BIRDS (AVES) ACROSS THE PALEOCENE-EOCENE BOUNDARY: EVIDENCE FROM WYOMING

The response of birds to Paleogene hyperthermal events is understudied. However, new fossils from the late Paleocene (Clarkforkian) and early Eocene (Wasatchian) of Wyoming provide insight into the response of birds to the Paleocene-Eocene Thermal Maximum. Birds appear to have emigrated, immigrated, and possibly speciated during warming events. Even though there are significant differences between the composition of the avifaunas from the northern Bighorn/Clark's Fork Basins and the southern Greater Green River Basin from the late Paleocene through the early Eocene, fossils from Wyoming indicate a gross change in avifaunal composition across the Paleocene-Eocene Boundary, particularly marked by increased diversity. No clade-level extinction of birds is yet known at the P-E Boundary, but the species diversity of birds in the Clarkforkian of Wyoming is not well enough known to access any potential species extinction. Present data indicate the local survival of sandcoliids, owls, lithornithids, and other bird groups through the warming event. The PETM is marked by many bird appearances, both locally and globally. The oldest fossil of the presbyornithid species Presbyornis pervetus (typical of early Eocene lake deposits) is from the PETM (Wa-0). The large flightless Diatryma (an immigrant from Europe) makes its first North American appearance with immigrant turtles and Haplomylus speirianus shortly after the warming event. Other avian taxa recorded in the Wasatchian Turtle Graveyard locality indicate the presence of certain bird clades, including messelornithids, in Wyoming prior the expansion of the Green River lake system and prior to the oldest fossil records of those clades in Europe. Dispersal of those bird clades to Europe from North America does not appear to be related to the PETM, but may have been influenced by later hyperthermal events. These later events also may have contributed to the local (North American) extinction of Diatryma in the later part of the Wasatchian (early Eocene).