Paleoclimate and mammal paleocology during the paleocene of North America: insights from stable isotopes.

Abstract

Paleocene climate and its relationship to mammal ecology and biogeography were examined at continental scale to test for long-term stasis of ecogeographical patterns among mammals and to better understand the effects of climate change on mammalian faunal dynamics. I also investigated local paleoclimatic and paleohydrologic conditions in a region associated with well-preserved fossil mammals to assess the local effects of greenhouse warming and the relationship between paleoenvironment and taphonomy of fossil mammals. The combination of unique and unstable faunas and globally equable climate resulted in complex ecological and biogeographical patterns among Paleocene mammals that contrast from well-structured patterns that exist today. Latitudinal gradients in Paleocene mammal species richness and body size differ from the patterns observed today among extant mammals. Differences between Paleocene and modern biogeographic patterns could be a function of unique Paleocene faunas with distinct ecology, ongoing ecological recovery after the Cretaceous-Paleogene extinction, and/or the diversity and body-size gradients being geologically recent or episodic phenomena and not general features of the geographic distribution of mammals. Sedimentary carbonates found throughout exposures of Paleocene terrestrial formations of the Crazy Mountains Basin, south-central Montana are unlike most other non-marine carbonates described previously in the literature, but may have formed under similar conditions as proposed for some Paleocene carbonates from the Clarks Fork Basin, Wyoming. Select carbonates from both regions contain exceptionally preserved vertebrate fossils and exhibit similar taphonomy.