Before Leviathan

The biggest animals on Earth–the biggest animals to have ever lived, in fact–are baleen whales. They can grow to over 100 feet long thanks in part to their ability to snarf colossal amounts of food. To do so, they swing open their toothless lower jaws, which inflate like a parachute with water. Then they haul their lower jaw shut again and then use a titanic tongue to push out a school bus worth of water through a filter. The filter is baleen: a set of fronds that hangs from their upper jaws. They trap shrimp and other tiny creatures in the baleen, which the whales then swallow before preparing for the next gulp. Each one of these operations can snag a blue whale up to half a million calories.

The baleen whale is a mammal. It rears its young in the womb, complete with a placenta. It makes milk to feed its newborn calves. Yet the baleen whale is obviously a far cry from any mammal on land. This 30-million-year transformation is pretty irresistible, because it's so radical and because it comes into sharper focus as the years go by. ...