An order of extinct flightless birds known from Paleocene and Eocene deposits in North America, Europe, and Asia. They are believed to have dispersed across the North Atlantic via a land bridge when those continents were connected in the Eocene. These were giant, 2-m-tall (7-ft) birds with large heads, huge laterally compressed bills, broad cervical vertebrae, wide pelves, massive legs with relatively short tarsi and heavy toes suggestive of a slow-moving gait, and reduced wings that were evidently too short to permit flight.