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[dinosaur] Late Triassic World: marine reptiles, terrestrial tetrapods, cynodonts + mass extinction question




Ben Creisler
bcreisler@gmail.com


New book: Late Triassic World

Lawrence H. Tanner (editor) (2018)
The Late Triassic World: Earth in a Time of Transition
Topics in GeobiologyÂvolume 46
Springer International Publishing AG 2018
ISBN 978-3-319-68008-8 ISBN 978-3-319-68009-5Â
doi: https://doi.org/10.1007/978-3-319-68009-5
https://link.springer.com/book/10.1007/978-3-319-68009-5


Chapters about Triassic tetrapods in particular:




Silvio Renesto & Fabio Marco Dalla Vecchia (2018)
Late Triassic Marine Reptiles.
In: Tanner L. (eds) The Late Triassic World. Topics in Geobiology 46: 263-313
DOI: https://doi.org/10.1007/978-3-319-68009-5_8
https://link.springer.com/chapter/10.1007/978-3-319-68009-5_8

During faunal recovery after the Permo-Triassic mass extinction (PTME), several tetrapod lineages independently evolved adaptations to marine life. Thus reptiles became significant elements of marine environments already at the beginning of the Mesozoic Era. The emergence of a diverse assemblage of marine reptiles in the Triassic marked the development of ecosystem complexity comparable with that of modern oceans. Different lineages (ichthyopterygians, sauropterygians and thalattosaurs) diversified quickly throughout the Middle Triassic and their disparity peaked during the late Anisian-early Carnian interval. Subsequently, both diversity and disparity underwent a substantial decrease during the Late Triassic. The last âpachypleurosaurâ and nothosauroid record is early Carnian in age; non-cyamodontoid placodonts were already extinct before the Carnian. Ichthyosaur diversity decreases from the Carnian to the Norian and reaches its minimum in the Rhaetian. Cyamodontoid placodonts are practically missing in the upper Carnian-middle Norian, to appear again in the upper Norian-Rhaetian with the single genus Psephoderma. The last record of the tanystropheid Tanystropheus is late Norian in age, and the range of the enigmatic Pachystropheus is possibly late Norian to early Rhaetian. Non-plesiosaurian sauropterygians, thalattosaurs, and non-parvipelvian ichthyosaurs were already extinct before the Triassic-Jurassic boundary. Pelagic forms, i.e. parvipelvian ichthyosaurs among ichthyosaurs and plesiosaurs among sauropterygians, which had appeared during the Late Triassic, crossed the Triassic-Jurassic boundary, giving rise to subsequent radiations in the Jurassic. Also, chelonians obviously crossed the boundary, while the earliest Jurassic reported record of phytosaurs needs to be confirmed.



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Spencer G. Lucas (2018)
Late Triassic Terrestrial Tetrapods: Biostratigraphy, Biochronology and Biotic Events.
In: Tanner L. (eds) The Late Triassic World. Topics in Geobiology 46: 351-405
DOI: https://doi.org/10.1007/978-3-319-68009-5_10
https://link.springer.com/chapter/10.1007/978-3-319-68009-5_10


The fossil record of Late Triassic tetrapods can be organized biostratigraphically and biochronologically into five, temporally successive land-vertebrate faunachrons (LVFs) that encompass Late Triassic time (in ascending order): Berdyankian, Otischalkian, Adamanian, Revueltian and Apachean. An up-to-date review of the age constraints on Late Triassic tetrapod fossil assemblages and correlation within the framework of the LVFs is presented. This makes possible a much more accurate evaluation of the timing of biotic events of Late Triassic tetrapod evolution, including: (1) Otischalkian, HO (highest occurrence) of almasaurids and chroniosuchians?, LOs (lowest occurrences) of crocodylomorphs and dinosaurs; (2) Adamanian, HO of mastodonsaurids and trematosaurids, LO of mammals; (3) Revueltian, HOs of capitosaurids, rhynchosaurs and dicynodonts; and (4) Apachean, HOs of metoposaurids, plagiosaurids and aetosaurs. The LO of turtles is Early Triassic or older, and the HO of phytosaurs is an Early Jurassic record. There is no compelling evidence of tetrapod mass extinctions at either the Carnian-Norian or the Triassic-Jurassic boundaries.


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Fernando Abdala & Leandro C. Gaetano (2018)
The Late Triassic Record of Cynodonts: Time of Innovations in the Mammalian Lineage.
In: Tanner L. (eds) The Late Triassic World. Topics in Geobiology 46: 407-445Â
DOI: https://doi.org/10.1007/978-3-319-68009-5_11
https://link.springer.com/chapter/10.1007/978-3-319-68009-5_11


The Triassic period witnessed a great diversification of lineages, recovering from one of the worst extinction events known in Earthâs history. Therapsids, the lineage that includes mammals as the only living members, enjoyed remarkable success during the Triassic. This clade includes the Late Permian to Early Cretaceous non-mammaliaform cynodonts, represented by a paraphyletic array of taxa successively more closely related to mammaliaforms (considered as basal mammals by several palaeontologists). In the Middle Triassic, cynodonts are represented by numerous taxa that thrived mostly in Gondwana, whereas only one taxon, Nanogomphodon, has been registered in Laurasia. Cynodont diversity during this time interval is mainly composed of gomphodonts, featuring bucco-lingually expanded postcanines, whereas the members of their sister-group, the mostly sectorial-toothed probainognathians, are very scarce. On the contrary, Early Jurassic non-mammaliaform cynodonts are most abundant in Laurasia (although also present in Gondwana) and only represented by probainognathians, particularly the sectorial-toothed tritheledontids and the ubiquitous herbivorous tritylodontids. The Late Triassic thus constitutes a pivotal time lapse, marked by an expansion of the geographical distribution and diversification of cynodonts. During this time, cynodont assemblages include representatives of old and new lineages and the first mammaliaforms are documented. This contribution presents a review of the diversity and geographic distribution of Late Triassic to Early Jurassic cynodonts, and summarizes the main morphologies represented in the lineage, including Mammaliaformes, a key group in our understanding of the early evolution of mammals.


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Adrian P. Hunt, Spencer G. Lucas & Hendrik Klein (2018)
Late Triassic Nonmarine Vertebrate and Invertebrate Trace Fossils and the Pattern of the Phanerozoic Record of Vertebrate Trace Fossils.
In: Tanner L. (eds) The Late Triassic World. Topics in Geobiology 46: 447-544Â
DOI: https://doi.org/10.1007/978-3-319-68009-5_12
https://link.springer.com/chapter/10.1007/978-3-319-68009-5_12


The diverse ichnofaunas of the Late Triassic have been studied for almost 200 years. During the Late Triassic, facies favorable for the preservation of trace fossils were the result of low sea levels, monsoonal climates and the development of extensive depositional basins as Pangea began to fragment. The most abundant vertebrate trace fossils in the Late Triassic are tetrapod tracks, including Brachychirotherium, Chirotherium, âParachirotherium,â Synaptichnium, Atreipus, Grallator, Eubrontes, Banisterobates, Trisauropodiscus, Evazoum, Tetrasauropus, Pseudotetrasauropus, Eosauropus, Apatopus, Batrachopus, Rhynchosauroides, Gwyneddichnium, Procolophonichnium, Chelonipus, Brasilichnium and Dicynodontipus. There are five tetrapod footprint biochrons of Triassic age that can be identified across the Pangaean footprint record. Coprolites are the second most abundant vertebrate trace fossils in the Late Triassic and include Heteropolacopros, Alococoprus, Dicynodontocopros, Liassocoprus, Saurocoprus, Strabelocoprus, Malericoprus, Falcatocoprus and Revueltobromus. Coprolites are useful in biochronology in the Late Triassic. Consumulites, dentalites (new term for bite marks), and burrows are moderately common in the Late Triassic. Nests and gastroliths are rare. All groups of vertebrate trace fossils demonstrate different diversity and abundance patterns through the Phanerozoic. Most vertebrate trace fossils have their earliest occurrences in the Devonian. The early Permian is an acme for both tracks and coprolites. The Late Triassic yields abundant tracks and coprolites, and tracks are also common in the Early Jurassic. The Jurassic and Cretaceous represent the times with the greatest diversity of vertebrate traces (tracks, coprolites, consumulites, dentalites, nests and gastroliths). The Quaternary also represents a time of vertebrate ichnological diversity (tracks, coprolites, regurgitalites, nests and burrows).



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Spencer G. Lucas & Lawrence H. Tanner (2018)
The Missing Mass Extinction at the Triassic-Jurassic Boundary.
In: Tanner L. (eds) The Late Triassic World. Topics in Geobiology 46: 721-785
DOI: https://doi.org/10.1007/978-3-319-68009-5_15
https://link.springer.com/chapter/10.1007/978-3-319-68009-5_15


The Late Triassic was a prolonged episode characterized by high rates of biotic turnover and discrete extinction events due to elevated extinction rates for some biotic groups and low origination rates for many. An end-Triassic mass extinction continues to be cited as one of the âbig fiveâ mass extinctions of the Phanerozoic. However, a detailed examination of the fossil record, especially by best-sections analysis, indicates that many of the groups usually claimed to have suffered catastrophic extinction at the end of the Triassic, such as ammonoids, marine bivalves, conodonts and tetrapod vertebrates, experienced multiple extinctions throughout the Late Triassic, not a single mass extinction at the end of the Period. Many other groups were relatively unaffected, whereas some other groups, such as reef communities, were subject to only regional effects. Indeed, the lack of evidence of a collapse of trophic networks in the sea and on land makes the case for an end-Triassic mass extinction untenable. Still, marked evolutionary turnover of radiolarians and ammonoids did occur across the Triassic-Jurassic boundary. The end of the Triassic encompassed temporary disruptions of the marine and terrestrial ecosystems, driven by the environmental effects of the eruption of the flood basalts of the Circum-Atlantic Magmatic Province (CAMP), through outgassing in particular, but these disruptions did not produce a global mass extinction.


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