Although North American and Europe were separated by the end of the Cretaceous, there must have been a landbrige still in place somewhere. This is because the European and North American "Diatryma"s were so similar. Other bird and mammal genera also occur on both sides of the (present-day) North Atlantic in the Palaeocene and Eocene. This is evidence that Europe and North America were once connected by dry land in part of the early Cainozoic.