The blue whale is the largest animal that has ever lived. And yet they feed almost exclusively on tiny crustaceans known as krill. The secret is in the baleen, a complex filter-feeding system that allows the enormous whales to strain huge volumes of saltwater, leaving only krill and other small organisms behind. Now, researchers who have described an extinct relative of baleen whales in Current Biology on June 29 offer new insight into how baleen first evolved.