Evidence from ammonoids and conodonts for multiple Early Triassic mass extinctions

Abstract

Ammonoids and conodonts, being characterized by exceptionally high background rates of origination and extinction, were vulnerable to global environmental crises, which characteristically intensified background rates of extinction. Thus, it is not surprising that these taxa suffered conspicuous mass extinctions at the times of three negative Early Triassic global carbon isotopic excursions that resembled those associated with the two preceding Permian mass extinctions. In keeping with their high rates of origination, both the ammonoids and conodonts rediversified dramatically between the Early Triassic crises. Other marine taxa, characterized by much lower intrinsic rates of origination, were held at low levels of diversity by the Early Triassic crises; because global mass extinctions affect all marine life, these taxa must have experienced relatively modest expansions and contractions that have yet to be discovered, because they do not stand out in the fossil record and because the stratigraphic ranges of these taxa, being of little value for temporal correlation, have not been thoroughly studied.carbon isotopes ͉ Permian

Amelioration of marine environments at the Smithian–Spathian boundary, Early Triassic

“…The SSB witnessed major changes among marine biotas, including a severe loss of biodiversity among conodonts and ammonoids (Orchard, 2007;Stanley, 2009;Brayard et al, 2009), size reduction (Lilliput effect) among surviving conodont taxa , and a contraction of the paleolatitudinal range of surviving ammonoid taxa (Galfetti et al, 2007;Brayard et al, 2009). The SSB also marked a major change in global climate, with strong tropical sea-surface cooling (Sun et al, 2012;Romano et al, 2013) and a steepening of the latitudinal temperature gradient (Galfetti et al, 2007).…”

“…Several invertebrate clades, including ammonoids, conodonts, and foraminifera, appear to have suffered severe losses of biodiversity at this time (Orchard, 2007;Stanley, 2009;Song et al, 2011). Ammonoids diversified greatly during the Griesbachian to Smithian but underwent a major evolutionary turnover at the SSB, followed by a stepwise increase in biodiversity in the early to middle Spathian (Brayard et al, 2009).…”

“…Although literature surveys show that marine clades such as conodonts, ammonoids, and foraminifera experienced a sharp decline in diversity at the SSB (Orchard, 2007;Stanley, 2009;Song et al, 2011), this pattern may be biased by data binning effects. In fact, an examination of the stratigraphic distribution of these marine clades in actual geological sections suggests that diversity losses occurred slightly prior to the SSB (Zhao et al, 2007;Song et al, 2011;Zakharov and Popov, 2014) and were probably associated with the late Smithian thermal maximum (Sun et al, 2012;Romano et al, 2013;Fig.…”

“…6) rather than the Smithian-Spathian boundary itself. The affected marine clades also did not recover immediately when climatic and environmental conditions ameliorated abruptly at the SSB but, rather, underwent a stepwise recovery during the early to middle Spathian (Orchard, 2007;Stanley, 2009;Brayard et al, 2009).…”

Evolutionary history of the seagrass genus Posidonia

“…This catastrophic episode might have been responsible for a high number of extinctions of Posidonia ancestors, which explains the long branches separating Mediterranean and Australian clades in the reconstructed phylogenies. Stanley (2009) states that geographic range plays a role in survival from extinction at the genus level. Groups that have narrow geographic ranges or are ecologically 125 Fig.…”