1,721,009 research outputs found
Newly integrated approaches towards understanding Late Triassic terrestrial ecosystems
No full textThe Late Triassic (~235–201.3 Ma) is one of the critical intervals of Phanerozoic earth history. Against a backdrop of marked climatic differences across Pangea (Sellwood and Valdes, 2006) and changing global atmospheric conditions (e.g., Berner, 2006), the Late Triassic saw the final recovery from the Permo–Triassic mass extinction, just before the end-Triassic mass extinction, and was punctuated by at least one major extraterrestrial bolide impact (Hodych and Dunning, 1992; Ramezani et al., 2005). Late Triassic terrestrial ecosystems are of particular interest, because they saw the origin of many modern vertebrate groups (e.g., Hugall et al., 2007), including the origin and early diversification of dinosaurs, while continents drifted through distinctly different climate zones (Kent and Tauxe, 2005). A variety of recent research examining the terrestrial realm with new analytical tools has dramatically changed our understanding of this time interval on land
Delayed recovery of non-marine tetrapods after the end-Permian mass extinction tracks global carbon cycle
No full textDuring 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
Non-biotic controls of observed diversity in the paleontologic record: an example from the Permo-Triassic Karoo Basin of South Africa
No full textPaleodiversity trends through geologic time can be affected by a number of geologic, taphonomic, and anthropogenic biases that obscure or prejudice paleoecological patterns in the fossil record. Although much work has concentrated on the relationship between geologic exposure, sample size, and taxonomic richness (i.e., number of taxa), few studies have investigated the potential effects of dataset quality and changing taxonomy. We use four different specimen-level datasets of Permo-Triassic tetrapods from the Karoo Basin of South Africa to investigate how sample size, geologic outcrop, dataset quality, and taxonomic revision all affect observed estimates of generic richness, evenness, and relative abundance. Our results indicate that large-scale patterns of richness, evenness, and abundance, such as the effects of the end-Permian mass extinction, are generally robust to these potential biases across the four different datasets. In contrast, absolute values vary significantly as do finer-scale patterns. In agreement with past studies, taxonomic errors, revised taxonomy, and new taxa have little effect on patterns of richness and evenness; instead, the addition of large numbers of new specimens to the dataset has the largest effect on these paleodiversity metrics, despite application of sample-standardization. We conclude that although large specimen datasets (hundreds to thousands of specimens) are robust to various potential biases, and can recover large-scale paleobiologic trends, they are still affected by many non-biotic controls, and workers should strive to improve dataset quality and understand the underlying reasons for observed paleodiversity patterns
Palynology of the upper Chinle Formation in northern New Mexico, U.S.A.: Implications for biostratigraphy and terrestrial ecosystem change during the Late Triassic (Norian–Rhaetian)
Get PDFA new densely sampled palynological record from the vertebrate-bearing upper Chinle Formation at Ghost Ranch in the Chama Basin of northwestern New Mexico provides insights into the biostratigraphy and terrestrial ecosystem changes during the Late Triassic of northwestern Pangaea. Spore–pollen assemblages from the Poleo Sandstone, Petrified Forest, and ‘siltstone’ members are dominated by pollen of corystospermous seed ferns (Alisporites) and voltziacean conifers (Enzonalasporites, Patinasporites). Other abundant taxa include Klausipollenites gouldii and the enigmatic fused tetrad Froelichsporites traversei, whereas spores of ferns and fern allies are generally rare. The assemblages are correlated with Zone III Chinle palynofloras of previous authors. The lower assemblages contain rare occurrences of typical Zone II taxa, namely Cycadopites stonei, Equisetosporites chinleanus and Lagenella martini, that may either be reworked or represent relictual floral elements. Marked step-wise losses of species richness, along with only minor appearances of new taxa, led to a total 50% drop in range-through diversity during the late Norian of the Chama Basin. Correlations with other Chinle records in the western U.S. reveal differences in the stratigraphic ranges of some spore–pollen taxa, likely attributable to local/regional differences in environmental conditions, such as groundwater availability, precipitation, nutrients, and temperature, rather than stratigraphic miscorrelation. This is interpreted as a consequence of environmental stress resulting from increased aridity coincident with the northward movement of Pangaea. Similarly, major differences between the western and eastern U.S. and northwestern Europe can be attributed to floral provincialism governed by climatic zones during the Late Triassic
Understanding Triassic tetrapod community evolution across Pangaea: Contributions from the South American record
No full textThe Triassic Period witnessed major macroevolutionary patterns among non-marine faunas including the origin and diversification of many key tetrapod linages that later dominated terrestrial ecosystems during the rest of the Mesozoic and Cenozoic. In this context, detailed knowledge of individual Triassic tetrapod fossil assemblages in a precise geochronologic framework is of upmost importance for elucidating similarities and differences in communities across biogeographic boundaries. Although, there is a bias towards data from the modern Northern Hemisphere continents, the importance and relevance of the Southern Hemisphere tetrapod fossil record has been widely recognized, particularly the record of non-mammalian therapsids (cynodonts and dicynodonts), stem turtles, non-archosaurian archosauromorphs, early crocodylomorphs, and early dinosaurs and dinosaur precursors. This volume focused in the southern South American record highlights how this outstanding fossil record, together with its temporal and paleoenvironmental context, impacts on our perception of Triassic non-marine ecosystems across Gondwana and the rest of Pangea.Fil: Marsicano, Claudia Alicia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Gaetano, Leandro Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Irmis, Randall B.. University of Utah; Estados Unido
Extreme ecosystem instability suppressed tropical dinosaur dominance for 30 million years
No full textThis is, to our knowledge, the first multiproxy study of climate and associated faunal change for an early Mesozoic terrestrial ecosystem containing an extensive vertebrate fossil record, including early dinosaurs. Our detailed and coupled high-resolution records allow us to sensitively examine the interplay between climate change and ecosystem evolution at low paleolatitudes during this critical interval of Earth's history when modern terrestrial ecosystems first evolved against a backdrop of high CO2 in a hothouse world. We demonstrate that these terrestrial ecosystems evolved within a generally arid but strongly fluctuating paleoclimate that was subject to pervasive wildfires, and that these environmental conditions in the early Mesozoic prevented large active warm-blooded herbivorous dinosaurs from becoming established in subtropical low latitudes until later in the Mesozoic
Revision of the early crocodylomorph Trialestes romeri (Archosauria, Suchia) from the lower Upper Triassic Ischigualasto Formation of Argentina: one of the oldest-known crocodylomorphs
No full textTrialestes romeri (Reig) is an early crocodylomorph from the Ischigualasto Formation (late Carnian – early Norian; Ischigualasto – Villa Unión Basin, Argentina) and one of the oldest-known members of this clade. Two specimens of this species are known, the holotype (PVL 2561) and a referred specimen (PVL 3889), both consisting of associated cranial and postcranial remains. These specimens are incomplete and poorly preserved thus leading previous authors to propose different phylogenetic hypotheses for the species. Trialestes romeri was originally interpreted as a basal dinosaur, subsequently considered to be a crocodylomorph with some dinosaurian characters (e.g. mesotarsal ankle joint, functionally tridactyl pes), and even proposed as a chimera representing two different genera. Some recent workers have mentioned and discussed Trialestes, but none have described it in detail or included it in a quantitative phylogenetic analysis. Here, we describe in detail all the material assignable to the species and test its phylogenetic relationships using a comprehensive data matrix focused on early archosaurs. We support the referral of PVL 3889 to Trialestes and reject the presence of a mesotarsal ankle joint in this specimen. We recovered Trialestes within Crocodylomorpha, closer to Crocodyliformes than Pseudhesperosuchus, Hesperosuchus, Dromicosuchus and Sphenosuchus. Several stratigraphical units worldwide approximately coeval with the Ischigualasto Formation, have also yielded early crocodylomorph remains, such as the upper Santa María (Brazil), Pekin (USA), and lower Maleri (India) formations. However, the crocodylomorph specimens recovered from those units are more incomplete, possess uncertain phylogenetic affinities, or are part of chimaerae. Therefore, Trialestes represents the most completely known of the earliest non-crocodyliform crocodylomorph taxa known to date.Fil: Lecuona, Agustina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Museo Paleontológico Egidio Feruglio; ArgentinaFil: Ezcurra, Martin Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina. University of Birmingham; Reino UnidoFil: Irmis, Randall B.. University of Utah; Estados Unido
Triassic Gondwanan floral assemblages reflect paleogeography more than geologic time
No full textTriassic non-marine strata from Gondwana are dated almost exclusively by biostratigraphic means, given the rarity of precise radioisotopic and magnetostratigraphic datasets. A primary method for constraining the age of these sedimentary sequences is palynomorph biostratigraphy, which implicitly assumes that differences in the presence/absence of taxa between two or more assemblages reflect a difference in geological ages. But without biostratigraphically-independent age data, this assumption often remains untested. The Triassic El Peñasco Group of the Santa Clara sub-basin in the Cuyana Basin of centralwest Argentina is an excellent study system to help test these assumptions, because the upper part of the sequence comprises a fluvio-deltaic-lacustrine succession that preserves volcaniclastic horizons and extensive palynomorph assemblages. Previous palynostratigraphic analyses had inferred a Late Triassic (Carnian-Norian) age for the Santa Clara Abajo and overlying Santa Clara Arriba formations, but we present new precise U-Pb CA-TIMS zircon ages that suggest an upper Anisian (Middle Triassic) age for both formations. This makes it the only non-marine Anisian Gondwanan sequence, and one of only a handful globally, to be precisely dated geochronologically. These new ages also constrain the deposition of the >700 m-thick succession of the Santa Clara Abajo and Santa Clara Arriba formations to no more than 2.1 my of time, suggesting it represents a synrift phase of the sub-basin. Combining these and existing geochronologic data with a newly assembled comprehensive presence/absence dataset of palynomorphs from the Anisian-Norian of Gondwana, we demonstrate that paleogeography (paleolatitude) has a significantly stronger correlation with taxonomic composition of assemblages than does geologic time. These results imply that geography is an important null hypothesis in explaining differences in early Mesozoic Gondwanan palynomorph assemblages, and that precise geochronologic age constraints are important for refining the accuracy of Triassic palynomorph biochronology.Fil: Benavente, Cecilia Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Irmis, Randall B.. University of Utah; Estados UnidosFil: Pedernera, Tomas Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Mancuso, Adriana Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Mundil, Roland. No especifíca
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