This eliminates the marine tie for the Otischalkian Land Vertebrate Faunachron, although the identification of this specimen as 'Paleorhinus' was already pretty weak as argued by Irmis et al. (2010).
Butler, R. J., 2013. ‘Francosuchus’ trauthi is not Paleorhinus: implications for Late Triassic
vertebrate biostratigraphy, Journal of Vertebrate Paleontology, 33:858-864.
Abstract - A rostrum fragment from the marginal marine upper Lunz Formation of Austria (early Late Triassic: late Carnian) was previously identified as a new species of phytosaurian archosauriform, ‘Francosuchus’ trauthi. ‘Francosuchus’ trauthi was subsequently synonymized with the non-phytosaurid phytosaur Paleorhinus, and this synonymy was used as evidence to correlate the ‘Paleorhinus biochron’ and the Otischalkian land-vertebrate faunachron to the marine timescale. Here, I provide a redescription of ‘Francosuchus’ trauthi and document anatomical features that differ substantially from all known species of non-phytosaurid phytosaur. There is no evidence to support synonymy of ‘Francosuchus’ trauthi with Paleorhinus, and no unambiguous features to support a phytosaurian identification. However, ‘Francosuchus’ trauthi possesses a unique combination of characters that distinguish it from all other Triassic tetrapods, and necessitates referral of the species to a new genus, Dolerosaurus, gen. nov. Rejection of the proposed synonymy between ‘Francosuchus’ trauthi and Paleorhinus means that the ‘Paleorhinus biochron’ cannot be tied to the marine late Carnian as previously suggested, and provides further evidence of the problems inherent in attempting to correlate the terrestrial Triassic to the marine timescale.
Showing posts with label biostratigraphy. Show all posts
Showing posts with label biostratigraphy. Show all posts
Footprints of Large Theropod Dinosaurs from the Late Triassic of Brazil
The Caturrita Formation may be younger than previously thought and there is a currently undiscovered large theropod in the latest Triassic of Brazil.
da Silva, R. C., Barboni, R., Dutra, T., Godoy, M. M., and R. B. Binotto. 2012. Footprints of large theropod dinosaurs and implications on the age of Triassic biotas from southern Brazil. Journal of South American Earth Sciences 39:16-23. http://dx.doi.org/10.1016/j.jsames.2012.06.017
Abstract - Dinosaur footprints found in an outcrop of the Caturrita Formation (Rio Grande do Sul State, Southern Brazil), associated with a diverse and well preserved record of fauna and flora, reopen the debate about its exclusive Triassic age. The studied footprints were identified as Eubrontes isp. and are interpreted as having been produced by large theropod dinosaurs. The morphological characteristics and dimensions of the footprints are more derived than those commonly found in the Carnian–Norian, and are more consistent with those found during the Rhaetian–Jurassic. The trackmaker does not correspond to any type of dinosaur yet known from Triassic rocks of Brazil. Recent studies with the paleofloristic content of this unit also support a more advanced Rhaetian or even Jurassic age for this unit.
da Silva, R. C., Barboni, R., Dutra, T., Godoy, M. M., and R. B. Binotto. 2012. Footprints of large theropod dinosaurs and implications on the age of Triassic biotas from southern Brazil. Journal of South American Earth Sciences 39:16-23. http://dx.doi.org/10.1016/j.jsames.2012.06.017
Abstract - Dinosaur footprints found in an outcrop of the Caturrita Formation (Rio Grande do Sul State, Southern Brazil), associated with a diverse and well preserved record of fauna and flora, reopen the debate about its exclusive Triassic age. The studied footprints were identified as Eubrontes isp. and are interpreted as having been produced by large theropod dinosaurs. The morphological characteristics and dimensions of the footprints are more derived than those commonly found in the Carnian–Norian, and are more consistent with those found during the Rhaetian–Jurassic. The trackmaker does not correspond to any type of dinosaur yet known from Triassic rocks of Brazil. Recent studies with the paleofloristic content of this unit also support a more advanced Rhaetian or even Jurassic age for this unit.
Taphonomic Effects on the Stratigraphic Ranges of Rare Taxa in the Chinle Formation of Arizona
Loughney, K. M., Fastovsky, D. E., and W. G. Parker. 2011. Vertebrate fossil preservation in blue paleosols from the Petrified Forest National Park, Arizona, with implications for vertebrate biostratigraphy in the Chinle Formation. Palaios 26:700-719.
Abstract - Exposures of the Chinle Formation in Petrified Forest National Park (PEFO), Arizona, preserve one of the most important Upper Triassic terrestrial faunal assemblages in the world: in it are found key elements in the global and regional correlation of continental deposits of Upper Triassic age. Rare components of the Chinle Formation faunal assemblage, including dinosaurs and small-bodied amniotes, appear to be mostly restricted to distinctive blue-colored horizons observed at only a few sites in PEFO. The blue sites represent paleosols formed in fine-grained, abandoned channel fills and contrast markedly with red-colored floodplain deposits and paleosols that characterize most fossil localities in the Chinle Formation. The distinctive blue color is interpreted as a weathered feature of hydromorphically reduced iron. The coincidence of rare taxa and sites bearing the blue-colored paleosols suggests that the stratigraphic positions of the sites and the rare taxa they contain appear to relate to fluvial sequence tracts in PEFO and may not reflect the true stratigraphic ranges of these taxa.
A Sectorial Toothed Cynodont (Therapsida) from the Triassic of Southern Brazil
Soares M. B., Abdala F. and C. Bertoni-Machado. 2011. A sectorial toothed cynodont (Therapsida) from the Triassic Santa Cruz do Sul fauna, Santa Maria Formation, Southern Brazil. Geodiversitas 33: 265-278.
ABSTRACT - A sectorial toothed cynodont from the Triassic Santa Cruz do Sul fauna, Santa Maria Formation, Parana Basin, southern Brazil, is described. The taxon is represented by a tiny portion of a right lower jaw which preserves partially the last postcanine. A comparative analysis of the postcanine morphology of the Santa Cruz do Sul specimen with South American Triassic cynodonts is made. The crown morphology of the Santa Cruz do Sul cynodont is closer to that of the juvenile single specimen of cf. Probainognathus from the Carnian Ischigualasto Formation and of juveniles of Probainognathus jenseni Romer, 1970 from the Ladinian Chañares Formation in Argentina. There are, however, some important differences between the tooth of the new specimen and those of P. jenseni juveniles, and therefore we provisionally assign the new Santa Cruz do Sul material to cf. Probainognathus. The fauna of Santa Cruz do Sul, dominated by traversodontid cynodonts, is now composed of a proterochampsid archosauriform, three traversodontids and two sectorial toothed cynodonts and we refer to it as Santacruzodon Assemblage Zone. We also propose the name of Riograndia Assemblage Zone for the faunas from the Upper Triassic Caturrita Formation, on the basis of the abundance yet restricted record of this taxon in these faunas. A brief summary of the Brazilian Middle and Upper Triassic biostratigraphy is presented within the framework of two different time scales.
ABSTRACT - A sectorial toothed cynodont from the Triassic Santa Cruz do Sul fauna, Santa Maria Formation, Parana Basin, southern Brazil, is described. The taxon is represented by a tiny portion of a right lower jaw which preserves partially the last postcanine. A comparative analysis of the postcanine morphology of the Santa Cruz do Sul specimen with South American Triassic cynodonts is made. The crown morphology of the Santa Cruz do Sul cynodont is closer to that of the juvenile single specimen of cf. Probainognathus from the Carnian Ischigualasto Formation and of juveniles of Probainognathus jenseni Romer, 1970 from the Ladinian Chañares Formation in Argentina. There are, however, some important differences between the tooth of the new specimen and those of P. jenseni juveniles, and therefore we provisionally assign the new Santa Cruz do Sul material to cf. Probainognathus. The fauna of Santa Cruz do Sul, dominated by traversodontid cynodonts, is now composed of a proterochampsid archosauriform, three traversodontids and two sectorial toothed cynodonts and we refer to it as Santacruzodon Assemblage Zone. We also propose the name of Riograndia Assemblage Zone for the faunas from the Upper Triassic Caturrita Formation, on the basis of the abundance yet restricted record of this taxon in these faunas. A brief summary of the Brazilian Middle and Upper Triassic biostratigraphy is presented within the framework of two different time scales.
Why We Don't Find Cynodonts in the Chinle Formation
Whiteside, J. H., Grogan, D. S., Olsen, P. E., and D. V. Kent. 2011. Climatically driven biogeographic provinces of Late Triassic tropical Pangea. PNAS Published online before print May 13, 2011,
doi: 10.1073/pnas.1102473108 [supplemental info]
Abstract - Although continents were coalesced into the single landmass Pangea, Late Triassic terrestrial tetrapod assemblages are surprisingly provincial. In eastern North America, we show that assemblages dominated by traversodont cynodonts are restricted to a humid 6° equatorial swath that persisted for over 20 million years characterized by “semiprecessional” (approximately 10,000-y) climatic fluctuations reflected in stable carbon isotopes and sedimentary facies in lacustrine strata. More arid regions from 5–20°N preserve procolophonid-dominated faunal assemblages associated with a much stronger expression of approximately 20,000-y climatic cycles. In the absence of geographic barriers, we hypothesize that these variations in the climatic expression of astronomical forcing produced latitudinal climatic zones that sorted terrestrial vertebrate taxa, perhaps by excretory physiology, into distinct biogeographic provinces tracking latitude, not geographic position, as the proto-North American plate translated northward. Although the early Mesozoic is usually assumed to be characterized by globally distributed land animal communities due to of a lack of geographic barriers, strong provinciality was actually the norm, and nearly global communities were present only after times of massive ecological disruptions.
doi: 10.1073/pnas.1102473108 [supplemental info]
Abstract - Although continents were coalesced into the single landmass Pangea, Late Triassic terrestrial tetrapod assemblages are surprisingly provincial. In eastern North America, we show that assemblages dominated by traversodont cynodonts are restricted to a humid 6° equatorial swath that persisted for over 20 million years characterized by “semiprecessional” (approximately 10,000-y) climatic fluctuations reflected in stable carbon isotopes and sedimentary facies in lacustrine strata. More arid regions from 5–20°N preserve procolophonid-dominated faunal assemblages associated with a much stronger expression of approximately 20,000-y climatic cycles. In the absence of geographic barriers, we hypothesize that these variations in the climatic expression of astronomical forcing produced latitudinal climatic zones that sorted terrestrial vertebrate taxa, perhaps by excretory physiology, into distinct biogeographic provinces tracking latitude, not geographic position, as the proto-North American plate translated northward. Although the early Mesozoic is usually assumed to be characterized by globally distributed land animal communities due to of a lack of geographic barriers, strong provinciality was actually the norm, and nearly global communities were present only after times of massive ecological disruptions.
The South American Aetosaur Aetosauroides is Not Referable to Stagonolepis
In a series of papers Heckert and Lucas (1999, 2000, 2002) and Lucas and Heckert (2001) proposed that the American aetosaur taxon Aetosauroides was a junior synonym of Stagonolepis, and that as a result the Ischigualasto (Argentina) and the Santa Maria (Brazil) formations were Adamanian (latest Carnian) in age based upon vertebrate biostratigraphy and correlable with other Adamanian strata such as the lower part of the Chinle Formation in western North America. However, these synonomies were based on very superficial resemblances and not on apomorphy based comparisons (Parker, 2008).
The new issue of the Journal of Vertebrate Paleontology has a paper by Julia Desojo and Martin Ezcurra redescribing some of the Aetosauroides material and refuting the synonomy with Stagonolepis using a detailed comparison of characters. Especially important are characters of the skull, which clearly demonstrates strong differences between the two taxa.
As a result Stagonolepis is not known from South America and therefore the proposed biostratigraphic correlations between South America, North America, and Europe using aetosaurs is not supported by this study. This is also supported by radiometric dates which show a 10 million year difference between the main fossil horizon in ht eIschigualasto Formation and the base of the main fossil bearing beds in the Chinle Formation (Irmis and Mundil, 2008).
I have suggested elsewhere (Parker, 2008) that Stagonolepis does not occur in North America either and thus aetosaur taxa appear much more endemic than argued by Heckert and Lucas and thus of limited (only regional) biostratigraphic utility.
Biostratigraphy and taxonomy aside, this redescription highlights the plesiomorphic nature of Aetosauroides, especially regarding features of the skull including a gracile, fully-toothed dentary, different from the "slipper-shaped", anteriorly edentulous mandibles of more derived aetosaurs, and the meeting of the premaxilla and nasal to exclude the maxilla from the margin of the external naris. Thus, Aetosauroides is an interesting and clearly plesiomorphic form with an armor ornamentation convergent with more derived forms such as Stagonolepis and Calyptosuchus.
Desojo, J. B., and M. D. Ezcurra. 2011. A reappraisal of the taxonomic status of Aetosauroides (Archosauria, Aetosauria) specimens from the Late Triassic of South America and their proposed synonymy with Stagonolepis. Journal of Vertebrate Paleontology 31:596-609. DOI: 10.1080/02724634.2011.572936
Abstract - The South American record of early Late Triassic aetosaurs is composed of two species: Aetosauroides scagliai and “Aetosauroides subsulcatus.” Previously undescribed materials belonging to “Aetosauroides subsulcatus” allow us to reassess its taxonomy, leading us to consider it a junior synonym of Aetosauroides scagliai. Based on the emended diagnosis of the species provided here, we recognize that specimens assignable to Aetosauroides scagliai are less common than thought previously and several of them are not diagnostic beyond indeterminate non-typothorasicine aetosaurins. Previous assignments of Aetosauroides as a junior synonym of Stagonolepis are not followed because the South American taxon is distinct due to the presence of a maxilla excluded from the external narial margin, tooth crowns with a straight distal margin and without a constriction between the root and crown, a gradually convex ventral margin of the dentary, oval fossae ventral to the neurocentral suture on the lateral sides of the centra, and a ratio between the length and the width between the distal-most tips of the postzygapophyses equal to or lower than 0.75. The evidence provided here bolsters the validity of Aetosauroides and extends the distribution of Aetosauroides scagliai into southern Brazil. Although Stagonolepis was employed as an index taxon for the Adamanian LVF, this genus is currently restricted to Europe and North America. Thus, no overlapping genera or species of aetosaur are shared between South America and other landmasses. Accordingly, the record of aetosaurs is not useful for providing biostratigraphical correlations between Late Triassic South American beds and those in other regions.
REFERENCES
Heckert, A. B., and S. G. Lucas. 1999. A new aetosaur from the Upper Triassic of Texas and the phylogeny of aetosaurs. Journal of Vertebrate Paleontology 19:50–68.
Heckert, A. B., and S. G. Lucas. 2000. Taxonomy, phylogeny, biostratigraphy, biochronology, paleobiogeography, and evolution of the Late Triassic Aetosauria (Archosauria: Crurotarsi). Zentralblatt fur Geologie und Palaontologie, 1998, Teil I, Heft 11–12:1539–1587.
Heckert, A. B., and S. G. Lucas. 2002. South American occurrences of the Adamanian (Late Triassic, Latest Carnian) index taxon Stagonolepis (Archosauria: Aetosauria) and their biochronological significance. Journal of Paleontology 76:852–863.
Irmis, R. B., and R. Mundil. 2008. New age constraints from the Chinle Formation revise global comparisons of Late Triassic vertebrate assemblages. Journal of Vertebrate Paleontology 28:95A.
Lucas, S. G., and A. B. Heckert. 2001. The aetosaur Stagonolepis from the Upper Triassic of Brazil and its biochronological significance. Neues Jahrebuch fur Geologie und Palaontologie, Monatshefte 2001:719–732.
Parker, W. G. 2008. How many valid aetosaur taxa are there? Reviewing the alpha-taxonomy of the Aetosauria (Archosauria: Pseudosuchia) and its implications for Late Triassic global biostratigraphy. Journal of Vertebrate Paleontology 28:125A.
The new issue of the Journal of Vertebrate Paleontology has a paper by Julia Desojo and Martin Ezcurra redescribing some of the Aetosauroides material and refuting the synonomy with Stagonolepis using a detailed comparison of characters. Especially important are characters of the skull, which clearly demonstrates strong differences between the two taxa.
As a result Stagonolepis is not known from South America and therefore the proposed biostratigraphic correlations between South America, North America, and Europe using aetosaurs is not supported by this study. This is also supported by radiometric dates which show a 10 million year difference between the main fossil horizon in ht eIschigualasto Formation and the base of the main fossil bearing beds in the Chinle Formation (Irmis and Mundil, 2008).
I have suggested elsewhere (Parker, 2008) that Stagonolepis does not occur in North America either and thus aetosaur taxa appear much more endemic than argued by Heckert and Lucas and thus of limited (only regional) biostratigraphic utility.
Biostratigraphy and taxonomy aside, this redescription highlights the plesiomorphic nature of Aetosauroides, especially regarding features of the skull including a gracile, fully-toothed dentary, different from the "slipper-shaped", anteriorly edentulous mandibles of more derived aetosaurs, and the meeting of the premaxilla and nasal to exclude the maxilla from the margin of the external naris. Thus, Aetosauroides is an interesting and clearly plesiomorphic form with an armor ornamentation convergent with more derived forms such as Stagonolepis and Calyptosuchus.
Desojo, J. B., and M. D. Ezcurra. 2011. A reappraisal of the taxonomic status of Aetosauroides (Archosauria, Aetosauria) specimens from the Late Triassic of South America and their proposed synonymy with Stagonolepis. Journal of Vertebrate Paleontology 31:596-609. DOI: 10.1080/02724634.2011.572936
Abstract - The South American record of early Late Triassic aetosaurs is composed of two species: Aetosauroides scagliai and “Aetosauroides subsulcatus.” Previously undescribed materials belonging to “Aetosauroides subsulcatus” allow us to reassess its taxonomy, leading us to consider it a junior synonym of Aetosauroides scagliai. Based on the emended diagnosis of the species provided here, we recognize that specimens assignable to Aetosauroides scagliai are less common than thought previously and several of them are not diagnostic beyond indeterminate non-typothorasicine aetosaurins. Previous assignments of Aetosauroides as a junior synonym of Stagonolepis are not followed because the South American taxon is distinct due to the presence of a maxilla excluded from the external narial margin, tooth crowns with a straight distal margin and without a constriction between the root and crown, a gradually convex ventral margin of the dentary, oval fossae ventral to the neurocentral suture on the lateral sides of the centra, and a ratio between the length and the width between the distal-most tips of the postzygapophyses equal to or lower than 0.75. The evidence provided here bolsters the validity of Aetosauroides and extends the distribution of Aetosauroides scagliai into southern Brazil. Although Stagonolepis was employed as an index taxon for the Adamanian LVF, this genus is currently restricted to Europe and North America. Thus, no overlapping genera or species of aetosaur are shared between South America and other landmasses. Accordingly, the record of aetosaurs is not useful for providing biostratigraphical correlations between Late Triassic South American beds and those in other regions.
REFERENCES
Heckert, A. B., and S. G. Lucas. 1999. A new aetosaur from the Upper Triassic of Texas and the phylogeny of aetosaurs. Journal of Vertebrate Paleontology 19:50–68.
Heckert, A. B., and S. G. Lucas. 2000. Taxonomy, phylogeny, biostratigraphy, biochronology, paleobiogeography, and evolution of the Late Triassic Aetosauria (Archosauria: Crurotarsi). Zentralblatt fur Geologie und Palaontologie, 1998, Teil I, Heft 11–12:1539–1587.
Heckert, A. B., and S. G. Lucas. 2002. South American occurrences of the Adamanian (Late Triassic, Latest Carnian) index taxon Stagonolepis (Archosauria: Aetosauria) and their biochronological significance. Journal of Paleontology 76:852–863.
Irmis, R. B., and R. Mundil. 2008. New age constraints from the Chinle Formation revise global comparisons of Late Triassic vertebrate assemblages. Journal of Vertebrate Paleontology 28:95A.
Lucas, S. G., and A. B. Heckert. 2001. The aetosaur Stagonolepis from the Upper Triassic of Brazil and its biochronological significance. Neues Jahrebuch fur Geologie und Palaontologie, Monatshefte 2001:719–732.
Parker, W. G. 2008. How many valid aetosaur taxa are there? Reviewing the alpha-taxonomy of the Aetosauria (Archosauria: Pseudosuchia) and its implications for Late Triassic global biostratigraphy. Journal of Vertebrate Paleontology 28:125A.
Revised Biostratigraphy-based Correlations for Determining the Position of the TR/J Boundary on the Colorado Plateau
This is an online published corrected proof utilizing paleomagnetic and biostratigraphic data to attempt to precisely locate the Triassic/Jurassic boundary in terrestrial strata of the Colorado Plateau in the Western U.S. It provides corrections based on conchostracan biostratigraphy for previous proposed correlations to other global magnetostrat sections presented in a paper just published by many of the same authors this last October. Unfortunately, because of a lack of isotopic dates to calibrate the magnetostrat sections and the limitations of biostratigraphy for such correlations (e.g., Irmis et al., 2010; Olsen et al., in press), it is not yet clear how reliable these corrections are.
One interesting conclusion of this paper is that pseudosuchian extinctions and the first appearance of large theropod dinosaurs (represented by the ichnotaxon Eubrontes) may have occurred within the Late Triassic and not at or even near the Triassic-Jurassic boundary. Of course this observation is simply a result of moving the TR/J boundary upwards in terrestrial strata.
Lucas, S.G., Tanner, L.H., Donohoo-Hurley, L.L., Geissman, J.W., Kozur, H.W., Heckert, A.B., Weems, R.E.in press. Position of the Triassic-Jurassic boundary and timing of the end-Triassic extinctions on land: Data from the Moenave Formation on the southern Colorado Plateau, USA, Palaeogeography, Palaeoclimatology, Palaeoecology (2011). doi: 10.1016/j.palaeo.2011.01.009
Abstract - Strata of the Moenave Formation on and adjacent to the southern Colorado Plateau in Utah–Arizona, U.S.A., represent one of the best known and most stratigraphically continuous, complete and fossiliferous terrestrial sections across the Triassic–Jurassic boundary. We present a synthesis of new biostratigraphic and magnetostratigraphic data collected from across the Moenave Formation outcrop belt, which extends from the St. George area in southwestern Utah to the Tuba City area in northern Arizona. These data include palynomorphs, conchostracans and vertebrate fossils (including footprints) and a composite polarity record based on four overlapping magnetostratigraphic sections. Placement of the Triassic–Jurassic boundary in strata of the Moenave Formation has long been imprecise and debatable, but these new data (especially the conchostracans) allow us to place the Triassic–Jurassic boundary relatively precisely in the middle part of the Whitmore Point Member of the Moenave Formation, stratigraphically well above the highest occurrence of crurotarsan body fossils or footprints. Correlation to marine sections based on this placement indicates that major terrestrial vertebrate extinctions preceded marine extinctions across the Triassic–Jurassic boundary and therefore were likely unrelated to the Central Atlantic Magmatic Province (CAMP) volcanism.
REFERENCES
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
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.
Olsen, P. E., Kent, D. V., and J. H. Whiteside. In Press. Implications of the Newark Supergroup-based astrochronology and geomagnetic polarity time scale (Newark-APTS) for the tempo and mode of the early diversification of the Dinosauria. Environmental and Earth Science Transactions of the Royal Society of Edinburgh.
One interesting conclusion of this paper is that pseudosuchian extinctions and the first appearance of large theropod dinosaurs (represented by the ichnotaxon Eubrontes) may have occurred within the Late Triassic and not at or even near the Triassic-Jurassic boundary. Of course this observation is simply a result of moving the TR/J boundary upwards in terrestrial strata.
Lucas, S.G., Tanner, L.H., Donohoo-Hurley, L.L., Geissman, J.W., Kozur, H.W., Heckert, A.B., Weems, R.E.in press. Position of the Triassic-Jurassic boundary and timing of the end-Triassic extinctions on land: Data from the Moenave Formation on the southern Colorado Plateau, USA, Palaeogeography, Palaeoclimatology, Palaeoecology (2011). doi: 10.1016/j.palaeo.2011.01.009
Abstract - Strata of the Moenave Formation on and adjacent to the southern Colorado Plateau in Utah–Arizona, U.S.A., represent one of the best known and most stratigraphically continuous, complete and fossiliferous terrestrial sections across the Triassic–Jurassic boundary. We present a synthesis of new biostratigraphic and magnetostratigraphic data collected from across the Moenave Formation outcrop belt, which extends from the St. George area in southwestern Utah to the Tuba City area in northern Arizona. These data include palynomorphs, conchostracans and vertebrate fossils (including footprints) and a composite polarity record based on four overlapping magnetostratigraphic sections. Placement of the Triassic–Jurassic boundary in strata of the Moenave Formation has long been imprecise and debatable, but these new data (especially the conchostracans) allow us to place the Triassic–Jurassic boundary relatively precisely in the middle part of the Whitmore Point Member of the Moenave Formation, stratigraphically well above the highest occurrence of crurotarsan body fossils or footprints. Correlation to marine sections based on this placement indicates that major terrestrial vertebrate extinctions preceded marine extinctions across the Triassic–Jurassic boundary and therefore were likely unrelated to the Central Atlantic Magmatic Province (CAMP) volcanism.
REFERENCES
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
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.
Olsen, P. E., Kent, D. V., and J. H. Whiteside. In Press. Implications of the Newark Supergroup-based astrochronology and geomagnetic polarity time scale (Newark-APTS) for the tempo and mode of the early diversification of the Dinosauria. Environmental and Earth Science Transactions of the Royal Society of Edinburgh.
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.
Biogeography of Triassic tetrapods
Interesting approach and personally timely as I just happen to really be into Triassic biogeography at the moment; however, I think this study suffers somewhat from the usual culprits, lack of taxon sampling and unresolved taxonomic issues (weak primary data). For example, basal phytosaurs are completely left out which have an early and widespread appearance in the Late Triassic. These are extremely important as they are found in Europe, North America, North Africa, and interestingly in India. Including these would have changed several of the paper's conclusions. Likewise, the aetosaur Calyptosuchus (Stagonolepis) wellesi is purposefully left out as is Coahomasuchus, which are two important datapoints for aetosaurs in the Ischigualastian of North America. I wish I had been contacted regarding this study as I would have gladly suggested some less "key" aetosaur taxa to leave out if better resolution was needed for the basal aetosaurines. It is also not entirely clear if the Ischigulastian and Coloradian are applicable outside of South America. It appears that they are presented as equivalent to the Otischalkian + Adamanian and Revueltian + Apachean of North America. This was first put forth by Max Langer in 2005 and has some support, but needs further testing, especially regarding the relationships of all of the Stagonolepis-like aetosaurs, the lack of good phytosaur material in South America, and lack of good (or any) comparable rhynchosaur, cynodont, and sauropodomorph material in North America.
On a side note, it was nice to see Heliocanthus used in there.
Ezcurra, M. D. 2010. Biogeography of Triassic tetrapods: evidence for provincialism and driven sympatric cladogenesis in the early evolution of modern tetrapod lineages. Proceedings of the Royal Society B, doi:10.1098/rspb.2010.0508 Published online.
Abstract - Triassic tetrapods are of key importance in understanding their evolutionary history, because several tetrapod clades, including most of their modern lineages, first appeared or experienced their initial evolutionary radiation during this Period. In order to test previous palaeobiogeographical hypotheses of Triassic tetrapod faunas, tree reconciliation analyses (TRA) were performed with the aim of recovering biogeographical patterns based on phylogenetic signals provided by a composite tree of Middle and Late Triassic tetrapods. The TRA found significant evidence for the presence of different palaeobiogeographical patterns during the analysed time spans. First, a Pangaean distribution is observed during the Middle Triassic, in which several cosmopolitan tetrapod groups are found. During the early Late Triassic a strongly palaeolatitudinally influenced pattern is recovered, with some tetrapod lineages restricted to palaeolatitudinal belts. During the latest Triassic, Gondwanan territories were more closely related to each other than to Laurasian ones, with a distinct tetrapod fauna at low palaeolatitudes. Finally, more than 75 per cent of the cladogenetic events recorded in the tetrapod phylogeny occurred as sympatric splits or within-area vicariance, indicating that evolutionary processes at the regional level were the main drivers in the radiation of Middle and Late Triassic tetrapods and the early evolution of several modern tetrapod lineages.
On a side note, it was nice to see Heliocanthus used in there.
Ezcurra, M. D. 2010. Biogeography of Triassic tetrapods: evidence for provincialism and driven sympatric cladogenesis in the early evolution of modern tetrapod lineages. Proceedings of the Royal Society B, doi:10.1098/rspb.2010.0508 Published online.
Abstract - Triassic tetrapods are of key importance in understanding their evolutionary history, because several tetrapod clades, including most of their modern lineages, first appeared or experienced their initial evolutionary radiation during this Period. In order to test previous palaeobiogeographical hypotheses of Triassic tetrapod faunas, tree reconciliation analyses (TRA) were performed with the aim of recovering biogeographical patterns based on phylogenetic signals provided by a composite tree of Middle and Late Triassic tetrapods. The TRA found significant evidence for the presence of different palaeobiogeographical patterns during the analysed time spans. First, a Pangaean distribution is observed during the Middle Triassic, in which several cosmopolitan tetrapod groups are found. During the early Late Triassic a strongly palaeolatitudinally influenced pattern is recovered, with some tetrapod lineages restricted to palaeolatitudinal belts. During the latest Triassic, Gondwanan territories were more closely related to each other than to Laurasian ones, with a distinct tetrapod fauna at low palaeolatitudes. Finally, more than 75 per cent of the cladogenetic events recorded in the tetrapod phylogeny occurred as sympatric splits or within-area vicariance, indicating that evolutionary processes at the regional level were the main drivers in the radiation of Middle and Late Triassic tetrapods and the early evolution of several modern tetrapod lineages.
New Biostratigraphical Constraints for the Norian⁄Rhaetian Boundary
Once even questioned as a valid stage the Rhaetian has made quite a comeback research-wise, especially since the GSSP for the Norian/Rhaetian boundary has yet to be determined.
Giordano, N., Rigo, M., Ciarapica G. & Bertinelli A. 2010. New biostratigraphical constraints for the Norian ⁄Rhaetian boundary: data from Lagonegro Basin, Southern Apennines, Italy. Lethaia, 10.1111/j.1502-3931.2010.00219.x.
Abstract - Four stratigraphic sections belonging to Lagonegro succession (Southern Apennines) at Mt S. Enoc, Pignola-Abriola, Sasso di Castalda and Mt Volturino have been studied in detail under to provide a new micro-palaeontological data set based on conodonts and radiolarians for the characterization of the Norian ⁄Rhaetian interval. The studied sections represent the different settings of the Lagonegro Basin (from proximal to distal facies) and permit a detailed, integrated, biostratigraphy of the Calcari con Selce (cherty limestones) and Scisti Silicei formations (bedded cherts with radiolarians) to be drawn up. The upper portion of the Calcari con Selce Formation, exhibits intermediate characteristics between the Calcari con Selce and Scisti Silicei Formation, in particular the progressive decrease in carbonate content against an increase in shales and cherts. Within the four sections studied, the Norian ⁄Rhaetian interval has been documented both with conodonts and radiolarians. Because of the continuity and the absence of condensed facies, it has been possible to recognize the morphocline between species Misikella hernsteini and Misikella posthernsteini, here represented by all the transitional forms characterized by common features between the two species, gathered in three evolutionary steps. Moreover, the morphocline between M. hernsteini and M. posthernsteini has been involved in the definition of the Norian ⁄ Rhaetian Boundary, recognizing thus the FAD of M. posthernsteini, one of the possible biomarkers proposed for the boundary. The rich, well-preserved, radiolarian associations of Pignola-Abriola, Sasso di Castalda and Mt Volturino permit the correlation of Tethyan and American conodont successions, highlighting the importance of the mostly coincident occurrences of M. posthernsteini and Epigondolella mosheri morphotype A, which correspond to the base of Proparvicingula moniliformis A. Z. and the disappearance of bivalve Monotis. These coincident bioevents are used here to define the base of the Rhaetian stage.
Giordano, N., Rigo, M., Ciarapica G. & Bertinelli A. 2010. New biostratigraphical constraints for the Norian ⁄Rhaetian boundary: data from Lagonegro Basin, Southern Apennines, Italy. Lethaia, 10.1111/j.1502-3931.2010.00219.x.
Abstract - Four stratigraphic sections belonging to Lagonegro succession (Southern Apennines) at Mt S. Enoc, Pignola-Abriola, Sasso di Castalda and Mt Volturino have been studied in detail under to provide a new micro-palaeontological data set based on conodonts and radiolarians for the characterization of the Norian ⁄Rhaetian interval. The studied sections represent the different settings of the Lagonegro Basin (from proximal to distal facies) and permit a detailed, integrated, biostratigraphy of the Calcari con Selce (cherty limestones) and Scisti Silicei formations (bedded cherts with radiolarians) to be drawn up. The upper portion of the Calcari con Selce Formation, exhibits intermediate characteristics between the Calcari con Selce and Scisti Silicei Formation, in particular the progressive decrease in carbonate content against an increase in shales and cherts. Within the four sections studied, the Norian ⁄Rhaetian interval has been documented both with conodonts and radiolarians. Because of the continuity and the absence of condensed facies, it has been possible to recognize the morphocline between species Misikella hernsteini and Misikella posthernsteini, here represented by all the transitional forms characterized by common features between the two species, gathered in three evolutionary steps. Moreover, the morphocline between M. hernsteini and M. posthernsteini has been involved in the definition of the Norian ⁄ Rhaetian Boundary, recognizing thus the FAD of M. posthernsteini, one of the possible biomarkers proposed for the boundary. The rich, well-preserved, radiolarian associations of Pignola-Abriola, Sasso di Castalda and Mt Volturino permit the correlation of Tethyan and American conodont successions, highlighting the importance of the mostly coincident occurrences of M. posthernsteini and Epigondolella mosheri morphotype A, which correspond to the base of Proparvicingula moniliformis A. Z. and the disappearance of bivalve Monotis. These coincident bioevents are used here to define the base of the Rhaetian stage.
End of 2009 Literature
Two last minute papers for 2009 from Palaeodiversity. This is an open access journal so these papers and others can be downloaded for free from here.
Maisch, M.V., Vega, C.S., and R.R. Schoch. 2009. No dicynodont in the Keuper – a reconsideration of the occurrence of aff. Dinodontosaurus in the Middle Triassic of Southern Germany. Palaeodiversity 2:271-278.
Abstract - An isolated humerus, attributed to a dicynodont therapsid and identified as aff. Dinodontosaurus, from the Lower Keuper (Middle Ladinian, Middle Triassic) of southwestern Germany is redescribed. An additional but smaller humerus that is similar in morphology might pertain to the same taxon. Several morphological features preclude an identification of the material as either aff. Dinodontosaurus, a dicynodont, or even a synapsid. The deltopectoral crest shows a number of tubercles, probably for muscle attachment. The supinator process is strongly developed and clearly offset from the rest of the bone. The distal articulation facet is very narrow transversely. There is no foramen entepicondyloideum. The ectepicondyle has a deeply concave distal surface, at least in the large and presumably adult specimen. An alternative identification for the two humeri proves difficult, as they do not agree with any other known tetrapod from the Lower Keuper. They bear close resemblance, however, to the humerus of the Permian temnospondyl Eryops, suggesting the presence of an as yet unknown temnospondyl.
This paper also emphasizes the importance of correctly determining taxonomic identity when using incomplete or unique specimens for biostratigraphic correlations.
Spielmann, J.A., Lucas, S.G., Heckert, A.B., Rinehart, L.F., and H. R. Richards III. 2009. Redescription of Spinosuchus caseanus (Archosauromorpha: Trilophosauridae) from the Upper Triassic of North America. Palaeodiversity 2: 283–313.
Abstract - Our reexamination of the holotype of Spinosuchus caseanus from the Upper Triassic of West Texas, in addition to the recognition of additional records of this taxon, demonstrates that it is closely related to the trilophosaurid archosauromorph Trilophosaurus and thus is included in a revised Trilophosauridae. Previous arguments suggesting that features that unite Spinosuchus and Trilophosaurus are not limited to these two taxa or are symplesiomorphies shared with a wide variety of contemporaneous Triassic archosauromorphs are not substantiated based on a detailed comparative analysis of the two taxa. The distinctive neural spine morphology of Spinosuchus allows for recognition of this taxon based on isolated vertebrae and thus increases its biostratigraphic value. Spinosuchus is restricted to strata of Adamanian age and is therefore an index taxon of the Adamanian land-vertebrate faunachron.
One interesting aspect of the new referred specimens of Spinosuchus is that they co-occur in a quarry in which the only other recovered material (cranial and postcranial) has been referred to Trilophosaurus jacobsi (Spielmann et al., 2007). Dorsal and sacral vertebrae from the quarry represent Spinosuchus, whereas all of the other material (that does not include dorsal and sacral vertebrae) where referred to T. jacobsi (i.e. there is no duplication of elements). Thus, although discounted by Spielmann et al. (2009) is seems possible that all of the material may indeed belong to a single taxon and that T. jacobsi would be a junior synonym of S. caseanus. Spielmann et al. (2009) claim that dorsal vertebrae from the quarry exist that are more similar to Trilophosaurus buettneri and not Spinosuchus, thus the taxa are not the same, but this will have to await future description of this material.
It also seems strange (and unstable) to diagnose Trilophosauridae based solely on shared vertebral laminae and not including characters of the unique skull and tooth morphology that has historically diagnosed the taxon, but again this determination will rely on future material being recovered.
Maisch, M.V., Vega, C.S., and R.R. Schoch. 2009. No dicynodont in the Keuper – a reconsideration of the occurrence of aff. Dinodontosaurus in the Middle Triassic of Southern Germany. Palaeodiversity 2:271-278.
Abstract - An isolated humerus, attributed to a dicynodont therapsid and identified as aff. Dinodontosaurus, from the Lower Keuper (Middle Ladinian, Middle Triassic) of southwestern Germany is redescribed. An additional but smaller humerus that is similar in morphology might pertain to the same taxon. Several morphological features preclude an identification of the material as either aff. Dinodontosaurus, a dicynodont, or even a synapsid. The deltopectoral crest shows a number of tubercles, probably for muscle attachment. The supinator process is strongly developed and clearly offset from the rest of the bone. The distal articulation facet is very narrow transversely. There is no foramen entepicondyloideum. The ectepicondyle has a deeply concave distal surface, at least in the large and presumably adult specimen. An alternative identification for the two humeri proves difficult, as they do not agree with any other known tetrapod from the Lower Keuper. They bear close resemblance, however, to the humerus of the Permian temnospondyl Eryops, suggesting the presence of an as yet unknown temnospondyl.
This paper also emphasizes the importance of correctly determining taxonomic identity when using incomplete or unique specimens for biostratigraphic correlations.
Spielmann, J.A., Lucas, S.G., Heckert, A.B., Rinehart, L.F., and H. R. Richards III. 2009. Redescription of Spinosuchus caseanus (Archosauromorpha: Trilophosauridae) from the Upper Triassic of North America. Palaeodiversity 2: 283–313.
Abstract - Our reexamination of the holotype of Spinosuchus caseanus from the Upper Triassic of West Texas, in addition to the recognition of additional records of this taxon, demonstrates that it is closely related to the trilophosaurid archosauromorph Trilophosaurus and thus is included in a revised Trilophosauridae. Previous arguments suggesting that features that unite Spinosuchus and Trilophosaurus are not limited to these two taxa or are symplesiomorphies shared with a wide variety of contemporaneous Triassic archosauromorphs are not substantiated based on a detailed comparative analysis of the two taxa. The distinctive neural spine morphology of Spinosuchus allows for recognition of this taxon based on isolated vertebrae and thus increases its biostratigraphic value. Spinosuchus is restricted to strata of Adamanian age and is therefore an index taxon of the Adamanian land-vertebrate faunachron.
One interesting aspect of the new referred specimens of Spinosuchus is that they co-occur in a quarry in which the only other recovered material (cranial and postcranial) has been referred to Trilophosaurus jacobsi (Spielmann et al., 2007). Dorsal and sacral vertebrae from the quarry represent Spinosuchus, whereas all of the other material (that does not include dorsal and sacral vertebrae) where referred to T. jacobsi (i.e. there is no duplication of elements). Thus, although discounted by Spielmann et al. (2009) is seems possible that all of the material may indeed belong to a single taxon and that T. jacobsi would be a junior synonym of S. caseanus. Spielmann et al. (2009) claim that dorsal vertebrae from the quarry exist that are more similar to Trilophosaurus buettneri and not Spinosuchus, thus the taxa are not the same, but this will have to await future description of this material.
It also seems strange (and unstable) to diagnose Trilophosauridae based solely on shared vertebral laminae and not including characters of the unique skull and tooth morphology that has historically diagnosed the taxon, but again this determination will rely on future material being recovered.
The Aetosaur Paper That Changed Everything
Recent events have gained the aetosaurs, those Late Triassic armored pseudosuchians, as bit of notoriety lately (see here, here, here, and here), but all of this aside the truth is that these critters are important index fossils for non-marine Upper Triassic strata worldwide.
Unbenownst to many is the impressive pedigree of paleontologists who have worked on aetosaurs. Louis Agassiz named the first aetosaur taxon (Stagonolepis robertsoni) in 1844 (admittedly he thought he was describing large ganoid fish scales from the Devonian, hence the name); Thomas Huxley (yeah, that Thomas Huxley) wrote two monographs on crocodian nature of Stagonolepis, and indeed it was this work that finally convinced poor old Roderick Murchison and his colleagues that portions of the Old Red Sandstone where actually "new" and Triassic in age. The famous German paleontologist H. von Meyer described aetosaur material from Germany in 1861, although until fairly recently these osteoderms were thought to belong to the phytosaur Phytosaurus. Aetosaurus was also described from Germany by O. Fraas in 1887.
E.D. Cope described the first North American aetosaur material, Typothorax and Episcoposaurus in the late 1800s, and not to be outdone, his bitter rival O.C. Marsh also described an aetosaur (Stegomus), but the first two taxa were thought to be phytosaurs at the time. Other European and North American paleontologists to collect and or publish on aetosaurs include Freidrich von Huene, E.C. Case, Barnum Brown, Charles Camp, Ned Colbert, Glen Jepsen, John Wilson, Joe Gregory, and Don Baird. But again to many of the early workers the majority of these remains were considered to be phytosaurs. Aetosaurus was considered an "aetosaur" obviously, but in reality few workers really understood what an aetosaur was. Work in the 1940s through 1960s by Howard Sawin, Joe Gregory, Glen Jepsen, and Don Baird started differentiating aetosaurs from phytosaurs. In 1962, Gregory even suggested that the Phytosaurus material from Germany actually belonged to aetosaurs, however, he retracted this in 1969. By this time aetosaurs has also been found in South America (e.g., Casimiquela, 1961) and Alick Walker had published his influential monograph on Stagonolepis in 1961.
By the earlier 1980s aetosaurs were relegated to a role of being relatively uninteresting "armored thecodonts" and in western North America only two taxa were recognized, Typothorax and Desmatosuchus, but this was all about to change.
In the 1920s Charles Camp of the University of California Museum of Paleontology (UCMP) at Berkeley had conducted extensive research in the Chinle Formation of Arizona, including in the area of Petrified Forest National Park (it was a monument at the time and much smaller in size). Camp collected numerous specimens, took copious field notes and also photographed some of his sites. Although he only published on the phytosaurs (Camp, 1930) and the dicynodonts (Camp and Welles, 1957) he had collected the remains of many different groups including aetosaurs.
In 1981 Robert Long and Kevin Padian of the UCMP reinstituted Camp's field program at the Petrified Forest. Literally following in Camp's footsteps through the detailed notes and photos they relocated the majority of Camp's old collecting sites and discovered many more new ones. Through 1985, numerous specimens were collected including lots of aetosaur material. Camp (1930) had suggested that the phytosaurs of the Chinle Formation were of biostratigraphic significance and Long and his colleagues discovered that the same thing was true for the aetosaurs.
The results of this work culminated in a large monograph on Upper Triassic non-marine tetrapods of the American Southwest (Long and Murry, 1995); however, in 1985 a shorter article was published that would have far reaching affects for the studies of phytosaurs and aetosaurs. The paper titled "Aetosaur dermal armor from the Late Triassic of southwestern North America, with special reference to material from the Chinle Formation of Petrified Forest National Park" by Robert Long and Karen Ballew was published in a symposium volume (Museum of Northern Arizona Bulletin 54). The paper described and figured new and existing aetosaur material from the Chinle Formation and erected several new taxa. Groundbreaking were the following hypotheses:
1) The dorsal ornamentation pattern on aetosaur osteoderms was diagnostic to taxa and even small pieces of osteoderms could be accurately identified.
2) Instead of only two aetosaur taxa in the American Southwest, there were five, each dignosable by a unique combination of osteoderm characters. Recognozed taxa were Typothorax coccinarum, Desmatosuchus haplocerus, Calyptosuchus wellesi (new taxon), Paratypothorax sp., and "Typothorax" meadei.
3) Based on osteoderm characters "Typothorax" meadei was not referable to Typothorax but instead represented a new genus. This was also later stated by Murry and Long (1989) and Small (1989); however, the new genus was named by Hunt and Lucas in 1990 (who coincidently had edited the 1989 volume containing the first two papers).
4) The purported wide osteoderms of the phytosaur Phytosaurus actually belonged to an aetosaur, which Long and Ballew named Paratypothorax andressi.
5) Following Camp (1930) and Gregory (1957) the aetosaurs and phytosaurs of the American southwest had biochronological significance, demonstrating two distinct assemblages in the Chinle Formation (the type faunas of the Adamanian and Revueltian land vertebrate faunachrons of Lucas and Hunt, 1993).
These five hypotheses revolutionized aetosaur (and phytosaur) research by demonstrating a wide diversity of forms through distinguishable character diagnoses, whereas prior to this spiked forms were assigned to Desmatosuchus and forms with a radial plate ornamentation were assigned to Typothorax despite the fact that the type species of Typothorax, T. coccinarum, does not possess this type of armor ornamantation.
Although recent work (e.g., Martz and Small, 2006, Parker, 2003, 2007, 2008a, b; Parker et al. 2008) has demonstrated that paramedian osteoderm ornamentation is shared within more inclusive clades rather than species and that the shoehorning of taxa into Long and Ballew's five recognized taxa was masking aetosaur diversity, this 1985 paper forms the foundation of all current work on aetosaurs.
Artwork from top to bottom: paramedian plates of Desmatosuchus spurensis, Calyptosuchus (Stagonolepis) wellesi, and Typothorax coccinarum based on material from the southwest USA. All are from Long and Ballew (1985).
REFERENCES
Agassiz, L., 1844. Monographie des poisons fossils du Vieux Grés Rouge ou Systéme Dévonien (Old Red Sandstone) des Iles Britanniques ed de Russie. Jent et Gassman, Neuchâtel, 171 pp.
Camp, C. L., 1930. A study of the phytosaurs with description of new material from western North America. Memoirs of the University of California 10:1-174.
Casamiquela, R. M., 1961. Dos nuevos estagonolepoideos Argentinos (de Ischigualasto, San Juan). Revista Asocíacion Geológia de Argentina 16:143-203.
Case, E. C., 1920. Preliminary description of a new suborder of phytosaurian reptiles with a description of a new species of Phytosaurus. Journal of Geology 28:524- 535.
Cope, E. D., 1877. Report upon the extinct Vertebrata obtained in New Mexico by parties of the expedition of 1874: U.S. Geographical Surveys west of the 100th Meridian [Wheeler], part 2, p. 1-370.
Cope, E. D., 1892. A contribution to the vertebrate paleontology of Texas. Proceedings of the American Philosophical Society 30:123-131.
Fraas, O., 1877. Aëtosaurus ferratus Fr. Die gepanzerte Vogel-Eshe aus dem Stubensandstein bei Stuttgart. Württembergische naturwissenschaftliche Jahreshefte 33(3):1-22.
Gregory, J. T., 1953b. Typothorax and Desmatosuchus. Postilla 16:1-27.
Gregory, J. T., 1962b. The genera of phytosaurs. American Journal of Science 260:652-690.
Unbenownst to many is the impressive pedigree of paleontologists who have worked on aetosaurs. Louis Agassiz named the first aetosaur taxon (Stagonolepis robertsoni) in 1844 (admittedly he thought he was describing large ganoid fish scales from the Devonian, hence the name); Thomas Huxley (yeah, that Thomas Huxley) wrote two monographs on crocodian nature of Stagonolepis, and indeed it was this work that finally convinced poor old Roderick Murchison and his colleagues that portions of the Old Red Sandstone where actually "new" and Triassic in age. The famous German paleontologist H. von Meyer described aetosaur material from Germany in 1861, although until fairly recently these osteoderms were thought to belong to the phytosaur Phytosaurus. Aetosaurus was also described from Germany by O. Fraas in 1887.
E.D. Cope described the first North American aetosaur material, Typothorax and Episcoposaurus in the late 1800s, and not to be outdone, his bitter rival O.C. Marsh also described an aetosaur (Stegomus), but the first two taxa were thought to be phytosaurs at the time. Other European and North American paleontologists to collect and or publish on aetosaurs include Freidrich von Huene, E.C. Case, Barnum Brown, Charles Camp, Ned Colbert, Glen Jepsen, John Wilson, Joe Gregory, and Don Baird. But again to many of the early workers the majority of these remains were considered to be phytosaurs. Aetosaurus was considered an "aetosaur" obviously, but in reality few workers really understood what an aetosaur was. Work in the 1940s through 1960s by Howard Sawin, Joe Gregory, Glen Jepsen, and Don Baird started differentiating aetosaurs from phytosaurs. In 1962, Gregory even suggested that the Phytosaurus material from Germany actually belonged to aetosaurs, however, he retracted this in 1969. By this time aetosaurs has also been found in South America (e.g., Casimiquela, 1961) and Alick Walker had published his influential monograph on Stagonolepis in 1961.
By the earlier 1980s aetosaurs were relegated to a role of being relatively uninteresting "armored thecodonts" and in western North America only two taxa were recognized, Typothorax and Desmatosuchus, but this was all about to change.
In the 1920s Charles Camp of the University of California Museum of Paleontology (UCMP) at Berkeley had conducted extensive research in the Chinle Formation of Arizona, including in the area of Petrified Forest National Park (it was a monument at the time and much smaller in size). Camp collected numerous specimens, took copious field notes and also photographed some of his sites. Although he only published on the phytosaurs (Camp, 1930) and the dicynodonts (Camp and Welles, 1957) he had collected the remains of many different groups including aetosaurs.
In 1981 Robert Long and Kevin Padian of the UCMP reinstituted Camp's field program at the Petrified Forest. Literally following in Camp's footsteps through the detailed notes and photos they relocated the majority of Camp's old collecting sites and discovered many more new ones. Through 1985, numerous specimens were collected including lots of aetosaur material. Camp (1930) had suggested that the phytosaurs of the Chinle Formation were of biostratigraphic significance and Long and his colleagues discovered that the same thing was true for the aetosaurs.
The results of this work culminated in a large monograph on Upper Triassic non-marine tetrapods of the American Southwest (Long and Murry, 1995); however, in 1985 a shorter article was published that would have far reaching affects for the studies of phytosaurs and aetosaurs. The paper titled "Aetosaur dermal armor from the Late Triassic of southwestern North America, with special reference to material from the Chinle Formation of Petrified Forest National Park" by Robert Long and Karen Ballew was published in a symposium volume (Museum of Northern Arizona Bulletin 54). The paper described and figured new and existing aetosaur material from the Chinle Formation and erected several new taxa. Groundbreaking were the following hypotheses:
1) The dorsal ornamentation pattern on aetosaur osteoderms was diagnostic to taxa and even small pieces of osteoderms could be accurately identified.
2) Instead of only two aetosaur taxa in the American Southwest, there were five, each dignosable by a unique combination of osteoderm characters. Recognozed taxa were Typothorax coccinarum, Desmatosuchus haplocerus, Calyptosuchus wellesi (new taxon), Paratypothorax sp., and "Typothorax" meadei.
3) Based on osteoderm characters "Typothorax" meadei was not referable to Typothorax but instead represented a new genus. This was also later stated by Murry and Long (1989) and Small (1989); however, the new genus was named by Hunt and Lucas in 1990 (who coincidently had edited the 1989 volume containing the first two papers).
4) The purported wide osteoderms of the phytosaur Phytosaurus actually belonged to an aetosaur, which Long and Ballew named Paratypothorax andressi.
5) Following Camp (1930) and Gregory (1957) the aetosaurs and phytosaurs of the American southwest had biochronological significance, demonstrating two distinct assemblages in the Chinle Formation (the type faunas of the Adamanian and Revueltian land vertebrate faunachrons of Lucas and Hunt, 1993).
These five hypotheses revolutionized aetosaur (and phytosaur) research by demonstrating a wide diversity of forms through distinguishable character diagnoses, whereas prior to this spiked forms were assigned to Desmatosuchus and forms with a radial plate ornamentation were assigned to Typothorax despite the fact that the type species of Typothorax, T. coccinarum, does not possess this type of armor ornamantation.
Although recent work (e.g., Martz and Small, 2006, Parker, 2003, 2007, 2008a, b; Parker et al. 2008) has demonstrated that paramedian osteoderm ornamentation is shared within more inclusive clades rather than species and that the shoehorning of taxa into Long and Ballew's five recognized taxa was masking aetosaur diversity, this 1985 paper forms the foundation of all current work on aetosaurs.
Artwork from top to bottom: paramedian plates of Desmatosuchus spurensis, Calyptosuchus (Stagonolepis) wellesi, and Typothorax coccinarum based on material from the southwest USA. All are from Long and Ballew (1985).
REFERENCES
Agassiz, L., 1844. Monographie des poisons fossils du Vieux Grés Rouge ou Systéme Dévonien (Old Red Sandstone) des Iles Britanniques ed de Russie. Jent et Gassman, Neuchâtel, 171 pp.
Camp, C. L., 1930. A study of the phytosaurs with description of new material from western North America. Memoirs of the University of California 10:1-174.
Casamiquela, R. M., 1961. Dos nuevos estagonolepoideos Argentinos (de Ischigualasto, San Juan). Revista Asocíacion Geológia de Argentina 16:143-203.
Case, E. C., 1920. Preliminary description of a new suborder of phytosaurian reptiles with a description of a new species of Phytosaurus. Journal of Geology 28:524- 535.
Cope, E. D., 1877. Report upon the extinct Vertebrata obtained in New Mexico by parties of the expedition of 1874: U.S. Geographical Surveys west of the 100th Meridian [Wheeler], part 2, p. 1-370.
Cope, E. D., 1892. A contribution to the vertebrate paleontology of Texas. Proceedings of the American Philosophical Society 30:123-131.
Fraas, O., 1877. Aëtosaurus ferratus Fr. Die gepanzerte Vogel-Eshe aus dem Stubensandstein bei Stuttgart. Württembergische naturwissenschaftliche Jahreshefte 33(3):1-22.
Gregory, J. T., 1953b. Typothorax and Desmatosuchus. Postilla 16:1-27.
Gregory, J. T., 1962b. The genera of phytosaurs. American Journal of Science 260:652-690.
Gregory, J. T., and F. Westphal, 1969. Remarks on the phytosaur genera of the European Trias. Journal of Paleontology 43(5):1296-1298.
Gregory, J.T. 1957. Significance of fossil vertebrates for correlation of Late Triassic continental deposits of North America. 20th Internat. Geol. Cong. Seccion I - El Mesozoico del hemisferio occidental y sus correlaciones mundiales, 1956, pp. 7-25.
Huene, F. von, 1915. On reptiles of the New Mexico Trias in the Cope Collection. American Museum of Natural History Bulletin 24(15):485-507.
Huene, F. von, 1920a. Osteologie von Aëtosaurus ferratus O. Fraas. Acta Zoologica 1:465-491.
Hunt, A. P., and S. G. Lucas, 1990. Re-evaluation of “Typothorax” meadei, a Late Triassic aetosaur from the United States. Paläontologishe Zeitschrift 64:317-328.
Jepsen, G. L. 1948. A Triassic armored reptile from New Jersey. State of New Jersey Department of Conservation Miscellaneous Geologic Paper, pp. 1-20.
Long, R. A., and K. L. Ballew. 1985. Aetosaur dermal armor from the late Triassic of southwestern North America, with special reference to material from the Chinle Formation of Petrified Forest National Park. Museum of Northern Arizona Bulletin 47:45-68.
Long, R. A, and K. Padian, 1986. Vertebrate biostratigraphy of the Late Triassic Chinle
Formation, Petrified Forest National Park, Arizona: preliminary results; pp. 161- 169 in Padian, K. (ed.), The Beginning of the age of Dinosaurs: faunal change across the Triassic-Jurassic boundary. Cambridge University Press, Cambridge.
Long, R. A., and P. A. Murry. 1995. Late Triassic (Carnian and Norian) tetrapods from the southwestern United States. New Mexico Museum of Natural History and Science Bulletin 4:1-254.
Lucas, S. G., and A. P. Hunt, 1993a. Tetrapod biochronology of the Chinle Group (Upper Triassic), Western United States.
Meyer, H. von, 1861. Reptilien aus dem Stubensandstein des oberen Keupers. Palaeotographica 7:253-346.
Murry, P. A., and R. A. Long, 1989. Geology and paleontology of the Chinle Formation, Petrified Forest National Park and vicinity, Arizona and a discussion of vertebrate fossils of the southwestern upper Triassic, pp. 29-64 in S. G. Lucas and A. P. Hunt (eds.), Dawn of the age of dinosaurs in the American southwest. New Mexico Museum of Natural History. Albuquerque.
Parker, W. G. 2003. Description of a new specimen of Desmatosuchus haplocerus from the Late Triassic of Northern Arizona. Unpublished M. S. thesis, Northern Arizona University, Flagstaff, 315 p.
Parker, W. G. 2007. Reassessment of the aetosaur “Desmatosuchus” chamaensis with a reanalysis of the phylogeny of the Aetosauria (Archosauria: Pseudosuchia). Journal of Systematic Palaeontology 5:41–68.
Parker, W. G. 2008a. 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 281–40.
Parker, W.G. 2008b. How many valid aetosaur species are there? Reviewing the alpha-taxonomy of the Aetosauria (Archosauria: Pseudosuchia) and its implications for Late Triassic global biostratigraphy. Journal of Vertebrate Paleontology 28:125A.
Parker, W.G., Stocker, M.R., and R.B. Irmis. 2008. A new Desmatosuchine aetosaur (Archosauria: Suchia) from the Upper Triassic Tecovas Formation (Dockum Group) of Texas. Journal of Vertebrate Paleontology 28:692-701.
Sawin, H. J., 1947. The Pseudosuchian reptile Typothorax meadei. Journal of Paleontology 21:201-238.
Small, B. J., 1989b. Aetosaurs from the Upper Triassic Dockum Formation, Post Quarry,
West Texas; pp. 301-308 in S.G. Lucas and A.P. Hunt (eds.), Dawn of the age of dinosaurs in the American Southwest. University of New Mexico Press, Albuquerque.
Walker, A. D., 1961. Triassic reptiles from the Elgin area: Stagonolepis, Dasygnathus and their allies. Philosophical Transactions of the Royal Society, London, Series B, 248:103-204.
Wilson, J. A., 1950. Cope’s types of fossil reptiles in the collection of the Bureau of Economic Geology, the University of Texas. Journal of Paleontology 24:113-115.
Gregory, J.T. 1957. Significance of fossil vertebrates for correlation of Late Triassic continental deposits of North America. 20th Internat. Geol. Cong. Seccion I - El Mesozoico del hemisferio occidental y sus correlaciones mundiales, 1956, pp. 7-25.
Huene, F. von, 1915. On reptiles of the New Mexico Trias in the Cope Collection. American Museum of Natural History Bulletin 24(15):485-507.
Huene, F. von, 1920a. Osteologie von Aëtosaurus ferratus O. Fraas. Acta Zoologica 1:465-491.
Hunt, A. P., and S. G. Lucas, 1990. Re-evaluation of “Typothorax” meadei, a Late Triassic aetosaur from the United States. Paläontologishe Zeitschrift 64:317-328.
Jepsen, G. L. 1948. A Triassic armored reptile from New Jersey. State of New Jersey Department of Conservation Miscellaneous Geologic Paper, pp. 1-20.
Long, R. A., and K. L. Ballew. 1985. Aetosaur dermal armor from the late Triassic of southwestern North America, with special reference to material from the Chinle Formation of Petrified Forest National Park. Museum of Northern Arizona Bulletin 47:45-68.
Long, R. A, and K. Padian, 1986. Vertebrate biostratigraphy of the Late Triassic Chinle
Formation, Petrified Forest National Park, Arizona: preliminary results; pp. 161- 169 in Padian, K. (ed.), The Beginning of the age of Dinosaurs: faunal change across the Triassic-Jurassic boundary. Cambridge University Press, Cambridge.
Long, R. A., and P. A. Murry. 1995. Late Triassic (Carnian and Norian) tetrapods from the southwestern United States. New Mexico Museum of Natural History and Science Bulletin 4:1-254.
Lucas, S. G., and A. P. Hunt, 1993a. Tetrapod biochronology of the Chinle Group (Upper Triassic), Western United States.
Meyer, H. von, 1861. Reptilien aus dem Stubensandstein des oberen Keupers. Palaeotographica 7:253-346.
Murry, P. A., and R. A. Long, 1989. Geology and paleontology of the Chinle Formation, Petrified Forest National Park and vicinity, Arizona and a discussion of vertebrate fossils of the southwestern upper Triassic, pp. 29-64 in S. G. Lucas and A. P. Hunt (eds.), Dawn of the age of dinosaurs in the American southwest. New Mexico Museum of Natural History. Albuquerque.
Parker, W. G. 2003. Description of a new specimen of Desmatosuchus haplocerus from the Late Triassic of Northern Arizona. Unpublished M. S. thesis, Northern Arizona University, Flagstaff, 315 p.
Parker, W. G. 2007. Reassessment of the aetosaur “Desmatosuchus” chamaensis with a reanalysis of the phylogeny of the Aetosauria (Archosauria: Pseudosuchia). Journal of Systematic Palaeontology 5:41–68.
Parker, W. G. 2008a. 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 281–40.
Parker, W.G. 2008b. How many valid aetosaur species are there? Reviewing the alpha-taxonomy of the Aetosauria (Archosauria: Pseudosuchia) and its implications for Late Triassic global biostratigraphy. Journal of Vertebrate Paleontology 28:125A.
Parker, W.G., Stocker, M.R., and R.B. Irmis. 2008. A new Desmatosuchine aetosaur (Archosauria: Suchia) from the Upper Triassic Tecovas Formation (Dockum Group) of Texas. Journal of Vertebrate Paleontology 28:692-701.
Sawin, H. J., 1947. The Pseudosuchian reptile Typothorax meadei. Journal of Paleontology 21:201-238.
Small, B. J., 1989b. Aetosaurs from the Upper Triassic Dockum Formation, Post Quarry,
West Texas; pp. 301-308 in S.G. Lucas and A.P. Hunt (eds.), Dawn of the age of dinosaurs in the American Southwest. University of New Mexico Press, Albuquerque.
Walker, A. D., 1961. Triassic reptiles from the Elgin area: Stagonolepis, Dasygnathus and their allies. Philosophical Transactions of the Royal Society, London, Series B, 248:103-204.
Wilson, J. A., 1950. Cope’s types of fossil reptiles in the collection of the Bureau of Economic Geology, the University of Texas. Journal of Paleontology 24:113-115.
Conodonts Squished by Thoughtless Dinosaurs
The 52nd annual meeting of the Palaeontological Association was held in December 2008 in the University of Glasgow. Although I was unable to attend (someday I will) the following poster presentation caught my eye. Probably not too many people are experts on World War I tunnels, stromatolites, conodonts, dinosaurs, and archosaur trackways but here is where all of these fields finally collide....
Belvedere, M., Mietto, P., Avanzini, M., and M. Rigo. 2008. Dinosaurs stepping on the conodont animals; p. 44 in Programme and Abstracts for the 52nd meeting of the Palaeontological Association. The Palaeontological Association Newsletter 69.
On the roof of a First World War tunnel in the Monte Pasubio (North Eastern Italy), on a supratidal stromatolitic bed of the Dolomia Principale Formation, 11 tracks have been found. Among them occur some clear dinosaurian tridactyl footprints, from small grallatorid-like to medium-large eubrontid, as well as some tetradactyl footprints. This formation contains the principal dinosaur footprints for the Triassic of the southern alps. All previous findings were on fallen blocks which, given the poor paleontological content of the formation, and the lack of precise stratigraphical position, made their biostratigraphical constraints very difficult to determine. In this case, for the first time, the trampled surface crops out in situ, about 500m from the bottom of the formation. Conodont sampling was carried out on the subtidal level just below the trampled surface. Unexpectedly, two conodonts were found: an advanced Epigondolella praeslovakensis and a true Mockina slovakensis, an association exclusive for the Middle Norian (latest Alaunian). Thus being so precisely contrained, the ichnoassociation could be used to date the other isolated blocks of the Dolomites. Moreover this co-occurrence of tetrpod footprints and conodonts can be used to confirm the Middle Norian age of the Eubrontes-Grallator biochron.
Dinosaur skeletons covered with ammonites have been found in marine strata , but as the authors state this is a first for conodonts and footprints. It's too bad that this does not happen more often to tie together marine and non-marine biostratigraphies. By the way, the small tridactyl tracks probably are ornithodiran as no self respecting pseudosuchian would stomp on conodonts ;).
Belvedere, M., Mietto, P., Avanzini, M., and M. Rigo. 2008. Dinosaurs stepping on the conodont animals; p. 44 in Programme and Abstracts for the 52nd meeting of the Palaeontological Association. The Palaeontological Association Newsletter 69.
On the roof of a First World War tunnel in the Monte Pasubio (North Eastern Italy), on a supratidal stromatolitic bed of the Dolomia Principale Formation, 11 tracks have been found. Among them occur some clear dinosaurian tridactyl footprints, from small grallatorid-like to medium-large eubrontid, as well as some tetradactyl footprints. This formation contains the principal dinosaur footprints for the Triassic of the southern alps. All previous findings were on fallen blocks which, given the poor paleontological content of the formation, and the lack of precise stratigraphical position, made their biostratigraphical constraints very difficult to determine. In this case, for the first time, the trampled surface crops out in situ, about 500m from the bottom of the formation. Conodont sampling was carried out on the subtidal level just below the trampled surface. Unexpectedly, two conodonts were found: an advanced Epigondolella praeslovakensis and a true Mockina slovakensis, an association exclusive for the Middle Norian (latest Alaunian). Thus being so precisely contrained, the ichnoassociation could be used to date the other isolated blocks of the Dolomites. Moreover this co-occurrence of tetrpod footprints and conodonts can be used to confirm the Middle Norian age of the Eubrontes-Grallator biochron.
Dinosaur skeletons covered with ammonites have been found in marine strata , but as the authors state this is a first for conodonts and footprints. It's too bad that this does not happen more often to tie together marine and non-marine biostratigraphies. By the way, the small tridactyl tracks probably are ornithodiran as no self respecting pseudosuchian would stomp on conodonts ;).
Polish Dragon - Revisited
Back in August I briefly discussed the find of a large theropod and dicynodont from a quarry in Lisowice in southern Poland. This find is significant because it represents the latest stratigraphical unambiguous occurrence of a dicynodont in the Late Triassic, as well as the possible earliest occurrence of a tetnuran theropod. The peer-reviewed article detailing this find is now out in Acta Palaeontologica Polonica.
I still need to read through the paper to comment some more but in the meantime here is the abstract:
It is generally accepted that during the Triassic the composition of tetrapod faunas underwent a series of fundamental transformations, mainly as a result of diversification of
archosaurs and decline of therapsids (Benton 1994, 2004, 2006). The last herbivorous basal synapsids, dicynodonts, disappeared from the record in the early Norian of the
Americas, about 220 Ma (Langer et al. 2007), being unknown from the Late Triassic of Europe. Here, we report a partially articulated skeleton and isolated bones of a giant
rhino−size dicynodont in the Upper Triassic fluvial sediments at Lisowice (Lipie Śląskie clay−pit) in southern Poland. Paleobotanical data indicate an early Rhaetian age for
the fauna (Dzik et al. 2008; Niedźwiedzki and Sulej 2008). The dicynodont bones are associated with bones of carnivorous dinosaurs, pterosaurs, as well as capitosaur and plagiosaur amphibians. Dicynodonts were represented in the Germanic Basin throughout the Late Triassic, as proven by findings of smaller dicynodonts in older deposits in the same area, associated there with temnospondyl amphibians. It appears, thus, that the fossil record of tetrapod succession in the Late Triassic was strongly controlled by ecological factors and biased by uneven representation of particular environments. The Lisowice assemblage proves that faunas dominated by dicynodonts did not entirely disappear at least until the end of the Triassic.
REFERENCE
Dzik, J., Sulej, T., and G. Niedźwiedzki. 2008. A dicynodont−theropod association in the latest Triassic of Poland. Acta Palaeontologica Polonica 53:733–738.
I still need to read through the paper to comment some more but in the meantime here is the abstract:
It is generally accepted that during the Triassic the composition of tetrapod faunas underwent a series of fundamental transformations, mainly as a result of diversification of
archosaurs and decline of therapsids (Benton 1994, 2004, 2006). The last herbivorous basal synapsids, dicynodonts, disappeared from the record in the early Norian of the
Americas, about 220 Ma (Langer et al. 2007), being unknown from the Late Triassic of Europe. Here, we report a partially articulated skeleton and isolated bones of a giant
rhino−size dicynodont in the Upper Triassic fluvial sediments at Lisowice (Lipie Śląskie clay−pit) in southern Poland. Paleobotanical data indicate an early Rhaetian age for
the fauna (Dzik et al. 2008; Niedźwiedzki and Sulej 2008). The dicynodont bones are associated with bones of carnivorous dinosaurs, pterosaurs, as well as capitosaur and plagiosaur amphibians. Dicynodonts were represented in the Germanic Basin throughout the Late Triassic, as proven by findings of smaller dicynodonts in older deposits in the same area, associated there with temnospondyl amphibians. It appears, thus, that the fossil record of tetrapod succession in the Late Triassic was strongly controlled by ecological factors and biased by uneven representation of particular environments. The Lisowice assemblage proves that faunas dominated by dicynodonts did not entirely disappear at least until the end of the Triassic.
REFERENCE
Dzik, J., Sulej, T., and G. Niedźwiedzki. 2008. A dicynodont−theropod association in the latest Triassic of Poland. Acta Palaeontologica Polonica 53:733–738.
No Carnian aged deposits in the Chinle Formation?
For the last couple of years one of the more intriguing hypotheses regarding the Chinle Formation is the possibility, based on proposed revisions of the Late Triassic time scale (Muttoni et al., 2004; Furin et al., 2006), that the entire unit was Norian-Rhaetian in age, rather than Carnian-Norian. The Carnian-Norian age was based on palynology (e.g., Litwin et al., 1991) as well as vertebrate biostratigraphy (e.g., Lucas and Hunt, 1993). In fact, a faunal and floral turnover near the middle of the Chinle Formation was hypothesized by many workers to possibly represent the Carnian-Norian boundary and was evidence for an end-Carnian terrestrial extinction. First noticed by Camp (1930) and Gregory (1957) this turnover was more fully documented by Long and Ballew (1985) who noted the presence of two distinct faunas differentiated by the phytosaurs “Rutiodon A” and “Rutiodon B”, as well as the aetosaurs Calyptosuchus and Typothorax. Lucas and Hunt (1993) subsequently named these the Adamanian and Revueltian land-vertebrate faunachrons.
Considered controversial, the hypothesis that most if not all of the Chinle is actually Norian received strong support by the recent announcement of a new 206Pb/238U age of 219.2 ± 0.7 Ma from the base of the Blue Mesa Member in New Mexico (Mundil and Irmis, 2008). This is important for several reasons, firstly, the Chinle Formation has very well documented vertebrate, invertebrate, plant and trace fossil assemblages and is arguably a keystone unit for study of the Late Triassic terrestrial record. Second, it is the basis for the Adamanian land-vertebrate faunachron which has been used to correlate the first appearance of dinosaurs globally (e.g., Heckert and Lucas 1999, 2000). The implications of this will be the focus of Randy Irmis’ presentation at the Society of Vertebrate Paleontology annual meeting next month and therefore will not be discussed further here. What I would like to discuss is the slight possibility that despite these new findings maybe not all of the lower Chinle is now Norian.
In the four corners are of the western United States (Arizona, Utah, Colorado, New Mexico), the Chinle Formation uncomformably overlies the Middle Triassic (Anisian) Moenkopi Formation and consists of seven members which from oldest to youngest are the Shinarump, Bluewater Creek, Blue Mesa, Sonsela, Petrified Forest, Owl Rock, and Rock Point (Note: another unit, the Mesa Redondo Member, is locally situated between the Shinarump and Blue Mesa members but is lithologically distinct from the Bluewater Creek and the relationships between these units are not completely understood). The date provided by Mundil and Irmis (2008) is near the Bluewater Creek/Blue Mesa contact. As the new hypothesized date for the Carnian-Norian boundary is now around 230 ma, this would still leave approximately 10 million years of Norian time below this contact and would presumably include the Shinarump and Bluewater Creek. This is important because instead of just having an uncomformity between the Moenkopi and Chinle that encompasses the Ladinian, this unconformity would now encompass the Ladinian-Carnian as well as a portion of the early Norian. Whereas this might possibly explain the lack of rhynchosaur material (believed to have died out at the end of the Carnian or in the early Norian) from the Chinle Formation, it would also suggest that the Chinle is not temporally equivalent to all of the Dockum Group (eastern New Mexico and Texas) or most of the Newark Supergroup (eastern U.S.) as previously supposed. I’m getting dangerously close to the contents of Randy’s SVP abstract here which is embargoed for the next month, so I will stop this line of thought, but what I want to look at in more detail is the possibility that the Shinarump may not be Norian.
The Shinarump member consists mainly of extrabasinal conglomerates and sandstones that fill paleovalleys carved into the underlying Moenkopi Formation. Once considered its own formation, the Shinarump is now considered to represent the basal member of the Chinle Formation. Unfortunately, the high energy environment that deposited the conglomerates and sands is not conducive to preserving fossils; however in some places mudstone facies do preserve material, most notably near Cameron Arizona. Ash (2005, 2006) has documented this flora and found that it is distinct from the rest of the Chinle Formation in possessing several forms, most notably a seed fern, that more closely resembles archaic forms from the Paleozoic. This suggests that the Shinarump, although still Late Triassic, may be much older than the rest of the Chinle. Unfortunately the vertebrates are not any help. Heckert et al. (2003) documented material that is purportedly from the Shinarump near Cameron, and found that the fauna contains metoposaur and phytosaur material typical of the rest of the Chinle. Furthermore, the flora does also contain forms found in the younger Chinle units including the pollen (Litwin et al., 1991; Ash, 2005). Finally in his excellent dissertation, Jeff Martz discusses in detail that Riggs et al. (1996), in an important but often overlooked paper, used detrital zircons to correlate the Shinarump (and the Santa Rosa Formation of the Dockum) with the marine Auld Lang Syne Group, which is early Norian in age (Martz, 2008). Thus, these authors (Riggs et al., 1996) had suggested a Norian age for the entire Chinle over a decade ago. Despite this, the idea that the Shinarump may still be Carnian is intriguing because it would suggest the presence of a sizeable unconformity (TR-4?) between that unit and the rest of the Chinle Formation.
One final note is that the faunal turnover mentioned at the beginning of this post is close to the base of the Sonsela Member based on detailed mapping and revised biostratigraphic work done by Jeff Martz and myself in Petrified Forest National Park. Thus this turnover (which may also correspond with a floral turnover) is in the early-middle Norian and does not represent an end-Carnian event. More on this later.
REFERENCES
Ash, S.R. 2005. A new Upper Triassic flora and associated invertebrate fossils from
the basal beds of the Chinle Formation, near Cameron, Arizona. PaleoBios 25:17–34.
Ash, S.R. 2006. Chilbinia gen. nov., an archaic seed fern in the Late Triassic Chinle Formation of Arizona, USA. Palaeontology 49:237–245.
Camp, C. L. 1930. A study of the phytosaurs with description of new material from western North America. Memoirs of the University of California 10:1-174.
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.
Gregory, J.T. 1957. Significance of fossil vertebrates for correlation of Late Triassic continental deposits of North America. Report of the 20th Session of the International Geological Congress 1956, Section II:7-25.
Heckert, A.B., and S.G. Lucas. 1999. Global correlation and chronology of Triassic theropods (Archosauria: Dinosauria). Albertiana 23:22-35.
Heckert, A.B., and S.G. Lucas. 2000 [imprint 1998]. Global correlation and chronology of Triassic theropods. Gaia 15:63-74.
Heckert, A.B., Lucas, S.G., and J. W. Estep. 2003 [imprint 2002]. Lower Chinle Group (Upper Triassic: Upper Carnian) tetrapods from the vicinity of Cameron, Arizona. New Mexico Museum of Natural History and Science Bulletin 21:73-76.
Litwin, R.J., Traverse, A., and S.R. Ash. 1991. Preliminary palynological zonation of the Chinle Formation, southwestern U.S.A., and its correlation to the Newark Supergroup (eastern U.S.A.). Review of Palaeobotany and Palynology 68: 269-287.
Long, R. A. and K. L. Ballew. 1985. Aetosaur dermal armor from the Late Triassic of southwestern North America, with special reference to material from the Chinle Formation of Petrified Forest National Park. Museum of Northern Arizona Bulletin 54:45-68.
Lucas, S.G., and A.P. Hunt. 1993. Tetrapod biochronology of the Chinle Group (Upper Triassic), western United States. New Mexico Museum of Natural History and Science Bulletin 3:327-329.
Martz, J.W. 2008. Lithostratigraphy, chemostratigraphy, and vertebrate biostratigraphy of the Dockum Group (Upper Triassic), of southern Garza County, West Texas. Unpublished PhD dissertation. Texas Tech University, Lubbock, 504p.
Mundil, R., and R. Irmis. 2008. New U-Pb age constraints for terrestrial sediments in the Late Triassic: Implications for faunal evolution and correlations with marine environments. International Union of Geological Sciences (IUGS) meeting abstracts Oslo 2008 (online at: http://www.cprm.gov.br/33IGC/1342538.html).
Muttoni, G., Kent, D.V., Olsen, P.E., Di Stefano, P., Lowrie, W., Bernasconi, S.M., and F. M. Hernandez. 2004 Tethyan magnetostratigraphy from Pizzo Mondello (Sicily) and correlation to the Late Triassic Newark astrochronological polarity time scale: Geological Society of America Bulletin 116:1043–1058.
Riggs, N. R., T. M. Lehman, G. E. Gehrels, and W. R. Dickinson. 1996. Detrital zircon
link between headwaters and terminus of the Upper Triassic Chinle-Dockum
paleoriver system. Science 273:97-100.
Considered controversial, the hypothesis that most if not all of the Chinle is actually Norian received strong support by the recent announcement of a new 206Pb/238U age of 219.2 ± 0.7 Ma from the base of the Blue Mesa Member in New Mexico (Mundil and Irmis, 2008). This is important for several reasons, firstly, the Chinle Formation has very well documented vertebrate, invertebrate, plant and trace fossil assemblages and is arguably a keystone unit for study of the Late Triassic terrestrial record. Second, it is the basis for the Adamanian land-vertebrate faunachron which has been used to correlate the first appearance of dinosaurs globally (e.g., Heckert and Lucas 1999, 2000). The implications of this will be the focus of Randy Irmis’ presentation at the Society of Vertebrate Paleontology annual meeting next month and therefore will not be discussed further here. What I would like to discuss is the slight possibility that despite these new findings maybe not all of the lower Chinle is now Norian.
In the four corners are of the western United States (Arizona, Utah, Colorado, New Mexico), the Chinle Formation uncomformably overlies the Middle Triassic (Anisian) Moenkopi Formation and consists of seven members which from oldest to youngest are the Shinarump, Bluewater Creek, Blue Mesa, Sonsela, Petrified Forest, Owl Rock, and Rock Point (Note: another unit, the Mesa Redondo Member, is locally situated between the Shinarump and Blue Mesa members but is lithologically distinct from the Bluewater Creek and the relationships between these units are not completely understood). The date provided by Mundil and Irmis (2008) is near the Bluewater Creek/Blue Mesa contact. As the new hypothesized date for the Carnian-Norian boundary is now around 230 ma, this would still leave approximately 10 million years of Norian time below this contact and would presumably include the Shinarump and Bluewater Creek. This is important because instead of just having an uncomformity between the Moenkopi and Chinle that encompasses the Ladinian, this unconformity would now encompass the Ladinian-Carnian as well as a portion of the early Norian. Whereas this might possibly explain the lack of rhynchosaur material (believed to have died out at the end of the Carnian or in the early Norian) from the Chinle Formation, it would also suggest that the Chinle is not temporally equivalent to all of the Dockum Group (eastern New Mexico and Texas) or most of the Newark Supergroup (eastern U.S.) as previously supposed. I’m getting dangerously close to the contents of Randy’s SVP abstract here which is embargoed for the next month, so I will stop this line of thought, but what I want to look at in more detail is the possibility that the Shinarump may not be Norian.
The Shinarump member consists mainly of extrabasinal conglomerates and sandstones that fill paleovalleys carved into the underlying Moenkopi Formation. Once considered its own formation, the Shinarump is now considered to represent the basal member of the Chinle Formation. Unfortunately, the high energy environment that deposited the conglomerates and sands is not conducive to preserving fossils; however in some places mudstone facies do preserve material, most notably near Cameron Arizona. Ash (2005, 2006) has documented this flora and found that it is distinct from the rest of the Chinle Formation in possessing several forms, most notably a seed fern, that more closely resembles archaic forms from the Paleozoic. This suggests that the Shinarump, although still Late Triassic, may be much older than the rest of the Chinle. Unfortunately the vertebrates are not any help. Heckert et al. (2003) documented material that is purportedly from the Shinarump near Cameron, and found that the fauna contains metoposaur and phytosaur material typical of the rest of the Chinle. Furthermore, the flora does also contain forms found in the younger Chinle units including the pollen (Litwin et al., 1991; Ash, 2005). Finally in his excellent dissertation, Jeff Martz discusses in detail that Riggs et al. (1996), in an important but often overlooked paper, used detrital zircons to correlate the Shinarump (and the Santa Rosa Formation of the Dockum) with the marine Auld Lang Syne Group, which is early Norian in age (Martz, 2008). Thus, these authors (Riggs et al., 1996) had suggested a Norian age for the entire Chinle over a decade ago. Despite this, the idea that the Shinarump may still be Carnian is intriguing because it would suggest the presence of a sizeable unconformity (TR-4?) between that unit and the rest of the Chinle Formation.
One final note is that the faunal turnover mentioned at the beginning of this post is close to the base of the Sonsela Member based on detailed mapping and revised biostratigraphic work done by Jeff Martz and myself in Petrified Forest National Park. Thus this turnover (which may also correspond with a floral turnover) is in the early-middle Norian and does not represent an end-Carnian event. More on this later.
REFERENCES
Ash, S.R. 2005. A new Upper Triassic flora and associated invertebrate fossils from
the basal beds of the Chinle Formation, near Cameron, Arizona. PaleoBios 25:17–34.
Ash, S.R. 2006. Chilbinia gen. nov., an archaic seed fern in the Late Triassic Chinle Formation of Arizona, USA. Palaeontology 49:237–245.
Camp, C. L. 1930. A study of the phytosaurs with description of new material from western North America. Memoirs of the University of California 10:1-174.
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.
Gregory, J.T. 1957. Significance of fossil vertebrates for correlation of Late Triassic continental deposits of North America. Report of the 20th Session of the International Geological Congress 1956, Section II:7-25.
Heckert, A.B., and S.G. Lucas. 1999. Global correlation and chronology of Triassic theropods (Archosauria: Dinosauria). Albertiana 23:22-35.
Heckert, A.B., and S.G. Lucas. 2000 [imprint 1998]. Global correlation and chronology of Triassic theropods. Gaia 15:63-74.
Heckert, A.B., Lucas, S.G., and J. W. Estep. 2003 [imprint 2002]. Lower Chinle Group (Upper Triassic: Upper Carnian) tetrapods from the vicinity of Cameron, Arizona. New Mexico Museum of Natural History and Science Bulletin 21:73-76.
Litwin, R.J., Traverse, A., and S.R. Ash. 1991. Preliminary palynological zonation of the Chinle Formation, southwestern U.S.A., and its correlation to the Newark Supergroup (eastern U.S.A.). Review of Palaeobotany and Palynology 68: 269-287.
Long, R. A. and K. L. Ballew. 1985. Aetosaur dermal armor from the Late Triassic of southwestern North America, with special reference to material from the Chinle Formation of Petrified Forest National Park. Museum of Northern Arizona Bulletin 54:45-68.
Lucas, S.G., and A.P. Hunt. 1993. Tetrapod biochronology of the Chinle Group (Upper Triassic), western United States. New Mexico Museum of Natural History and Science Bulletin 3:327-329.
Martz, J.W. 2008. Lithostratigraphy, chemostratigraphy, and vertebrate biostratigraphy of the Dockum Group (Upper Triassic), of southern Garza County, West Texas. Unpublished PhD dissertation. Texas Tech University, Lubbock, 504p.
Mundil, R., and R. Irmis. 2008. New U-Pb age constraints for terrestrial sediments in the Late Triassic: Implications for faunal evolution and correlations with marine environments. International Union of Geological Sciences (IUGS) meeting abstracts Oslo 2008 (online at: http://www.cprm.gov.br/33IGC/1342538.html).
Muttoni, G., Kent, D.V., Olsen, P.E., Di Stefano, P., Lowrie, W., Bernasconi, S.M., and F. M. Hernandez. 2004 Tethyan magnetostratigraphy from Pizzo Mondello (Sicily) and correlation to the Late Triassic Newark astrochronological polarity time scale: Geological Society of America Bulletin 116:1043–1058.
Riggs, N. R., T. M. Lehman, G. E. Gehrels, and W. R. Dickinson. 1996. Detrital zircon
link between headwaters and terminus of the Upper Triassic Chinle-Dockum
paleoriver system. Science 273:97-100.
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