SUSPENDING THE RULES: UNRAVELING THE ICHNOLOGICAL SIGNATURE OF THE LOWER TRIASSIC POST-EXTINCTION RECOVERY INTERVAL

Abstract

The biotic crisis that heralded the end of the Paleozoic era and simultaneously ushered in the Mesozoic era occurred during an interval of profound environmental change, including strongly increased levels of greenhouse gases (Payne et al., 2004; Kump et al., 2005; Luo et al., 2011), and a sharp decline in the proportion of dissolved oxygen in the world's oceans (Isozaki, 1994, 1997; Grice et al., 2005; Berner et al., 2007). Numerous geochemical and biogeochemical methodologies have documented the changing chemistry of the world's oceans through the Permian-Triassic boundary interval (e.g., Musashi et al., 2001; Rampino and Caldeira, 2005; Grice et al., 2005; Ward and Berner, 2007; Luo et al., 2011). Furthermore, these techniques have illustrated that dissolved oxygen levels and oceanic and atmospheric chemistry fluctuated wildly during the several million years after the initial crisis (Payne et al., 2004; Rampino and Caldeira, 2005; Kakuwa, 2008; Meyer et al., 2008). Prolonged adverse environmental chemistry undoubtedly contributed strongly to the delayed biotic recovery, a delay that lasted the extent of the Early Triassic (Hallam, 1991; Payne et al., 2004; Erwin, 2007; Meyer et al., 2011). Although geochemical studies provide crucial evidence regarding oceanic toxicity, they cannot provide information on biotic responses to fluctuating conditions nor can this line of investigation provide details on the nature of biotic recovery once environmental conditions regained stability. For this, direct observation of fossil evidence is essential. Studies of lowermost Triassic biota have focused primarily on skeletonized invertebrate and vertebrate taxa (i.e., Schubert and Bottjer, 1995; Jin et al., 2000; Chen et al., 2006; Twitchett, 2006; Zonneveld et al., 2007, and references therein). Comparatively few papers have focused on ichnological aspects of the Permian-Triassic extinction and recovery …