Gastornis
At the time, the environment where Gastornis lived had dense forest and a moist to dry subtropical or even tropical climate. North America and Europe were still rather close. Greenland was  probably covered with lush woodland and grassland. Only narrow straits of a few 100 km at most would have blocked landbound dispersal of the Gastornis ancestors. Land in North American was connected. Their European range was an archipelago, with the Alps building up, and high sea levels in the Paleocene and Eocene. Geographically, it was roughly similar to today's Indonesia.