LINKING TERRESTRIAL AND MARINE EXTINCTIONS: DISASTER SPECIES AND THE END-TRIASSIC EXTINCTION

Paleoecological characterization of disaster taxa provide an effective means of biocorrelation of the latest Triassic mass extinction and its aftermath in both marine and continental settings. Although no GSSP or formal definition has been accepted for the base of the Jurassic, the latest Triassic mass extinction was severe and appears coincident with the initiation of a two-fold carbon isotopic anomaly. In marine sections, disaster taxa appear to be coincident or just above the initial delta13C minimum and often range through a “pre-Planorbis” boundary interval and concurrent positive excursion. Their appearance precedes the first that of Jurassic psiloceratid and neophyllitid ammonoids and persist into younger strata of the recovery phase. The low diversity post-extinction bivalve fauna is comprised mostly of pectinaceans (e.g., Agerchlamys and “Chlamys textoria”), mytiloids, and cardiniids and is interpreted as the marine equivalent of the spike in fern spore and megafossil abundance seen marking the extinction phase in many continental (and a few marine) settings. These marine taxa are considered ecological minimalists with low nutritional requirements. In tropical and subtropical latitudes the fern spike and extinction phase is followed by exceptionally low diversity floral assemblages very strongly dominated by cheirolepidaceous conifers, notably the pollen taxon Classopollis (Corollina) meyeriana and Brachyphyllum spp. foliage, which we interpret as floral disaster elements. Post-extinction terrestrial tetrapods also of very low diversity at least at high taxonomic levels, with both osseous and ichnological assemblages being overwhelmingly dominated by theropod and prosauropod dinosaurs and protosuchid crocodylomorphs, with other forms being much less abundant. Most notable is the absence of diverse herbivores, and the terrestrial tetrapods may have subsisted as much on an aquatic-based economy as a terrestrial one. This post-extinction assemblage of what we interpret as eurytopic opportunistic generalists is globally distributed and differs markedly from the provincial high diversity assemblages of the latest Triassic.