Survival, but…! new tales of ‘dead clade walking’ from Austral and boreal post-K-T assemblages

Our knowledge of postmass extinction biotic trajectories is at the mercy of available data and detailed research on the governing factors of differential extinction/survivorship patterns of fossil biotas. Some taxa managed-barely-to survive major extinction events, but only for the short-term, becoming extinct at variable times in the following geologic stage, having succumbed to myriad natural forces generated by severe paleoenvironmental perturbations. These ‘Dead Clade Walking’ (DCW) organisms should be included in investigations on the resultant effects of the extinction bottleneck and subsequent rebound phase(s). Significantly, even though the ‘big five’ mass extinctions of the Phanerozoic are distinguished primarily by their overwhelming intensities, their magnitudes-and thus importance for shaping the present-day biosphere-have been systematically underestimated, when time frames including immediate, post-apocalyptic DCW taxa are included in survivorship/extinction analyses. Our research from recent studies of Austral and Boreal invertebrates and vertebrates in relation to the Cretaceous-Tertiary (K-T) boundary provides alluring new evidence of the DCW phenomenon, including the short-term survivorship of ammonoid cephalopods and possible non-avian dinosaurs into the dawn of the Cenozoic.