There are quite a few Triassic themed posts out there right now, most of them dealing with recent publications by staff from the New Mexico Museum of Natural History and Science and Appalachian State University.
Dinosaur Tracking - Articulated skeletons give a new look at "armodillodiles".
Brian Switek provides a brief overview of the new Typothorax paper from the most recent Journal of Vertebrate Paleontology.
http://blogs.smithsonianmag.com/dinosaur/2010/05/27/articulated-skeletons-give-a-new-look-at-armadillodiles/
The Hairy Museum of Natural History - A new look for Typothorax
Matt Celeskey's post provided the original announcement and a really cool reconstruction.
http://www.hmnh.org/archives/2010/05/20/a-new-look-for-typothorax/
Paleo Errata - The JVP Typothorax paper - Jeff is still best
Jeff Martz provides a more detailed analysis as only he can.
http://paleoerrata.blogspot.com/2010/05/jvp-typothorax-paper-jeff-is-still-best.html
The Theropod Database - Rinehart et al's (2009) Coelophysis monograph - a review
Finally, Mickey Mortimer provides a review of the recent Coelophysis monograph by the same workers, which sounds eerily similar to something else I've read recently.
http://theropoddatabase.blogspot.com/2010/05/rinehart-et-al-2009s-coelophysis.html
Can We Actually Determine the Thermophysiology of Extinct Animals as well as the Paleoclimate from Fossil Bones?
Eaglea, R. A., Schaubleb, E. A., Tripatia, A. K., Tütkend, T., Hulbert, R. C., and J. M. Eiler. 2010. temperatures of modern and extinct vertebrates from 13C-18O bond abundances in bioapatite. Proceedings of the National Academy of Sciences. Published online before print May 24, 2010, doi: 10.1073/pnas.0911115107
Abstract - The stable isotope compositions of biologically precipitated apatite in bone, teeth, and scales are widely used to obtain information on the diet, behavior, and physiology of extinct organisms and to reconstruct past climate. Here we report the application of a new type of geochemical measurement to bioapatite, a “clumped-isotope” paleothermometer, based on the thermodynamically driven preference for 13C and 18O to bond with each other within carbonate ions in the bioapatite crystal lattice. This effect is dependent on temperature but, unlike conventional stable isotope paleothermometers, is independent from the isotopic composition of water from which the mineral formed. We show that the abundance of 13C-18O bonds in the carbonate component of tooth bioapatite from modern specimens decreases with increasing body temperature of the animal, following a relationship between isotope “clumping” and temperature that is statistically indistinguishable from inorganic calcite. This result is in agreement with a theoretical model of isotopic ordering in carbonate ion groups in apatite and calcite. This thermometer constrains body temperatures of bioapatite-producing organisms with an accuracy of 1–2 °C. Analyses of fossilized tooth enamel of both Pleistocene and Miocene age yielded temperatures within error of those derived from similar modern taxa. Clumped-isotope analysis of bioapatite represents a new approach in the study of the thermophysiology of extinct species, allowing the first direct measurement of their body temperatures. It will also open new avenues in the study of paleoclimate, as the measurement of clumped isotopes in phosphorites and fossils has the potential to reconstruct environmental temperatures.
Abstract - The stable isotope compositions of biologically precipitated apatite in bone, teeth, and scales are widely used to obtain information on the diet, behavior, and physiology of extinct organisms and to reconstruct past climate. Here we report the application of a new type of geochemical measurement to bioapatite, a “clumped-isotope” paleothermometer, based on the thermodynamically driven preference for 13C and 18O to bond with each other within carbonate ions in the bioapatite crystal lattice. This effect is dependent on temperature but, unlike conventional stable isotope paleothermometers, is independent from the isotopic composition of water from which the mineral formed. We show that the abundance of 13C-18O bonds in the carbonate component of tooth bioapatite from modern specimens decreases with increasing body temperature of the animal, following a relationship between isotope “clumping” and temperature that is statistically indistinguishable from inorganic calcite. This result is in agreement with a theoretical model of isotopic ordering in carbonate ion groups in apatite and calcite. This thermometer constrains body temperatures of bioapatite-producing organisms with an accuracy of 1–2 °C. Analyses of fossilized tooth enamel of both Pleistocene and Miocene age yielded temperatures within error of those derived from similar modern taxa. Clumped-isotope analysis of bioapatite represents a new approach in the study of the thermophysiology of extinct species, allowing the first direct measurement of their body temperatures. It will also open new avenues in the study of paleoclimate, as the measurement of clumped isotopes in phosphorites and fossils has the potential to reconstruct environmental temperatures.
A New Procolophonid Parareptile from the Lower Triassic of South Africa
Modesto, S. P. , Scott, D. M. , Botha-Brink, J., and R. R. Reisz. 2010. A new and unusual procolophonid parareptile from the Lower Triassic Katberg Formation of South Africa. Journal of Vertebrate Paleontology, 30:715-723.
DOI: 10.1080/02724631003758003
Abstract - A small skull collected from the base of the Katberg Formation of South Africa represents a new Early Triassic procolophonid parareptile. Phonodus dutoitorum, gen. et sp. nov., is diagnosed by a roughly straight ventral temporal margin, prefrontals that contact each other along the dorsal midline, presence of a large posterior maxillary tooth, an edentulous pterygoid, a reduced transverse flange of the pterygoid, and other autapomorphies. A cladistic analysis identifies P. dutoitorum as a basal member of the procolophonid clade Leptopleuroninae. The presence of large maxillary teeth, their positioning ventral to strongly developed antorbital buttresses, and the loss of the ventral temporal emargination are suggestive of a durophagous diet. Phonodus dutoitorum is recognized as the oldest known leptopleuronine. Optimization of geographic distributions onto procolophonid phylogeny indicates that the presence of P. dutoitorum in the Karoo Basin of South Africa is explained most parsimoniously as the result of migration from Laurasia. Phonodus dutoitorum is the fifth procolophonoid species to be described from the Induan of the Karoo Basin, providing further support for the hypothesis that procolophonoid evolution was not greatly perturbed by the end-Permian extinction event.
DOI: 10.1080/02724631003758003
Abstract - A small skull collected from the base of the Katberg Formation of South Africa represents a new Early Triassic procolophonid parareptile. Phonodus dutoitorum, gen. et sp. nov., is diagnosed by a roughly straight ventral temporal margin, prefrontals that contact each other along the dorsal midline, presence of a large posterior maxillary tooth, an edentulous pterygoid, a reduced transverse flange of the pterygoid, and other autapomorphies. A cladistic analysis identifies P. dutoitorum as a basal member of the procolophonid clade Leptopleuroninae. The presence of large maxillary teeth, their positioning ventral to strongly developed antorbital buttresses, and the loss of the ventral temporal emargination are suggestive of a durophagous diet. Phonodus dutoitorum is recognized as the oldest known leptopleuronine. Optimization of geographic distributions onto procolophonid phylogeny indicates that the presence of P. dutoitorum in the Karoo Basin of South Africa is explained most parsimoniously as the result of migration from Laurasia. Phonodus dutoitorum is the fifth procolophonoid species to be described from the Induan of the Karoo Basin, providing further support for the hypothesis that procolophonoid evolution was not greatly perturbed by the end-Permian extinction event.
Typothorax in the New Issue of JVP
Heckert, A. B., Lucas, S. G., Rinehart, L. F., Celeskey, M. D., Justin A. Spielmann, J. A., and A. P. Hunt. 2010. Articulated skeletons of the aetosaur Typothorax coccinarum Cope (Archosauria: Stagonolepididae) from the Upper Triassic Bull Canyon Formation (Revueltian: Early-Mid Norian), Eastern New Mexico, USA. Journal of Vertebrate Paleontology 30:619-642.
Abstract - We report two nearly complete, articulated skeletons of the crurotarsan archosaur Typothorax coccinarum from the Upper Triassic Bull Canyon Formation of east-central New Mexico. These are the most complete, articulated aetosaurs from North America and provide a wealth of new anatomical and paleobiological data, including articulated presacral armor that confirms the distinctiveness of T. coccinarum from the closely related T. antiquum and from Redondasuchus. Cervical vertebrae are small, but the corresponding reduction in armor is accomplished by a reduced number of cervical osteoderms. The third row of osteoderms includes a thin, elongate, lateral spike. The ventral armor consists of 10 thoracic columns and four caudal columns of osteoderms. Spiked osteoderms near the cloacal vent are the first spikes reported in aetosaurian ventral osteoderms. The forelimb of T. coccinarum was very short, only ∼0.65 the length of the hind limb, possesses some adaptations found in digging taxa, and was held in a sprawling or ‘semi-erect’ position. In contrast the hind limb is much more robust, ‘pillar erect,’ and functionally mesotarsal. The articulated pes, including unguals, has, minimally, the phalangeal formula 2-3-3?-4?-3? with relative digit lengths III > II > IV > I > V, digits I–IV equally as wide as long and other characteristics of the footprint ichnogenus Brachychirotherium, often attributed to an aetosaurian trackmaker. Both specimens are ∼2.5 m long and the preserved armor and limb bones are as large or larger than known Typothorax fossils, suggesting that this approximates the upper size limit of T. coccinarum, and we calculate body mass estimates of ∼100–104 kg for both specimens.
Abstract - We report two nearly complete, articulated skeletons of the crurotarsan archosaur Typothorax coccinarum from the Upper Triassic Bull Canyon Formation of east-central New Mexico. These are the most complete, articulated aetosaurs from North America and provide a wealth of new anatomical and paleobiological data, including articulated presacral armor that confirms the distinctiveness of T. coccinarum from the closely related T. antiquum and from Redondasuchus. Cervical vertebrae are small, but the corresponding reduction in armor is accomplished by a reduced number of cervical osteoderms. The third row of osteoderms includes a thin, elongate, lateral spike. The ventral armor consists of 10 thoracic columns and four caudal columns of osteoderms. Spiked osteoderms near the cloacal vent are the first spikes reported in aetosaurian ventral osteoderms. The forelimb of T. coccinarum was very short, only ∼0.65 the length of the hind limb, possesses some adaptations found in digging taxa, and was held in a sprawling or ‘semi-erect’ position. In contrast the hind limb is much more robust, ‘pillar erect,’ and functionally mesotarsal. The articulated pes, including unguals, has, minimally, the phalangeal formula 2-3-3?-4?-3? with relative digit lengths III > II > IV > I > V, digits I–IV equally as wide as long and other characteristics of the footprint ichnogenus Brachychirotherium, often attributed to an aetosaurian trackmaker. Both specimens are ∼2.5 m long and the preserved armor and limb bones are as large or larger than known Typothorax fossils, suggesting that this approximates the upper size limit of T. coccinarum, and we calculate body mass estimates of ∼100–104 kg for both specimens.
Rhaetian Ichnology and Geochemistry of the Westbury Formation, England
Allington-Jones, L., Braddy, S. J., and Trueman, C. N. 2010. Palaeoenvironmental implications of the ichnology and geochemistry of the Westbury Formation (Rhaetian), Westburyon- Severn, South-West England. Palaeontology 53:491-506. doi: 10.1111/j.1475-4983.2010.00947.x
Abstract - The Westbury Formation (Rhaetian) beds of Westbury Garden Cliff, Westbury-on-Severn, west of Gloucester, Britain, show an unusual combination of features. Both deep water and emergent characteristics are present within the sediments and the trace fossils. The ichnoassemblage consists of abundant Selenichnites, Planolites beverlyensis and Lockeia with rarer Oniscoidichnus, Chondrites, Rhizocorallium irregulare, Taenidium serpentium, an unusual form of Walcottia and Merostomichnites-like traces. These trace fossils display an interesting relationship with the sediments: low-energy Cruziana ichnofacies is found within high-energy sandstones. The sandstones are interbedded with laminated mudstones, apparently deposited in deep water, but some aspects of the ichnoassemblage, preservation and sedimentation indicate shallower water. One new trace fossil, Radichnus allingtona igen. et isp. nov., closely resembles the traces of modern fiddler crabs and imply emergence, by analogy. This ichnofauna is similar to early stage disaster colonisation in recent experiments in Long Island Sound (south of Connecticut, USA) and with storm influenced deposits within the Cardium Formation (Seebe, Alberta, Canada). This indicates a lagoonal environment with influxes of sand and oxygen. Total organic carbon levels were found to fluctuate greatly between stratigraphic layers but remained relatively high. This implies low oxygen conditions. The abundance of sulphur (in pyrite) also supports an interpretation of anoxic conditions, and low sedimentation rates within the shale layers. A restricted shallow basin or lagoonal environment is proposed for the palaeoenvironment, with fluctuating oxygen influencing diversity.
Abstract - The Westbury Formation (Rhaetian) beds of Westbury Garden Cliff, Westbury-on-Severn, west of Gloucester, Britain, show an unusual combination of features. Both deep water and emergent characteristics are present within the sediments and the trace fossils. The ichnoassemblage consists of abundant Selenichnites, Planolites beverlyensis and Lockeia with rarer Oniscoidichnus, Chondrites, Rhizocorallium irregulare, Taenidium serpentium, an unusual form of Walcottia and Merostomichnites-like traces. These trace fossils display an interesting relationship with the sediments: low-energy Cruziana ichnofacies is found within high-energy sandstones. The sandstones are interbedded with laminated mudstones, apparently deposited in deep water, but some aspects of the ichnoassemblage, preservation and sedimentation indicate shallower water. One new trace fossil, Radichnus allingtona igen. et isp. nov., closely resembles the traces of modern fiddler crabs and imply emergence, by analogy. This ichnofauna is similar to early stage disaster colonisation in recent experiments in Long Island Sound (south of Connecticut, USA) and with storm influenced deposits within the Cardium Formation (Seebe, Alberta, Canada). This indicates a lagoonal environment with influxes of sand and oxygen. Total organic carbon levels were found to fluctuate greatly between stratigraphic layers but remained relatively high. This implies low oxygen conditions. The abundance of sulphur (in pyrite) also supports an interpretation of anoxic conditions, and low sedimentation rates within the shale layers. A restricted shallow basin or lagoonal environment is proposed for the palaeoenvironment, with fluctuating oxygen influencing diversity.
The Braincase of the Late Triassic Archosauriform Proterochampsa and its Implications for Archosauriform Phylogeny.
Trotteyn, M. J. and J. A. Haro. In Press. The braincase of a specimen of Proterochampsa Reig (Archosauriformes: Proterochampsidae) from the Late Triassic of Argentina. Paläontologische Zeitschrift. Published on-line May 11 2010. DOI 10.1007/s12542-010-0068-7
Abstract: The proterochampsids are a Triassic group of superficially crocodile-like forms belonging to the Archosauriformes. In the present contribution, we present new information regarding the braincase of the proterochampsid Proterochampsa Reig 1959, from the Ischigualasto Formation (Carnian) of Argentina, and discuss its phylogenetic considerations. Some unique neurocranial features of Proterochampsa are described, including: the prominence and thickness of the V-shaped ridge that surrounds the basisphenoidal fossa; the medially concave lateral arms of the same ridge; and the semilunar depression on the parabasisphenoid ventrolaterally exposed. Other features are only shared with likely unrelated archosauriforms, including: the great lateral development of the basipterygoid processes and caudal development of its distal end; an eight-shaped metotic foramen; laterally directed basipterygoid processes; and rostral boundary of the basisphenoidal recess V-shaped. Proterochampsa differs in many other aspects from the archosauriform Chanaresuchus, including: a proportionally shorter basioccipital basal tubera; cultriform process ovoid in cross-section; longitudinal sulcus dorsal to the basipterygoid process; deep basisphenoidal recess; and the absence of a prominent intertuberal plate. In many braincase features, Proterochampsa is more similar to archosaurs than to Euparkeria, erythrosuchids and Proterosuchus. They include a reduced semilunar depression. A ventral border of the basioccipital forming a wide convexity and a dorsoventrally thin paroccipital process likely represents a feature shared with Chanaresuchus, but not with Doswellia and other basal archosauriforms.
Comments: There is currently no clear consensus among Triassic workers on the phylogentic relationships of the archosauriforms. Older (e.g., Sereno 1990, Juul, 1994) analyses recover the proterochampsids as the sister taxon of Archosauria, with Euparkeria, Erythrosuchus, and Proterosuchus as successive outgroups, relationships that were also recovered in a more recent analysis of the Triassic archosauriform Vancleavea campi by Parker and Barton (2008). However, two more recent analyses Dilkes and Sues (2009) and Nesbitt et al. (2009) have challenged this. Dilkes and Sues (2009), in a study of Doswellia, still recovered Proterochampsidae as the sister taxon of Archosauria, but found Erythrosuchus to be more closely related to that clade than Euparkeria. Contrastingly Nesbitt et al. (2009) found Euparkeria more closely related to Archosauria than proterochampsids. Furthermore, analyses based solely on braincase characters (e.g., Gower and Sennikov, 1996) have not included preterochampsids.
The Trotteyn and Haro paper provides a much needed, up to date, description and comparison of a referred braincase of the proterochampsid Proterochampsa barrionuevoi. Interestingly the braincase of Proterochampsa implies a closer relationship with Archosauria, rather than Euparkeria and Erythrosuchus; however, it is important to remember to a recent study by Rauhut (2007) found that braincase characters are not 'conservative' in nature and instead highly prone to homoplasy and dependence on other character suites. Nonetheless, this paper provides important information for workers wishing to incorporate proterochampsid braincase data into their analysis. We are still awaiting a phylogenetic analysis of the Archosauriformes that incorporates all proposed archosauromorph taxa.
REFERENCES
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.
Gower, D.J., and A.G. Sennikov. 1996. Morphology and phylogenetic informativeness of early archosaur braincases. Palaeontology 39: 883–906.
Juul, L. 1994. The phylogeny of basal archosaurs. Palaeontologia Africana 31: 1–38.
Nesbitt, S. J., Stocker, M. R., Small, B. J. and A. Downs. 2009. The osteology and relationships of Vancleavea campi (Reptilia: Archosauriformes). Zoological Journal of the Linnaean Society 157: 814-864.
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; http://palaeo-electronica.org/2008_3/158/index.html
Rauhut, O. W. M. 2007. The myth of the conservative character: braincase characters in theropod phylogenies. Hallesches Jahrbuch für Geowissenschaften, Beiheft 23: 51-54.
Sereno, P.C., and F.E. Novas. 1994. The skull and neck of the basal theropod Herrerasaurus ischigualastensis. Journal of Vertebrate Paleontology 13: 451–476.
Abstract: The proterochampsids are a Triassic group of superficially crocodile-like forms belonging to the Archosauriformes. In the present contribution, we present new information regarding the braincase of the proterochampsid Proterochampsa Reig 1959, from the Ischigualasto Formation (Carnian) of Argentina, and discuss its phylogenetic considerations. Some unique neurocranial features of Proterochampsa are described, including: the prominence and thickness of the V-shaped ridge that surrounds the basisphenoidal fossa; the medially concave lateral arms of the same ridge; and the semilunar depression on the parabasisphenoid ventrolaterally exposed. Other features are only shared with likely unrelated archosauriforms, including: the great lateral development of the basipterygoid processes and caudal development of its distal end; an eight-shaped metotic foramen; laterally directed basipterygoid processes; and rostral boundary of the basisphenoidal recess V-shaped. Proterochampsa differs in many other aspects from the archosauriform Chanaresuchus, including: a proportionally shorter basioccipital basal tubera; cultriform process ovoid in cross-section; longitudinal sulcus dorsal to the basipterygoid process; deep basisphenoidal recess; and the absence of a prominent intertuberal plate. In many braincase features, Proterochampsa is more similar to archosaurs than to Euparkeria, erythrosuchids and Proterosuchus. They include a reduced semilunar depression. A ventral border of the basioccipital forming a wide convexity and a dorsoventrally thin paroccipital process likely represents a feature shared with Chanaresuchus, but not with Doswellia and other basal archosauriforms.
Comments: There is currently no clear consensus among Triassic workers on the phylogentic relationships of the archosauriforms. Older (e.g., Sereno 1990, Juul, 1994) analyses recover the proterochampsids as the sister taxon of Archosauria, with Euparkeria, Erythrosuchus, and Proterosuchus as successive outgroups, relationships that were also recovered in a more recent analysis of the Triassic archosauriform Vancleavea campi by Parker and Barton (2008). However, two more recent analyses Dilkes and Sues (2009) and Nesbitt et al. (2009) have challenged this. Dilkes and Sues (2009), in a study of Doswellia, still recovered Proterochampsidae as the sister taxon of Archosauria, but found Erythrosuchus to be more closely related to that clade than Euparkeria. Contrastingly Nesbitt et al. (2009) found Euparkeria more closely related to Archosauria than proterochampsids. Furthermore, analyses based solely on braincase characters (e.g., Gower and Sennikov, 1996) have not included preterochampsids.
The Trotteyn and Haro paper provides a much needed, up to date, description and comparison of a referred braincase of the proterochampsid Proterochampsa barrionuevoi. Interestingly the braincase of Proterochampsa implies a closer relationship with Archosauria, rather than Euparkeria and Erythrosuchus; however, it is important to remember to a recent study by Rauhut (2007) found that braincase characters are not 'conservative' in nature and instead highly prone to homoplasy and dependence on other character suites. Nonetheless, this paper provides important information for workers wishing to incorporate proterochampsid braincase data into their analysis. We are still awaiting a phylogenetic analysis of the Archosauriformes that incorporates all proposed archosauromorph taxa.
REFERENCES
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.
Gower, D.J., and A.G. Sennikov. 1996. Morphology and phylogenetic informativeness of early archosaur braincases. Palaeontology 39: 883–906.
Juul, L. 1994. The phylogeny of basal archosaurs. Palaeontologia Africana 31: 1–38.
Nesbitt, S. J., Stocker, M. R., Small, B. J. and A. Downs. 2009. The osteology and relationships of Vancleavea campi (Reptilia: Archosauriformes). Zoological Journal of the Linnaean Society 157: 814-864.
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; http://palaeo-electronica.org/2008_3/158/index.html
Rauhut, O. W. M. 2007. The myth of the conservative character: braincase characters in theropod phylogenies. Hallesches Jahrbuch für Geowissenschaften, Beiheft 23: 51-54.
Sereno, P.C., and F.E. Novas. 1994. The skull and neck of the basal theropod Herrerasaurus ischigualastensis. Journal of Vertebrate Paleontology 13: 451–476.
Another Article on the New Prestosuchus find from Brazil
Here is another news article on the absolutely beautiful partial articulated Prestosuchus specimen from Brazil. The skull looks complete and relatively undistorted, the cervical series appears to be present and in articulation, the scapulocoracoid is fused and absolutely huge, and there also appears to be a fused clavicle and interclavicle pretty much in place. A forelimb lies under the skull and ribs and other limb bones are at the back of the jacket. Phenomenal!
I do have to shake my head though at how the name "thecodont" made into an article published in 2010!
The photos below are from this article and here.
If Azendohsaurus is not a Sauropodomorph Then What is it?
Would you believe an basal archosauromorph?
Flynn, J. J., Nesbitt, S. J., Parrish, J. M., Ranivoharimanana, L., and A. R. Wyss. 2010. A new species of Azendohsaurus (Diapsida: Archosauromorpha) from the Triassic Isalo Group of southwestern Madagascar: cranium and mandible. Palaeontology 53:669-688.
As if the Triassic couldn't get any weirder. If this discovery does not finally demonstrate the peril of assigning isolated jaw fragments and teeth to various dinosaurian subgroups, I do not know what will. The placement of Azendohsaurus as a basal archosauromorph demonstrates that herbivory has evolved independently numerous times within Archosauromorpha and was actually much more common in this clade than previously believed. Some of the primitive cranial features found in Azendohsaurus include a pineal opening, an incomplete lower temporal bar, and palatal teeth. One unique feature of Azendohsaurus is that the palatal teeth are actually leaf-shaped with denticles, very similar to the marginal teeth.
Abstract - Here, we describe a new species of Azendohsaurus from the Middle–Late Triassic of Madagascar, extending the geographical range of a taxon known otherwise only by a single species from Morocco. Although Azendohsaurus has consistently been regarded as an early dinosaur (based on various advanced dental and gnathic features resembling those characterizing certain dinosaur subgroups), the relatively complete skeletal material, now available from Madagascar, argues strongly against its dinosaurian affinities. Rather, the retention of numerous primitive cranial and postcranial features indicates a surprisingly early divergence of Azendohsaurus within Archosauromorpha and an unusual mosaic of characters in this taxon. Features considered diagnostic of Sauropodomorpha thus are inferred to occur homoplastically in at least one clade of nondinosaurian archosauromorphs, indicating a complex evolution and distribution of features traditionally thought to be derived within archosaurs. Azendohsaurus has teeth resembling those of both early sauropodomorph and ornithischian dinosaurs, yet also possesses numerous inarguable basal archosauromorph cranial and postcranial attributes. This highlights the risk of uncritically referring isolated, Middle–Late Triassic (or even later), ‘leafshaped’ teeth with denticles to the Dinosauria. Similarly, the occurrence of such teeth in an early diverging archosauromorph indicates that specializations for herbivory originated more frequently within this clade than conventionally assumed. For example, Azendohsaurus and numerous basal sauropodomorph dinosaur taxa share an array of convergently acquired features associated with herbivory, including tooth denticles, expanded tooth crowns, a downturned dentary and the articular located at the ventral margin of the mandible. Some of these features (denticles, expanded crowns and the ventrally deflected articular) are even more widespread among archosauromorphs, including aetosaurs, silesaurs and ornithischian dinosaurs. A downturned dentary also occurs in Trilophosaurus, a taxon further marked by unique specializations for herbivory, including transversely lophate, tricuspid teeth. An array of features associated with herbivory also occur in rhynchosaurs and certain crocodilians (e.g. Simosuchus). This distribution suggests that craniodental features associated with herbivory were much more pervasive across the archosauromorph clade than previously recognized, possibly evolving at least six to eight times independently.
Flynn, J. J., Nesbitt, S. J., Parrish, J. M., Ranivoharimanana, L., and A. R. Wyss. 2010. A new species of Azendohsaurus (Diapsida: Archosauromorpha) from the Triassic Isalo Group of southwestern Madagascar: cranium and mandible. Palaeontology 53:669-688.
As if the Triassic couldn't get any weirder. If this discovery does not finally demonstrate the peril of assigning isolated jaw fragments and teeth to various dinosaurian subgroups, I do not know what will. The placement of Azendohsaurus as a basal archosauromorph demonstrates that herbivory has evolved independently numerous times within Archosauromorpha and was actually much more common in this clade than previously believed. Some of the primitive cranial features found in Azendohsaurus include a pineal opening, an incomplete lower temporal bar, and palatal teeth. One unique feature of Azendohsaurus is that the palatal teeth are actually leaf-shaped with denticles, very similar to the marginal teeth.
 |
| Skull reconstruction of Azendohsaurus. From Flynn et al. 2010. |
Abstract - Here, we describe a new species of Azendohsaurus from the Middle–Late Triassic of Madagascar, extending the geographical range of a taxon known otherwise only by a single species from Morocco. Although Azendohsaurus has consistently been regarded as an early dinosaur (based on various advanced dental and gnathic features resembling those characterizing certain dinosaur subgroups), the relatively complete skeletal material, now available from Madagascar, argues strongly against its dinosaurian affinities. Rather, the retention of numerous primitive cranial and postcranial features indicates a surprisingly early divergence of Azendohsaurus within Archosauromorpha and an unusual mosaic of characters in this taxon. Features considered diagnostic of Sauropodomorpha thus are inferred to occur homoplastically in at least one clade of nondinosaurian archosauromorphs, indicating a complex evolution and distribution of features traditionally thought to be derived within archosaurs. Azendohsaurus has teeth resembling those of both early sauropodomorph and ornithischian dinosaurs, yet also possesses numerous inarguable basal archosauromorph cranial and postcranial attributes. This highlights the risk of uncritically referring isolated, Middle–Late Triassic (or even later), ‘leafshaped’ teeth with denticles to the Dinosauria. Similarly, the occurrence of such teeth in an early diverging archosauromorph indicates that specializations for herbivory originated more frequently within this clade than conventionally assumed. For example, Azendohsaurus and numerous basal sauropodomorph dinosaur taxa share an array of convergently acquired features associated with herbivory, including tooth denticles, expanded tooth crowns, a downturned dentary and the articular located at the ventral margin of the mandible. Some of these features (denticles, expanded crowns and the ventrally deflected articular) are even more widespread among archosauromorphs, including aetosaurs, silesaurs and ornithischian dinosaurs. A downturned dentary also occurs in Trilophosaurus, a taxon further marked by unique specializations for herbivory, including transversely lophate, tricuspid teeth. An array of features associated with herbivory also occur in rhynchosaurs and certain crocodilians (e.g. Simosuchus). This distribution suggests that craniodental features associated with herbivory were much more pervasive across the archosauromorph clade than previously recognized, possibly evolving at least six to eight times independently.
Re-evaluating Late Triassic Global Biostratigraphic Correlations
Irmis, R. B., Martz, J. W., Parker, W. G., and S. J. Nesbitt. 2010. Re-evaluating the correlation between Late Triassic terrestrial vertebrate biostratigraphy and the GSSP-defined marine stages. Albertiana 38:40-52.
A series of four land-vertebrate faunachrons have been proposed for biostratigraphical correlation of Upper Triassic non-marine strata, particularly in western North America but purportedly of global utility (Lucas, 1998). As these faunachrons are supposed to represent units of time it is necessary to tie them to the various stages of the Late Triassic, which are defined by marine fossils. Fortunately metoposaurs, phytosaurs, and aetosaurs have been found in both marine and non-marine strata and these have been used to provide ties to the marine scale (Lucas and Heckert, 2000). To aid in this attempt, these often fragmentary specimens have been identified to the genus level and synonymy of numerous taxa have been proposed to "smooth" global correlations (e.g., Lucas, 1998; Lucas and Heckert, 2000). Furthermore, first appearances of index taxa have been assumed to be synchronous across Pangea, allowing for hypothetical timing of major events in the Late Triassic such as the first appearance of groups such as the dinosaurs (Heckert and Lucas, 1999).
In this paper we critically examine these taxonomic assignments and conclude that they, and thus the correlations they provide, are unsupported. Furthermore, we argue that assuming the synchronous appearance of taxa globally masks potentially diachronous patterns of vertebrate dispersal. This has already been supported by comparison of dates from the Ischigualasto (Argentina) and Chinle (western North America)Formations, which biostratigraphy considered to be time equivalents, but may be separated by as much as 10 million years (Furin et al., 2006; Irmis and Mundil, 2008). Finally we argue that based on this detailed biostratigraphic frameworks must be constructed for particular regions and then correlated using independent methods such as radioisotopic dates.
To quote from the conclusions section "it is clear to us that the veracity of vertebrate biochronology as a means of correlating Upper Triassic strata has reached the present limits of its resolution, and has been compromised by controversial taxonomic practices and circular reasoning....To advance Late Triassic vertebrate biochronology, which has assumed an importance in chronostratigraphic correlation far in excess of its actual substance, must yield to other methods for understanding of Late Triassic vertebrate faunal change".
Albertiana is the official newsletter of the Subcommision on Triassic Stratigraphy and is published once a year. More information and past issues can be downloaded from here. Unfortunately, the current issue is not available on-line yet, but a PDF of this article can be obtained by e-mailing me or Randall Irmis. Be advised that if we get many requests it may take a bit to respond to them all so please be patient.
The full abstract for the article is below:
Abstract - One of the main methods for correlating Late Triassic terrestrial strata is through the use of land-vertebrate faunachrons (LVFs). Use of LVFs is widespread because of their supposed global application and ability to be correlated with the marine stages of the timescale. New magnetostratigraphic and radioisotopic data indicate that the traditional correlation of Late Triassic LVFs requires revision, although some authors maintain that these original correlations are sound, and that the new correlations of the marine stages to the numerical timescale are in error. Here, we examine the available evidence for cross-correlation of Late Triassic LVFs with the marine stages and numerical timescale. We conclude that the biostratigraphic links between the LVFs and marine stages are not robust; they are based on nondiagnostic specimens and/or taxonomically controversial specimens, endemic taxa, and/or ambiguously correlated assemblage zones. Given the available data, new correlations of the LVFs, marine stages, and the numerical timescale using magnetostratigraphy and radioisotopic ages that support a “long Norian” are preferential to those using largely vertebrate biostratigraphy that support a “long Tuvalian.” We also outline a framework for improving the accuracy and relevance of Late Triassic vertebrate biostratigraphy going forward in the near future.
REFERENCES
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.
Heckert, A. B., and S. G. Lucas. 1999. Global correlation and chronology of Triassic theropods (Archosauria: Dinosauria). Albertiana 23:22-35. [Note: this article is identical to the one published by the same authors in the Gaia volume in 2000].
Irmis, R. and Mundil, R. 2008. New age constraints from the Chinle Formation revise global comparisons of Late Triassic vertebrate assemblages. Journal of Vertebrate Paleontology, 28 (3 Supplement): 95A.
Lucas, S. G. 1998. Global Triassic tetrapod biostratigraphy and biochronology. Palaeogeogeography, Palaeoclimatology, Palaeoecology143:345-382.
Lucas, S. G. and A. B. Heckert. 2000. Biochronological significance of Triassic nonmarine tetrapod records from marine strata. Albertiana 24: 30-36.
A series of four land-vertebrate faunachrons have been proposed for biostratigraphical correlation of Upper Triassic non-marine strata, particularly in western North America but purportedly of global utility (Lucas, 1998). As these faunachrons are supposed to represent units of time it is necessary to tie them to the various stages of the Late Triassic, which are defined by marine fossils. Fortunately metoposaurs, phytosaurs, and aetosaurs have been found in both marine and non-marine strata and these have been used to provide ties to the marine scale (Lucas and Heckert, 2000). To aid in this attempt, these often fragmentary specimens have been identified to the genus level and synonymy of numerous taxa have been proposed to "smooth" global correlations (e.g., Lucas, 1998; Lucas and Heckert, 2000). Furthermore, first appearances of index taxa have been assumed to be synchronous across Pangea, allowing for hypothetical timing of major events in the Late Triassic such as the first appearance of groups such as the dinosaurs (Heckert and Lucas, 1999).
In this paper we critically examine these taxonomic assignments and conclude that they, and thus the correlations they provide, are unsupported. Furthermore, we argue that assuming the synchronous appearance of taxa globally masks potentially diachronous patterns of vertebrate dispersal. This has already been supported by comparison of dates from the Ischigualasto (Argentina) and Chinle (western North America)Formations, which biostratigraphy considered to be time equivalents, but may be separated by as much as 10 million years (Furin et al., 2006; Irmis and Mundil, 2008). Finally we argue that based on this detailed biostratigraphic frameworks must be constructed for particular regions and then correlated using independent methods such as radioisotopic dates.
To quote from the conclusions section "it is clear to us that the veracity of vertebrate biochronology as a means of correlating Upper Triassic strata has reached the present limits of its resolution, and has been compromised by controversial taxonomic practices and circular reasoning....To advance Late Triassic vertebrate biochronology, which has assumed an importance in chronostratigraphic correlation far in excess of its actual substance, must yield to other methods for understanding of Late Triassic vertebrate faunal change".
Albertiana is the official newsletter of the Subcommision on Triassic Stratigraphy and is published once a year. More information and past issues can be downloaded from here. Unfortunately, the current issue is not available on-line yet, but a PDF of this article can be obtained by e-mailing me or Randall Irmis. Be advised that if we get many requests it may take a bit to respond to them all so please be patient.
The full abstract for the article is below:
Abstract - One of the main methods for correlating Late Triassic terrestrial strata is through the use of land-vertebrate faunachrons (LVFs). Use of LVFs is widespread because of their supposed global application and ability to be correlated with the marine stages of the timescale. New magnetostratigraphic and radioisotopic data indicate that the traditional correlation of Late Triassic LVFs requires revision, although some authors maintain that these original correlations are sound, and that the new correlations of the marine stages to the numerical timescale are in error. Here, we examine the available evidence for cross-correlation of Late Triassic LVFs with the marine stages and numerical timescale. We conclude that the biostratigraphic links between the LVFs and marine stages are not robust; they are based on nondiagnostic specimens and/or taxonomically controversial specimens, endemic taxa, and/or ambiguously correlated assemblage zones. Given the available data, new correlations of the LVFs, marine stages, and the numerical timescale using magnetostratigraphy and radioisotopic ages that support a “long Norian” are preferential to those using largely vertebrate biostratigraphy that support a “long Tuvalian.” We also outline a framework for improving the accuracy and relevance of Late Triassic vertebrate biostratigraphy going forward in the near future.
REFERENCES
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.
Heckert, A. B., and S. G. Lucas. 1999. Global correlation and chronology of Triassic theropods (Archosauria: Dinosauria). Albertiana 23:22-35. [Note: this article is identical to the one published by the same authors in the Gaia volume in 2000].
Irmis, R. and Mundil, R. 2008. New age constraints from the Chinle Formation revise global comparisons of Late Triassic vertebrate assemblages. Journal of Vertebrate Paleontology, 28 (3 Supplement): 95A.
Lucas, S. G. 1998. Global Triassic tetrapod biostratigraphy and biochronology. Palaeogeogeography, Palaeoclimatology, Palaeoecology143:345-382.
Lucas, S. G. and A. B. Heckert. 2000. Biochronological significance of Triassic nonmarine tetrapod records from marine strata. Albertiana 24: 30-36.
New Cynodont from the Upper Triassic of Brazil
This is a sizeable monograph containing a description of a new taxon of cynodont, Trucidocynodon riograndensis, from the Upper Triassic Santa Maria Formation of Brazil. This paper includes a detailed phylogenetic analysis of the Cynodontia with 145 characters, and a detailed atlas depicting various character states used in the analysis. The resulting tree does appear to be significantly different than the one recently published by Liu and Olsen (2010). I don't study cynodonts so I cannot evaluate the phylogenetic, taxonomic, and descriptive work; however, it is maddening to see that the straigraphic section still considers the Ischigualasto Formation to be entirely Carnian in age ignoring much of the recent Triassic timescale revisions and studies showing good evidence that much of the Ischigulasto is actually Norian in age (Furin et al. 2006; Irmis and Mundil, 2008; Currie et al. 2009). Despite this, however, this still appears to be an impressive piece of work pending resolution of the differences with the Liu and Olsen study.
Oliveira, T. V., Soares, M. B. and C. L. Schultz. 2010. Trucidocynodon riograndensis gen. nov. et sp. nov. (Eucynodontia), a new cynodont from the Brazilian Upper Triassic (Santa Maria Formation). Zootaxa 2382:1–71.
Abstract - An almost complete skeleton of a new carnivorous cynodont from the Upper Triassic of Southern Brazil, Trucidocynodon riograndensis gen. nov. et sp. nov., is described. The new taxon is very similar to Ecteninion lunensis Martinez et al. 1996 from Upper Triassic of Argentina (Ischigualasto Formation). Both have an elongated skull, large pterygoid flanges, a well developed orbitosphenoid, a relatively short osseous secondary palate, greatly developed canines and sectorial postcanines with posteriorly directed cusps. However, the new taxon shows some differences relative to E. lunensis such as an open pterygoparoccipital foramen, the posterior opening of the post-temporal foramen enclosed by tabular and squamosal, and upper incisors with serrated cutting edges. The more remarkable features of the postcranium of T. riograndensis are the presence of 32 presacral vertebrae, a greater number than in most of non-mammaliaform cynodonts, the accentuated lumbarisation of the posterior trunk vertebrae and a remarkable morphological gradient in the caudal vertebrae; the femur and humerus show some interesting adaptations suggesting a more upright limb posture. The overall morphology of the astragalocalcaneal complex is similar to that of Diademodon and of the therocephalian Bauria.
REFERENCES
Currie, B. S., Colombi, C. E., Tabor, N. J., Shipman, T. C., and I. P. Montañez. 2009. Stratigraphy and architecture of the Upper Triassic Ischigualasto Formation, Ischigualasto Provincial Park, San Juan, Argentina, Journal of South American Earth Sciences 27:74-87. doi: 10.1016/j.jsames.2008.10.004
Furin, S., Preto, N., Rigo, M., Roghi, G., Gianolla, P., Crowley, J.L., and Bowring, S.A., 2006, High-precision U-Pb zircon age from the Triassic of Italy: Implications for the Triassic time scale and the Carnian origin of calcareous nannoplankton and dinosaurs: Geology, v. 34, p. 1009–1012, doi:10.1130/G22967A.1.
Irmis, R. B., and R. Mundil. 2008. New age constraints from the Chinle Formation resolve global comparisons of Late Triassic vertebrate assemblages. Journal of Vertebrate Paleontology 28:95A.
Liu, J., and P. Olsen. 2010. The Phylogenetic Relationships of Eucynodontia (Amniota: Synapsida). Journal of Mammalian Evolution. Published online April 13 2010. doi: 10.1007/s10914-010-9136-8
Oliveira, T. V., Soares, M. B. and C. L. Schultz. 2010. Trucidocynodon riograndensis gen. nov. et sp. nov. (Eucynodontia), a new cynodont from the Brazilian Upper Triassic (Santa Maria Formation). Zootaxa 2382:1–71.
Abstract - An almost complete skeleton of a new carnivorous cynodont from the Upper Triassic of Southern Brazil, Trucidocynodon riograndensis gen. nov. et sp. nov., is described. The new taxon is very similar to Ecteninion lunensis Martinez et al. 1996 from Upper Triassic of Argentina (Ischigualasto Formation). Both have an elongated skull, large pterygoid flanges, a well developed orbitosphenoid, a relatively short osseous secondary palate, greatly developed canines and sectorial postcanines with posteriorly directed cusps. However, the new taxon shows some differences relative to E. lunensis such as an open pterygoparoccipital foramen, the posterior opening of the post-temporal foramen enclosed by tabular and squamosal, and upper incisors with serrated cutting edges. The more remarkable features of the postcranium of T. riograndensis are the presence of 32 presacral vertebrae, a greater number than in most of non-mammaliaform cynodonts, the accentuated lumbarisation of the posterior trunk vertebrae and a remarkable morphological gradient in the caudal vertebrae; the femur and humerus show some interesting adaptations suggesting a more upright limb posture. The overall morphology of the astragalocalcaneal complex is similar to that of Diademodon and of the therocephalian Bauria.
REFERENCES
Currie, B. S., Colombi, C. E., Tabor, N. J., Shipman, T. C., and I. P. Montañez. 2009. Stratigraphy and architecture of the Upper Triassic Ischigualasto Formation, Ischigualasto Provincial Park, San Juan, Argentina, Journal of South American Earth Sciences 27:74-87. doi: 10.1016/j.jsames.2008.10.004
Furin, S., Preto, N., Rigo, M., Roghi, G., Gianolla, P., Crowley, J.L., and Bowring, S.A., 2006, High-precision U-Pb zircon age from the Triassic of Italy: Implications for the Triassic time scale and the Carnian origin of calcareous nannoplankton and dinosaurs: Geology, v. 34, p. 1009–1012, doi:10.1130/G22967A.1.
Irmis, R. B., and R. Mundil. 2008. New age constraints from the Chinle Formation resolve global comparisons of Late Triassic vertebrate assemblages. Journal of Vertebrate Paleontology 28:95A.
Liu, J., and P. Olsen. 2010. The Phylogenetic Relationships of Eucynodontia (Amniota: Synapsida). Journal of Mammalian Evolution. Published online April 13 2010. doi: 10.1007/s10914-010-9136-8
This is What Triassic Archosaur Workers Dream About at Night.
This is an absolutely incredible find and akin to the fully articulated Poposaurus gracilis skeleton found in Utah by a Yale Peabody Museum field crew in 2003. I was fortunate enough to be present in 2003 to help with the initial uncovering and will never forget it. Articulated pseudosuchian finds like this are pretty rare in the Triassic.
The announcement is here:
http://forgottenarchosaurs.blogspot.com/2010/05/nearly-complete-prestosuchus-found.html
The original article is here:
http://br.noticias.yahoo.com/s/11052010/25/manchetes-fossil-megapredador-pre-historico-encontrado.html
....and what is sure to drive all fossil preparators who see this crazy, notice that the underside of the specimen is already jacketed and it appears to be undergoing prep in the field! Maybe the jacket was just moved to an outcrop for the photo op.
The announcement is here:
http://forgottenarchosaurs.blogspot.com/2010/05/nearly-complete-prestosuchus-found.html
The original article is here:
http://br.noticias.yahoo.com/s/11052010/25/manchetes-fossil-megapredador-pre-historico-encontrado.html
....and what is sure to drive all fossil preparators who see this crazy, notice that the underside of the specimen is already jacketed and it appears to be undergoing prep in the field! Maybe the jacket was just moved to an outcrop for the photo op.
Revision of the Basal Sauropodomorph Anchisaurus polyzelus
This is the latest paper in the ongoing debate regarding the taxonomic validity of Anchisaurus polyzelus (Sauropodomorpha: Anchisauria) and the referral of three other partial specimens from the Early Jurassic Portland Formation of Massachusetts and Connecticut. Whereas, all workers now agree that the four specimens all belong to the same species, the debate has centered around the status of the type materials of A. polyzelus, because if they are not diagnostic, the next available name for this material is Ammosaurus major. Through reanalysis of the material Yates proposes seven autapomorphies diagnosing this material, including one of these also found in the holotype specimen of A. polyzelus. Thus, Yates argues that A. polyzelus is valid, all four specimens can unambiguously be referred to it, and that Ammosaurus major is the junior synonym. This paper also features a revised phylogentic analysis of the sauropodomorpha based on the reanalysis including repreparation of the skull found in one of the referred specimens. Anchisaurus is recovered at the base of Anchisauria and outside of Sauropoda.
As this is about the 6th paper in a little more than a decade dealing with this, I am awaiting the next installment ;).
Yates, A. M. in press. A revision of the problematic sauropodomorph dinosaurs from Manchester, Connecticut and the status of Anchisaurus Marsh. Palaeontology. doi: 10.1111/j.1475-4983.2010.00952.x
Abstract: The taxonomic status of the sauropodomorph dinosaurs from the Newark Supergroup of north-eastern USA is reviewed. The inclusion of the three articulated skeletons from Wolcott’s Quarry, Manchester, Connecticut in a single species is supported. Despite claims to the contrary the Manchester skeletons can be referred to the species Anchisaurus polyzelus, which is based on a fragmentary specimen from Massachusetts. Two autapomorphies: dorsoventrally flattened ischial blades set at a low angle to each other and slender sacral ribs of the first sacral vertebra, link the holotype of A. polyzelus to the Manchester specimens. A revised diagnosis of the species and new skull reconstruction are presented. Recent anatomical observations of A. polyzelus indicate that several character states used to assess its phylogenetic position require revision. However, these are not sufficient to overturn previous cladistic analyses. A revised cladistic analysis continues to find support for Anchisaurus as a relatively derived basal sauropodomorph that lies outside of the clade Melanorosaurus + Sauropoda but is more closely related to it than to ‘core prosauropods’ such as Plateosaurus and Massospondylus.
As this is about the 6th paper in a little more than a decade dealing with this, I am awaiting the next installment ;).
Yates, A. M. in press. A revision of the problematic sauropodomorph dinosaurs from Manchester, Connecticut and the status of Anchisaurus Marsh. Palaeontology. doi: 10.1111/j.1475-4983.2010.00952.x
Abstract: The taxonomic status of the sauropodomorph dinosaurs from the Newark Supergroup of north-eastern USA is reviewed. The inclusion of the three articulated skeletons from Wolcott’s Quarry, Manchester, Connecticut in a single species is supported. Despite claims to the contrary the Manchester skeletons can be referred to the species Anchisaurus polyzelus, which is based on a fragmentary specimen from Massachusetts. Two autapomorphies: dorsoventrally flattened ischial blades set at a low angle to each other and slender sacral ribs of the first sacral vertebra, link the holotype of A. polyzelus to the Manchester specimens. A revised diagnosis of the species and new skull reconstruction are presented. Recent anatomical observations of A. polyzelus indicate that several character states used to assess its phylogenetic position require revision. However, these are not sufficient to overturn previous cladistic analyses. A revised cladistic analysis continues to find support for Anchisaurus as a relatively derived basal sauropodomorph that lies outside of the clade Melanorosaurus + Sauropoda but is more closely related to it than to ‘core prosauropods’ such as Plateosaurus and Massospondylus.
The Origin and Early Radiation of Dinosaurs
Finally this is out, although presently only as an accepted manuscript in Earth Science Reviews. I was one of the reviewers for this paper and felt that it constitutes a very well written overview of early dinosaur work to the present, including many of the recent cool finds from the Chinle Formation of course. I was reviewing this manuscript last year about the time another early dinosaur review paper came out by Max Langer and colleagues (not sure why this paper is so delayed) and feel that these papers are nice complements to each other.
[Note: after writing this I noticed that Brusatte et al. added a similarily worded paragraph to the end of the introduction. I also noticed that they use the word "compliment" when they mean "complement". See the difference here ;)].
Brusatte, S. L., Nesbitt, S. J., Irmis, R. B., Butler, R. J., Benton, M. J., and M. A. Norell. 2010. The origin and early radiation of dinosaurs. Earth Science Reviews. Early online. doi: 10.1016/j.earscirev.2010.04.001
Abstract - Dinosaurs were remarkably successful during the Mesozoic and one subgroup, birds, remain an important component of modern ecosystems. Although the extinction of non-avian dinosaurs at the end of the Cretaceous has been the subject of intense debate, comparatively little attention has been given to the origin and early evolution of dinosaurs during the Late Triassic and Early Jurassic, one of the most important evolutionary radiations in earth history. Our understanding of this keystone event has dramatically changed over the past 25 years, thanks to an influx of new fossil discoveries, reinterpretations of long-ignored specimens, and quantitative macroevolutionary analyses that synthesize anatomical and geological data. Here we provide an overview of the first 50 million years of dinosaur history, with a focus on the large-scale patterns that characterize the ascent of dinosaurs from a small, almost marginal group of reptiles in the Late Triassic to the pre-eminent terrestrial vertebrates of the Jurassic and Cretaceous. We provide both a biological and geological background for early dinosaur history. Dinosaurs are deeply nested among the archosaurian reptiles, diagnosed by only a small number of characters, and are subdivided into a number of major lineages. The first unequivocal dinosaurs are known from the late Carnian of South America, but the presence of their sister group in the Middle Triassic implies that dinosaurs possibly originated much earlier. The three major dinosaur lineages, theropods, sauropodomorphs, and ornithischians, are all known from the Triassic, when continents were joined into the supercontinent Pangaea and global climates were hot and arid. Although many researchers have long suggested that dinosaurs outcompeted other reptile groups during the Triassic, we argue that the ascent of dinosaurs was more of a matter of contingency and opportunism. Dinosaurs were overshadowed in most Late Triassic ecosystems by crocodile-line archosaurs and showed no signs of outcompeting their rivals. Instead, the rise of dinosaurs was a two-stage process, as dinosaurs expanded in taxonomic diversity, morphological disparity, and absolute faunal abundance only after the extinction of most crocodile-line reptiles and other groups.
[Note: after writing this I noticed that Brusatte et al. added a similarily worded paragraph to the end of the introduction. I also noticed that they use the word "compliment" when they mean "complement". See the difference here ;)].
Brusatte, S. L., Nesbitt, S. J., Irmis, R. B., Butler, R. J., Benton, M. J., and M. A. Norell. 2010. The origin and early radiation of dinosaurs. Earth Science Reviews. Early online. doi: 10.1016/j.earscirev.2010.04.001
Abstract - Dinosaurs were remarkably successful during the Mesozoic and one subgroup, birds, remain an important component of modern ecosystems. Although the extinction of non-avian dinosaurs at the end of the Cretaceous has been the subject of intense debate, comparatively little attention has been given to the origin and early evolution of dinosaurs during the Late Triassic and Early Jurassic, one of the most important evolutionary radiations in earth history. Our understanding of this keystone event has dramatically changed over the past 25 years, thanks to an influx of new fossil discoveries, reinterpretations of long-ignored specimens, and quantitative macroevolutionary analyses that synthesize anatomical and geological data. Here we provide an overview of the first 50 million years of dinosaur history, with a focus on the large-scale patterns that characterize the ascent of dinosaurs from a small, almost marginal group of reptiles in the Late Triassic to the pre-eminent terrestrial vertebrates of the Jurassic and Cretaceous. We provide both a biological and geological background for early dinosaur history. Dinosaurs are deeply nested among the archosaurian reptiles, diagnosed by only a small number of characters, and are subdivided into a number of major lineages. The first unequivocal dinosaurs are known from the late Carnian of South America, but the presence of their sister group in the Middle Triassic implies that dinosaurs possibly originated much earlier. The three major dinosaur lineages, theropods, sauropodomorphs, and ornithischians, are all known from the Triassic, when continents were joined into the supercontinent Pangaea and global climates were hot and arid. Although many researchers have long suggested that dinosaurs outcompeted other reptile groups during the Triassic, we argue that the ascent of dinosaurs was more of a matter of contingency and opportunism. Dinosaurs were overshadowed in most Late Triassic ecosystems by crocodile-line archosaurs and showed no signs of outcompeting their rivals. Instead, the rise of dinosaurs was a two-stage process, as dinosaurs expanded in taxonomic diversity, morphological disparity, and absolute faunal abundance only after the extinction of most crocodile-line reptiles and other groups.
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