Hofmann, R., Hautmann, M. and H. Bucher. 2013. A New Paleoecological Look at the Dinwoody Formation (Lower Triassic, Western USA): Intrinsic Versus Extrinsic Controls on Ecosystem Recovery After the End-Permian Mass Extinction Journal of Paleontology 87:854-880. 2013 doi: http://dx.doi.org/10.1666/12-153
Abstract - The Dinwoody Formation of the western United States represents an important archive of Early Triassic ecosystems in the immediate aftermath of the end-Permian mass extinction. We present a systematic description and a quantitative paleoecological analysis of its benthic faunas in order to reconstruct benthic associations and to explore the temporal and spatial variations of diversity, ecological structure and taxonomic composition throughout the earliest Triassic of the western United States. A total of 15 bivalve species, two gastropod species, and two brachiopod species are recognized in the study area. The paleoecological analysis shows that the oldest Dinwoody communities are characterized by low diversity, low ecological complexity and high dominance of few species. We suggest that this low diversity most likely reflects the consequences of the mass extinction in the first place and not necessarily the persistence of environmental stress. Whereas this diversity pattern persists into younger strata of the Dinwoody Formation in outer shelf environments, an increase in richness, evenness and guild diversity occurred around the Griesbachian–Dienerian boundary in more shallow marine habitats. This incipient recovery towards the end of the Griesbachian is in accordance with observations from other regions and thus probably represents an interregional signal. In contrast to increasing richness within communities (alpha-diversity), beta-diversity remained low during the Griesbachian and Dienerian in the study area. This low beta-diversity reflects a wide environmental and geographical range of taxa during the earliest Triassic, indicating that the increase of within-habitat diversity has not yet led to significant competitive exclusion. We hypothesize that the well-known prevalence of generalized taxa in post-extinction faunas is primarily an effect of reduced competition that allows species to exist through the full range of their fundamental niches, rather than being caused by unusual and uniform environmental stress.
Showing posts with label extinction. Show all posts
Showing posts with label extinction. Show all posts
New Triassic Papers
Thanks to Ben Creisler for originally compiling these...
Chen, Z. Q-., and M. J. Benton. 2012. The timing and pattern of biotic recovery following the end-Permian mass extinction. Nature Geoscience 5: 375–383doi:10.1038/ngeo1475
Abstract - The aftermath of the great end-Permian period mass extinction 252 Myr ago shows how life can recover from the loss of >90% species globally. The crisis was triggered by a number of physical environmental shocks (global warming, acid rain, ocean acidification and ocean anoxia), and some of these were repeated over the next 5–6 Myr. Ammonoids and some other groups diversified rapidly, within 1–3 Myr, but extinctions continued through the Early Triassic period. Triassic ecosystems were rebuilt stepwise from low to high trophic levels through the Early to Middle Triassic, and a stable, complex ecosystem did not re-emerge until the beginning of the Middle Triassic, 8–9 Myr after the crisis. A positive aspect of the recovery was the emergence of entirely new groups, such as marine reptiles and decapod crustaceans, as well as new tetrapods on land, including — eventually — dinosaurs. The stepwise recovery of life in the Triassic could have been delayed either by biotic drivers (complex multispecies interactions) or physical perturbations, or a combination of both. This is an example of the wider debate about the relative roles of intrinsic and extrinsic drivers of large-scale evolution.
==
Lindström, S., van de Schootbrugge, B., Dybkjær, K., Pedersen, G. K., Fiebig, J., Nielsen, L. H., and S. Richoz. 2012. No causal link between terrestrial ecosystem change and methane release during the end-Triassic mass extinction.
Geology 40(6): 531-534 doi: 10.1130/G32928.1
Abstract - Profound changes in both marine and terrestrial biota during the end-Triassic mass extinction event and associated successive carbon cycle perturbations across the Triassic-Jurassic boundary (T-J, 201.3 Ma) have primarily been attributed to volcanic emissions from the Central Atlantic Magmatic Province and/or injection of methane. Here we present a new extended organic carbon isotope record from a cored T-J boundary succession in the Danish Basin, dated by high-resolution palynostratigraphy and supplemented by a marine faunal record. Correlated with reference C-isotope and biotic records from the UK, it provides new evidence that the major biotic changes, both on land and in the oceans, commenced prior to the most prominent negative C-isotope excursion. If massive methane release was involved, it did not trigger the end-Triassic mass extinction. Instead, this negative C-isotope excursion is contemporaneous with the onset of floral recovery on land, whereas marine ecosystems remained perturbed. The decoupling between ecosystem recovery on land and in the sea is more likely explained by long-term flood basalt volcanism releasing both SO2 and CO2 with short- and long-term effects, respectively.
===
Hamad, A. M. B. A. Jasper, A., and D. Uhl. 2012. The record of Triassic charcoal and other evidence for palaeo-wildfires: Signal for atmospheric oxygen levels, taphonomic biases or lack of fuel? International Journal of Coal Geology 96–97: 60–71 http://dx.doi.org/10.1016/j.coal.2012.03.006
Abstract - As wildfires are today important sources of disturbance in many terrestrial ecosystems, it is of great interest to understand how different environmental parameters and fire-activity interacted during past periods of the Earth history. Fossil charcoal, inertinites, and pyrogenic polycyclic aromatic hydrocarbons (PAHs) represent the only direct evidence for the occurrence of such palaeo-wildfires. In the present study, a review of published data, together with new data on the occurrence of fossil charcoal for the Permian and the Triassic is presented. For a long time, it has been speculated, that an assumed lack of evidence for palaeo-wildfires during the Triassic should be explained by a large drop in atmospheric oxygen concentration following or during the end-Permian mass extinction event, preventing the occurrence of wildfires. However, evidence for palaeo-wildfires is relatively common in many middle and late Triassic strata, whereas such evidence is almost totally lacking from early Triassic sediments. The interpretation of this “charcoal gap” or depression is difficult, as many factors (e.g. atmospheric oxygen concentration, taphonomical biases, lack of sediments suitable for the preservation of macroscopic charcoal, lack of fuel, and “ignorance” of scientists) may have influenced not only the production, but also the preservation and recovery of evidence for palaeo-wildfires during this period. Thus, it is not clear whether this Early Triassic “charcoal gap” can also be seen as evidence for an assumed “wildfire gap” or not. Without any doubt further investigations on the early Triassic record of charcoal and other evidence for palaeo-wildfires will be necessary before this problem can be solved. In fact, it can be expected that the number of published records of (early) Triassic evidence for palaeo-wildfires will increase in the future as more and more scientist working on
sediments of this age may become aware of the interest in fires from this time. This will certainly make it possible to give a much better picture of the temporal and regional distribution of wildfires during this period in the future.
==
Bodzioch, A., and M. Kowal-Linka. 2012. Unraveling the origin of the Late Triassic multitaxic bone accumulation at Krasiejów (S Poland) by diagenetic analysis. Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication) http://dx.doi.org/10.1016/j.palaeo.2012.05.015
Abstract - A study of aquatic and terrestrial vertebrate remains from a bonebed in the Late Triassic continental succession near Krasiejów (S Poland) shows it was deposited by a single catastrophic event, perhaps a flood. Hardparts of Metoposaurus, Paleorhinus, and Stagonolepis show sedimentary infill and geochemical evidence for early diagenesis at different times and in different microenvironments. The infills in the aquatic animal bones (sediment, pyrite, calcite) show deposition in a freshwater environment, while those in the terrestrial Stagonolepis remains (mainly barite) point to an arid terrestial environment. The trace element content of the remains, together with the absence of a distinct pattern of element distribution, supports the conclusion that individual hardparts underwent diagenesis in various microenvironments and at different times. The accumulation of multitaxic vertebrate remains in a single bed clearly indicates event deposition. The hardparts must originally have been deposited at various locations during different times, but were later transported and deposited together in a pond by a short-lived, high-energy event, probably a flood after catastrophic rainfall.
Chen, Z. Q-., and M. J. Benton. 2012. The timing and pattern of biotic recovery following the end-Permian mass extinction. Nature Geoscience 5: 375–383doi:10.1038/ngeo1475
Abstract - The aftermath of the great end-Permian period mass extinction 252 Myr ago shows how life can recover from the loss of >90% species globally. The crisis was triggered by a number of physical environmental shocks (global warming, acid rain, ocean acidification and ocean anoxia), and some of these were repeated over the next 5–6 Myr. Ammonoids and some other groups diversified rapidly, within 1–3 Myr, but extinctions continued through the Early Triassic period. Triassic ecosystems were rebuilt stepwise from low to high trophic levels through the Early to Middle Triassic, and a stable, complex ecosystem did not re-emerge until the beginning of the Middle Triassic, 8–9 Myr after the crisis. A positive aspect of the recovery was the emergence of entirely new groups, such as marine reptiles and decapod crustaceans, as well as new tetrapods on land, including — eventually — dinosaurs. The stepwise recovery of life in the Triassic could have been delayed either by biotic drivers (complex multispecies interactions) or physical perturbations, or a combination of both. This is an example of the wider debate about the relative roles of intrinsic and extrinsic drivers of large-scale evolution.
==
Lindström, S., van de Schootbrugge, B., Dybkjær, K., Pedersen, G. K., Fiebig, J., Nielsen, L. H., and S. Richoz. 2012. No causal link between terrestrial ecosystem change and methane release during the end-Triassic mass extinction.
Geology 40(6): 531-534 doi: 10.1130/G32928.1
Abstract - Profound changes in both marine and terrestrial biota during the end-Triassic mass extinction event and associated successive carbon cycle perturbations across the Triassic-Jurassic boundary (T-J, 201.3 Ma) have primarily been attributed to volcanic emissions from the Central Atlantic Magmatic Province and/or injection of methane. Here we present a new extended organic carbon isotope record from a cored T-J boundary succession in the Danish Basin, dated by high-resolution palynostratigraphy and supplemented by a marine faunal record. Correlated with reference C-isotope and biotic records from the UK, it provides new evidence that the major biotic changes, both on land and in the oceans, commenced prior to the most prominent negative C-isotope excursion. If massive methane release was involved, it did not trigger the end-Triassic mass extinction. Instead, this negative C-isotope excursion is contemporaneous with the onset of floral recovery on land, whereas marine ecosystems remained perturbed. The decoupling between ecosystem recovery on land and in the sea is more likely explained by long-term flood basalt volcanism releasing both SO2 and CO2 with short- and long-term effects, respectively.
===
Hamad, A. M. B. A. Jasper, A., and D. Uhl. 2012. The record of Triassic charcoal and other evidence for palaeo-wildfires: Signal for atmospheric oxygen levels, taphonomic biases or lack of fuel? International Journal of Coal Geology 96–97: 60–71 http://dx.doi.org/10.1016/j.coal.2012.03.006
Abstract - As wildfires are today important sources of disturbance in many terrestrial ecosystems, it is of great interest to understand how different environmental parameters and fire-activity interacted during past periods of the Earth history. Fossil charcoal, inertinites, and pyrogenic polycyclic aromatic hydrocarbons (PAHs) represent the only direct evidence for the occurrence of such palaeo-wildfires. In the present study, a review of published data, together with new data on the occurrence of fossil charcoal for the Permian and the Triassic is presented. For a long time, it has been speculated, that an assumed lack of evidence for palaeo-wildfires during the Triassic should be explained by a large drop in atmospheric oxygen concentration following or during the end-Permian mass extinction event, preventing the occurrence of wildfires. However, evidence for palaeo-wildfires is relatively common in many middle and late Triassic strata, whereas such evidence is almost totally lacking from early Triassic sediments. The interpretation of this “charcoal gap” or depression is difficult, as many factors (e.g. atmospheric oxygen concentration, taphonomical biases, lack of sediments suitable for the preservation of macroscopic charcoal, lack of fuel, and “ignorance” of scientists) may have influenced not only the production, but also the preservation and recovery of evidence for palaeo-wildfires during this period. Thus, it is not clear whether this Early Triassic “charcoal gap” can also be seen as evidence for an assumed “wildfire gap” or not. Without any doubt further investigations on the early Triassic record of charcoal and other evidence for palaeo-wildfires will be necessary before this problem can be solved. In fact, it can be expected that the number of published records of (early) Triassic evidence for palaeo-wildfires will increase in the future as more and more scientist working on
sediments of this age may become aware of the interest in fires from this time. This will certainly make it possible to give a much better picture of the temporal and regional distribution of wildfires during this period in the future.
==
Bodzioch, A., and M. Kowal-Linka. 2012. Unraveling the origin of the Late Triassic multitaxic bone accumulation at Krasiejów (S Poland) by diagenetic analysis. Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication) http://dx.doi.org/10.1016/j.palaeo.2012.05.015
Abstract - A study of aquatic and terrestrial vertebrate remains from a bonebed in the Late Triassic continental succession near Krasiejów (S Poland) shows it was deposited by a single catastrophic event, perhaps a flood. Hardparts of Metoposaurus, Paleorhinus, and Stagonolepis show sedimentary infill and geochemical evidence for early diagenesis at different times and in different microenvironments. The infills in the aquatic animal bones (sediment, pyrite, calcite) show deposition in a freshwater environment, while those in the terrestrial Stagonolepis remains (mainly barite) point to an arid terrestial environment. The trace element content of the remains, together with the absence of a distinct pattern of element distribution, supports the conclusion that individual hardparts underwent diagenesis in various microenvironments and at different times. The accumulation of multitaxic vertebrate remains in a single bed clearly indicates event deposition. The hardparts must originally have been deposited at various locations during different times, but were later transported and deposited together in a pond by a short-lived, high-energy event, probably a flood after catastrophic rainfall.
New Findings on the Early Triassic Recovery of the Terrestrial Vertebrate Fauna - Redux
Here is the abstract and link to the new article and it is currently open access.
Irmis, R. B. and J. H. Whiteside. 2011.Delayed recovery of non-marine tetrapods after the end-Permian mass extinction tracks global carbon cycle. Proceedings of the Royal Society B (advance online publication) doi: 10.1098/rspb.2011.1895
Abstract - During the end-Permian mass extinction, marine ecosystems suffered a major drop in diversity, which was maintained throughout the Early Triassic until delayed recovery during the Middle Triassic. This depressed diversity in the Early Triassic correlates with multiple major perturbations to the global carbon cycle, interpreted as either intrinsic ecosystem or external palaeoenvironmental effects. In contrast, the terrestrial record of extinction and recovery is less clear; the effects and magnitude of the end-Permian extinction on non-marine vertebrates are particularly controversial. We use specimen-level data from southern Africa and Russia to investigate the palaeodiversity dynamics of non-marine tetrapods across
the Permo-Triassic boundary by analysing sample-standardized generic richness, evenness and relative abundance. In addition, we investigate the potential effects of sampling, geological and taxonomic biases on these data. Our analyses demonstrate that non-marine tetrapods were severely affected by the end-Permian mass extinction, and that these assemblages did not begin to recover until the Middle Triassic. These data are congruent with those from land plants and marine invertebrates. Furthermore, they are consistent with the idea that unstable low-diversity post-extinction ecosystems were subject to boom-bust cycles, reflected in multiple Early Triassic perturbations of the carbon cycle.
Irmis, R. B. and J. H. Whiteside. 2011.Delayed recovery of non-marine tetrapods after the end-Permian mass extinction tracks global carbon cycle. Proceedings of the Royal Society B (advance online publication) doi: 10.1098/rspb.2011.1895
Abstract - During the end-Permian mass extinction, marine ecosystems suffered a major drop in diversity, which was maintained throughout the Early Triassic until delayed recovery during the Middle Triassic. This depressed diversity in the Early Triassic correlates with multiple major perturbations to the global carbon cycle, interpreted as either intrinsic ecosystem or external palaeoenvironmental effects. In contrast, the terrestrial record of extinction and recovery is less clear; the effects and magnitude of the end-Permian extinction on non-marine vertebrates are particularly controversial. We use specimen-level data from southern Africa and Russia to investigate the palaeodiversity dynamics of non-marine tetrapods across
the Permo-Triassic boundary by analysing sample-standardized generic richness, evenness and relative abundance. In addition, we investigate the potential effects of sampling, geological and taxonomic biases on these data. Our analyses demonstrate that non-marine tetrapods were severely affected by the end-Permian mass extinction, and that these assemblages did not begin to recover until the Middle Triassic. These data are congruent with those from land plants and marine invertebrates. Furthermore, they are consistent with the idea that unstable low-diversity post-extinction ecosystems were subject to boom-bust cycles, reflected in multiple Early Triassic perturbations of the carbon cycle.
TR-J Carbon Isotope Excursions Caused by Global Disturbance and not by Vegetation Change
Bacon, K. L., Belcher, C. M., Hesselbo, S. P., and J. C. McElwain. 2011. The Triassic–Jurassic boundary carbon-isotope excursions expressed in taxonomically identified leaf cuticles. Palaios 26:461-469. http://www.bioone.org/doi/abs/10.2110/palo.2010.p10-120r
Abstract - A negative stable carbon-isotope excursion (CIE) has been identified at sites across the globe in strata that span the Triassic–Jurassic boundary. Different studies have suggested that this negative CIE could be the result of either a change in vegetation or a massive perturbation in the global carbon cycle at this time. To determine which, 84 hand-picked leaf cuticle fragments from plant macrofossils previously identified to genus level were analyzed for stable carbon-isotope values. The samples were taken from known heights in nine plant beds spanning the Rhaetian–Hettangian (Upper Triassic–Lower Jurassic) at Astartekløft, East Greenland. We have constructed taxon-specific stable carbon-isotope curves for Ginkgoales and Bennettitales and compared these to an existing δ13C curve based on fossil wood from the same section. This study reveals that taxon-specific carbon-isotope curves based on the leaf data from these two seed-plant groups both record the same negative CIE as the fossil wood, despite having different ecological roles and different relative abundances in the section. Correspondence analysis of the macrofossil abundance data, where the plants are considered in their ecological groups, shows that the δ13C values bear no relationship to changes in vegetation. This result further suggests that vegetation change had little role in determining the δ13C values at this time. Considered together, the bulk cuticle and taxon-specific δ13C record indicate that the negative CIE at the Triassic–Jurassic boundary is likely to have been caused by a massive perturbation of the global carbon cycle and not by vegetation change.
Atmospheric Carbon Injection Linked to End-Triassic Mass Extinction
http://news.sciencemag.org/sciencenow/2011/07/did-greenhouse-gasses-unleash-th.html?ref=hp
Ruhl, M., Bonis, M. R., Reichart, G-.R., Sinninghe Damste, J. S., and W. M. Kürschner. 2011. Atmospheric Carbon Injection Linked to End-Triassic Mass Extinction. Science 333:430-434. DOI:10.1126/science.1204255.
Abstract - The end-Triassic mass extinction (~201.4 million years ago), marked by terrestrial ecosystem turnover and up to ~50% loss in marine biodiversity, has been attributed to intensified volcanic activity during the break-up of Pangaea. Here, we present compound-specific carbon-isotope data of long-chain n-alkanes derived from waxes of land plants, showing a ~8.5 per mil negative excursion, coincident with the extinction interval. These data indicate strong carbon-13 depletion of the end-Triassic atmosphere, within only 10,000 to 20,000 years. The magnitude and rate of this carbon-cycle disruption can be explained by the injection of at least ~12 × 103 gigatons of isotopically depleted carbon as methane into the atmosphere. Concurrent vegetation changes reflect strong warming and an enhanced hydrological cycle. Hence, end-Triassic events are robustly linked to methane-derived massive carbon release and associated climate change.
Ruhl, M., Bonis, M. R., Reichart, G-.R., Sinninghe Damste, J. S., and W. M. Kürschner. 2011. Atmospheric Carbon Injection Linked to End-Triassic Mass Extinction. Science 333:430-434. DOI:10.1126/science.1204255.
Abstract - The end-Triassic mass extinction (~201.4 million years ago), marked by terrestrial ecosystem turnover and up to ~50% loss in marine biodiversity, has been attributed to intensified volcanic activity during the break-up of Pangaea. Here, we present compound-specific carbon-isotope data of long-chain n-alkanes derived from waxes of land plants, showing a ~8.5 per mil negative excursion, coincident with the extinction interval. These data indicate strong carbon-13 depletion of the end-Triassic atmosphere, within only 10,000 to 20,000 years. The magnitude and rate of this carbon-cycle disruption can be explained by the injection of at least ~12 × 103 gigatons of isotopically depleted carbon as methane into the atmosphere. Concurrent vegetation changes reflect strong warming and an enhanced hydrological cycle. Hence, end-Triassic events are robustly linked to methane-derived massive carbon release and associated climate change.
Coal Combustion as a Contributor to the End-Permian Extinction
A break from one fingered dinosaurs and the speculations of use for such a limb. This is a new article regarding a possible contributor to end-Permian marine extinctions. A popular news article is here.
Grasby, S. E., Sanei, H. and B. Beauchamp. 2011. Catastrophic dispersion of coal fly ash into oceans during the latest Permian extinction. Nature Geoscience. Published online 23 January 2011 http://www.nature.com/ngeo/journal/vaop/ncurrent/abs/ngeo1069.html
Abstract - During the latest Permian extinction about 250 Myr ago, more than 90% of marine species went extinct, and biogeochemical cycles were disrupted globally. The cause of the disruption is unclear, but a link between the eruption of the Siberian Trap flood basalts and the extinction has been suggested on the basis of the rough coincidence of the two events. The flood basalt volcanism released CO2. In addition, related thermal metamorphism of Siberian coal measures and organic-rich shales led to the emission of methane, which would have affected global climate and carbon cycling, according to model simulations. This scenario is supported by evidence for volcanic eruptions and gas release in the Siberian Tunguska Basin, but direct indicators of coal combustion have not been detected. Here we present analyses of terrestrial carbon in marine sediments that suggest a substantial amount of char was deposited in Permian aged rocks from the Canadian High Arctic immediately before the mass extinction. Based on the geochemistry and petrology of the char, we propose that the char was derived from the combustion of Siberian coal and organic-rich sediments by flood basalts, which was then dispersed globally. The char is remarkably similar to modern coal fly ash, which can create toxic aquatic conditions when released as slurries. We therefore speculate that the global distribution of ash could have created toxic marine conditions.
Grasby, S. E., Sanei, H. and B. Beauchamp. 2011. Catastrophic dispersion of coal fly ash into oceans during the latest Permian extinction. Nature Geoscience. Published online 23 January 2011 http://www.nature.com/ngeo/journal/vaop/ncurrent/abs/ngeo1069.html
Abstract - During the latest Permian extinction about 250 Myr ago, more than 90% of marine species went extinct, and biogeochemical cycles were disrupted globally. The cause of the disruption is unclear, but a link between the eruption of the Siberian Trap flood basalts and the extinction has been suggested on the basis of the rough coincidence of the two events. The flood basalt volcanism released CO2. In addition, related thermal metamorphism of Siberian coal measures and organic-rich shales led to the emission of methane, which would have affected global climate and carbon cycling, according to model simulations. This scenario is supported by evidence for volcanic eruptions and gas release in the Siberian Tunguska Basin, but direct indicators of coal combustion have not been detected. Here we present analyses of terrestrial carbon in marine sediments that suggest a substantial amount of char was deposited in Permian aged rocks from the Canadian High Arctic immediately before the mass extinction. Based on the geochemistry and petrology of the char, we propose that the char was derived from the combustion of Siberian coal and organic-rich sediments by flood basalts, which was then dispersed globally. The char is remarkably similar to modern coal fly ash, which can create toxic aquatic conditions when released as slurries. We therefore speculate that the global distribution of ash could have created toxic marine conditions.
Jurassic Phytosaur??
A new paper by Maisch and Kapitzke (2010) describes a mandibular fragment from a phytosaur from marine shales in England. This is supposedly the first record of a phytosaur from the Jurassic (Hettangian) as the specimen was found in-situ beneath beds that provide the lowest occurrence of the ammonoid Psiloceras. Thus some phytosaurs, in this case a marine one from Europe, purportedly survived the end-Triassic extinction.
However, as Randall Irmis (who also informed me of this paper) reminded me, this is non-sensical regarding this specimen as the base of the Jurassic is presently defined by the first appearance of Psiloceras. Thus the phytosaur bearing strata are latest Triassic in age and not Jurassic.
I'm not adverse to the possibility that some basal pseudosuchians such as phytosaurs, aetosaurs, and rauisuchians may have survived into the Triassic, especially given our poor control on the determination of the Triassic-Jurassic boundary in non-marine strata. Obviously crocodylomorphs make it through and we have no evidence for an abrupt global-wide non-marine extinction event for other pseudosuchians.
The specimen mentioned by Maisch and Kapitzke appears to currently hold the title of the "last phytosaur", but unfortunately it does not provide clear evidence for the survival of this clade past the end-Triassic.
Maisch, M. W. & Kapitzke, M. 2010. A presumably marine phytosaur (Reptilia: Archosauria) from the pre-planorbis beds (Hettangian) of England. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 257: 373–379.
Abstract: A mandibular fragment of a longirostrine archosaur is decribed from the lowermost Jurassic (pre-planorbis beds, lowermost Hettangian) of Watchet, Somerset, England. The specimen is compared to both marine crocodilians (Thalattosuchia) and phytosaurs, groups which are either unknown (Thalattosuchia) or only doubtfully represented (Phytosauria) in lowermost Jurassic strata so far. The specimen shows striking morphological similarity to the Late Triassic phytosaur Mystriosuchus, but differs from known teleosaurid and metriorhynchid thalattosuchians. It is consequently
determined as aff. Mystriosuchus. It supports previous assumptions that phytosaurs crossed the Triassic-Jurassic boundary, at least in Europe. It also provides additional evidence that at least some phytosaurs, particularly the longirostrine forms, may have been facultative marine animals. The persistence of amphibious, piscivorous, longirostrine phytosaurs in the earliest Jurassic of Europe may have hampered the distribution of the ecologically similar teleosaurids, which are not known from strata that are older than the latest Sinemurian to date.
However, as Randall Irmis (who also informed me of this paper) reminded me, this is non-sensical regarding this specimen as the base of the Jurassic is presently defined by the first appearance of Psiloceras. Thus the phytosaur bearing strata are latest Triassic in age and not Jurassic.
I'm not adverse to the possibility that some basal pseudosuchians such as phytosaurs, aetosaurs, and rauisuchians may have survived into the Triassic, especially given our poor control on the determination of the Triassic-Jurassic boundary in non-marine strata. Obviously crocodylomorphs make it through and we have no evidence for an abrupt global-wide non-marine extinction event for other pseudosuchians.
The specimen mentioned by Maisch and Kapitzke appears to currently hold the title of the "last phytosaur", but unfortunately it does not provide clear evidence for the survival of this clade past the end-Triassic.
Maisch, M. W. & Kapitzke, M. 2010. A presumably marine phytosaur (Reptilia: Archosauria) from the pre-planorbis beds (Hettangian) of England. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 257: 373–379.
Abstract: A mandibular fragment of a longirostrine archosaur is decribed from the lowermost Jurassic (pre-planorbis beds, lowermost Hettangian) of Watchet, Somerset, England. The specimen is compared to both marine crocodilians (Thalattosuchia) and phytosaurs, groups which are either unknown (Thalattosuchia) or only doubtfully represented (Phytosauria) in lowermost Jurassic strata so far. The specimen shows striking morphological similarity to the Late Triassic phytosaur Mystriosuchus, but differs from known teleosaurid and metriorhynchid thalattosuchians. It is consequently
determined as aff. Mystriosuchus. It supports previous assumptions that phytosaurs crossed the Triassic-Jurassic boundary, at least in Europe. It also provides additional evidence that at least some phytosaurs, particularly the longirostrine forms, may have been facultative marine animals. The persistence of amphibious, piscivorous, longirostrine phytosaurs in the earliest Jurassic of Europe may have hampered the distribution of the ecologically similar teleosaurids, which are not known from strata that are older than the latest Sinemurian to date.
...and one more from the End-Triassic Event.
Mander, L., Kuerschner, W. M., and J. C. McElwain. 2010. An explanation for conflicting records of Triassic–Jurassic plant diversity. PNAS Early Edition, www.pnas.org/cgi/doi/10.1073/pnas.1004207107. Suppl.files at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1004207107/-/DCSupplemental.
Abstract - Macrofossils (mostly leaves) and sporomorphs (pollen and spores) preserve conflicting records of plant biodiversity during the end-Permian (P-Tr), Triassic–Jurassic (Tr-J), and end-Cretaceous (K-T) mass extinctions. Estimates of diversity loss based on macrofossils are typically much higher than estimates of diversity loss based on sporomorphs. Macrofossils from the Tr-J of East Greenland indicate that standing species richness declined by as much as 85% in the Late Triassic, whereas sporomorph records from the same region, and from elsewhere in Europe, reveal little evidence of such catastrophic diversity loss. To understand this major discrepancy, we have used a new high-resolution dataset of sporomorph assemblages from Astartekløft, East Greenland, to directly compare the macrofossil and sporomorph records of Tr-J plant biodiversity. Our results show that sporomorph assemblages from the Tr-J boundary interval are 10–12% less taxonomically diverse than sporomorph assemblages from the Late Triassic, and that vegetation composition changed rapidly in the boundary interval as a result of emigration and/or extirpation of taxa rather than immigration and/or origination of taxa. An analysis of the representation of different plant groups in the macrofossil and sporomorph records at Astartekløft reveals that reproductively specialized plants, including cycads, bennettites and the seed-fern Lepidopteris are almost absent from the sporomorph record. These results provide a means of reconciling the macrofossil and sporomorph records of Tr-J vegetation change, and may help to understand vegetation change during the P-Tr and K-T mass extinctions and around the Paleocene– Eocene Thermal Maximum.
Abstract - Macrofossils (mostly leaves) and sporomorphs (pollen and spores) preserve conflicting records of plant biodiversity during the end-Permian (P-Tr), Triassic–Jurassic (Tr-J), and end-Cretaceous (K-T) mass extinctions. Estimates of diversity loss based on macrofossils are typically much higher than estimates of diversity loss based on sporomorphs. Macrofossils from the Tr-J of East Greenland indicate that standing species richness declined by as much as 85% in the Late Triassic, whereas sporomorph records from the same region, and from elsewhere in Europe, reveal little evidence of such catastrophic diversity loss. To understand this major discrepancy, we have used a new high-resolution dataset of sporomorph assemblages from Astartekløft, East Greenland, to directly compare the macrofossil and sporomorph records of Tr-J plant biodiversity. Our results show that sporomorph assemblages from the Tr-J boundary interval are 10–12% less taxonomically diverse than sporomorph assemblages from the Late Triassic, and that vegetation composition changed rapidly in the boundary interval as a result of emigration and/or extirpation of taxa rather than immigration and/or origination of taxa. An analysis of the representation of different plant groups in the macrofossil and sporomorph records at Astartekløft reveals that reproductively specialized plants, including cycads, bennettites and the seed-fern Lepidopteris are almost absent from the sporomorph record. These results provide a means of reconciling the macrofossil and sporomorph records of Tr-J vegetation change, and may help to understand vegetation change during the P-Tr and K-T mass extinctions and around the Paleocene– Eocene Thermal Maximum.
The End-Triassic Extinction Event is Really Popular Right Now....
here is another new paper...
Paris, G., V. Beaumont, A. Bartolini, M.-E. Clémence, S. Gardin, and K. Page. 2010. Nitrogen isotope record of a perturbed paleoecosystem in the aftermath of the end-Triassic crisis, Doniford section, SW England, Geochemistry, Geophysics, Geosystems 11, Q08021, doi:10.1029/2010GC003161.
Abstract - The Triassic-Jurassic transition (TJ) is characterized by successive perturbations of the carbon cycle during a time of biotic disruption as recorded by the carbon isotopic composition of organic matter (δ13Corg). The nitrogen isotopic composition of sedimentary organic matter (δ15Norg) constitutes a key parameter to explore the functioning of the ecosystem during carbon cycle perturbations and biological crises, because it provide information on seawater redox conditions and/or nutrient cycling. Here we report the first continuous δ15Norg record across the TJ transition at the Doniford Bay section (Bristol Channel Basin, UK), combined with δ13Corg, kerogen typology and carbon (δ13Cmin) and oxygen (δ18Omin) isotopic composition of bulk carbonates. The end Triassic is characterized by a major negative excursion both in δ13Corg and δ13Cmin, very low TOC (Total Organic Carbon, wt%) and high δ15Norg values, associated with a sea level lowstand. A second δ13Corg negative excursion occurs during the lower Hettangian. This interval is characterized by phases of carbonate production increase alternated with phases of exceptional accumulations of type I organic matter (up to 12%) associated with lower δ15Norg and δ13Corg. This alternation likely reflects a succession of nutrient input increase to the basin leading to enhanced productivity and eutrophication, which promoted a primary production driven by organic-walled prokaryotic organisms. The following OM export increase generates anaerobic conditions within the basin. These events occur between periods of relatively good seawater column ventilation and nutrient recycling boosting the carbonate producer recovery. Ecosystems remain perturbed in the Bristol Channel Basin during the aftermath of the end-Triassic crisis.
Paris, G., V. Beaumont, A. Bartolini, M.-E. Clémence, S. Gardin, and K. Page. 2010. Nitrogen isotope record of a perturbed paleoecosystem in the aftermath of the end-Triassic crisis, Doniford section, SW England, Geochemistry, Geophysics, Geosystems 11, Q08021, doi:10.1029/2010GC003161.
Abstract - The Triassic-Jurassic transition (TJ) is characterized by successive perturbations of the carbon cycle during a time of biotic disruption as recorded by the carbon isotopic composition of organic matter (δ13Corg). The nitrogen isotopic composition of sedimentary organic matter (δ15Norg) constitutes a key parameter to explore the functioning of the ecosystem during carbon cycle perturbations and biological crises, because it provide information on seawater redox conditions and/or nutrient cycling. Here we report the first continuous δ15Norg record across the TJ transition at the Doniford Bay section (Bristol Channel Basin, UK), combined with δ13Corg, kerogen typology and carbon (δ13Cmin) and oxygen (δ18Omin) isotopic composition of bulk carbonates. The end Triassic is characterized by a major negative excursion both in δ13Corg and δ13Cmin, very low TOC (Total Organic Carbon, wt%) and high δ15Norg values, associated with a sea level lowstand. A second δ13Corg negative excursion occurs during the lower Hettangian. This interval is characterized by phases of carbonate production increase alternated with phases of exceptional accumulations of type I organic matter (up to 12%) associated with lower δ15Norg and δ13Corg. This alternation likely reflects a succession of nutrient input increase to the basin leading to enhanced productivity and eutrophication, which promoted a primary production driven by organic-walled prokaryotic organisms. The following OM export increase generates anaerobic conditions within the basin. These events occur between periods of relatively good seawater column ventilation and nutrient recycling boosting the carbonate producer recovery. Ecosystems remain perturbed in the Bristol Channel Basin during the aftermath of the end-Triassic crisis.
Increased fire activity at the Triassic/Jurassic Boundary Due to Climate Driven Floral Change
Belcher, C. M, Mander, L., Rein, G., Jervis, F. X., Haworth, M., Hesselbo, S. P., Glasspool, I. J., and J. C. McElwain. 2010. Increased fire activity at the Triassic/Jurassic boundary in Greenland due to climate-driven floral change. Nature Geoscience 3:426-429.
Abstract - One of the largest mass extinctions of the past 600 million years (Myr) occurred 200 Myr ago, at the Triassic/Jurassic boundary. The major floral and faunal turnovers have been linked to a marked increase in atmospheric carbon dioxide levels, probably resulting from massive volcanism in the Central Atlantic Magmatic Province. Future climate change predictions suggest that fire activity may increase, in part because higher global temperatures are thought to increase storminess. Here we use palaeontological reconstructions of the fossil flora from East Greenland to assess forest
flammability along with records of fossil charcoal preserved in the rocks to show that fire activity increased markedly across the Triassic/Jurassic boundary. We find a fivefold increase in the abundance of fossil charcoal in the earliest Jurassic, which we attribute to a climate-driven shift from a prevalence of broad-leaved taxa to a predominantly narrow leaved assemblage. Our fire calorimetry experiments show that narrow leaf morphologies are more flammable than broad leaved morphologies.We suggest that the warming associated with increased atmospheric carbon dioxide levels favoured a dominance of narrow-leaved plants, which, coupled with more frequent lightening strikes, led to an increase in fire activity at the Triassic/Jurassic boundary.
Abstract - One of the largest mass extinctions of the past 600 million years (Myr) occurred 200 Myr ago, at the Triassic/Jurassic boundary. The major floral and faunal turnovers have been linked to a marked increase in atmospheric carbon dioxide levels, probably resulting from massive volcanism in the Central Atlantic Magmatic Province. Future climate change predictions suggest that fire activity may increase, in part because higher global temperatures are thought to increase storminess. Here we use palaeontological reconstructions of the fossil flora from East Greenland to assess forest
flammability along with records of fossil charcoal preserved in the rocks to show that fire activity increased markedly across the Triassic/Jurassic boundary. We find a fivefold increase in the abundance of fossil charcoal in the earliest Jurassic, which we attribute to a climate-driven shift from a prevalence of broad-leaved taxa to a predominantly narrow leaved assemblage. Our fire calorimetry experiments show that narrow leaf morphologies are more flammable than broad leaved morphologies.We suggest that the warming associated with increased atmospheric carbon dioxide levels favoured a dominance of narrow-leaved plants, which, coupled with more frequent lightening strikes, led to an increase in fire activity at the Triassic/Jurassic boundary.
The Permian-Triassic Global Extinction Was Possibly Not Global
Hochuli, P. A., Os Vigran, J., Hermann, E., and H. Bucher. 2010. Multiple climatic changes around the Permian-Triassic boundary event revealed by an expanded palynological record from mid-Norway. Geological Society of America Bulletin 122:884-896. doi: 10.1130/B26551.1
Abstract - Here, we present the palynological record from two shallow core holes(6611/09-U-01 and -02) from the Trøndelag Platform offshore mid-Norway consisting of 750 m of Upper Permian and Lower Triassic sediments. The relatively homogeneous assemblages recovered from the Upper Permian deposits are dominated by gymnosperm pollen, mainly pteridosperms. At the base of the Griesbachian, numerous spore species appear in the record, leading to an increased diversity. The change at this boundary is also marked by the massive reduction of one group of pteridosperm pollen (Vittatina). Together with other typical Permianelements (e.g., Lueckisporites virkkiae), this group is rare but consistently present in the lower part of the Griesbachian, and it gradually disappears in its upper part. The distribution of other groups such as taeniate and non-taeniate bisaccate gymnosperm pollen (pterido sperms and conifers) shows no significant change across the boundary, whereas spores and other gymnosperm pollen increase in diversity and abundance. These changes coincide with the formational change between the Schuchert Dal Formation (Upper Permian) and the Wordie Creek Formation (Griesbachian) equivalents. Late Permian and Griesbachian palynomorph assemblages display different patterns. The former show a homogeneous composition of low diversity, whereas the latter reflect diverse and variably composed floras. The data suggest that the arid phase of the Late Permian was followed by a humid phase at the base of the Griesbachian. In the Griesbachian section, a succession of six distinct palynological assemblages (phase II–VII) can be inferred. Comparable changes have been described from East Greenland. The variations in the palynological record are interpreted to reflect changing ecological conditions (e.g., changing humidity). Comparable variations in the distribution of δ13C isotope values reported from various sections from Greenland and China, showing stable values during the Late Permian and highly variable values during the Griesbachian, suggest common causes for the observed fluctuations. Multiphase volcanic activity of the Siberian traps seems to be the most likely candidate to have caused the variations in the δ13C isotope as well as in the palynological record. In contrast to the common claim that marine and terrestrial biota both suffered a mass extinction related to the Permian- Triassic boundary event, the studied material from the Norwegian midlatitudinal sites shows no evidence for destruction of plant ecosystems. The presence of diverse microfloras of Griesbachian age supports the idea that the climate in this area allowed most plants to survive the Permian-Triassic boundary event.
Abstract - Here, we present the palynological record from two shallow core holes(6611/09-U-01 and -02) from the Trøndelag Platform offshore mid-Norway consisting of 750 m of Upper Permian and Lower Triassic sediments. The relatively homogeneous assemblages recovered from the Upper Permian deposits are dominated by gymnosperm pollen, mainly pteridosperms. At the base of the Griesbachian, numerous spore species appear in the record, leading to an increased diversity. The change at this boundary is also marked by the massive reduction of one group of pteridosperm pollen (Vittatina). Together with other typical Permianelements (e.g., Lueckisporites virkkiae), this group is rare but consistently present in the lower part of the Griesbachian, and it gradually disappears in its upper part. The distribution of other groups such as taeniate and non-taeniate bisaccate gymnosperm pollen (pterido sperms and conifers) shows no significant change across the boundary, whereas spores and other gymnosperm pollen increase in diversity and abundance. These changes coincide with the formational change between the Schuchert Dal Formation (Upper Permian) and the Wordie Creek Formation (Griesbachian) equivalents. Late Permian and Griesbachian palynomorph assemblages display different patterns. The former show a homogeneous composition of low diversity, whereas the latter reflect diverse and variably composed floras. The data suggest that the arid phase of the Late Permian was followed by a humid phase at the base of the Griesbachian. In the Griesbachian section, a succession of six distinct palynological assemblages (phase II–VII) can be inferred. Comparable changes have been described from East Greenland. The variations in the palynological record are interpreted to reflect changing ecological conditions (e.g., changing humidity). Comparable variations in the distribution of δ13C isotope values reported from various sections from Greenland and China, showing stable values during the Late Permian and highly variable values during the Griesbachian, suggest common causes for the observed fluctuations. Multiphase volcanic activity of the Siberian traps seems to be the most likely candidate to have caused the variations in the δ13C isotope as well as in the palynological record. In contrast to the common claim that marine and terrestrial biota both suffered a mass extinction related to the Permian- Triassic boundary event, the studied material from the Norwegian midlatitudinal sites shows no evidence for destruction of plant ecosystems. The presence of diverse microfloras of Griesbachian age supports the idea that the climate in this area allowed most plants to survive the Permian-Triassic boundary event.
No Permian-Triassic Boundary Tetrapod Fauna Preserved in South America
Modesto, S. P. and J. Botha-Brink. 2010. Problems of correlation of South African and South American tetrapod faunas across the Permian–Triassic boundary. Journal of South African Earth Sciences 57:242-248. doi:10.1016/j.jafrearsci.2009.08.004
Abstract - The best record of continental tetrapod faunas crossing the Permo–Triassic boundary (PTB) is found in the Karoo Basin of South Africa. Similar records are not known elsewhere among the former Gondwanan land masses, but it was recently proposed on the basis of palaeontological evidence that the Buena Vista Formation of Uruguay preserves a South American record of continental PTB tetrapods. The Buena Vista Formation was previously correlated to the Lower Triassic (Olenekian) Sanga do Cabral Formation of Brazil on the basis of lithostratigraphic evidence, but recent collecting in the former unit has produced a tetrapod fauna that is distinct to that documented for the latter. The unequivocal tetrapod fossils that have been described thus far from the Buena Vista Formation include indeterminate mastodonsaurid temnospondyls, a plagiosauroid temnospondyl, and a procolophonid reptile. The temnospondyls belong to Triassic groups, whereas the procolophonid is allied most closely with Early Triassic taxa from the Karoo Basin. We conclude that there is no compelling palaeontological evidence for placing any part of the Buena Vista Formation in the Permian. A precise placement of the Buena Vista Formation in the Triassic on the basis of its tetrapod fauna is not possible at this time. Accordingly, the Karoo Basin of South Africa remains the only Gondwanan basin that records a PTB tetrapod fauna.
Abstract - The best record of continental tetrapod faunas crossing the Permo–Triassic boundary (PTB) is found in the Karoo Basin of South Africa. Similar records are not known elsewhere among the former Gondwanan land masses, but it was recently proposed on the basis of palaeontological evidence that the Buena Vista Formation of Uruguay preserves a South American record of continental PTB tetrapods. The Buena Vista Formation was previously correlated to the Lower Triassic (Olenekian) Sanga do Cabral Formation of Brazil on the basis of lithostratigraphic evidence, but recent collecting in the former unit has produced a tetrapod fauna that is distinct to that documented for the latter. The unequivocal tetrapod fossils that have been described thus far from the Buena Vista Formation include indeterminate mastodonsaurid temnospondyls, a plagiosauroid temnospondyl, and a procolophonid reptile. The temnospondyls belong to Triassic groups, whereas the procolophonid is allied most closely with Early Triassic taxa from the Karoo Basin. We conclude that there is no compelling palaeontological evidence for placing any part of the Buena Vista Formation in the Permian. A precise placement of the Buena Vista Formation in the Triassic on the basis of its tetrapod fauna is not possible at this time. Accordingly, the Karoo Basin of South Africa remains the only Gondwanan basin that records a PTB tetrapod fauna.
Further Evidence for a Volcanic Eruption Cause for the End-Triassic Extinction
Whiteside, J. H., Olsen, P. E., Eglinton, T., Brookfield, M. E., and R. N. Sambrotto. 2010. Compound-specific carbon isotopes from Earth’s largest flood basalt eruptions directly linked to the end-Triassic mass extinction. PNAS Published online before print March 22, 2010, doi: 10.1073/pnas.1001706107
Abstract - A leading hypothesis explaining Phanerozoic mass extinctions and associated carbon isotopic anomalies is the emission of greenhouse, other gases, and aerosols caused by eruptions of continental flood basalt provinces. However, the necessary serial relationship between these eruptions, isotopic excursions, and extinctions has never been tested in geological sections preserving all three records. The end-Triassic extinction (ETE) at 201.4 Ma is among the largest of these extinctions and is tied to a large negative carbon isotope excursion, reflecting perturbations of the carbon cycle including a transient increase in CO2. The cause of the ETE has been inferred to be the eruption of the giant Central Atlantic magmatic province (CAMP). Here, we show that carbon isotopes of leaf wax derived lipids (n-alkanes), wood, and total organic carbon from two orbitally paced lacustrine sections interbedded with the CAMP in eastern North America show similar excursions to those seen in the mostly marine St. Audrie’s Bay section in England. Based on these results, the ETE began synchronously in marine and terrestrial environments slightly before the oldest basalts in eastern North America but simultaneous with the eruption of the oldest flows in Morocco, a CO2 super greenhouse, and marine biocalcification crisis. Because the temporal relationship between CAMP eruptions, mass extinction, and the carbon isotopic excursions are shown in the same place, this is the strongest case for a volcanic cause of a mass extinction to date.
Abstract - A leading hypothesis explaining Phanerozoic mass extinctions and associated carbon isotopic anomalies is the emission of greenhouse, other gases, and aerosols caused by eruptions of continental flood basalt provinces. However, the necessary serial relationship between these eruptions, isotopic excursions, and extinctions has never been tested in geological sections preserving all three records. The end-Triassic extinction (ETE) at 201.4 Ma is among the largest of these extinctions and is tied to a large negative carbon isotope excursion, reflecting perturbations of the carbon cycle including a transient increase in CO2. The cause of the ETE has been inferred to be the eruption of the giant Central Atlantic magmatic province (CAMP). Here, we show that carbon isotopes of leaf wax derived lipids (n-alkanes), wood, and total organic carbon from two orbitally paced lacustrine sections interbedded with the CAMP in eastern North America show similar excursions to those seen in the mostly marine St. Audrie’s Bay section in England. Based on these results, the ETE began synchronously in marine and terrestrial environments slightly before the oldest basalts in eastern North America but simultaneous with the eruption of the oldest flows in Morocco, a CO2 super greenhouse, and marine biocalcification crisis. Because the temporal relationship between CAMP eruptions, mass extinction, and the carbon isotopic excursions are shown in the same place, this is the strongest case for a volcanic cause of a mass extinction to date.
Sedimentary Organic Matter Characterization of the Triassic–Jurassic Boundary
Ruhl, M., Veld, H., and W.M. Kürschner. 2010. Sedimentary organic matter characterization of the Triassic–Jurassic boundary GSSP at Kuhjoch (Austria). Earth and Planetary Science Letters 292:17–26. doi:10.1016/j.epsl.2009.12.046
Abstract - The Triassic–Jurassic (T–J) boundary interval coincides with enhanced extinction rates in the marine realm and pronounced changes in terrestrial ecosystems on the continents. It is further marked by distinct negative excursions in the δ13Corg and 13Ccarb signature that may represent strong perturbations of the global carbon cycle. We present integrated geochemical, stable-isotope and palynological data from the Kuhjoch section, the Global boundary Stratotype Section and Point (GSSP) for the base of the Jurassic (Northern Calcareous Alps, Austria). We show that the initial carbon isotope excursion (CIE), coinciding with the marine extinction interval and the formation of black shales in the western Tethys Eiberg Basin, is marked by only minor changes in kerogen type, which is mainly of terrestrial origin. Increased Total Organic Carbon (TOC) concentrations of 9% at the first half of the initial CIE coincide with Hydrogen Index (HI) values of over 600 mg HC/g TOC. The high correlation (with R2=0.93) between HI values and terrestrial Cheirolepidiaceaen conifer pollen suggests a terrestrial source for the hydrogen enriched organic compounds. The lack of major changes in source of the sedimentary organic matter suggests that changes in the δ13Corg composition are genuine and represent true disturbances of the global C-cycle. The sudden decrease in total inorganic carbon (TIC) concentrations likely represents the onset of a biocalcification crisis. It coincides with a 4.5‰ negative shift in δ13Corg values and possibly corresponds to the onset of CAMP related volcanic activity. The second half of the initial CIE is marked by the dramatic increase of green algae remains in the sediment. The simultaneous increase of the Corg/Ntot ratio suggests increased marine primary production at the final stage of black shale formation.
Abstract - The Triassic–Jurassic (T–J) boundary interval coincides with enhanced extinction rates in the marine realm and pronounced changes in terrestrial ecosystems on the continents. It is further marked by distinct negative excursions in the δ13Corg and 13Ccarb signature that may represent strong perturbations of the global carbon cycle. We present integrated geochemical, stable-isotope and palynological data from the Kuhjoch section, the Global boundary Stratotype Section and Point (GSSP) for the base of the Jurassic (Northern Calcareous Alps, Austria). We show that the initial carbon isotope excursion (CIE), coinciding with the marine extinction interval and the formation of black shales in the western Tethys Eiberg Basin, is marked by only minor changes in kerogen type, which is mainly of terrestrial origin. Increased Total Organic Carbon (TOC) concentrations of 9% at the first half of the initial CIE coincide with Hydrogen Index (HI) values of over 600 mg HC/g TOC. The high correlation (with R2=0.93) between HI values and terrestrial Cheirolepidiaceaen conifer pollen suggests a terrestrial source for the hydrogen enriched organic compounds. The lack of major changes in source of the sedimentary organic matter suggests that changes in the δ13Corg composition are genuine and represent true disturbances of the global C-cycle. The sudden decrease in total inorganic carbon (TIC) concentrations likely represents the onset of a biocalcification crisis. It coincides with a 4.5‰ negative shift in δ13Corg values and possibly corresponds to the onset of CAMP related volcanic activity. The second half of the initial CIE is marked by the dramatic increase of green algae remains in the sediment. The simultaneous increase of the Corg/Ntot ratio suggests increased marine primary production at the final stage of black shale formation.
The Central Atlantic Magmatic Province and its Connection with the Triassic/Jurassic Extinction
The Central Atlantic magmatic province (CAMP) is a large igneous province formed during the breakup of Pangaea during the Mesozoic era. Rifting of North America from Europe and Africa (i.e., the open of the present day Atlantic Ocean) occurred during the Latest Triassic and or/ Earliest Jurassic and resulted in the emplacement of at least 10 million square kilometers of basalt in eastern North America, South America, Northern Africa, and Europe, the largest known igneous province in area of extent.
The CAMP is of significance because of its possible relationship with the Triassic/Jurassic boundary and thus a contributor to the Triassic/Jurassic extinction event. However, the exact timing of the event and whether or not it was a factor in extinction is highly debated with one group of workers arguing for it as a cause and another group denying this. Interestingly, support for or against the CAMP being a cause for the TR/J extinction depends on where the rocks are studied and dated. In Morocco the age of lava flows appears to coincide with the TR/J boundary (e.g., Marzoli et al., 2004, 2008; Verati et al., 2007), whereas in North America the flows appear to be too young (e.g., Whiteside et al, 2007, 2008).
A recent paper by Jourdan et al. (2009) provides new dates of CAMP deposits from North America and again argues for a causal effect on the end Triassic extinction (see the full abstract below), thus this issue is far from resolved.
You can read more on the CAMP at these websites:
http://en.wikipedia.org/wiki/Central_Atlantic_Magmatic_Province
http://www.auburn.edu/academic/science_math/res_area/geology/camp/
Jourdan, F., Marzoli A., Bertrand, H., S. Cirilli, S., Tanner, L.H., Kontak, D.J.,
McHone, G, Renne, P.R., and G. Bellieni. 2009. 40Ar/39Ar ages of CAMP in North America: Implications for the Triassic–Jurassic boundary and the 40K decay constant bias. Lithos 110:167-180. doi:10.1016/j.lithos.2008.12.011
ABSTRACT - The Central Atlantic magmatic province (CAMP) is one of the largest igneous provinces on Earth (greater than 10 million square km), spanning four continents. Recent high-precision 40Ar/39Ar dating of mineral separates has provided important constraints on the age, duration, and geodynamic history of CAMP. Yet the North American CAMP is strikingly under-represented in this dating effort.
Here we present 13 new statistically robust plateau, mini-plateau and isochron ages obtained on plagioclase and sericite separates from lava flows from the Fundy (n=10; Nova Scotia, Canada), Hartford and Deerfield (n=3; U.S.A.) basins. Ages mostly range from 198.6±1.1 to 201.0±1.4 Ma (2σ), with 1 date substantially younger at 190.6±1.0 Ma. Careful statistical regression shows that ages from the upper (199.7.0±1.5 Ma) and bottom (200.1±0.9 Ma) units of the lava pile in the Fundy basin are statistically indistinguishable, confirming a short duration of emplacement (≪1.6 Ma; ≤1 Ma). Three ages obtained on the Hartford (198.6±2.0 Ma and 199.8±1.1 Ma) and Deerfield (199.3±1.2 Ma) basins were measured on sericite from the upper lava flow units. We interpret these dates as reflecting syn-emplacement hydrothermal activity within these units. Collectively, CAMP ages gathered so far suggest a short duration of the main magmatic activity (2–3 Ma), but also suggest the possibility of a temporal migration of the active magmatic centers from north to south. Such a migration challenges a plume model that would postulate a radial outward migration of the magmatism and is more compatible with other models, such as the supercontinent global warming hypothesis. When compared to the age of the Triassic–Jurassic boundary, the filtered CAMP age database suggests that the onset of the magmatic activity precedes the limit by at least few hundred thousand years, thereby suggesting a causal relationship between CAMP and the end of Triassic mass extinction.
An age at 191 Ma possibly suggests a minor CAMP late tailing activity (190–194 Ma) which has been observed already for dykes and sills in Africa and Brazil. We speculate that, if genuine, this late activity can be due to a major extensional event, possibly heralding the oceanization process at ~190 Ma. Comparison between high quality U/Pb and 40Ar/39Ar ages of pegmatite lenses from the North Mountain basalts confirms a ~1% bias between the two chronometers. This discrepancy is likely attributed to the miscalibration of the 40K decay constants, in particular the electron capture branch.
REFERENCES
Marzoli, A., Bertrand, H., Knight, K.B., Cirilli, S., Buratti, N., Vérati, C., Nomade, S., Renne, P.R., Youbi, N., Martini, R., Allenbach, K., Neuwerth, R., Rapaille, C., Zaninetti, L., and G. Bellieni. 2004. Synchrony of the Central Atlantic magmatic province and the Triassic-Jurassic boundary climatic and biotic crisis. Geology 32:973–976. doi: 10.1130/G20652.1
Marzoli, A., Bertrand, H., Knight, K., Cirilli, S., Nomade, S., Renne, P.R., Verati, C., Youbi, N., Martini, R., and G. Bellieni. 2008. Synchrony between the Central Atlantic magmatic province and the Triassic–Jurassic mass-extinction event? Comment. Palaeogeography, Palaeoclimatology, Palaeoecology 262, 189–193. doi:10.1016/j.palaeo.2008.01.016
Verati, C., Rapaille, C., Féraud, G., Marzoli, A., Bertrand, H., and N. Youbi. 2007. Timing the Tr–J boundary: further constraints on duration and age of the CAMP volcanism recorded in Morocco and Portugal. Palaeogeography Palaeoclimatology Palaeoecology 246. doi:10.1016/j.palaeo.2006.06.033
Whiteside, J.H., Olsen, P.E., Kent, D.V., Fowell, S.J., and M. Et-Touhami. 2007. Synchrony between the Central Atlantic magmatic province and the Triassic-Jurassic mass-extinction event? Palaeogeography, Palaeoclimatology, Palaeoecology 244:345-367. doi:10.1016/j.palaeo.2006.06.035
Whiteside, J.H., Olsen, P.E., Kent, D.V., Fowell, S.J., and M. Et-Touhami. 2008. Synchrony between the Central Atlantic magmatic province and the Triassic–Jurassic mass-extinction event? Reply to Marzoli et al. Palaeogeography,Palaeoclimatology, Palaeoecology 262, 194–198. doi:10.1016/j.palaeo.2008.02.010
Graphic is from here.
The CAMP is of significance because of its possible relationship with the Triassic/Jurassic boundary and thus a contributor to the Triassic/Jurassic extinction event. However, the exact timing of the event and whether or not it was a factor in extinction is highly debated with one group of workers arguing for it as a cause and another group denying this. Interestingly, support for or against the CAMP being a cause for the TR/J extinction depends on where the rocks are studied and dated. In Morocco the age of lava flows appears to coincide with the TR/J boundary (e.g., Marzoli et al., 2004, 2008; Verati et al., 2007), whereas in North America the flows appear to be too young (e.g., Whiteside et al, 2007, 2008).
A recent paper by Jourdan et al. (2009) provides new dates of CAMP deposits from North America and again argues for a causal effect on the end Triassic extinction (see the full abstract below), thus this issue is far from resolved.
You can read more on the CAMP at these websites:
http://en.wikipedia.org/wiki/Central_Atlantic_Magmatic_Province
http://www.auburn.edu/academic/science_math/res_area/geology/camp/
Jourdan, F., Marzoli A., Bertrand, H., S. Cirilli, S., Tanner, L.H., Kontak, D.J.,
McHone, G, Renne, P.R., and G. Bellieni. 2009. 40Ar/39Ar ages of CAMP in North America: Implications for the Triassic–Jurassic boundary and the 40K decay constant bias. Lithos 110:167-180. doi:10.1016/j.lithos.2008.12.011
ABSTRACT - The Central Atlantic magmatic province (CAMP) is one of the largest igneous provinces on Earth (greater than 10 million square km), spanning four continents. Recent high-precision 40Ar/39Ar dating of mineral separates has provided important constraints on the age, duration, and geodynamic history of CAMP. Yet the North American CAMP is strikingly under-represented in this dating effort.
Here we present 13 new statistically robust plateau, mini-plateau and isochron ages obtained on plagioclase and sericite separates from lava flows from the Fundy (n=10; Nova Scotia, Canada), Hartford and Deerfield (n=3; U.S.A.) basins. Ages mostly range from 198.6±1.1 to 201.0±1.4 Ma (2σ), with 1 date substantially younger at 190.6±1.0 Ma. Careful statistical regression shows that ages from the upper (199.7.0±1.5 Ma) and bottom (200.1±0.9 Ma) units of the lava pile in the Fundy basin are statistically indistinguishable, confirming a short duration of emplacement (≪1.6 Ma; ≤1 Ma). Three ages obtained on the Hartford (198.6±2.0 Ma and 199.8±1.1 Ma) and Deerfield (199.3±1.2 Ma) basins were measured on sericite from the upper lava flow units. We interpret these dates as reflecting syn-emplacement hydrothermal activity within these units. Collectively, CAMP ages gathered so far suggest a short duration of the main magmatic activity (2–3 Ma), but also suggest the possibility of a temporal migration of the active magmatic centers from north to south. Such a migration challenges a plume model that would postulate a radial outward migration of the magmatism and is more compatible with other models, such as the supercontinent global warming hypothesis. When compared to the age of the Triassic–Jurassic boundary, the filtered CAMP age database suggests that the onset of the magmatic activity precedes the limit by at least few hundred thousand years, thereby suggesting a causal relationship between CAMP and the end of Triassic mass extinction.
An age at 191 Ma possibly suggests a minor CAMP late tailing activity (190–194 Ma) which has been observed already for dykes and sills in Africa and Brazil. We speculate that, if genuine, this late activity can be due to a major extensional event, possibly heralding the oceanization process at ~190 Ma. Comparison between high quality U/Pb and 40Ar/39Ar ages of pegmatite lenses from the North Mountain basalts confirms a ~1% bias between the two chronometers. This discrepancy is likely attributed to the miscalibration of the 40K decay constants, in particular the electron capture branch.
REFERENCES
Marzoli, A., Bertrand, H., Knight, K.B., Cirilli, S., Buratti, N., Vérati, C., Nomade, S., Renne, P.R., Youbi, N., Martini, R., Allenbach, K., Neuwerth, R., Rapaille, C., Zaninetti, L., and G. Bellieni. 2004. Synchrony of the Central Atlantic magmatic province and the Triassic-Jurassic boundary climatic and biotic crisis. Geology 32:973–976. doi: 10.1130/G20652.1
Marzoli, A., Bertrand, H., Knight, K., Cirilli, S., Nomade, S., Renne, P.R., Verati, C., Youbi, N., Martini, R., and G. Bellieni. 2008. Synchrony between the Central Atlantic magmatic province and the Triassic–Jurassic mass-extinction event? Comment. Palaeogeography, Palaeoclimatology, Palaeoecology 262, 189–193. doi:10.1016/j.palaeo.2008.01.016
Verati, C., Rapaille, C., Féraud, G., Marzoli, A., Bertrand, H., and N. Youbi. 2007. Timing the Tr–J boundary: further constraints on duration and age of the CAMP volcanism recorded in Morocco and Portugal. Palaeogeography Palaeoclimatology Palaeoecology 246. doi:10.1016/j.palaeo.2006.06.033
Whiteside, J.H., Olsen, P.E., Kent, D.V., Fowell, S.J., and M. Et-Touhami. 2007. Synchrony between the Central Atlantic magmatic province and the Triassic-Jurassic mass-extinction event? Palaeogeography, Palaeoclimatology, Palaeoecology 244:345-367. doi:10.1016/j.palaeo.2006.06.035
Whiteside, J.H., Olsen, P.E., Kent, D.V., Fowell, S.J., and M. Et-Touhami. 2008. Synchrony between the Central Atlantic magmatic province and the Triassic–Jurassic mass-extinction event? Reply to Marzoli et al. Palaeogeography,Palaeoclimatology, Palaeoecology 262, 194–198. doi:10.1016/j.palaeo.2008.02.010
Graphic is from here.
What Do We Really Know About Anything?
Wow. Stratigraphy and vertebrate biochronology are tricky fields, especially when they are the basis for determination of the timing of major historical events such as mass extinctions. Erroneous correlation can really skew our hypotheses such as the example from the paper below (the Permian-Triassic terrestrial extinction event in South Africa) or in a case more relevent to myself, whether or not the two major Chinle faunal assemblages (Adamanian and Revueltian) are distinct or overlap (see discussion at Paleo Errata). The Karoo case is intriguing to me as I just finally read Peter Ward's book "Gorgon" a few months back, which detailed the discovery of the postulated extinction interval. As with the Petrified Forest case, vertebrate biostratigraphy data are only as good as the stratigraphic framework upon which they are built. And again an idea that was thought to be pretty well established and supported must be reexamined in light of new data or a new reinterpretation of existing data. As exciting as this seems it is sometimes a nightmare for the non-specialist who is just trying to keep up (especially when they are using this material to teach classes). My own specialist fields (aetosaurs, Chinle Formation)have changed so much, I wonder what do we really know for certain? What are the data really telling us? And how premature are we being when we publish ideas? What is still out there for us to find and what ideas will these new finds turn on their heads next? Of course this is why I find science absolutely thrilling....and why it is so important for us to continue to test ideas (and allow others to test our own).
R. A. Gastaldo, J. Neveling, C. K. Clark, S. S. Newbury (2009). The terrestrial Permian-Triassic boundary event bed is a nonevent Geology, 37 (3), 199-202 DOI: 10.1130/G25255A.1
ABSTRACT - A unique isochronous interval in the Karoo Basin, South Africa, previously has been interpreted to postdate vertebrate extinction at the Permian-Triassic boundary in the Bethulie area, Lootsberg Pass, and elsewhere. It is demonstrated that the laminated beds, or laminites, in the Bethulie region are stratigraphically indistinct. The heterolithic interval exposed on the Heldenmoed farm is ~8 m below the Bethel farm section, <1 km away. At Lootsberg Pass, the laminated interval is below the Permian-Triassic boundary as defined by vertebrate biostratigraphy, rather than overlying it. Hence, this interval, critical to models of end-Permian mass extinction, is neither isochronous across the basin nor unique. Rather, the lithofacies represents avulsion channel-fill deposits within aggradational landscapes. South African models for the response of terrestrial ecosystems to the perturbation in the marine realm require critical reevaluation.
R. A. Gastaldo, J. Neveling, C. K. Clark, S. S. Newbury (2009). The terrestrial Permian-Triassic boundary event bed is a nonevent Geology, 37 (3), 199-202 DOI: 10.1130/G25255A.1
ABSTRACT - A unique isochronous interval in the Karoo Basin, South Africa, previously has been interpreted to postdate vertebrate extinction at the Permian-Triassic boundary in the Bethulie area, Lootsberg Pass, and elsewhere. It is demonstrated that the laminated beds, or laminites, in the Bethulie region are stratigraphically indistinct. The heterolithic interval exposed on the Heldenmoed farm is ~8 m below the Bethel farm section, <1 km away. At Lootsberg Pass, the laminated interval is below the Permian-Triassic boundary as defined by vertebrate biostratigraphy, rather than overlying it. Hence, this interval, critical to models of end-Permian mass extinction, is neither isochronous across the basin nor unique. Rather, the lithofacies represents avulsion channel-fill deposits within aggradational landscapes. South African models for the response of terrestrial ecosystems to the perturbation in the marine realm require critical reevaluation.
What exactly is going on with the dinosaurs in the Early Jurassic?
It is considered by some to be, and should have been, a classic example of adaptive radiation. At the end of the Triassic the majority of pseudosuchians go extinct, removing the biggest competitors of the dinosaurs and leaving the door open for an evolutionary explosion of the dinosaurs. Interestingly, however, this is not what happened according to a new study by Steve Brusatte and colleagues (Brusatte et al., 2008b) who found, in the continuation of their research comparing morphospace disparity between ornithidirans and pseudosuchians (Brusatte et al., 2008a), that dinosaur disparity remained relatively unchanged through the Triassic/Jurassic boundary. It would be expected that once the extinction of the pseudosuchians freed up a large amount of morphospace, the dinosaur record (with whom the pseudosuchians occupied a lot of the same niches and had similar body plans) would show a strong response, yet the dinosaurs show only a "slight non-significant increase" (Brusatte et al., 2008b). Thus, these authors argue, "different aspects of dinosaur radiation (diversity, disparity, and abundance) were decoupled, and the overall macroevolutionary pattern of the first 50 Myr of dinosaur evolution is more complex than often considered (Brusatte et al., 2008b).
Adam Yates had discussed this (and his hypothesis) a few weeks ago at Dracovenator and I had provided some follow-up discussion here. Nonetheless, despite the timing of the extinction it is apparent that not to much is going on for the dinosaurs immediately after the TR/J extinction (which by the way took out the non-dinosaurian dinosauromorphs). Sure to the record of coelophysoids and sauropodomorphs you add a few large theropods such as Dilophosaurus and you see the first good records of heterodontosaurids and the earliest thyreophorans (including the first ornithischians and sauropodomorphs in N. America), but you do not see a true explosion of dinosaur diversity until you get to the Late Jurassic. How much of this is a sampling and/or preservation problem is unclear, but simply look at the Weishampel et al. (2004) chapter on dinosaur distribution in the 2nd edition of The Dinosauria and compare the faunal lists for these epochs. You really have to clean up the Late Triassic portion removing many of the Ornithischia references, indeterminate theropods (could be shuvosaurids), and all of the footprint evidence (no ornithischian or sauropodomorph tracks in N. America; the "theropod" tracks worldwide could be made by convergent dinosauriforms, and pseudosuchians), not to mention the really messed up stratigraphy for the Chinle and Dockum which caused some duplicate entries. Now compare the Late Triassic, Early Jurassic, and Middle Jurassic lists to the rest of the chapter. Surprised? I commend Brusatte et al. (2008a, 2008b) for setting the stage and providing a baseline framework for some much needed future research to address this enigma.
REFERENCES
Brusatte, S.L., Benton, M.J., Ruta, M., and G.T. Lloyd. 2008a. Superiority, competition, and opportunism in the evolutionary radiation of dinosaurs. Science 321:1485-1488.
Brusatte, S.L., Benton, M.J., Ruta, M., and G.T. Lloyd. 2008b. The first 50 Myr of dinosaur evolution: macroevolutionary pattern and morphological disparity. Biology Letters, doi:10.1098/rsbl.2008.0441, published online.
Weishampel, D. B., Barrett, P. M., Coria, R. E., Le Loeuff, J., Gomani, E. S., Zhao Z., Xu X., Sahni, A., and C. Noto. 2004. Dinosaur distribution. In: Weishampel, D. B., Dodson, P., and Osmólska, H. eds. The Dinosauria. 2nd edition. Univ. California Press, Berkeley. pp. 517-606.
Adam Yates had discussed this (and his hypothesis) a few weeks ago at Dracovenator and I had provided some follow-up discussion here. Nonetheless, despite the timing of the extinction it is apparent that not to much is going on for the dinosaurs immediately after the TR/J extinction (which by the way took out the non-dinosaurian dinosauromorphs). Sure to the record of coelophysoids and sauropodomorphs you add a few large theropods such as Dilophosaurus and you see the first good records of heterodontosaurids and the earliest thyreophorans (including the first ornithischians and sauropodomorphs in N. America), but you do not see a true explosion of dinosaur diversity until you get to the Late Jurassic. How much of this is a sampling and/or preservation problem is unclear, but simply look at the Weishampel et al. (2004) chapter on dinosaur distribution in the 2nd edition of The Dinosauria and compare the faunal lists for these epochs. You really have to clean up the Late Triassic portion removing many of the Ornithischia references, indeterminate theropods (could be shuvosaurids), and all of the footprint evidence (no ornithischian or sauropodomorph tracks in N. America; the "theropod" tracks worldwide could be made by convergent dinosauriforms, and pseudosuchians), not to mention the really messed up stratigraphy for the Chinle and Dockum which caused some duplicate entries. Now compare the Late Triassic, Early Jurassic, and Middle Jurassic lists to the rest of the chapter. Surprised? I commend Brusatte et al. (2008a, 2008b) for setting the stage and providing a baseline framework for some much needed future research to address this enigma.
REFERENCES
Brusatte, S.L., Benton, M.J., Ruta, M., and G.T. Lloyd. 2008a. Superiority, competition, and opportunism in the evolutionary radiation of dinosaurs. Science 321:1485-1488.
Brusatte, S.L., Benton, M.J., Ruta, M., and G.T. Lloyd. 2008b. The first 50 Myr of dinosaur evolution: macroevolutionary pattern and morphological disparity. Biology Letters, doi:10.1098/rsbl.2008.0441, published online.
Weishampel, D. B., Barrett, P. M., Coria, R. E., Le Loeuff, J., Gomani, E. S., Zhao Z., Xu X., Sahni, A., and C. Noto. 2004. Dinosaur distribution. In: Weishampel, D. B., Dodson, P., and Osmólska, H. eds. The Dinosauria. 2nd edition. Univ. California Press, Berkeley. pp. 517-606.
Dinosauria vs. Pseudosuchia - New paper in Science
Very recently there has been a resurgence of interest in the early appearance and diversification of the Dinosauria mainly due to the recognition that there exists strong convergence between early dinosaurs and pseudosuchian archosaurs such as Revueltosaurus and Shuvosaurus, and that dinosaur precursors such as Dromomeron and Silesaurus not only survived into the Late Triassic but also coexisted with the dinosaurs for millions of years (Dzik, 2003; Ezcurra, 2006; Irmis et al. 2007b; Nesbitt et al., 2007; Parker et al., 2005; Nesbitt and Norell, 2006). This has been accompanied by studies demonstrating that in some faunas (especially those of North America) dinosaurs were neither dominant or diverse, and that in fact there is no unambiguous evidence of Triassic ornithischians or sauropodomorphs in North America, and that the global record of Triassic ornithischians is extremely poor (Irmis et al., 2007a; Nesbitt et al., 2007). These and other studies have also demonstrated that Late Triassic pseudosuchians were extremely diverse and that their occurrence together with ornithodirans in most Late Triassic assemblages demonstrates that they were filling similar ecological roles. Thus, one of the biggest mysteries is why the majority of pseudosuchian lineages die out at the end of the Triassic, while the more conservative dinosaurs go on to have great success for the next 140 million years.
Today in the new issue of Science, Brusatte et al. provide the results of a multifaceted study addressing this question. They provide a new phylogenetic analysis of the Archosauria (supplementary materials) and compare evolutionary rates and morphological disparity between pseudosuchians and ornithodirans. Interestingly they found that the dinosaurs had lower disparity and represented a lesser amount of morphospace occupation compared to the pseudosuchians. Furthermore rates of character evolution between the two groups were indistinguishable. Previous hypotheses that the dinosaurs were more successful due to physiological superiority and were “preordained for success” are discounted (as was also argued by Irmis et al., 2007b). Instead Brusatte et al., suggest that the “dinosaurs were the beneficiaries of two mass extinction events – and some good luck”.
I admit that I am not surprised at all by their findings, but am probably biased because this trend is readily apparent in North America (where I work) where with the exception of the Hayden and Coelophysis Quarries at Ghost Ranch New Mexico (and trackways in the youngest Triassic units) there is a marked paucity of Triassic dinosaur fossils and an abundance of diverse pseudosuchians. I am a bit flummoxed over the basal positioning of Revueltosaurus in their phylogeny, but this is based on an incomplete coding which I have not thoroughly reviewed.
Overall I find the paper to be a useful contribution in the attempt to discern why such a wonderful diversity of crocodile-line archosaurs lineages was extinguished at the end Triassic. Their data helps quantify some of the trends seen by other workers, especially that the competition model is most likely untenable. However, disproving the competition scenario does not necessarily support the "lucky break" hypothesis. Furthermore, I have not seen strong evidence for a Carnian-Norian terrestrial extinction in the fossil record, a claim that is even more weakened by the recent announcement of a Rhaetian dicynodont, which supports known Norian dicynodonts in Arizona and rhynchosaurs in Brazil and Argentina. Recent published and unpublished studies revising the Late Triassic timescale demonstrate that much of the hypothesized Carnian terrestrial strata worldwide is probably actually Norian, thus at best there are very few Carnian age terrestrial assemblages (e.g., Muttoni et al., 2004; Furin et al., 2004). There is still much work to be done on this mystery and I for one am not quite ready yet to simply attribute it a “lucky break”; however if this is the case then I truly rue what would appear to be a cruel twist of fate, and can only wonder what might have come to pass if the pendulum had swung the other way.
REFERENCES
Brusatte, S.L., Benton, M.J., Ruta, M., and G.T. Lloyd. 2008. Superiority, competition, and opportunism in the evolutionary radiation of dinosaurs. Science 321:1485-1488.
Dzik, J. A beaked herbivorous archosaurs with dinosaur affinities from the early Late Triassic of Poland. Journal of Vertebrate Paleontology 23:556-574.
Ezcurra, M.D. 2007. A review of the systematic position of the dinosauriform archosaur Eucoelophysis baldwini Sullivan & Lucas, 1999 from the Upper Triassic of New Mexico, USA. Geodiversitas 28:649-684.
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.
Irmis, R.B., Parker, W.G., Nesbitt, S.J., and J. Liu, 2007a. Early ornithischian dinosaurs: the Triassic Record. Historical Biology 19:3-22.
Irmis, R.B., Nesbitt, S.J., Padian, K., Smith, N.D., Turner, A.H., Woody, D., and A. Downs. 2007b. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science 317:358-361.
Muttoni, G., Kent, D. V., Olsen, P. E., DiStefano, P., Lowrie, W., Bernasconi, S. M., and F. M. Hernández. 2004. Tethyan magnetostratigraphy from Pizzo Mondello (Sicily) and correlation to the Late Triassic Newark astrochronological polarity timescale. Geological Society of America Bulletin 116:1043-1058.
Nesbitt, S.J, and M.A. Norell. 2006. Extreme convergence in the body plans of an
early suchian (Archosauria) and ornithomimid dinosaurs (Theropoda). Proceedings of the Royal Society of London Series B 273: 1045–1048.
Nesbitt, S.J., Irmis, R.B., and W.G. Parker, 2007. A critical reevaluation of the Late Triassic dinosaur taxa of North America. Journal of Systematic Palaeontology 5:209-243.
Parker, W.G., Irmis, R.B., Nesbitt, S.N., Martz, J. W., and L. S. Browne, 2005. The pseudosuchian Revueltosaurus callenderi and its implications for the diversity of early ornithischian dinosaurs. Proceedings of the Royal Society London B 272:963-969.
Today in the new issue of Science, Brusatte et al. provide the results of a multifaceted study addressing this question. They provide a new phylogenetic analysis of the Archosauria (supplementary materials) and compare evolutionary rates and morphological disparity between pseudosuchians and ornithodirans. Interestingly they found that the dinosaurs had lower disparity and represented a lesser amount of morphospace occupation compared to the pseudosuchians. Furthermore rates of character evolution between the two groups were indistinguishable. Previous hypotheses that the dinosaurs were more successful due to physiological superiority and were “preordained for success” are discounted (as was also argued by Irmis et al., 2007b). Instead Brusatte et al., suggest that the “dinosaurs were the beneficiaries of two mass extinction events – and some good luck”.
I admit that I am not surprised at all by their findings, but am probably biased because this trend is readily apparent in North America (where I work) where with the exception of the Hayden and Coelophysis Quarries at Ghost Ranch New Mexico (and trackways in the youngest Triassic units) there is a marked paucity of Triassic dinosaur fossils and an abundance of diverse pseudosuchians. I am a bit flummoxed over the basal positioning of Revueltosaurus in their phylogeny, but this is based on an incomplete coding which I have not thoroughly reviewed.
Overall I find the paper to be a useful contribution in the attempt to discern why such a wonderful diversity of crocodile-line archosaurs lineages was extinguished at the end Triassic. Their data helps quantify some of the trends seen by other workers, especially that the competition model is most likely untenable. However, disproving the competition scenario does not necessarily support the "lucky break" hypothesis. Furthermore, I have not seen strong evidence for a Carnian-Norian terrestrial extinction in the fossil record, a claim that is even more weakened by the recent announcement of a Rhaetian dicynodont, which supports known Norian dicynodonts in Arizona and rhynchosaurs in Brazil and Argentina. Recent published and unpublished studies revising the Late Triassic timescale demonstrate that much of the hypothesized Carnian terrestrial strata worldwide is probably actually Norian, thus at best there are very few Carnian age terrestrial assemblages (e.g., Muttoni et al., 2004; Furin et al., 2004). There is still much work to be done on this mystery and I for one am not quite ready yet to simply attribute it a “lucky break”; however if this is the case then I truly rue what would appear to be a cruel twist of fate, and can only wonder what might have come to pass if the pendulum had swung the other way.
REFERENCES
Brusatte, S.L., Benton, M.J., Ruta, M., and G.T. Lloyd. 2008. Superiority, competition, and opportunism in the evolutionary radiation of dinosaurs. Science 321:1485-1488.
Dzik, J. A beaked herbivorous archosaurs with dinosaur affinities from the early Late Triassic of Poland. Journal of Vertebrate Paleontology 23:556-574.
Ezcurra, M.D. 2007. A review of the systematic position of the dinosauriform archosaur Eucoelophysis baldwini Sullivan & Lucas, 1999 from the Upper Triassic of New Mexico, USA. Geodiversitas 28:649-684.
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.
Irmis, R.B., Parker, W.G., Nesbitt, S.J., and J. Liu, 2007a. Early ornithischian dinosaurs: the Triassic Record. Historical Biology 19:3-22.
Irmis, R.B., Nesbitt, S.J., Padian, K., Smith, N.D., Turner, A.H., Woody, D., and A. Downs. 2007b. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science 317:358-361.
Muttoni, G., Kent, D. V., Olsen, P. E., DiStefano, P., Lowrie, W., Bernasconi, S. M., and F. M. Hernández. 2004. Tethyan magnetostratigraphy from Pizzo Mondello (Sicily) and correlation to the Late Triassic Newark astrochronological polarity timescale. Geological Society of America Bulletin 116:1043-1058.
Nesbitt, S.J, and M.A. Norell. 2006. Extreme convergence in the body plans of an
early suchian (Archosauria) and ornithomimid dinosaurs (Theropoda). Proceedings of the Royal Society of London Series B 273: 1045–1048.
Nesbitt, S.J., Irmis, R.B., and W.G. Parker, 2007. A critical reevaluation of the Late Triassic dinosaur taxa of North America. Journal of Systematic Palaeontology 5:209-243.
Parker, W.G., Irmis, R.B., Nesbitt, S.N., Martz, J. W., and L. S. Browne, 2005. The pseudosuchian Revueltosaurus callenderi and its implications for the diversity of early ornithischian dinosaurs. Proceedings of the Royal Society London B 272:963-969.
The TR-J Terrestrial Extinction Actually Early Jurassic?
Adam Yates most recent post over at Dracovenator and a new abstract by Zeigler and Geissman has got me thinking more about faunal transitions between the Late Triassic and Middle Jurassic. As I stated in an earlier post, Chinle Formation faunal composition remains relatively consistent from the oldest to youngest localities and it is not until you get into the uppermost units of the formation and higher that you start to see some changes. Lucas and Tanner (2007) provides a good documentation of faunal change in the western U.S.A. through this interval and demonstrates that the lowermost Dinosaur Canyon Member (Moenave Formation) and the basal portion of the Wingate Sandstone (both units previously argued to be Jurassic in age and in the Glen Canyon Group) are most likely latest Triassic in age. This is based several lines of evidence including magnetostratigraphy, lithostratigraphic correlation, and biostratigraphy (the presence of phytosaur body fossils and pseudosuchian trace fossils). The upper Moenave, upper Wingate, and the Kayenta Formation lack these fossils. In addition, Lucas and Tanner (2007) place the youngest known Chinle Formation fossil assemblage (the Ghost Ranch Coelophysis Quarry) in the Rock Point Member, which they consider to be laterally equivalent to the base of the Wingate and the lower Dinosaur Canyon Member. They also consider this assemblage to be latest Norian in age based on palynology and the presence of the aetosaur Aetosaurus.
Zeigler and Geissman (2008) argue that based on magnetostratigraphy that the Ghost Ranch Coelophysis Quarry is not in the Rock Point and that it may be even younger than previously supposed. As I have noted previously, Zeigler (2008) correlates the site (using magnetostratigraphy) with the lower Moenave and now Zeigler and Geissman (2008) suggest that the uppermost Chinle Formation is at least Rhaetian and may even be Hettangian in age! This would extend the range of phytosaurs and other non-crocodylomorph pseudosuchians into the Early Jurassic. Thus there would be no terrestrial Triassic/Jurassic extinction, at least not in western North America.
Furthermore, Adam Yates recent post suggests that there may have been an end Early Jurassic extinction that spelled the end of coelophysoids and basal sauropodomorphs, followed by the rise of tetanurans and eusauropods in the Middle Jurassic. If Zeigler and Geissman and Yates are correct there would have been two major faunal turnovers in the very short period of time (approx. 30 million years) encompassing the Early Jurassic. In the earliest Jurassic we would see the disappearance of non-crocodylomorph pseudosuchians and the rise of a dinosaur dominated fauna, including the first basal sauropodomorphs in North America (which are not found in the Late Triassic of that continent*). Approximately 24 million years later we get the Early-Middle Jurassic turnover discussed by Yates and an explosion in dinosaurian diversity. Very interesting and the reason why research on the vertebrate fossil record of the lower Glen Canyon Group in becoming very important and needs to be expanded.
*Note: the only purported evidence of Late Triassic sauropodomorphs in North America are the ichnotaxa Tetrasauropus and Pseudotetrasauropus (e.g., Lucas and Tanner, 2007); however, Rainforth (2003) has determined that these taxa probably represent tracks made by pseudosuchians.
REFERENCES
Lucas, S.G., and L.H. Tanner. 2007. Tetrapod biostratigraphy and biochronology of the Triassic–Jurassic transition on the southern Colorado Plateau, USA. Palaeogeography, Palaeoclimatology, Palaeoecology 244:242–256.
Rainforth, E.C. 2003. Revision and re-evaluation of the Early Jurassic dinosaurian ichnogenus Otozoum. Palaeontology 46, 803–838.
Zeigler, K.E., and J.W. Geissman. 2008. Magnetostratigraphy of the Upper Triassic Chinle Group and Implications for the Age and Correlation of Upper Triassic Strata in North America. Geological Society of America Abstracts with programs (online).
Zeigler and Geissman (2008) argue that based on magnetostratigraphy that the Ghost Ranch Coelophysis Quarry is not in the Rock Point and that it may be even younger than previously supposed. As I have noted previously, Zeigler (2008) correlates the site (using magnetostratigraphy) with the lower Moenave and now Zeigler and Geissman (2008) suggest that the uppermost Chinle Formation is at least Rhaetian and may even be Hettangian in age! This would extend the range of phytosaurs and other non-crocodylomorph pseudosuchians into the Early Jurassic. Thus there would be no terrestrial Triassic/Jurassic extinction, at least not in western North America.
Furthermore, Adam Yates recent post suggests that there may have been an end Early Jurassic extinction that spelled the end of coelophysoids and basal sauropodomorphs, followed by the rise of tetanurans and eusauropods in the Middle Jurassic. If Zeigler and Geissman and Yates are correct there would have been two major faunal turnovers in the very short period of time (approx. 30 million years) encompassing the Early Jurassic. In the earliest Jurassic we would see the disappearance of non-crocodylomorph pseudosuchians and the rise of a dinosaur dominated fauna, including the first basal sauropodomorphs in North America (which are not found in the Late Triassic of that continent*). Approximately 24 million years later we get the Early-Middle Jurassic turnover discussed by Yates and an explosion in dinosaurian diversity. Very interesting and the reason why research on the vertebrate fossil record of the lower Glen Canyon Group in becoming very important and needs to be expanded.
*Note: the only purported evidence of Late Triassic sauropodomorphs in North America are the ichnotaxa Tetrasauropus and Pseudotetrasauropus (e.g., Lucas and Tanner, 2007); however, Rainforth (2003) has determined that these taxa probably represent tracks made by pseudosuchians.
REFERENCES
Lucas, S.G., and L.H. Tanner. 2007. Tetrapod biostratigraphy and biochronology of the Triassic–Jurassic transition on the southern Colorado Plateau, USA. Palaeogeography, Palaeoclimatology, Palaeoecology 244:242–256.
Rainforth, E.C. 2003. Revision and re-evaluation of the Early Jurassic dinosaurian ichnogenus Otozoum. Palaeontology 46, 803–838.
Zeigler, K.E., and J.W. Geissman. 2008. Magnetostratigraphy of the Upper Triassic Chinle Group and Implications for the Age and Correlation of Upper Triassic Strata in North America. Geological Society of America Abstracts with programs (online).
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