a period of increased isolation of the continent. Extinction The reason for the extinction of Gastornis is currently unclear. Competition with mammals has often been cited as a possible factor, but Gastornis did occur in faunas dominated by mammals, and did co-exist with several megafaunal forms like pantodonts. Likewise, extreme climatic events like the Paleocene–Eocene Thermal Maximum (PETM) appear to have had little impact. Nonetheless, the extended survival in Europe is thought to coincide with increased isolation of the landmass. References External links Gastornithiformes Paleogene birds of Europe Paleogene birds of North America Fossil taxa described in 1855 Paleocene birds Eocene birds Paleocene first appearances Eocene genus extinctions