National Geographic : 2010 Aug
• huge snapping jaws, like a hairy saltwater croc; Dalanistes, with a long neck and head like a heron; and Makaracetus, with a short, curved, muscular proboscis that it may have used for eating mollusks. Around 45 million years ago, as the advan- tages of a water environment drew whales far- ther out to sea, their necks compressed and sti ened to push more e ciently through the water, behind faces lengthening and sharpen- ing like a ship's prow. Hind legs thickened into pistons; toes stretched and grew webbing, so they resembled enormous ducks' feet tipped with tiny hooves inherited from their ungulate ancestors. Swimming methods improved: Some whales developed thick, powerful tails, bulleting ahead with vigorous up-and-down undulations of their lower bodies. Selection pressure for this e cient style of locomotion favored longer and more exible spinal columns. Nostrils slid back up the snout toward the crown of the head, be- coming blowholes. Over time, as the animals dived deeper, their eyes began to migrate from the top toward the sides of the head, the better to see laterally in the water. And whale ears grew ever more sensitive to underwater sound, aided by pads of fat that ran in channels the length of their jaws, gathering vibrations like underwater antennae and funneling them to the middle ear. Though finely tuned to water, these 45- million-year-old whales still had to hitch them- selves ashore on webbed fingers and toes, in search of fresh water to drink, a mate, or a safe place to bear their young. But within a few mil- lion years whales had passed the point of no re- turn: Basilosaurus, Dorudon, and their relatives never set foot on land, swimming con dently on the high seas and even crossing the Atlantic to reach the shores of what is now Peru and the southern United States. eir bodies adjusted to their exclusively aquatic lifestyle, forelimbs shortening and sti ening to serve as ippers for planing, tails broadening at the tip in horizontal ukes to create a hydrofoil. e pelvis decou- pled from the spine, allowing the tail a broader range of vertical motion. Yet like talismans from Shiny as a mudflat, dry as the Sahara, nummulite basins (above) are named for the coin-shaped fossils that litter their soil (right). Nummulites and other tiny desert relics provide vital clues to how early whales lived and died.