Extinction and survival of salamander and salamander-like amphibians across the Cretaceous-Paleogene boundary in northeastern Montana, USA

Modern amphibians (lissamphibians) are highly sensitive indicators of environmental disturbance. As such, fossil lissamphibians are an excellent model for testing causal hypotheses of the Cretaceous-Paleogene mass extinction and secondary effects of Deccan volcanism and a bolide impact (e.g., acid rain). We quantitatively analyzed high-resolution temporal changes in diversity and community structure of a succession of salamander and salamander-like lissamphibian assemblages from the Hell Creek Formation and Tullock Member of the Fort Union Formation of Garfi eld County, northeastern Montana (ca. 67.5–65.3 Ma). Richness, evenness, and taxonomic composition remained stable through the lower Hell Creek Formation. Peak richness (11 species) occurred in the middle of the formation coincident with a shortterm drop in evenness. Following a return to preexisting levels of evenness, diversity progressively declined in the upper third of the formation. This pattern refl ects plummeting relative abundances of Scapherpeton tectum and a stepwise disappearance of fi ve species, of which three represent extirpation (33%) and two represent extinction (22%). These results suggest that ecological instability increased in the local fauna during the last ~400 k.y. of the Cretaceous. Temporal correlation with local, regional, and global changes in other aspects of the terrestrial (mammals, plants) and marine (planktonic foraminifera, mollusks) biota and environment (volcanism, paleotemperature) implies a global phenomenon (late Maastrichtian event). The post–CretaceousPaleogene “survival” fauna from the lowermost Tullock Member was taxonomically depauperate and predominated by the “bloom taxon” Opisthotriton kayi. Together, our results lend growing support in favor of a complex multiple-cause scenario for the Cretaceous-Paleogene mass extinction event. *[email protected] Wilson, G.P., DeMar, D.G., Jr., and Carter, G., 2014, Extinction and survival of salamander and salamander-like amphibians across the Cretaceous-Paleogene boundary in northeastern Montana, USA, in Wilson, G.P., Clemens, W.A., Horner, J.R., and Hartman, J.H., eds., Through the End of the Cretaceous in the Type Locality of the Hell Creek Formation in Montana and Adjacent Areas: Geological Society of America Special Paper 503, p. 271–297, doi:10.1130/2014.2503(10). For permission to copy, contact [email protected]. © 2014 The Geological Society of America. All rights reserved. on January 24, 2014 specialpapers.gsapubs.org Downloaded from