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 Developing professional relationships with colleagues including the sharing of unpublished information not only makes science fun, it is integral to doing good science.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Jeff has offered to provide his unpublished ideas on various subjects on his blog and I would like to do the same from time to time here as well.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...... ;)
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.
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.
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.
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.
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 ;).
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