Society Publishing Opens the Vault
Until February 1, 2009 Royal Society Publishing is partnering with Jstor to provide free access to the Royal Society Digital Archive, covering almost 350 years of publishing in a variety of disciplines including paleontology. This includes a large number of Triassic papers. You can access the archives at the link below:
http://journals.royalsociety.org/home/main.mpx
Information on the archive can be found here.
Happy hunting (and downloading)!
http://journals.royalsociety.org/home/main.mpx
Information on the archive can be found here.
Happy hunting (and downloading)!
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!
Chinle Confusion
The word 'nomenclature' (syn: terminology) is defined as “a system of terms used in a particular science” and allows for more precise communication and understanding of ideas. All scientific disciplines have established nomenclature (called ‘jargon’ by those outside of the discipline) and many have rules regarding the establishment of nomenclature. The Chinle Formation (mainly) of Arizona, Utah, and western New Mexico and the Dockum Group (mainly) of eastern New Mexico and western Texas are Late Triassic terrestrial units that are often correlated to each other on the basis of similar fossil content. Both have been widely studied by geologists and paleontologists since the beginning of last century and it is still debated whether the units were deposited within separate basins. Current thinking shows that the two depocenters may have been connected early in their history (Riggs et al., 1996) and separated later (Lehman and Chatterjee, 2005). The Dockum was named in 1890, the Chinle in 1917.
In 1993 Spencer Lucas advocated raising the name Chinle to Group status (and thus all of its constituent members to Formation rank). In doing so he reduced to Dockum in Texas to formational rank and included it within his Chinle Group. His rationale was that both units were the same age (based on fossils) and deposited in the same basin. It is important to note that he included all Late Triassic terrestrial rocks (including the Popo Agie Fm. of Wyoming) in his newly established group and eliminated some other older names (e.g., Dolores Fm. of Colorado). In later papers Lucas and colleagues completely abandoned use of the name Dockum as well. Lucas et al. (1985) argued that the term Dockum was meaningless, having been widely applied and lacks specificity as it used to include strata later determined to be Middle Triassic in age (Anton Chico Formation). Lucas argued that the term Chinle was better established; however, when originally defined, the Chinle contained units that are now considered to be Jurassic in age (Glen Canyon Group). Nonetheless, this is irrelevant as lithostratigraphic units can be time transgressive and do not need to be restricted by chronstratigraphic boundaries. Moreover, revising lithostratigraphic units does not invalidate them.
Furthermore, the term Dockum has long (since the 1890s) been generally understood to be restricted to Upper Triassic strata exposed around the southern High Plains in eastern New Mexico and west Texas. However, the term “Chinle” has been applied in a much more varied fashion, not only to the upper Triassic strata of the Colorado Plateau, but to strata in northern Utah and Colorado (e.g., Eagle Basin) deposited in a separate basin, and to strata within the Dockum Group which is probably only equivalent to parts of the Chinle Formation on the Colorado Plateau. However, by 1993 the scope of the term “Chinle” was well understood. Ironically the most confusing application of the term “Chinle” has been its extension to all Upper Triassic strata in the southwest by Lucas (1993), which has created two very different understandings of the term in the literature. Given that Lucas (1993) argued that the term Dockum should only be restricted to its type area in Texas, his radical extension of the term “Chinle” through the whole western U.S. is puzzling.
Nonetheless, since first being proposed in 1993, the use of Chinle as a Group has been published in hundreds of papers and abstracts by Lucas and colleagues and has also been used by a few other workers as well. There is also a large group of researchers who insist on leaving the Chinle at Formational rank, as well as researchers from Texas who refuse to abandon the term Dockum. Arguments as to why the Chinle should not subsume the Dockum were provided by Lehman (1994) and Dubiel (1994) and most recently addressed by Carpenter (1997) who wrote: “substituting one name for another (Chinle Group for Dockum Group) violates nomenclatural stability. Furthermore, as a stratigraphic unit, the Dockum Group is not defined by time” making the arguments by Lucas and colleagues “meaningless”. He then writes “the term Dockum Group must be retained, and because it has priority, can be used to encompass the Upper Triassic formations of the American southwest”. He also notes that because Upper Triassic formations in Colorado, Wyoming, and Idaho were most likely not deposited in the same basins as the Chinle or Dockum they should be left alone.
Although Carpenter (1997) was just making a point and not really advocating using the term Dockum in Arizona and Utah, this is where the issue of nomenclatural utility comes to play. Admittedly these names were erected at different times by different researchers who may not have been looking at all of the Triassic rocks in the western U.S. as a whole, but this does not negate their utility. When we hear the term Dockum we think Texas, whereas Chinle suggests Arizona., to mix the two only causes confusion. Even more so IMHO combining all of these units under a single name tells us nothing new scientifically, we already knew that they were roughly of the same age. In fact, again IMHO, “Chinle Group” appears to basically be synonymous with “Upper Triassic” and tells us nothing about local lithostratigraphic variation. This is contrary to Lucas’ (1993) stated intent to “simplify” the basic nomenclatural framework. Essentially, you have two groups of workers, one producing a plethora of papers in in-house bulletins and geological society guidebooks, independently utilizing two differing schemes. In summary, not only is one scheme considered to be against the North American Stratigraphic Code, the situation also creates serious confusion especially among outside researchers, as I will document next with a couple cases.
Weishampel et al. (2004) provide a listing of all known dinosaur occurrences along with their stratigraphic information. Under their Triassic section for North America they refer to the Chinle Formation, but also refer to the members within it also as formations (e.g., “Chinle Formation/Petrified Forest Fm”.). This is non-sensical as they are actually referring to the Petrified Forest Member of the Chinle Formation. Furthermore they list “Chinle Formation/Santa Rosa Fm” regardless of the fact that the Santa Rosa has never been considered a member of the Chinle Formation. Again this makes no sense and would only confuse workers with no familiarity with the conflicting schemes. It certainly does appear that Weishampel et al. (2004) were confused.
Cleveland et al. (2007, 2008a, 2008b) have recently published a series of papers documenting Late Triassic paleosols from New Mexico. The earliest paper (Cleveland et al., 2007) explicitly states that they prefer the nomenclature of Lucas (1993), and in the second paper (Cleveland et al., 2008a) this is implied. However, in the third paper (Cleveland et al., 2008b) they drop the Chinle back to Formational rank, presumably to move away from the Lucas nomenclature (although they do not state why), and return all lesser units back to member rank. Unfortunately, it is not this simple. For example, Cleveland et al. (2008b) now list one of their units as the Painted Desert Member of the Chinle Formation. No such member has ever been proposed. This is the Painted Desert Member of the Petrified Forest Formation of the Chinle Group according to Lucas (1993). Thus, Cleveland et als. (2008b) unit is actually the Petrified Forest Member (Chinle Formation). Likewise, upon dropping Chinle Group they do not appear to resurrect the term Dockum for their units in eastern New Mexico. This provides a similar scheme to that of Weishampel et al. (2004) where the Santa Rosa and Redonda Formations are considered part of the Chinle Formation (equal rank?). Clearly Cleveland and colleagues are confused by the changes in nomenclature and are possibly propagating more confusion. By the way, this is not meant to be a criticism of their paleosol work or general conclusions, I’m just pointing out the stratigraphic nomenclature confusion. Obviously I support their switch back to Chinle as a formational name. I have provided the nomenclature from thier 2007 (top center) and 2008b (bottom left) papers below as well as a rough correction of the 2008b figure (bottom right) below.
In 1993 Spencer Lucas advocated raising the name Chinle to Group status (and thus all of its constituent members to Formation rank). In doing so he reduced to Dockum in Texas to formational rank and included it within his Chinle Group. His rationale was that both units were the same age (based on fossils) and deposited in the same basin. It is important to note that he included all Late Triassic terrestrial rocks (including the Popo Agie Fm. of Wyoming) in his newly established group and eliminated some other older names (e.g., Dolores Fm. of Colorado). In later papers Lucas and colleagues completely abandoned use of the name Dockum as well. Lucas et al. (1985) argued that the term Dockum was meaningless, having been widely applied and lacks specificity as it used to include strata later determined to be Middle Triassic in age (Anton Chico Formation). Lucas argued that the term Chinle was better established; however, when originally defined, the Chinle contained units that are now considered to be Jurassic in age (Glen Canyon Group). Nonetheless, this is irrelevant as lithostratigraphic units can be time transgressive and do not need to be restricted by chronstratigraphic boundaries. Moreover, revising lithostratigraphic units does not invalidate them.
Furthermore, the term Dockum has long (since the 1890s) been generally understood to be restricted to Upper Triassic strata exposed around the southern High Plains in eastern New Mexico and west Texas. However, the term “Chinle” has been applied in a much more varied fashion, not only to the upper Triassic strata of the Colorado Plateau, but to strata in northern Utah and Colorado (e.g., Eagle Basin) deposited in a separate basin, and to strata within the Dockum Group which is probably only equivalent to parts of the Chinle Formation on the Colorado Plateau. However, by 1993 the scope of the term “Chinle” was well understood. Ironically the most confusing application of the term “Chinle” has been its extension to all Upper Triassic strata in the southwest by Lucas (1993), which has created two very different understandings of the term in the literature. Given that Lucas (1993) argued that the term Dockum should only be restricted to its type area in Texas, his radical extension of the term “Chinle” through the whole western U.S. is puzzling.
Nonetheless, since first being proposed in 1993, the use of Chinle as a Group has been published in hundreds of papers and abstracts by Lucas and colleagues and has also been used by a few other workers as well. There is also a large group of researchers who insist on leaving the Chinle at Formational rank, as well as researchers from Texas who refuse to abandon the term Dockum. Arguments as to why the Chinle should not subsume the Dockum were provided by Lehman (1994) and Dubiel (1994) and most recently addressed by Carpenter (1997) who wrote: “substituting one name for another (Chinle Group for Dockum Group) violates nomenclatural stability. Furthermore, as a stratigraphic unit, the Dockum Group is not defined by time” making the arguments by Lucas and colleagues “meaningless”. He then writes “the term Dockum Group must be retained, and because it has priority, can be used to encompass the Upper Triassic formations of the American southwest”. He also notes that because Upper Triassic formations in Colorado, Wyoming, and Idaho were most likely not deposited in the same basins as the Chinle or Dockum they should be left alone.
Although Carpenter (1997) was just making a point and not really advocating using the term Dockum in Arizona and Utah, this is where the issue of nomenclatural utility comes to play. Admittedly these names were erected at different times by different researchers who may not have been looking at all of the Triassic rocks in the western U.S. as a whole, but this does not negate their utility. When we hear the term Dockum we think Texas, whereas Chinle suggests Arizona., to mix the two only causes confusion. Even more so IMHO combining all of these units under a single name tells us nothing new scientifically, we already knew that they were roughly of the same age. In fact, again IMHO, “Chinle Group” appears to basically be synonymous with “Upper Triassic” and tells us nothing about local lithostratigraphic variation. This is contrary to Lucas’ (1993) stated intent to “simplify” the basic nomenclatural framework. Essentially, you have two groups of workers, one producing a plethora of papers in in-house bulletins and geological society guidebooks, independently utilizing two differing schemes. In summary, not only is one scheme considered to be against the North American Stratigraphic Code, the situation also creates serious confusion especially among outside researchers, as I will document next with a couple cases.
Weishampel et al. (2004) provide a listing of all known dinosaur occurrences along with their stratigraphic information. Under their Triassic section for North America they refer to the Chinle Formation, but also refer to the members within it also as formations (e.g., “Chinle Formation/Petrified Forest Fm”.). This is non-sensical as they are actually referring to the Petrified Forest Member of the Chinle Formation. Furthermore they list “Chinle Formation/Santa Rosa Fm” regardless of the fact that the Santa Rosa has never been considered a member of the Chinle Formation. Again this makes no sense and would only confuse workers with no familiarity with the conflicting schemes. It certainly does appear that Weishampel et al. (2004) were confused.
Cleveland et al. (2007, 2008a, 2008b) have recently published a series of papers documenting Late Triassic paleosols from New Mexico. The earliest paper (Cleveland et al., 2007) explicitly states that they prefer the nomenclature of Lucas (1993), and in the second paper (Cleveland et al., 2008a) this is implied. However, in the third paper (Cleveland et al., 2008b) they drop the Chinle back to Formational rank, presumably to move away from the Lucas nomenclature (although they do not state why), and return all lesser units back to member rank. Unfortunately, it is not this simple. For example, Cleveland et al. (2008b) now list one of their units as the Painted Desert Member of the Chinle Formation. No such member has ever been proposed. This is the Painted Desert Member of the Petrified Forest Formation of the Chinle Group according to Lucas (1993). Thus, Cleveland et als. (2008b) unit is actually the Petrified Forest Member (Chinle Formation). Likewise, upon dropping Chinle Group they do not appear to resurrect the term Dockum for their units in eastern New Mexico. This provides a similar scheme to that of Weishampel et al. (2004) where the Santa Rosa and Redonda Formations are considered part of the Chinle Formation (equal rank?). Clearly Cleveland and colleagues are confused by the changes in nomenclature and are possibly propagating more confusion. By the way, this is not meant to be a criticism of their paleosol work or general conclusions, I’m just pointing out the stratigraphic nomenclature confusion. Obviously I support their switch back to Chinle as a formational name. I have provided the nomenclature from thier 2007 (top center) and 2008b (bottom left) papers below as well as a rough correction of the 2008b figure (bottom right) below.
To wrap this up (it is already much longer than I planned). IMHO the scheme presented by Lucas (1993) has caused more confusion than clarification regarding the stratigraphic nomenclature of the Upper Triassic rocks in the western U.S. Also, others have argued that his scheme is against the North American Stratigraphic Code. I am not adverse to the Chinle Formation being raised to group rank, but I cannot do so at the expense of the name Dockum. Moreover, given how radically the meaning of the term “Chinle” was stretched by Lucas (1993), this might propagate more confusion. I am certain that my colleagues in Texas will not call their rocks “Chinle”, and rightfully so. Likewise, I would never dream of calling the rocks in Arizona “Dockum”, because of the confusion it would introduce. Maybe this calls for a special symposium to straighten out the issue, or maybe we should all just stop using Chinle Group. Many of the southwestern U.S. Triassic workers already have (or never adopted it to begin with) but it is important that this issue is brought to the attention of outside workers to help cease the confusion.
REFERENCES
Carpenter, K. 1997. A giant coelophysoid (Certosauria) theropod from the Upper Triassic of New Mexico, USA. N. Jb. Geol. Palaeont. Abh. 205:189-208.
Cleveland, D.M., Atchley, S.C., and L.C. Nordt. 2007. Continental sequence-stratigraphy of the Late Triassic (Norian-Rhaetian) Chinle strata, northern New Mexico: Allo- and autocyclic origins of paleosol-bearing alluvial successions: Journal of Sedimentary Research 77:909–924.
Cleveland, D.M., Nordt, L.C., and S.C. Atchley. 2008a. Paleosols, trace fossils, and precipitation estimates of the uppermost Triassic strata in northern New Mexico: Palaeogeography, Palaeoclimatology, Palaeoecology 257:421–444.
Cleveland, D.M., Nordt, L.C., Dworkin, S.I., and S.C. Atchley. 2008a. Pedogenic carbonate isotopes as evidence for extreme climatic events preceding the Triassic-Jurassic boundary: Implications for the biotic crisis? GSA Bulletin 120:1408-1415.
Dubiel, R. F. 1994. Triassic deposystems, paleogeography, and paleoclimate of the western interior; pp. 133-168 in Caputo, M.V., Peterson, J.A., and K.J. Franczyk (eds.) Mesozoic systems of the Rocky Mountain Region, USA. RMS-SEPM.
Lehman, T.M. 1994. Save the Dockum Group. West Texas Geological Society Bulletin 34:5–10.
Lehman, T. and S. Chatterjee. 2005. Depositional setting and vertebrate biostratigraphy of the Triassic Dockum Group of Texas. Journal of Earth System Science 114:325-351.
Lucas, S.G. 1993. The Chinle Group: Revised stratigraphy and biochronology of Upper Triassic non-marine strata in the western United States. Museum of Northern Arizona Bulletin 59:27-50.
Lucas, S.G., Hunt, A.P., and M. Morales. 1985. Stratigraphic nomenclature and correlation of Triassic rocks in east-central New Mexico, a preliminary report. New Mexico Geological Society Guidebook 36:171-184.
Weishampel, D. B., Barrett, P. M., Coria, R. E., Le Loeuff, J., Gomani, E. S., Zhao Z., Xu X., Sahni, A., and C. Noto. 2004. Dinosaur Distribution, pp. 517-606 in Weishampel D. B., Dodson, P., and H. Osmólska, H. (eds.) The Dinosauria. 2nd edition. Univ. California Press, Berkeley.
Cleveland, D.M., Atchley, S.C., and L.C. Nordt. 2007. Continental sequence-stratigraphy of the Late Triassic (Norian-Rhaetian) Chinle strata, northern New Mexico: Allo- and autocyclic origins of paleosol-bearing alluvial successions: Journal of Sedimentary Research 77:909–924.
Cleveland, D.M., Nordt, L.C., and S.C. Atchley. 2008a. Paleosols, trace fossils, and precipitation estimates of the uppermost Triassic strata in northern New Mexico: Palaeogeography, Palaeoclimatology, Palaeoecology 257:421–444.
Cleveland, D.M., Nordt, L.C., Dworkin, S.I., and S.C. Atchley. 2008a. Pedogenic carbonate isotopes as evidence for extreme climatic events preceding the Triassic-Jurassic boundary: Implications for the biotic crisis? GSA Bulletin 120:1408-1415.
Dubiel, R. F. 1994. Triassic deposystems, paleogeography, and paleoclimate of the western interior; pp. 133-168 in Caputo, M.V., Peterson, J.A., and K.J. Franczyk (eds.) Mesozoic systems of the Rocky Mountain Region, USA. RMS-SEPM.
Lehman, T.M. 1994. Save the Dockum Group. West Texas Geological Society Bulletin 34:5–10.
Lehman, T. and S. Chatterjee. 2005. Depositional setting and vertebrate biostratigraphy of the Triassic Dockum Group of Texas. Journal of Earth System Science 114:325-351.
Lucas, S.G. 1993. The Chinle Group: Revised stratigraphy and biochronology of Upper Triassic non-marine strata in the western United States. Museum of Northern Arizona Bulletin 59:27-50.
Lucas, S.G., Hunt, A.P., and M. Morales. 1985. Stratigraphic nomenclature and correlation of Triassic rocks in east-central New Mexico, a preliminary report. New Mexico Geological Society Guidebook 36:171-184.
Weishampel, D. B., Barrett, P. M., Coria, R. E., Le Loeuff, J., Gomani, E. S., Zhao Z., Xu X., Sahni, A., and C. Noto. 2004. Dinosaur Distribution, pp. 517-606 in Weishampel D. B., Dodson, P., and H. Osmólska, H. (eds.) The Dinosauria. 2nd edition. Univ. California Press, Berkeley.
Historic Election (non-Triassic topic)
Last night many of us witnessed a historic event (I find this link amusing) in the United States with the election of the first African-American president. This is a momentous occasion for all African-Americans (and other ethic groups) and hopefully shows that the United States has turned the corner in race relations and is a step closer towards stomping out bigotry and prejudice.
What was particularly impressive on me, and I hope to all Americans, was how much attention this election received worldwide. I know that my in-laws and friends in Canada (and colleagues in other countries) were following very closely and were glued to the TV coverage last night, as were some international co-bloggers. It was heartening when CNN switched coverage to show the reaction to the election of Obama in places like Kenya and Australia, as well as follow-up articles discussing this response. It is interesting, yet discouraging, to see such a contrast where most Americans pay little or no attention to elections in other countries, whereas many people in other countries have an interest in who is running the show in the U.S. Hopefully Americans will start to realize that in this age of globalization we need to be a partner with other countries and lose the "go it alone" or "with us or against us" attitude that has prevailed during the last eight years. It is clear that in the eyes of other global leaders and citizens Obama is the greatest "hope" for mending these damaged relationships and reconciling with our allies and supporters. Let's hope that we never allow pettiness or ego to let us stray so far again.
What was particularly impressive on me, and I hope to all Americans, was how much attention this election received worldwide. I know that my in-laws and friends in Canada (and colleagues in other countries) were following very closely and were glued to the TV coverage last night, as were some international co-bloggers. It was heartening when CNN switched coverage to show the reaction to the election of Obama in places like Kenya and Australia, as well as follow-up articles discussing this response. It is interesting, yet discouraging, to see such a contrast where most Americans pay little or no attention to elections in other countries, whereas many people in other countries have an interest in who is running the show in the U.S. Hopefully Americans will start to realize that in this age of globalization we need to be a partner with other countries and lose the "go it alone" or "with us or against us" attitude that has prevailed during the last eight years. It is clear that in the eyes of other global leaders and citizens Obama is the greatest "hope" for mending these damaged relationships and reconciling with our allies and supporters. Let's hope that we never allow pettiness or ego to let us stray so far again.
New Vancleavea Material
The current issue of Palaeontologia Electronica contains an article by myself and Bronson Barton describing some new material of the enigmatic archosauriform Vancleavea campi from Petrified Forest National Park. First off a disclaimer, it is no secret that two well-preserved skeletons from the Coelophysis quarry at Ghost Ranch New Mexico have been assigned to Vancleavea and are currently being described by Sterling Nesbitt, Michelle Stocker, Bryan Small, and Alex Downs. This new paper does not figure or discuss that material, and therefore does not contain the awaited reconstruction of this interesting animal. Instead this paper describes two partial skeletons from Petrified Forest National Park which contain postcrania not preserved in the holotype, discusses taxonomic issues, and provides a tentative phylogenetic analysis.
Vancleavea campi was named by Long and Murry (1995) based on a very fragmentary postcranial skeleton from the Upper Triassic Chinle Formation (Blue Mesa Member) of Petrified Forest National Park. Because of the incomplete nature of the material, Long and Murry (1995) could only assign the taxon to Neodiapsida incertae sedis. However, the taxon can be diagnosed by the presence of its characteristic osteoderms (see photo to the left) Additional material, including the Ghost Ranch specimens, was assigned to Vancleavea by Hunt et al. (2002) and Hunt et al. (2005) including additional material from near Stinking Springs in Arizona (Blue Mesa Member, Chinle Formation) assigned to a neodiapsid similar to Vancleavea by Polcyn et al. (2002). In addition, two partial skeletons were collected in 2004 from the Petrified Forest Member (Chinle Formation) of Petrified Forest National Park (Parker and Irmis, 2005). Subsequently, one of these specimens was the focus of a senior thesis by Bronson Barton and both are described in the new paper.
The tentative phylogenetic analysis suggests that Vancleavea campi is a derived non-archosaurian archosauriform. This is based mainly of the morphology of the femur (see photo bottom left) which has a sigmoidal shaft, distinct head, and lacks a intertrochanteric fossa. A very autopomorphic feature of Vancleavea is the morphology of the ilium (see photo bottom right) which differs significantly from that of all other known archosauriform taxa. In fact, the ilium of Vancleavea most superficially resembles that of drepanosaurid archosauromorphs.
Why is this new description necessary, especially when better material (i.e., the Ghost Ranch specimens) exists? Because the original type materials are so scrappy, it is important to supplement the type material with additional material from Petrified Forest National Park. Furthermore, if none of the new specimens (including the Ghost Ranch and Stinking Springs material) differ from the type material, yet differ from each other, then the type materials are nondiagnostic and the name Vancleavea would be a nomen dubium (Parker and Irmis, 2005). Thus, the description of this new material begins this process and is intended to provide future workers some tools to provide more detailed comparisons and to better determine the taxonomic status of the name Vancleavea.
REFERENCES
Hunt, A.P., Lucas, S.G., and Spielmann, J.A. 2005. The holotype specimen of Vancleavea campi from Petrified Forest National Park, Arizona, with notes on the taxonomy and distribution of the taxon. New Mexico Museum of Natural History and Science Bulletin , 29:59-66.
Hunt, A.P., Heckert, A.B., Lucas, S.G., and Downs, A. 2002. The distribution of the enigmatic reptile Vancleavea in the Upper Triassic Chinle Group of the western United States. New Mexico Museum of Natural History and Science Bulletin , 21:269-273.
Long, R.A. and Murry, P.A. 1995. Late Triassic (Carnian and Norian) tetrapods from the southwestern United States. New Mexico Museum of Natural History and Science Bulletin , 4:1-254.
Parker, W.G. and Irmis, R.B. 2005. Advances in Late Triassic vertebrate paleontology based on new material from Petrified Forest National Park, Arizona. New Mexico Museum of Natural History and Science Bulletin , 29:45-58.
Polcyn, M.J., Winkler, D.A., Jacobs, L.L., and Newman, K. 2002. Fossil occurrences and structural disturbance in the Triassic Chinle Formation at North Stinking Springs Mountain near St. Johns, Arizona. New Mexico Museum of Natural History and Science Bulletin , 21:43-49.
Vancleavea campi was named by Long and Murry (1995) based on a very fragmentary postcranial skeleton from the Upper Triassic Chinle Formation (Blue Mesa Member) of Petrified Forest National Park. Because of the incomplete nature of the material, Long and Murry (1995) could only assign the taxon to Neodiapsida incertae sedis. However, the taxon can be diagnosed by the presence of its characteristic osteoderms (see photo to the left) Additional material, including the Ghost Ranch specimens, was assigned to Vancleavea by Hunt et al. (2002) and Hunt et al. (2005) including additional material from near Stinking Springs in Arizona (Blue Mesa Member, Chinle Formation) assigned to a neodiapsid similar to Vancleavea by Polcyn et al. (2002). In addition, two partial skeletons were collected in 2004 from the Petrified Forest Member (Chinle Formation) of Petrified Forest National Park (Parker and Irmis, 2005). Subsequently, one of these specimens was the focus of a senior thesis by Bronson Barton and both are described in the new paper.
The tentative phylogenetic analysis suggests that Vancleavea campi is a derived non-archosaurian archosauriform. This is based mainly of the morphology of the femur (see photo bottom left) which has a sigmoidal shaft, distinct head, and lacks a intertrochanteric fossa. A very autopomorphic feature of Vancleavea is the morphology of the ilium (see photo bottom right) which differs significantly from that of all other known archosauriform taxa. In fact, the ilium of Vancleavea most superficially resembles that of drepanosaurid archosauromorphs.
Why is this new description necessary, especially when better material (i.e., the Ghost Ranch specimens) exists? Because the original type materials are so scrappy, it is important to supplement the type material with additional material from Petrified Forest National Park. Furthermore, if none of the new specimens (including the Ghost Ranch and Stinking Springs material) differ from the type material, yet differ from each other, then the type materials are nondiagnostic and the name Vancleavea would be a nomen dubium (Parker and Irmis, 2005). Thus, the description of this new material begins this process and is intended to provide future workers some tools to provide more detailed comparisons and to better determine the taxonomic status of the name Vancleavea.REFERENCES
Hunt, A.P., Lucas, S.G., and Spielmann, J.A. 2005. The holotype specimen of Vancleavea campi from Petrified Forest National Park, Arizona, with notes on the taxonomy and distribution of the taxon. New Mexico Museum of Natural History and Science Bulletin , 29:59-66.
Hunt, A.P., Heckert, A.B., Lucas, S.G., and Downs, A. 2002. The distribution of the enigmatic reptile Vancleavea in the Upper Triassic Chinle Group of the western United States. New Mexico Museum of Natural History and Science Bulletin , 21:269-273.
Long, R.A. and Murry, P.A. 1995. Late Triassic (Carnian and Norian) tetrapods from the southwestern United States. New Mexico Museum of Natural History and Science Bulletin , 4:1-254.
Parker, W.G. and Irmis, R.B. 2005. Advances in Late Triassic vertebrate paleontology based on new material from Petrified Forest National Park, Arizona. New Mexico Museum of Natural History and Science Bulletin , 29:45-58.
Polcyn, M.J., Winkler, D.A., Jacobs, L.L., and Newman, K. 2002. Fossil occurrences and structural disturbance in the Triassic Chinle Formation at North Stinking Springs Mountain near St. Johns, Arizona. New Mexico Museum of Natural History and Science Bulletin , 21:43-49.
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