Late Triassic Ammonoids: Distribution, Biostratigraphy and Biotic Events

The Late Triassic Extinction at the Norian/Rhaetian boundary: Biotic evidence and geochemical signature

“…Most striking, and long known, are the ammonoid extinctions. It has long been clear that the largest extinction of Late Triassic ammonoids took place at the end of the Norian, not at the end of the Triassic (Kummel, 1957;House, 1963;Kennedy, 1977;Newell, 1967;Teichert, 1988;Whiteside and Ward, 2011;Lucas, 2018a). After this extinction, only a few ammonoid taxa populated the Rhaetian seas, limited to heteromorphs and some Arcestaceae and Clydonictacea (Wiedmann, 1973).…”

“…The Late Triassic ammonoid extinctions were a succession of diversity drops, with the last, most substantial drop at the end of the Norian, not at the end of the Triassic. Thus, ammonoid extinctions across the TJB are best described as stepwise (Wiedmann and Kullman, 1996;Lucas, 2018a).…”

“…A compilation of ammonoid global diversity at the stage level indicates that, after a Norian (mostly Alaunian) peak in diversity, the most substantial extinction of ammonoid families and genera took place across the NRB (Lucas, 2018a). This is best documented in the New York Canyon area of Nevada, USA, where Taylor et al (2000Taylor et al ( , 2001, Guex et al (2002Guex et al ( , 2003, and plotted ammonoid distribution based on decades of collecting and study.…”

Sedimentary record of Upper Triassic impact in the Lagonegro Basin, southern Italy: Insights from highly siderophile elements and Re-Os isotope stratigraphy across the Norian/Rhaetian boundary

“…Available biostratigraphic data suggest that prominent faunal groups in the marine realm, such as radiolarians, conodonts, and ammonoids, experienced a three-step extinction during the last 15 Myr of the Late Triassic, comprising (1) the end of the middle Norian, (2) the Norian/Rhaetian boundary (NRB), and (3) the end of the Rhaetian (Tanner et al, 2004;O'Dogherty et al, 2010;Whiteside and Ward, 2011;Martinez-Perez et al, 2014;Onoue et al, 2016;Lucas and Tanner, 2018;Rigo et al, 2020). Stepwise or episodic extinctions took place across the NRB, during which high extinction rates of ammonoids and marine bivalves, including pectinacean Monotis, have been documented (McRoberts, 2007(McRoberts, , 2010Wignall et al, 2007;Lucas and Tanner, 2008;Whiteside and Ward, 2011;Lucas, 2018aLucas, , 2018bRigo et al, 2020;Ogg et al, 2020), as well as significant faunal turnovers in radiolarians and conodonts occurred (O'Dogherty et al, 2010;Onoue et al, 2016;Du et al, 2020;Karádi et al, 2020). Most of these extinctions were long conflated as a single mass extinction at the end of the Triassic (Sepkoski Jr., 1982, 1996, but recent magneto-bio-stratigraphic (Gallet et al, 2007;Muttoni et al, 2010;Hüsing et al, 2011;Maron et al, 2015Maron et al, , 2019Kent et al, 2017) and carbon isotope stratigraphic studies (Sephton et al, 2002;Ward et al, 2004;Zaffani et al, 2017Zaffani et al, , 2018Rigo et al, 2020;Rigo ...…”

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“…From the beginning, it must be emphasized that historically the conodonts have had no contribution to building the standard Triassic timescale, except for their recent involvement in redrawing the base of the Triassic System, if this could be really qualified as a real contribution, and thus, in principle, the conodonts are not qualified to contribute to the building or rebuilding of the standard Triassic timescale. It seems that many Triassic conodont workers ignore that the Triassic chronostratigraphy, with its actual standard units, series, stages and substages, is primarily defined and calibrated on ammonoid biostratigraphy developed over two centuries in Europe and North America, with the most important development after the middle of the twentieth century (Tozer, 1965(Tozer, , 1967(Tozer, , 1971(Tozer, , 1984(Tozer, , 1994aSilberling & Tozer, 1968;Silberling & Nichols, 1982;Shevyrev, 1986Shevyrev, , 1995Shevyrev, , 2006Bucher, 1988Bucher, , 1989Bucher, , 1992Bucher, , 2002Mietto & Manfrin, 1995;Krystyn et al, 2004;Monnet & Bucher, 2005Lucas, 2010Lucas, , 2013Lucas, , 2018cBalini et al, 2010;Jenks et al, 2015). In the successive editions of The Geological Time Scale published by Gradstein et al (2004Gradstein et al ( , 2012Gradstein et al ( , 2020 is clearly stated that the ammonoid successions have basicaly served as global primary standards for the Triassic System.…”