Kent, D. V., and E. Irving. 2010. Influence of inclination error in sedimentary rocks on the Triassic and Jurassic apparent pole wander path for North America and implications for Cordilleran tectonics. Journal Of Geophysical Research 115: B10103, doi:10.1029/2009JB007205
Abstract - Because of paleomagnetic inclination error (I error) in sedimentary rocks, we argue that previous estimates of Triassic and Jurassic paleolatitudes of the North American craton have generally been too low, the record being derived mostly from sedimentary rocks. Using results from all major cratons, we construct a new composite apparent pole wander (APW) path for Triassic through Paleogene based on 69 paleopoles ranging in age from 243 to 43 Ma. The poles are from igneous rocks and certain sedimentary formations corrected for I error brought into North American coordinates using plate tectonic reconstructions. Key features of the new APW path are a 25° northward progression from 230 to 190 Ma to high latitudes (off northernmost Siberia) where the pole lingers until 160 Ma, a jump to the Aleutians followed by a hook in western Alaska by ∼145 Ma that leads to the 130–60 Ma stillstand, after which the pole moves to its present position. As an example of the application of this new path we use paleomagnetic results to determine that southern Wrangellia and Stikinia (W/S), the two most westerly terranes in the Canadian Cordillera, lay 630 to 1650 km farther south than at present relative to the craton during the Late Triassic and Early Jurassic. This is consistent with an exotic Tethyan origin as paleontological and mantle geochemical evidences imply. During the Late Triassic through Early Cretaceous, W/S moved northward more slowly than the craton, implying oblique sinistral net convergence over this 130 Myr interval. This was followed by dextral shear in latest Cretaceous through Eocene.
Donohoo-Hurley, L. L., Geissman, J. W., and S. G. Lucas. 2010. Magnetostratigraphy of the uppermost Triassic and lowermost Jurassic Moenave Formation, western United States: Correlation with strata in the United Kingdom, Morocco, Turkey, Italy, and eastern United States. Geological Society of America Bulletin 122: 2005-2019; doi: 10.1130/B30136.1
Abstract - A composite magnetostratigraphy based on the magnetic polarity data from four sections of the uppermost Triassic and lowermost Jurassic Moenave Formation, Utah and Arizona, USA, can be correlated to the marine successions at Saint Audrie’s Bay (UK), Oyuklu, Turkey, and the Southern Alps, Italy, and to the nonmarine sections in Morocco, northern Africa, and the Newark Basin, eastern North America, all deposited across the Triassic–Jurassic boundary. Our proposed correlation provides a stratigraphic framework to tie Triassic–Jurassic sedimentation in the American Southwest to the marine UK, Turkey, and Italy sections, and to the Pangea rift history, including extrusive igneous rocks, preserved in Morocco and in the Newark Basin. The Moenave polarity record is characterized by mostly normal polarity, as is consistent with other polarity records across the Triassic–Jurassic boundary, and is interrupted by at least two well-defined reverse-polarity magnetozones. On the basis of available paleontologic information, we interpret the oldest well defined, reverse-polarity magnetozone, M2r of the Moenave Formation, to correlate with SA5n.2r or SA5n.3r of the Saint Audrie’s Bay record, H– of the Oyuklu record, BIT5n.1r of the Italcementi Quarry record, the oldest reverse magnetozone in sedimentary rocks in Morocco, and with reverse magnetozone E23r of the Newark Basin. The youngest reverse magnetozone of the Moenave Formation, M3r, is correlated to the latest Triassic magnetozones SA5n.5r of the Saint Audrie’s Bay record, J– of the Oyuklu record, and with the interval of reverse polarity in the “intermediate unit” of the Morocco record. Magnetostratigraphic correlations and marine biostratigraphic information support placement of the Triassic–Jurassic boundary in the middle to upper Whitmore Point Member of the Moenave Formation, the Lias Group of the Saint Audrie’s Bay section, the chert-rich limestone of the Oyuklu section, above the Zu Limestone in Italy, and in the central Atlantic magmatic province extrusive zone in the Morocco and the Newark records.
New Seed Ferns and Cycadophytes from the Middle Triassic of Germany
Kustatscher, E., and J. H. A. van Konijnenburg-van Cittert. 2010. Seed ferns and Cycadophytes from the Triassic Flora of Thale (Germany). Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 258: 195–217.
Abstract: This is the second paper on the Middle Triassic flora from Thale, dealing with the seed ferns and cycadophytes. Scytophyllum bergeri Bornemann is one of the common elements in the flora, in contrast to Sagenopteris sp. which is rare in the assemblage. However, it is the first evidence of Sagenopteris for the German Basin. The specimen described as ?Peltaspermum sp. is the only peltasperm ovuliferous organ known to date with attached ovule-bearing discs from the Middle Triassic of Europe. The cycad Apoldia tener (Compter 1883) Zijlstra et al. 2009 (formerly Sphenozamites tener Compter) is by far the most common fossil plant in the assemblage. Nilssonia cf. neuberi Stur ex Pott et al. is relatively rare. The genus Bjuvia is emended to accommodate more species of large entire leaves characterised by amphistomy and cycadalean stomatal morphology. This includes Bjuvia thalensis n. sp., which is a common element in the Thale flora but is unknown from elsewhere. Narrow, long entire leaves from the Middle and Upper Triassic of Europe have been described under the name Taeniopteris angustifolia Schenk, but have now been transferred to Taeniopteris kelberi n. sp. for nomenclatorial reasons. The macrosporophyll Dioonitocarpidium pennaeformis (Schenk) Ruhle von Lilienstern also occurs in the Thale flora. Two cycadalean leaf species (Apoldia tener and Bjuvia thalensis) from Thale flora sometimes have stomata with only two subsidiary cells instead of the usual 4-6, a feature that in gymnosperms occurs mainly in the Bennettitales.
Abstract: This is the second paper on the Middle Triassic flora from Thale, dealing with the seed ferns and cycadophytes. Scytophyllum bergeri Bornemann is one of the common elements in the flora, in contrast to Sagenopteris sp. which is rare in the assemblage. However, it is the first evidence of Sagenopteris for the German Basin. The specimen described as ?Peltaspermum sp. is the only peltasperm ovuliferous organ known to date with attached ovule-bearing discs from the Middle Triassic of Europe. The cycad Apoldia tener (Compter 1883) Zijlstra et al. 2009 (formerly Sphenozamites tener Compter) is by far the most common fossil plant in the assemblage. Nilssonia cf. neuberi Stur ex Pott et al. is relatively rare. The genus Bjuvia is emended to accommodate more species of large entire leaves characterised by amphistomy and cycadalean stomatal morphology. This includes Bjuvia thalensis n. sp., which is a common element in the Thale flora but is unknown from elsewhere. Narrow, long entire leaves from the Middle and Upper Triassic of Europe have been described under the name Taeniopteris angustifolia Schenk, but have now been transferred to Taeniopteris kelberi n. sp. for nomenclatorial reasons. The macrosporophyll Dioonitocarpidium pennaeformis (Schenk) Ruhle von Lilienstern also occurs in the Thale flora. Two cycadalean leaf species (Apoldia tener and Bjuvia thalensis) from Thale flora sometimes have stomata with only two subsidiary cells instead of the usual 4-6, a feature that in gymnosperms occurs mainly in the Bennettitales.
There are no Known Aetosaur Fossils from Madagascar!
I happened to click on the Wikipedia page for aetosaurs today. It is really shaping up as someone (or maybe a few people) is putting a lot of work into it. A few errors here and there and a couple taxonomic issues that will be addressed in some future publications (not all by me). However, the most glaring thing that caught my eye was location column for Desmatosuchus lists Madagascar (Isalo Group) as a unit containing fossils of Desmatosuchus. This is an occurrence I addressed in my M.S. thesis (Parker, 2003) and in my 2008 paper on the genus Desmatosuchus. It all stems from a problem in assigning a geological age to a fossil bearing horizon in the upper part of the Isalo II (part of the Isalo Group; Burmeister, 2000; Burmeister et al., 2006). This horizon includes fish fossils, as well as the remains of dinosaurs (sauropod, theropod) and other archosaurs, including teeth that are superficially similar to those of phytosaurs and a handful of osteoderms that belong to some type of pseudosuchian (see photo below from Burmeister, 2000).
Kurtis Burmeister first approached me in the late 1990s asking my opinion if these osteoderms could be from aetosaurs. I though the resemblance was purely superficial and despite he presence of an anterior bar and pitted ornamantation, the overall morphology and the lateral sutures were not typical of aetosaurs. In his thesis, he suggested they could be crocodyliform (pers. comm. from Mike Parrish), but preliminarily assigned them to the Aetosauria and noted a possible assignment to Desmatosuchus. This identification was based on showing the osteoderms to another aetosaur "expert" (Burmeister, pers. comm.).
A few years later I was approached again by another member of the research team who showed me the specimens again. This time I was with a small group of Triassic workers and coincidently we had a crocodyliform specialist with us as well. We all agreed that they were definitely not Desmatosuchus, not aetosaurian, and most likely a crocodyliform. In a subsequent publication (Burmeister et al., 2006) they are refered to an indeterminate crocodylotarsian (pseudosuchian) and the superficial resemblance to aetosaurs is discussed, although the authors note the osteoderms probably represent a goniopholidid crocodyliform and that the horizon is probably Early Jurassic in age. Parker (2008) argued that they were not aetosaurian and possessed characters found in mesoeucrocodylians.
Despite all of this ambiguity, these specimens were explicitly assigned to the aetosaur Dematosuchus haplocerus by Lucas et al. (2003) and used to provide an Adamanian (late Carnian) age for these beds. This identification and correlation was followed by Lucas (2010). Discussions with colleagues and the current Wikipedia entry for aetosaurs demonstrates that the identification of these specimens as aetosaurian is still misunderstood. For the 4th time (and hopefully the last) I would like to propose my opinion (based on two personal observations of the material and the figure above) that these are not aetosaur plates and most certainly not referable to Desmatosuchus. The ornament is too deep and irregular, furhtermore, if these are fragments of paramedian plates then the ornament would be too large. Finally, the sutural edges are completely different than anything found in aetosaurs, and certainly does not represent the "tongue-and-groove" articular surface found in desmatosuchines. There currently is no evidence for aetosaurs in the Isalo II and the age of the upper beds is most likely Jurassic (Burmeister et al., 2006; Parker, 2008) and not Adamanian in age (contra Lucas, 2010).
REFERENCES
Burmeister, K.C., 2000, Paleogeographic and biostratigraphic implications of new early Mesozoic terrestrial vertebrate fossils from the Poamay site: central Morondava Basin, Madagascar [M.A. thesis]: Santa Barbara, University of California, 109 p.
Burmeister, K.C., J.J. Flynn, J.M. Parrish, and A.R. Wyss. 2006. Paleogeographic and biostratigraphic implications of new early Mesozoic vertebrates from Poamay, central Morondava Basin, Madagascar. New Mexico Museum of Natural History Science Bulletin 37:457–475.
Lucas, S.G. 2010. The Triassic timescale based on nonmarine tetrapod biostratigraphy and biochronology; pp. 447-500 in Lucas, S. G. (ed.) The Triassic Timescale. Geological Society, London, Special Publications, 334.
Lucas, S.G., K.E. Zeigler, A.B. Heckert, and A.P. Hunt. 2003. Upper Triassic stratigraphy and biostratigraphy, Chama Basin, north-central New Mexico. New Mexico Museum of Natural History & Science Bulletin 24:15–39.
Parker, W.G. 2003. Description of a new specimen of Desmatosuchus haplocerus from the Late Triassic of Northern Arizona. M.S. thesis. Northern Arizona University, Flagstaff, AZ.
Parker, W.G. 2008. Description of new material of the aetosaur Desmatosuchus spurensis (Archosauria: Suchia) from the Chinle Formation of Arizona and a revision of the genus Desmatosuchus. PaleoBios 28:1-40.
Kurtis Burmeister first approached me in the late 1990s asking my opinion if these osteoderms could be from aetosaurs. I though the resemblance was purely superficial and despite he presence of an anterior bar and pitted ornamantation, the overall morphology and the lateral sutures were not typical of aetosaurs. In his thesis, he suggested they could be crocodyliform (pers. comm. from Mike Parrish), but preliminarily assigned them to the Aetosauria and noted a possible assignment to Desmatosuchus. This identification was based on showing the osteoderms to another aetosaur "expert" (Burmeister, pers. comm.).
A few years later I was approached again by another member of the research team who showed me the specimens again. This time I was with a small group of Triassic workers and coincidently we had a crocodyliform specialist with us as well. We all agreed that they were definitely not Desmatosuchus, not aetosaurian, and most likely a crocodyliform. In a subsequent publication (Burmeister et al., 2006) they are refered to an indeterminate crocodylotarsian (pseudosuchian) and the superficial resemblance to aetosaurs is discussed, although the authors note the osteoderms probably represent a goniopholidid crocodyliform and that the horizon is probably Early Jurassic in age. Parker (2008) argued that they were not aetosaurian and possessed characters found in mesoeucrocodylians.
Despite all of this ambiguity, these specimens were explicitly assigned to the aetosaur Dematosuchus haplocerus by Lucas et al. (2003) and used to provide an Adamanian (late Carnian) age for these beds. This identification and correlation was followed by Lucas (2010). Discussions with colleagues and the current Wikipedia entry for aetosaurs demonstrates that the identification of these specimens as aetosaurian is still misunderstood. For the 4th time (and hopefully the last) I would like to propose my opinion (based on two personal observations of the material and the figure above) that these are not aetosaur plates and most certainly not referable to Desmatosuchus. The ornament is too deep and irregular, furhtermore, if these are fragments of paramedian plates then the ornament would be too large. Finally, the sutural edges are completely different than anything found in aetosaurs, and certainly does not represent the "tongue-and-groove" articular surface found in desmatosuchines. There currently is no evidence for aetosaurs in the Isalo II and the age of the upper beds is most likely Jurassic (Burmeister et al., 2006; Parker, 2008) and not Adamanian in age (contra Lucas, 2010).
REFERENCES
Burmeister, K.C., 2000, Paleogeographic and biostratigraphic implications of new early Mesozoic terrestrial vertebrate fossils from the Poamay site: central Morondava Basin, Madagascar [M.A. thesis]: Santa Barbara, University of California, 109 p.
Burmeister, K.C., J.J. Flynn, J.M. Parrish, and A.R. Wyss. 2006. Paleogeographic and biostratigraphic implications of new early Mesozoic vertebrates from Poamay, central Morondava Basin, Madagascar. New Mexico Museum of Natural History Science Bulletin 37:457–475.
Lucas, S.G. 2010. The Triassic timescale based on nonmarine tetrapod biostratigraphy and biochronology; pp. 447-500 in Lucas, S. G. (ed.) The Triassic Timescale. Geological Society, London, Special Publications, 334.
Lucas, S.G., K.E. Zeigler, A.B. Heckert, and A.P. Hunt. 2003. Upper Triassic stratigraphy and biostratigraphy, Chama Basin, north-central New Mexico. New Mexico Museum of Natural History & Science Bulletin 24:15–39.
Parker, W.G. 2003. Description of a new specimen of Desmatosuchus haplocerus from the Late Triassic of Northern Arizona. M.S. thesis. Northern Arizona University, Flagstaff, AZ.
Parker, W.G. 2008. Description of new material of the aetosaur Desmatosuchus spurensis (Archosauria: Suchia) from the Chinle Formation of Arizona and a revision of the genus Desmatosuchus. PaleoBios 28:1-40.
Sterling Nesbitt Online!
My very good friend and colleague Sterling Nesbitt has a new website detailing his work (mainly on Triassic archosauromorphs). Please go check it out and then totally harass him for PDFs of all of his papers.
Much of the renniassance in Triassic archosauromorph taxonomy and phylogeny is in a large part due to Sterling's work over the last decade. His forthcoming, in press, absolutely monstrous (over 500 manuscript pages) monograph on archosauromorph phylogeny (from his doctoral dissertation) promises to be the most comprehensive work ever done on this group (over 50 taxa and 400 characters, almost all scored through first hand observation of the actual specimens) and will be a foundation study for years to come.
Much of the renniassance in Triassic archosauromorph taxonomy and phylogeny is in a large part due to Sterling's work over the last decade. His forthcoming, in press, absolutely monstrous (over 500 manuscript pages) monograph on archosauromorph phylogeny (from his doctoral dissertation) promises to be the most comprehensive work ever done on this group (over 50 taxa and 400 characters, almost all scored through first hand observation of the actual specimens) and will be a foundation study for years to come.
The Future Direction of Late Triassic Terrestrial Ecosystem Research
Here is an excellent synthesis by Randall Irmis and Jessica Whiteside of ongoing and future research in the Late Triassic, particularly in North America. These are topics of great interest to me and Jeff Martz right now and we have a paper in press that will delve into our side of this research. We are also working closely with colleagues such as Randy and Jessica on some aspects of this work and I am proud that Petrified Forest National Park is one of the settings for this exciting research.
It is a Spotlight article so there is no abstract. You can e-mail Randall Irmis for a PDF.
This excerpt makes a key point that I have been a strong proponent for:
"The key for understanding Late Triassic terrestrial ecosystems is that all of these new studies focus on stratigraphic sections where multiple different research approaches can be applied to maximize the data recovered from the same area."
Instead of various researchers working haphazardly, conducting different studies on different outcrops, coordinating this research instead with everyone working in the same areas under the same detailed stratigraphic foundation allows for a final amalgamation of data leading to stronger supported interpretations for all parties involved. This is exactly what has been going on at the Petrified Forest over the last few years and the story coming out of the rocks and fossils is just amazing.
Irmis, R. B., and J. H. Whiteside. 2010. Newly integrated approaches to studying Late Triassic terrestrial ecosystems. Palaios 25:689-691. DOI: 10.2110/palo.2010.S06
It is a Spotlight article so there is no abstract. You can e-mail Randall Irmis for a PDF.
This excerpt makes a key point that I have been a strong proponent for:
"The key for understanding Late Triassic terrestrial ecosystems is that all of these new studies focus on stratigraphic sections where multiple different research approaches can be applied to maximize the data recovered from the same area."
Instead of various researchers working haphazardly, conducting different studies on different outcrops, coordinating this research instead with everyone working in the same areas under the same detailed stratigraphic foundation allows for a final amalgamation of data leading to stronger supported interpretations for all parties involved. This is exactly what has been going on at the Petrified Forest over the last few years and the story coming out of the rocks and fossils is just amazing.
Irmis, R. B., and J. H. Whiteside. 2010. Newly integrated approaches to studying Late Triassic terrestrial ecosystems. Palaios 25:689-691. DOI: 10.2110/palo.2010.S06
Sanjuansaurus gordilloi a new Herrerasaurid from Argentina
Here is a new herrerasaurid from the the Ischigualasto Formation of Argentina. Looks much more similar to Herrerasaurus than to Staurikosaurus or Chindesaurus, although the latter taxon was not included in the phylogenetic analysis. This analysis finds Herrerasauridae to be the sister taxon to Eoraptor + (Guaibasaurus + Neotheropoda), so we are back to the position of herrerasaurids still being dinosaurs but as basal saurischians rather than theropods. Comparison is provided in the text to Tawa hallae, but it is not included in the phylogenetic analysis. Too bad. However, I'm pretty certain that based on the current material coding Sanjuansaurus into the analysis of Nesbitt et al. (2009) would not change the position of herrerasaurids as basal theropods as recovered in that analysis. So whether or not herrerasaurids are theropods or not appears to be entirely dependent on the base matrix one uses. Thus, unfortunately, the analysis in this paper does not appear to offer anything particularly game-changing or significant in that regards. Also unfortunate is that there is no discussion of these differing hypotheses in the paper.
The further recognition of the increased diversity of basal saurischian dinosaurs in the latest Carnian is interesting and provides more circumstantial support for the earlier diversification of Archosauria in the Early Triassic as hypothesized by Nesbitt (2009) based on body fossils and more recently by Brusatte et al. (2010) based on footprint evidence.
Alcober O.A., and R. N. Martinez. 2010. A new herrerasaurid (Dinosauria, Saurischia) from the Upper Triassic Ischigualasto Formation of northwestern Argentina. ZooKeys 63 : 55 – 81 . doi: 10.3897/zookeys.63.550
Abstract - Herrerasauridae comprises a basal clade of dinosaurs best known from the Upper Triassic of Argentina and Brazil, which have yielded remains of Herrerasaurus ischigualastensis and Staurikosaurus pricei, respectively. Systematic opinion regarding the position of Herrerasauridae at the base of Dinosauria has varied. Here we describe a new herrerasaurid, Sanjuansaurus gordilloi gen. n., sp. n., based on a partial skeleton from Carnian-age strata of the the Upper Triassic Ischigualasto Formation of northwestern Argentina. The new taxon is diagnosed by numerous features, including long, band-shaped and posterolaterally oriented transverse process on the posterior cervical vertebrae; neural spines of the sixth to eighth dorsal vertebrae, at least, bearing acute anterior and posterior processes; scapula and coracoid with everted lateral margins of the glenoid; and short pubis (63% of the femoral length). Phylogenetic analysis placed Sanjuansaurus within a monophyletic Herrerasauridae, at the base of Theropoda and including Herrerasaurus and Staurikosaurus. The presence of Sanjuansaurus at the base of the Ischigualasto Formation, along with other dinosaurs such as Herrerasaurus, Eoraptor, Panphagia, and Chromogisaurus suggests that saurischian dinosaurs in southwestern Pangea were already widely diversified by the late Carnian rather than increasing in diversity across the Carnian-Norian boundary.
REFERENCES
Brusatte, S. L., Niedźwiedzki, G., and R. J. Butler. 2010. Footprints pull origin and diversification of dinosaur stem lineage deep into Early Triassic. Proceedings of the Royal Society B. doi: 10.1098/rspb.2010.1746
Nesbitt, S. J. 2009. The antiquity of Archosauria and the origin of Late Triassic archosaur assemblages. Journal of Vertebrate Paleontology 29:155A.
Nesbitt, S. J., Smith, N. D., Irmis, R. B.,Turner, A. H., Downs, A., and M. A. Norell. 2009. A Complete skeleton of a Late Triassic saurischian and the early evolution of dinosaurs. Science 326: 1530–1533.
The further recognition of the increased diversity of basal saurischian dinosaurs in the latest Carnian is interesting and provides more circumstantial support for the earlier diversification of Archosauria in the Early Triassic as hypothesized by Nesbitt (2009) based on body fossils and more recently by Brusatte et al. (2010) based on footprint evidence.
Alcober O.A., and R. N. Martinez. 2010. A new herrerasaurid (Dinosauria, Saurischia) from the Upper Triassic Ischigualasto Formation of northwestern Argentina. ZooKeys 63 : 55 – 81 . doi: 10.3897/zookeys.63.550
Abstract - Herrerasauridae comprises a basal clade of dinosaurs best known from the Upper Triassic of Argentina and Brazil, which have yielded remains of Herrerasaurus ischigualastensis and Staurikosaurus pricei, respectively. Systematic opinion regarding the position of Herrerasauridae at the base of Dinosauria has varied. Here we describe a new herrerasaurid, Sanjuansaurus gordilloi gen. n., sp. n., based on a partial skeleton from Carnian-age strata of the the Upper Triassic Ischigualasto Formation of northwestern Argentina. The new taxon is diagnosed by numerous features, including long, band-shaped and posterolaterally oriented transverse process on the posterior cervical vertebrae; neural spines of the sixth to eighth dorsal vertebrae, at least, bearing acute anterior and posterior processes; scapula and coracoid with everted lateral margins of the glenoid; and short pubis (63% of the femoral length). Phylogenetic analysis placed Sanjuansaurus within a monophyletic Herrerasauridae, at the base of Theropoda and including Herrerasaurus and Staurikosaurus. The presence of Sanjuansaurus at the base of the Ischigualasto Formation, along with other dinosaurs such as Herrerasaurus, Eoraptor, Panphagia, and Chromogisaurus suggests that saurischian dinosaurs in southwestern Pangea were already widely diversified by the late Carnian rather than increasing in diversity across the Carnian-Norian boundary.
 |
| Holotype specimen of Sanjuansaurus gordilloi (PVSJ 605) |
Brusatte, S. L., Niedźwiedzki, G., and R. J. Butler. 2010. Footprints pull origin and diversification of dinosaur stem lineage deep into Early Triassic. Proceedings of the Royal Society B. doi: 10.1098/rspb.2010.1746
Nesbitt, S. J. 2009. The antiquity of Archosauria and the origin of Late Triassic archosaur assemblages. Journal of Vertebrate Paleontology 29:155A.
Nesbitt, S. J., Smith, N. D., Irmis, R. B.,Turner, A. H., Downs, A., and M. A. Norell. 2009. A Complete skeleton of a Late Triassic saurischian and the early evolution of dinosaurs. Science 326: 1530–1533.
The Role of the Calcaneal 'Heel' in Basal Archosaurs
Sullivan, C. 2010. The role of the calcaneal 'heel' as a propulsive lever in basal archosaurs and extant monitor lizards. Journal of Vertebrate Paleontology 30:1422-1432.
Abstract - The structurally complex ankles of Triassic archosaurs (Reptilia: Diapsida) have been repeatedly described, and tarsal characters have played an important role in analyses of archosaur phylogeny. Morphological variations in the ankle joint undoubtedly had a major impact on locomotion, but the functional implications of many ankle features remain poorly understood. This paper investigates the function of one such structure, the prominent and highly distinctive lateral to posterolateral calcaneal process that occurs throughout basal archosaurs and is homologous to the heel-like calcaneal tuber of pseudosuchians. A morphologically analogous lateral process occurs in extant varanid lizards, and X-ray rotoscopic analysis of the limb movements of savannah monitors (Varanus exanthematicus) indicates that the lateral process rotates into a vertical orientation as the limb retracts. As the varanid lateral process approaches the vertical, it becomes increasingly effective in adding to the propulsive moment arm of m. peroneus longus. A computer model of the ankle was compared to modified versions in which the lateral process and the associated proximal expansion of the fifth metatarsal were eliminated, and this virtual experiment demonstrated that the combination of the two structures increases the peak propulsive moment arm of the varanid m. peroneus longus by over 26%. The lateral calcaneal process of basal archosaurs probably acted similarly, enhancing the ability of the peroneus musculature to contribute to propulsion during walking. Like the calcaneal tuber of pseudosuchian archosaurs, the primitive lateral process was a lever that contributed to locomotion by allowing ankle plantarflexion to generate a greater propulsive moment.
Abstract - The structurally complex ankles of Triassic archosaurs (Reptilia: Diapsida) have been repeatedly described, and tarsal characters have played an important role in analyses of archosaur phylogeny. Morphological variations in the ankle joint undoubtedly had a major impact on locomotion, but the functional implications of many ankle features remain poorly understood. This paper investigates the function of one such structure, the prominent and highly distinctive lateral to posterolateral calcaneal process that occurs throughout basal archosaurs and is homologous to the heel-like calcaneal tuber of pseudosuchians. A morphologically analogous lateral process occurs in extant varanid lizards, and X-ray rotoscopic analysis of the limb movements of savannah monitors (Varanus exanthematicus) indicates that the lateral process rotates into a vertical orientation as the limb retracts. As the varanid lateral process approaches the vertical, it becomes increasingly effective in adding to the propulsive moment arm of m. peroneus longus. A computer model of the ankle was compared to modified versions in which the lateral process and the associated proximal expansion of the fifth metatarsal were eliminated, and this virtual experiment demonstrated that the combination of the two structures increases the peak propulsive moment arm of the varanid m. peroneus longus by over 26%. The lateral calcaneal process of basal archosaurs probably acted similarly, enhancing the ability of the peroneus musculature to contribute to propulsion during walking. Like the calcaneal tuber of pseudosuchian archosaurs, the primitive lateral process was a lever that contributed to locomotion by allowing ankle plantarflexion to generate a greater propulsive moment.
This is the Kind of Study I'd Like to See Get Done More Often
I remain convinced that figuring out larger problems starts with the detailed collection of data at a smaller scale. This is exactly the type of study I'd like to consider for the Chinle Formation.....
Lyson, T. R., and N. R. Longrich. 2010. Spatial niche partitioning in dinosaurs from the latest cretaceous (Maastrichtian) of North America. Proceedings of the Royal Society B. Published online before print October 13, 2010, doi: 10.1098/rspb.2010.1444
Abstract - We examine patterns of occurrence of associated dinosaur specimens (n = 343) from the North American Upper Cretaceous Hell Creek Formation and equivalent beds, by comparing their relative abundance in sandstone and mudstone. Ceratopsians preferentially occur in mudstone, whereas hadrosaurs and the small ornithopod Thescelosaurus show a strong association with sandstone. By contrast, the giant carnivore Tyrannosaurus rex shows no preferred association with either lithology. These lithologies are used as an indicator of environment of deposition, with sandstone generally representing river environments, and finer grained sediments typically representing floodplain environments. Given these patterns of occurrence, we argue that spatial niche partitioning helped reduce competition for resources between the herbivorous dinosaurs. Within coastal lowlands ceratopsians preferred habitats farther away from rivers, whereas hadrosaurs and Thescelosaurus preferred habitats in close proximity to rivers, and T. rex, the ecosystem's sole large carnivore, inhabited both palaeoenvironments. Spatial partitioning of the environment helps explain how several species of large herbivorous dinosaurs coexisted. This study emphasizes that different lithologies can preserve dramatically dissimilar vertebrate assemblages, even when deposited in close proximity and within a narrow window of time. The lithology in which fossils are preserved should be recorded as these data can provide unique insights into the palaeoecology of the animals they preserve.
Lyson, T. R., and N. R. Longrich. 2010. Spatial niche partitioning in dinosaurs from the latest cretaceous (Maastrichtian) of North America. Proceedings of the Royal Society B. Published online before print October 13, 2010, doi: 10.1098/rspb.2010.1444
Abstract - We examine patterns of occurrence of associated dinosaur specimens (n = 343) from the North American Upper Cretaceous Hell Creek Formation and equivalent beds, by comparing their relative abundance in sandstone and mudstone. Ceratopsians preferentially occur in mudstone, whereas hadrosaurs and the small ornithopod Thescelosaurus show a strong association with sandstone. By contrast, the giant carnivore Tyrannosaurus rex shows no preferred association with either lithology. These lithologies are used as an indicator of environment of deposition, with sandstone generally representing river environments, and finer grained sediments typically representing floodplain environments. Given these patterns of occurrence, we argue that spatial niche partitioning helped reduce competition for resources between the herbivorous dinosaurs. Within coastal lowlands ceratopsians preferred habitats farther away from rivers, whereas hadrosaurs and Thescelosaurus preferred habitats in close proximity to rivers, and T. rex, the ecosystem's sole large carnivore, inhabited both palaeoenvironments. Spatial partitioning of the environment helps explain how several species of large herbivorous dinosaurs coexisted. This study emphasizes that different lithologies can preserve dramatically dissimilar vertebrate assemblages, even when deposited in close proximity and within a narrow window of time. The lithology in which fossils are preserved should be recorded as these data can provide unique insights into the palaeoecology of the animals they preserve.
Ouch! Spondarthritis in a Triassic Archosaur
Cisneros, J. C. , Gomes Cabral, U., de Beer, F., Damiani, R., and Costa Fortier, D. (2010) Spondarthritis in the Triassic. PLoS ONE 5(10): e13425. doi:10.1371/journal.pone.0013425
Abstract
Background: The evidence of several forms of arthritis has been well documented in the fossil record. However, for pre-Cenozoic vertebrates, especially regarding reptiles, this record is rather scarce. In this work we present a case report of spondarthritis found in a vertebral series that belonged to a carnivorous archosaurian reptile from the Lower Triassic (~245 million years old) of the South African Karoo.
Methodology/Principal Findings: Neutron tomography confirmed macroscopic data, revealing the ossification of the entire intervertebral disc space (both annulus fibrosus and nucleus pulposus), which supports the diagnosis of spondarthritis.
Conclusions/Significance: The presence of spondarthritis in the new specimen represents by far the earliest evidence of any form of arthritis in the fossil record. The present find is nearly 100 million years older than the previous oldest report of this pathology, based on a Late Jurassic dinosaur. Spondarthritis may have indirectly contributed to the death of the animal under study.
Abstract
Background: The evidence of several forms of arthritis has been well documented in the fossil record. However, for pre-Cenozoic vertebrates, especially regarding reptiles, this record is rather scarce. In this work we present a case report of spondarthritis found in a vertebral series that belonged to a carnivorous archosaurian reptile from the Lower Triassic (~245 million years old) of the South African Karoo.
Methodology/Principal Findings: Neutron tomography confirmed macroscopic data, revealing the ossification of the entire intervertebral disc space (both annulus fibrosus and nucleus pulposus), which supports the diagnosis of spondarthritis.
Conclusions/Significance: The presence of spondarthritis in the new specimen represents by far the earliest evidence of any form of arthritis in the fossil record. The present find is nearly 100 million years older than the previous oldest report of this pathology, based on a Late Jurassic dinosaur. Spondarthritis may have indirectly contributed to the death of the animal under study.
Did you Celebrate the 1st Annual National Fossil Day?
I spent the day guiding visitors at Petrified Forest National Park through our fossil preparation lab and conducted a tour out to a well known fossil locality known as the Dying Grounds.
You can read more about this at the following link. Check out the Official National Fossil Day song and video. Some of the people in the video look somewhat familiar.....
http://www.nature.nps.gov/geology/nationalfossilday/index.cfm
Preview of New Early Jurassic "Coelophysoid" Fossil from China
This is a link to an article discussing new finds of "coelophysoid" material from Lufeng.
http://english.peopledaily.com.cn/90001/90782/7161153.html
Photos of the new material can be seen here. Pretty impressive!
http://www.cnr.cn/newscenter/xwtz/201010/t20101008_507139251.html#javascript_intro
Added 9 pm 10/9/2010: Looking at this a bit closer now that I have some time... I'm not convinced it is coelophysoid. The snout is too short and the face isn't "pointed" enough. There is a short-snouted form of "Coelophysis" out of the Coelophysis quarry that was mentioned by David Smith in a 2006 paper (I don't have the ref right now), but this also appears to be different than that. Rather this appears to be some kind of basal theropod, which would be very interesting out of an Early Jurassic deposit.
http://english.peopledaily.com.cn/90001/90782/7161153.html
Photos of the new material can be seen here. Pretty impressive!
http://www.cnr.cn/newscenter/xwtz/201010/t20101008_507139251.html#javascript_intro
Added 9 pm 10/9/2010: Looking at this a bit closer now that I have some time... I'm not convinced it is coelophysoid. The snout is too short and the face isn't "pointed" enough. There is a short-snouted form of "Coelophysis" out of the Coelophysis quarry that was mentioned by David Smith in a 2006 paper (I don't have the ref right now), but this also appears to be different than that. Rather this appears to be some kind of basal theropod, which would be very interesting out of an Early Jurassic deposit.
Dispersal as a Key Factor in Early Dinosaur Diversification of North America and the Myth of a 'Cosmopolitan' Dinosaur Fauna in the Early Mesozoic
New and available free from the Royal Society website. Popular news story here.
Rowe, T. B., Sues, H.-D., and R. Reisz. 2010. Dispersal and diversity in the earliest North American sauropodomorph dinosaurs, with a description of a new taxon. Proceedings of the Royal Society B, First Cite. doi:10.1098/rspb.2010.1867
Abstract - Sauropodomorph dinosaurs originated in the Southern Hemisphere in the Middle or Late Triassic and are commonly portrayed as spreading rapidly to all corners of Pangaea as part of a uniform Late Triassic to Early Jurassic cosmopolitan dinosaur fauna. Under this model, dispersal allegedly inhibited dinosaurian diversification, while vicariance and local extinction enhanced it. However, apomorphy-based analyses of the known fossil record indicate that sauropodomorphs were absent in North America until the Early Jurassic, reframing the temporal context of their arrival. We describe a new taxon from the Kayenta Formation of Arizona that comprises the third diagnosable sauropodomorph from the Early Jurassic of North America. We analysed its relationships to test whether sauropodomorphs reached North America in a single sweepstakes event or in separate dispersals. Our finding of separate arrivals by all three taxa suggests dispersal as a chief factor in dinosaurian diversification during at least the early Mesozoic. It questions whether a ‘cosmopolitan’ dinosaur fauna ever existed, and corroborates that vicariance, extinction and dispersal did not operate uniformly in time or under uniform conditions during the Mesozoic. Their relative importance is best measured in narrow time slices and circumscribed geographical regions.
Rowe, T. B., Sues, H.-D., and R. Reisz. 2010. Dispersal and diversity in the earliest North American sauropodomorph dinosaurs, with a description of a new taxon. Proceedings of the Royal Society B, First Cite. doi:10.1098/rspb.2010.1867
Abstract - Sauropodomorph dinosaurs originated in the Southern Hemisphere in the Middle or Late Triassic and are commonly portrayed as spreading rapidly to all corners of Pangaea as part of a uniform Late Triassic to Early Jurassic cosmopolitan dinosaur fauna. Under this model, dispersal allegedly inhibited dinosaurian diversification, while vicariance and local extinction enhanced it. However, apomorphy-based analyses of the known fossil record indicate that sauropodomorphs were absent in North America until the Early Jurassic, reframing the temporal context of their arrival. We describe a new taxon from the Kayenta Formation of Arizona that comprises the third diagnosable sauropodomorph from the Early Jurassic of North America. We analysed its relationships to test whether sauropodomorphs reached North America in a single sweepstakes event or in separate dispersals. Our finding of separate arrivals by all three taxa suggests dispersal as a chief factor in dinosaurian diversification during at least the early Mesozoic. It questions whether a ‘cosmopolitan’ dinosaur fauna ever existed, and corroborates that vicariance, extinction and dispersal did not operate uniformly in time or under uniform conditions during the Mesozoic. Their relative importance is best measured in narrow time slices and circumscribed geographical regions.
Evidence for an Early Triassic Origin for the Dinosaur Stem Lineage
Brusatte, S. L., Niedźwiedzki, G., and R. J. Butler. 2010. Footprints pull origin and diversification of dinosaur stem lineage deep into Early Triassic. Proceedings of the Royal Society B. doi: 10.1098/rspb.2010.1746
Abstract - The ascent of dinosaurs in the Triassic is an exemplary evolutionary radiation, but the earliest phase of dinosaur history remains poorly understood. Body fossils of close dinosaur relatives are rare, but indicate that the dinosaur stem lineage (Dinosauromorpha) originated by the latest Anisian (ca 242–244 Ma). Here, we report footprints from the Early–Middle Triassic of Poland, stratigraphically well constrained and identified using a conservative synapomorphy-based approach, which shifts the origin of the dinosaur stem lineage back to the Early Olenekian (ca 249–251 Ma), approximately 5–9 Myr earlier than indicated by body fossils, earlier than demonstrated by previous footprint records, and just a few million years after the Permian/Triassic mass extinction (252.3 Ma). Dinosauromorph tracks are rare in all Polish assemblages, suggesting that these animals were minor faunal components. The oldest tracks are quadrupedal, a morphology uncommon among the earliest dinosauromorph body fossils, but bipedality and moderately large body size had arisen by the Early Anisian (ca 246 Ma). Integrating trace fossils and body fossils demonstrates that the rise of dinosaurs was a drawn-out affair, perhaps initiated during recovery from the Permo-Triassic extinction.
Popular news story here with a horrible title as they are not true dinosaur footprints.
Abstract - The ascent of dinosaurs in the Triassic is an exemplary evolutionary radiation, but the earliest phase of dinosaur history remains poorly understood. Body fossils of close dinosaur relatives are rare, but indicate that the dinosaur stem lineage (Dinosauromorpha) originated by the latest Anisian (ca 242–244 Ma). Here, we report footprints from the Early–Middle Triassic of Poland, stratigraphically well constrained and identified using a conservative synapomorphy-based approach, which shifts the origin of the dinosaur stem lineage back to the Early Olenekian (ca 249–251 Ma), approximately 5–9 Myr earlier than indicated by body fossils, earlier than demonstrated by previous footprint records, and just a few million years after the Permian/Triassic mass extinction (252.3 Ma). Dinosauromorph tracks are rare in all Polish assemblages, suggesting that these animals were minor faunal components. The oldest tracks are quadrupedal, a morphology uncommon among the earliest dinosauromorph body fossils, but bipedality and moderately large body size had arisen by the Early Anisian (ca 246 Ma). Integrating trace fossils and body fossils demonstrates that the rise of dinosaurs was a drawn-out affair, perhaps initiated during recovery from the Permo-Triassic extinction.
Popular news story here with a horrible title as they are not true dinosaur footprints.
Subscribe to:
Posts (Atom)