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Biochronology of Late Triassic Metoposauridae (Amphibia, Temnospondyli) and the Carnian pluvial episode

Lucas Spencer G.

Annales Societatis Geologorum Poloniae

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2020

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Vol. 90, No. 4

409--418

EN

During the Late Triassic, metoposaurids were one of the last significant families of temnospondyl amphibians, and they have long been used in the correlation of Late Triassic tetrapod assemblages. Their fossil record extends across much of Late Triassic Pangea, including important metoposaurid fossils from the USA, Canada, Portugal, Germany, Poland, Morocco, India and Madagascar. Six genera of metoposarids are recognized: 1) Adamanian-Apachean Apachesaurus, endemic to the western USA, 2) Otischalkian Arganasaurus and Dutuitosaurus, endemic to Morocco, 3) Otischalkian-Revueltian Koskinonodon, endemic to the western USA, 4) Panthasaurus from the Otischalkian of India, and 5) Otischalkian-Adamanian Metoposaurus, known from the western USA, eastern Canada, Portugal, Italy, Germany, and Poland. Of the metoposaurid genera, only Metoposaurus has a broad enough palaeogeographic distribution and relatively restricted temporal range to be of biochronological value; its biochron identifies the Otischalkian–Adamanian (middle–late Carnian). The oldest metoposaurids are of middle Carnian age, the age of the Carnian pluvial episode of global climate. The middle Carnian broad palaeogeographic distribution, diversity and cosmopolitanism of the metoposaurids, followed by reduced diversity and relative endemism, likely indicates that climate changes were an important factor in their evolution.

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Age and correlation of Late Triassic tetrapods from southern Poland

Lucas S. G.

Annales Societatis Geologorum Poloniae

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2015

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Vol. 85, No. 4

627--635

EN

Age assignments of Triassic tetrapod fossils can be achieved by direct reference to a scheme of Triassic land-vertebrate faunachrons (LVFs) that correlates Triassic tetrapod fossil assemblages to each other based solely on the tetrapod fossils. Correlation of Triassic tetrapod assemblages to the standard global chronostratigraphic scale (SGCS, the “marine timescale”) is a separate cross correlation between the vertebrate biochronology and marine biochronology that usually relies on other data (e. g., palynostratigraphy, magnetostratigraphy, radioisotopic ages) to be completed. Late Triassic tetrapod fossils in southern Poland are found at two stratigraphic positions, the Krasiejów and Lisowice levels. The tetrapod assemblage of the Krasiejów level is assigned to the early Adamanian LVF based primarily on the stratigraphic overlap of the phytosaur Parasuchus with the Adamanian index aetosaur Stagonolepis. The amphibians Cyclotosaurus and Gerrothorax, a Proterochersis-like turtle and the aetosaur Paratypothorax from the Lisowice level indicate it is assignable to the Revueltian LVF. Cross correlations to the SGCS are less definitive, but suggest that the Krasiejów level is late Carnian and the Lisowice level is early/middle Norian. However, this correlation of the Krasiejów level is confounded by disagreements over correlation of the marine Carnian–Norian boundary to nonmarine strata. Indeed, the possibility that the Krasiejów tetrapods fill a gap in the early Norian record of tetrapods merits consideration. Such difficulties emphasize the value of correlating tetrapod assemblages to each other using a land-vertebrate biostratigraphy/biochronology, instead of immediately attempting the more problematic correlation to the SGCS.

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Candidate sections for the GSSP of the base of the Bathonian Stage (Middle Jurassic)

Fernandez-Lopez S.

Volumina Jurassica

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2009

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Vol. 7, no. 1

77-88

EN

In accordance with the recommendations of the International Commission on Stratigraphy (ICS), the leading candidate for the Global Boundary Stratotype Section and Point (GSSP) of the base of the Bathonian Stage is located in the Ravin du B?s (Bas Auran area, SE France). This section was formally proposed as candidate nineteen years ago. A second potential candidate section is located in the Cabo Mondego area (Portugal). This Portuguese section, however, has not been formally proposed as a candidate for the Bathonian basal boundary stratotype. The formal selection and proposal of a GSSP for the Bathonian Stage is the responsibility of the Bathonian Working Group (BtWG) and is expected by September 2007. In accordance with the procedures to ratify GSSPs, a formal ballot on the selection and proposal of a GSSP for the Bathonian Stage, by post or email, by all members of the BtWG is the responsibility of the convenor and the International Subcommission on Jurassic Stratigraphy Executive, and will be carried out within this time scale.

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Global Jurassic tetrapod biochronology

Lucas S.

Volumina Jurassica

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2008

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Vol. 6, no. 1

99-108

EN

Jurassic tetrapod fossils are known from all of the continents, and their distribution documents a critical paleobiogeographic juncture in tetrapod evolution – the change from cosmopolitan Pangean tetrapod faunas to the provincialized faunas that characterize the late Mesozoic and Cenozoic. Two global tetrapod biochronological units (faunachrons) have been named for the Early Jurassic – Wassonian and Dawan – and reflect some Early Jurassic tetrapod cosmopolitanism. However, after the Dawan, a scattered and poorly-dated Middle Jurassic tetrapod record and a much better understood Upper Jurassic tetrapod record indicate that significant provincialization of the global tetrapod fauna had begun. Middle Jurassic tetrapod assemblages include distinct local genera of sauropod dinosaurs, which are large, mobile terrestrial tetrapods, and this suggests marked provinciality by Bajocian time. The obvious provincialism of well known Chinese Middle-Upper Jurassic dinosaur faunas also documents the end of tetrapod cosmopolitanism. The distribution of some Late Jurassic dinosaur taxa defines a province that extended from the western USA through Europe into eastern Africa. Provincial tetrapod biochronologies have already been proposed for this province and for the separate eastern Asian Late Jurassic province. Tetrapod footprints only identify two global assemblage zones, one of Early Jurassic and the other of Middle-Late Jurassic age. The incomplete state of Jurassic tetrapod biochronology reflects both an inadequate record with poor temporal constraints and a relative lack of study of the biostratigraphy of Jurassic fossil vertebrates.