Field of Science
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The skull of Doswellia is one of the more interesting features of the taxon. The skull possesses the euryapsid condition with only supratemporal fenestra being present. Unfortunately the anterior portion of the skull is missing so the presence of an antorbital fenestra cannot be ascertained. An elongated referred dentary suggests the presence of an elongated rostrum (Weems, 1980). The skull is broad and shallow and Doswellia possesses teeth on the pterygoid. The skull reconstructions in Weems (1980) can be difficult to interpret (but see the nice reconstruction from Palaeos below). Dilkes and Sues (2009) provide drawings of the actual specimen in dorsal, ventral and posterior views; however, I as left wishing that a lateral drawing was provided as well, including a close-up lateral view of the braincase.
Another unique feature of Doswellia is faceted transverse processes of the dorsal vertebrae for reception of the capitulum of the dorsal ribs. Furthermore, the dorsal ribs are strongly angled (~90˚) ventrally suggesting a deep body. The reconstruction below based on Weems (1980) is also from Palaeos.
Doswellia possesses a dorsal carapace of numerous rows of interdigitating osteoderms. Possession of these osteoderms has suggested to some past authors a close relationship with aetosaurs (e.g., Bonaparte, 1982). Articulated portions include a nuchal collar (osteoderms right behind the skull) and 5-6 rows of more posterior armor. These rows consist of at least eight columns of square plates with a pitted ornamentation of the dorsal surface and a distinct raised eminence. More posterior osteoderms appear to be flexed (possibly around the tail?).
Although superficially similar to the osteoderms of aetosaurs, the dorsal carapace of Doswellia differs from that of aetosaurs in the increased number of columns (8 vs. 4) and the lack of distinct lateral osteoderms. In fact, the dorsal carapace of Doswellia is more similar to known aetosaurian ventral carapaces, although aetosaur ventral osteoderms do not possess raised eminences. The reconstruction below is from Wikipedia.
The ilium is also distinct in that it is extremely expanded dorsally and laterally. Such an expanded ilium is only found in the archosauriforms Vancleavea campi and drepanosaurs (Parker and Barton, 2008), although in Vancleavea the iliac blade is less expanded anteroposteriorly and is not deflected as strongly laterally.
The femur is a characteristic bone (although poorly preserved according to Dilkes and Sues ) in that is is more derived than basal archosauriforms in lacking a distinct intertrochanteric fossa, a ventral ridge system, and possessing a distinct head. The drawing of the femur in both Weems (1980) and Dilkes and Sues (2009) is similar to that of Vancleavea campi (Parker and Barton, 2008) and differs from that of Erythrosuchus, Proterosuchus, and basal archosauromorphs.
The phylogenetic analysis includes 85 characters and 15 taxa including other enigmatic taxa such as Turfanosuchus and Yonghesuchus. Dilkes and Sues (2009) claim to be the first analysis to include these latter taxa (and should have been) although the phylogenetic analysis of Parker and Barton (2008) also includes Doswellia and Turfanosuchus. However, the Dilkes and Sues paper was in press at the time our paper was published. Furthermore, the initial submission by Parker and Barton did not include either Turfanosuchus or Doswellia in the phylogenetic analysis because I was aware of the forthcoming work by Dilkes; however, the non-inclusion of Doswellia and Turfanosuchus was criticized by a reviewer of the paper and thus these taxa were included in the final submission.
The analysis by Dilkes and Sues (2009) recovers Doswellia as the sister taxon of Proterochampsidae within Archosauriformes. Two interesting findings of this study are the recovery of Erythrosuchus as more derived than Euparkeria (traditionally the archetypal derived non-archosaurian archosauriform) and the recovery of phytosaurs (Parasuchia) as the sister taxon of aetosaurs and more derived than Gracilisuchus and Qianosuchus. The latter is a “rauisuchid” whereas the former has always been recovered as more derived than phytosaurs in all analyses in which it has been included.
Dilkes and Sues (2009) provide detailed discussion attempting to explain a more derived Erythrosuchus; however, I am still somewhat dubious based on the less derived morphology of the femur in Erythrosuchus. Furthermore, Dilkes and Sues code (and discuss) Erythrosuchus as possessing osteoderms; however, Gower (2003) has argued that osteoderms were not present in this taxon.
Another erroneous coding is the proposed synapomorphy of a ventral carapace in phytosaurs and aetosaurs. Although phytosaurs possessed gular (throat armor) they lack the elaborate ventral armor carapace found in aetosaurs. Changing this coding could possibly drop phytosaurs to a more basal position within Archosauria in this analysis (although I have not rerun it yet personally).
I have never felt comfortable with the basal placement of Turfanosuchus within Archosauriformes, despite it also falling out there in my own analysis (Parker and Barton, 2008). This is because of the morphology of the ankle, especially the presence of a hemispherical calcaneal condyle, which is generally a suchian character (Sereno, 1991). In fact, the calcaneum of Turfanosuchus is so similar to that of suchians it is hard for me believe that this morphology was derived twice in archosauriform phylogeny, but this will be up to future analyses to determine.
I did find the Systematic Paleontology section to be somewhat ambiguous as it is an unranked list, yet does not include Archosauriformes (the most inclusive named clade that includes the clade of Doswellia + Proterochamsidae). Furthermore, it also includes the taxonomic name Doswellidae, which is not diagnosed or established anywhere in the paper including the phylogenetic analysis. Thus, Doswellidae remains a Linnaean taxon (Family) which is not supported by a phylogenetic analysis.
Nonetheless, my criticisms are minor and somewhat "nit-picky" because overall I feel that Dilkes and Sues (2009) have provided a very good redescription of the material and a solid foundation for future workers to include this important taxon in phylogenetic analyses. Furthermore, they corroborate Long and Murry’s (1995) referral of osteoderms from the Dockum Group of Texas to Doswellia, demonstrating a North American distribution for this taxon and suggesting that it may have some biostratigraphic significance. In this case, the base of the Dockum Group (which possesses non-phytosaurid phytosaurs, the aetosaur Lucasuchus, rhynchosaurs, and Doswellia) may be latest Carnian in age and thus probably older than the base of the Chinle Formation.
Bonaparte, J.F. 1982. Classification of the Thecodontia. Geobios Mémoire Spécial 6:99-112.
Dilkes, D., and H.-D. Sues. 2009. Redescription and phylogenetic relationships of Doswellia kaltenbachi (Diapsida: Archosauriformes) from the Upper Triassic of Virginia. Journal of Vertebrate Paleontology 29:58-79.
Furin, S., Preto, N., Rigo, M., Roghi, G., Gianolla, P., Crowley, J.L., and S.A. Bowring. 2006. High-precision U-Pb zircon age from the Triassic of Italy: Implications for the Triassic time scale and the Carnian origin of calcareous nannoplankton and dinosaurs. Geology 34:1009-1012. doi: 10.1130/G22967A.1
Gower, D.J. 2003. Osteology of the early archosaurian reptile Erythrosuchus africanus, Broom. Annals of the South African Museum 110:1-84.
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.
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 Vol. 11, Issue 3; 14A: 20p;
Sereno, P.C. 1991. Basal archosaurs: phylogenetic relationships and functional implications. Society of Vertebrate Paleontology Memoir 2:1-53.
Weems, R.E. 1980. An unusual newly discovered archosaur from the Upper Triassic of Virginia, U.S.A. Transactions of the American Philosophical Society 70:1-53.
Da Silva, R.C., Carvalho, I., and A.C.S. Fernandes. 2009. Dinosaur footprints from the Triassic (Santa Maria Formation) of Brazil. Ameghiniana 45: 783-790.
Abstract. Dinosaur footprints in Jurassic and Cretaceous rocks are common in Brazil , but there are only a few records from Triassic. In Rio Grande do Sul State , tridactyl medium size footprints were found in Carnian rocks. The material proceeds from Predebon outcrop, São João do Polêsine County, Rio Grande do Sul State, that corresponds to the higher portion of the Alemoa Member, Santa Maria Formation. The footprints occur in sandstone lenses. The ichnofossils were identified as dinosaur footprints indet. and as Grallator ? sp. The footprints should correspond to undertracks, since many superficial characteristics are absent, so that the differences between the footprints could correspond to preservational factors. On the basis of morphologic and stratigraphic criteria, the footprints can be attributed to basal dinosaurs. Some dinosaurs known for the Brazilian Triassic, such as Staurikosaurus , Saturnalia, and Sacisaurus, could be the producers of these footprints. The occurrences of dinosaur footprints of the Predebon outcrop correspond to the oldest ones of Brazil , and moreover, they are compatible with the known paleofauna of Alemoa-Caturrita sequence.
You can check out the Petrified Forest portion here and make sure to read about the rest of the trip as well and how it relates to new research on Mars.
BTW.... the unidentified paleontologist is Petrified Forest Fossil Preparator Matt Brown, the "other" paleontologist guide (holding up the outcrop) is Jeff Martz.
Dilkes, D. and H.-D. Sues. 2009. Redescription and phylogenetic relationships of Doswellia kaltenbachi (Diapsida: Archosauriformes) from the Upper Triassic of Virginia. Journal of Vertebrate Paleontology 29:58-79.
ABSTRACT-A detailed redescription of the Late Triassic archosauromorph reptile Doswellia kaltenbachi Weems, 1980 from the Poor Farm Member of the Falling Creek Formation in the Taylorsville basin (Newark Supergroup) in Virginia is presented based upon additional preparation of the holotype. The euryapsid skull has a distinctive occiput with a prominent supraoccipital process that is flanked by posterior "horn-like" projections of the squamosals. Postfrontals, tabulars, and postparietals are absent. Plesiomorphic features of the palate and braincase include a plate-like horizontal parabasisphenoid, a pair of foramina for the internal carotid arteries on the ventral surface of the basisphenoid and two fields of teeth on the palatal surface of the pterygoid. A sharp angle along the cervical and anterior dorsal ribs clearly separates the dorsal and lateral sides of the neck and anterior thoracic region. The posterior thoracic region has shorter ribs that project laterally with only a slight curvature. The ilium has a laterally deflected blade with numerous deep grooves along its distal edge. The laterally extensive set of osteoderms includes a nuchal element that is composed of several interlocking osteoderms that lack the arrangement in distinct transverse rows that characterize the remainder of the osteoderms. A phylogenetic analysis of basal archosauriforms incorporates new data of Doswellia and the taxa Turfanosuchus, Yonghesuchus, and Qianosuchus that have not previously been combined in a single study. Results include a sister-group relationship between Doswellia and proterochampsids, placement of Qianosuchus as a crurotarsan archosaur, and Yonghesuchus and Turfanosuchus as successive sister taxa to Archosauria.
Rayfield, E.J., Barrett, P.M., and A. R. Milner. 2009. Utility and validity of Middle and Late Triassic 'land vertebrate faunachrons'. Journal of Vertebrate Paleontology 29:80-87.
ABSTRACT-A tetrapod-based biochronologic framework for the terrestrial Triassic, which subdivides the Triassic into eight 'Land Vertebrate Faunachrons' (LVFs), has been proposed and developed by Lucas and coworkers. In a recent article, these authors reiterated their support for this scheme and used this opportunity to respond to criticisms dealing with the validity and utility of Triassic LVFs. This article is a reply to Lucas and colleagues and demonstrates that many aspects of this Triassic biochronology are dependent on: (1) subjective opinions regarding the taxonomic assignments of key specimens; and (2) unjustified extrapolation of correlations on the basis of geographically restricted endemics. Furthermore, it is suggested that the methodological basis for recognizing the onset of a particular LVF, the identification of the 'first appearance datum' for those taxa deemed to be biochronologically significant, leads to imprecision in correlation and potential ambiguity in dating. Finally, it is argued that geographic information systems are ideal tools for testing biostratigraphic hypotheses.
Gower, D.J., and R.R. Schoch. 2009. Postcranial anatomy of the rauisuchian archosaur Batrachotomus kupferzellensis. Journal of Vertebrate Paleontology 29:103-122.
ABSTRACT-Batracholomus kupferzellensis is an upper Middle Triassic (Late Ladinian) rauisuchian archosaur. The postcranial skeleton of this species is well-represented by fossil material, including the holotype, from the localities of Kupferzell, Crailsheim and Vellberg-Eschenau in southern Germany, and is described here in detail for the first time. All postcranial elements are known except the interclavicle and parts of the carpus, manus, tarsus, pes and some osteoderms and axial elements. B. kupferzellensis is now one of the best-known rauisuchians and will be important in advancing understanding of the group's biology. A period of new anatomical and taxonomic work since 2000 has improved understanding of rauisuchians. Renewed effort in rauisuchian phylogenetics will benefit from these new data, but will also require a careful and detailed approach to character formulation.
Martínez, R.N. 2009. Adeopapposaurus mognai, gen. et sp. nov. (Dinosauria: Sauropodomorpha with comments on adaptations of basal Sauropodomorpha. Journal of Vertebrate Paleontology 29:142-164.
ABSTRACT-Prosauropods are basal sauropodomorphs that were the major terrestrial faunal components from the Norian until their extinction during the Toarcian. Their status as a natural group is debatable. In the present work I describe Adeopapposaurus mognai, a new sauropodomorph from the Cañon del Colorado Formation, in northwestern Argentina. Diagnostic autapomorphies and combination of characters of Adeopapposaurus include a series of large foramina in a sub-vertical row on the lateral surface of the premaxilla; strongly rugose depression bordered by a protuberance with a series of foramina in a sub-vertical row, on the lateral surface of the anterior end of the dentary; eleven anteroposteriorly elongated cervical vertebrae and thirteen dorsal vertebrae with neural arches taller than the respective centra. Phylogenetically Adeopapposaurus is resolved as the sister group to Massospondylus; differing from the latter based on differences in mandible and premaxilla and addition of one dorsal vertebra to the neck. The specimens described here reveal numerous herbivorous adaptations, including the presence of a highly vascularized bony plate in the premaxilla and dentary, which indicates that it had a horny beak.
These filaments are already known from the basal ceratopsian Psittacosaurus; however, a heterodontosaurid with feathers pushes this occurence to the base of Ornithischia (Butler et al. 2008).
It is not entirely clear whether the ornithischian filaments and saurischian protofeathers are the same, but if they are this would strongly suggest that protofeathers may be plesiomorphic for Dinosauria, and it is even hypothetical now that the successive ornithodiran outgroups to the dinosaurs may have also possessed this character. Now we just need a silesaurid from these Chinese deposits now or some better preservation in the Triassic! You can read more about this here, here, and here.
Butler, R., Upchurch, P., & Norman, D. (2007). The phylogeny of the ornithischian dinosaurs Journal of Systematic Palaeontology, 6 (01) DOI: 10.1017/S1477201907002271
Zheng, X., You, H., Xu, X., & Dong, Z. (2009). An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures Nature, 458 (7236), 333-336 DOI: 10.1038/nature07856
This paper came out earlier this year in Zootaxa.
Kammerer, C.F., and K.D. Angielczyk. 2009. A proposed higher taxonomy of anomodont therapsids. Zootaxa 2018:1-24.
Abstract- A higher-level taxonomic framework for the Permo-Triassic anomodont therapsids (dicynodonts and their relatives) is presented in order to bring concordance between reconstructions of anomodont phylogeny and nomenclature. Taxonomic histories, remarks on current usage, and phylogenetic definitions are provided for twenty-two higher level (i.e., suprageneric) anomodont taxa: Anomodontia, Bidentalia, Chainosauria, Cistecephalidae, Cryptodontia, Dicynodontia, Dicynodontoidea, Emydopidae, Emydopoidea, Endothiodontia, Eumantelliidae, Geikiidae, Geikiinae, Kingoriidae, Kistecephalia, Lystrosauridae, Myosauridae, Oudenodontidae, Pylaecephalidae, Rhachiocephalidae, Therochelonia, and Venyukovioidea. Additionally, lists of diagnostic characters supporting each of these higher taxa are given, utilizing the results of several recent phylogenetic analyses of anomodont relationships.
This recent paper is free in Palaeo3:
Diedrich, C. 2009. The vertebrates of the Anisian/Ladinian boundary (Middle Triassic) from Bissendorf (NW Germany) and their contribution to the anatomy, palaeoecology, and palaeobiogeography of the Germanic Basin reptiles.
Palaeogeography, Palaeoclimatology, Palaeoecology 273:1-16.
Abstract - Systematically excavated bones are described from Bissendorf (Osnabrücker Bergland, north-western Germany). The bone bed in the compressus zone of the Ceratitenschichten (Meißner Fm, Upper Muschelkalk, Anisian/Ladinian boundary, Middle Triassic) was dated by ceratites. Sedimentologically, it is a bioclastic rudstone built mainly from Coenothyris vulgaris brachiopods, which were heavily compressed into a 3 mm thin layer. Parts of the bone bed and the following 15 cm of autochthonous mud were partially eroded synsedimentary by the compressus storm event. The material of the not-rich bone bed in the Germanic Upper Muschelkalk consists of isolated teeth or fin spines from five well-known shark species: Hybodus longiconus Agassiz, 1843, Acrodus lateralis Agassiz, 1837, Acrodus gaillardoti Agassiz, 1837, Palaeobates angustissimus Agassiz, 1838 and Polyacrodus polycyphus Agassiz, 1837. Teeth and scales from the teleosteans Gyrolepis sp, Dollopterus sp., Colobodus maximus, Quenstedt, 1835, C. frequens, Dames [Dames, W., 1888. Die Ganoiden des Deutschen Muschelkalkes. Palaeontologische Abhandlungen 4, 133–180] and Saurichthys sp. have been proved. Found were mostly vertebra centra and ribs, but also teeth and some other postcranial bones from the small pachypleurosaurs Anarosaurus sp. as well as mostly Neusticosaurus sp. These originated from adult and juvenile animals which indicates the primary habitat and populations of this region. Large marine nothosaur reptiles found include Nothosaurus cf. mirabilis Münster, 1834, and N. giganteus Münster, 1834. Proof of two placodonts is given thanks to Placodus gigas Agassiz, 1833 and Cyamodus sp. Finally, a tooth from the terrestrial lepidosaur Tanystrophaeus longibardicus (Bassani, 1866) is the northerly most sample found. The recorded fauna is well-known with complete skeletons of the described species from the northern Tethys (Mte. San Giorgio, Switzerland). The reptile skeletons are presented here in reconstruction. The bone bed composition in Bissendorf shows differences in the younger and more terrestrial mixed as well as the age difference in bone beds of northern (enodis/posseckeri zone) and southern Germany (dorsoplanus zone). At Bissendorf, only nearly complete marine vertebrates occur within the maximum high stand. High marine ichthyosaurs seem to be absent, indicating a shallow marine position in the western Germanic Basin.
Kenneth closely examined the skeletons and documented hundreds of trace fossils of varying morphologies. Some were interpreted as tooth marks from predators and/or scavengers, but more interestingly many of the trace fossils can be attributed to various arthropods. Comparisons were made with arthropod traces and modern bones and from this a taphonomic hypothesis using forensic entomology can be proposed.
Bader et al. hypothesize that based on this evidence these sauropods died during the dry season, were scavenged, and then went through several detailed stages of decomposition, including a "dry stage" where tracemakers tunneled through dried flesh and created pupation chambers adjacent to bones. Larvae hatched and then contributed to the final removal of soft tissue from the bones. Total time from death until complete burial was estimate to be about 1-3 years.
Congrats again to Kenneth on a very interesting study.
BADER, K., HASIOTIS, S., & MARTIN, L. (2009). APPLICATION OF FORENSIC SCIENCE TECHNIQUES TO TRACE FOSSILS ON DINOSAUR BONES FROM A QUARRY IN THE UPPER JURASSIC MORRISON FORMATION, NORTHEASTERN WYOMING PALAIOS, 24 (3), 140-158 DOI: 10.2110/palo.2008.p08-058r
Abstract- Trace fossils on sauropod skeletons from a quarry in fluvial deposits of the Morrison Formation, Wyoming, are used to reconstruct the taphonomic history of the dinosaur bone accumulation. Shallow pits; rosettes; hemispherical pits; thin, curvilinear, branching grooves; and U- to V-shaped linear grooves make up trace fossils found on sauropod skeletons. The traces were interpreted by comparisons to traces on modern bone. Rosettes are circular rings of modified bone and are likely an early stage in the production of shallow pits. They are interpreted as pupation chambers constructed in dried flesh in contact with sauropod bone. Hemispherical pits are circular with a U-shaped cross section and interpreted as dermestid pupation chambers completed in sauropod bone. Thin, curvilinear, branching grooves are semicircular in cross section, form irregular dendritic or looping patterns, and are interpreted as root etchings. U- to V-shaped linear grooves are interpreted as theropod or crocodilian bite marks. Skeletal articulation and condition and distribution of bone modification traces suggest the skeletons accumulated at this site over no more than 3.5 years, with the bulk of the skeletons contributed during the dry season in the final 3–6 months. Carcasses went through all stages of decomposition—including the dry stage, represented by shallow pits, rosettes, and hemispherical pits. Vertebrate scavengers and necrophagous arthropods fed on the carcasses during all decomposition stages prior to burial of the assemblage.
This recent article has been getting a bit of attention in the blogosphere (e.g., here, here, and even here), although mainly on the functional implications of theropod manus and arm orientation. However, there are a few other tidbits in this article that I find of interest (and which are relevent to the Chinle Formation and the Late Triassic.
First up is this little comment regarding the rank of the Chinle:
"The Moenave Formation overlies the Chinle Formation (Chinle Group of Lucas , but in Utah, group status is not recognized for these same strata)."
By the way, I really dislike numerical citations in journal articles as you have to continuously flip to the reference section to follow along. The same goes for putting all of the figure abbreviations for an entire paper into a single list or appendix rather than under each figure. Hate, it, hate it, hate it.
Anyhow, as many of my readers are possible aware, the rank of the Chinle is heavily debated. As I have stated before I have no problem with the Chinle being raised to Group status, but I do have a problem with it subsuming the Dockum Group (which is an older established name and thus has priority) as advocated by Lucas (1993) (Lucas  states that the Dockum should be lost because of inconsistent usage, but this would also be true for the name Chinle). Thus we are kind of stuck with not using Chinle as a Group because of the confusion any future work advocating this (and leaving the Dockum separate) would cause with the necessity to then state continuously who's version of "Chinle Group" you are using.
In their paper Milner et al. (2009) have come right out (in a Jurassic-themed paper) and voiced their disapproval with using Chinle "Group" in Utah. We feel the same way in Arizona and I know my Texas colleagues feel just a strongly. This leaves only some workers in New Mexico using "Group" and two different versions at that. Of course, the North American Stratigraphic Code allows for units to be members, formations, or groups in different areas, however, it can cause some confusion.
Another important aspect of this paper is the useful taxonomic review of quite a few Late Triassic and Early Jurassic footprint taxa, which have been assigned to theropods, especially those that may be synonymous with Eubrontes and those that show manus impressions. Interesting is the hypothesis that based on the associated manus impressions the tracks of Atreipus are not theropodan, but rather those of a non-dinosaurian dinosauriform or possibly an ornithischian. Based on the body fossil record for the Late Triassic the former is most likely as was previously attributed to such by Olsen and Baird (1986) and Nesbitt et al. (2007).
In summary, although this new paper mainly focuses on proposed posture and behavior in theropods it also contains some key information on Triassic and Jurassic ichnofossil taxonomy and stratigraphy. For those interested this paper is available for free here.
Lucas, S.G. 1993. The Chinle Group: revised stratigraphy and biochronology of Upper Triassic nonmarine strata in the western United States. Museum of Northern Arizona Bulletin 59: 27–50.
Andrew R. C. Milner, Jerald D. Harris, Martin G. Lockley, James I. Kirkland, Neffra A. Matthews (2009). Bird-Like Anatomy, Posture, and Behavior Revealed by an Early Jurassic Theropod Dinosaur Resting Trace PLoS ONE, 4 (3) DOI: 10.1371/journal.pone.0004591
Nesbitt, S. J., Irmis, R. B., and W.G. Parker. 2007. A critical reevaluation of the Late Triassic dinosaur taxa of North America. Journal of Systematic Palaeontology 5:209-243.
Olsen, P. E. and D. Baird. 1986. The ichnogenus Atreipus and its importance for Triassic biostratigraphy. Pp. 61–87 in K. Padian (ed.) The beginning of the age of dinosaurs: faunal change across the Triassic–Jurassic boundary. Cambridge University Press, Cambridge.
R. A. Gastaldo, J. Neveling, C. K. Clark, S. S. Newbury (2009). The terrestrial Permian-Triassic boundary event bed is a nonevent Geology, 37 (3), 199-202 DOI: 10.1130/G25255A.1
ABSTRACT - A unique isochronous interval in the Karoo Basin, South Africa, previously has been interpreted to postdate vertebrate extinction at the Permian-Triassic boundary in the Bethulie area, Lootsberg Pass, and elsewhere. It is demonstrated that the laminated beds, or laminites, in the Bethulie region are stratigraphically indistinct. The heterolithic interval exposed on the Heldenmoed farm is ~8 m below the Bethel farm section, <1 km away. At Lootsberg Pass, the laminated interval is below the Permian-Triassic boundary as defined by vertebrate biostratigraphy, rather than overlying it. Hence, this interval, critical to models of end-Permian mass extinction, is neither isochronous across the basin nor unique. Rather, the lithofacies represents avulsion channel-fill deposits within aggradational landscapes. South African models for the response of terrestrial ecosystems to the perturbation in the marine realm require critical reevaluation.
Note: Someone e-mailed me asking about the recent Chinese Jurassic theropod paper. I accidentally deleted your message so please resend.
Gruszka, B. and T. Zielinski. 2008. Evidence for a very low-energy fluvial system: a case study from the dinosaur-bearing Upper Triassic rocks of Southern Poland. Geological Quarterly 52:239-252.
The Upper Triassic succession in S Poland in which dinosaur bones have been found consists predominantly of siltstones and claystones. Three units are distinguished. The lowermost and the upper most units reflect an alluvial environment, whereas the middle one represents lacustrine facies. The lower alluvial unit is interpreted as a record of ephemeral, sinuous, suspended-load channels with rapid vertical accretion. Channel barforms are lacking. The environment is interpreted as a low-energy anastomosing fluvial system. The clayey middle unit is interpreted as having formed in a wide long-lived lake. The top of the lacustrine deposits shows signs of vertisol-type pedogenesis, most probably under subtropical conditions, with seasonally-in duced wet and dry intervals. The upper unit reflects a low-energy meandering river system. Silty point bars were abundant and the channels migrated freely. The energy level of this fluvial system was slightly higher than that of the earlier one, which is interpreted as an effect of base-level lowering in combination with an increasingly humid climate. The almost exclusively silty/clayey alluvial deposits represent an exceptionally rare facies. The drainage basin must have been an extremely flat lowland. The presence of vertebrate bones within the anastomosing and meandering river deposits indicates that low-energy alluvial plains were apparently favourable habitats for both reptiles and amphibians during the Late Triassic: under the subtropical, seasonally dry conditions, the animals must have preferred moist low areas, i.e. the flood basins and abandoned channels on the flat valley floors.