The invertebrates that form the gray whales primary prey are restricted to shallow water environments, but global sea-level changes during the Pleistocene eliminated or reduced this critical habitat multiple times. Because the fossil record of gray whales is coincident with the onset of Northern Hemisphere glaciation, gray whales survived these massive changes by adapting their feeding habits. When continental glaciers locked up vast quantities of the earth 's water, ocean levels dropped up to 400 feet. This transformed what is now the sea bottom into wind-scoured steppes. At the height of the ice age, most of the modern gray whale food source would have been high and dry, and yet, the whales survived. If the gray whales could have only