North America and Europe were still rather close , and Greenland probably was 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 . North America and Europe were still rather close , and especially since Greenland probably was covered with lush woodland and grassland then , only narrow straits of a few 100 km at most would have blocked entirely landbound dispersal of the Gastornis ancestors .