Today, filter feeders like clams, sponges, krill, baleen whales, fishes, and many others fill the ocean, spending their days filtering and eating tiny particles from the water. But when did the first filter feeder evolve? The first known filter feeder is a large shrimp-like creature called Tamisiocaris borealis. This species is an anomalocarid, a group of early marine animals from the Cambrian period (around 485–540 million years ago) that are generally thought to have been apex predators—sitting at the top of the food chain and eating smaller animals. But not Tamisiocaris borealis. Based on new fossils discovered in Greenland, scientists think the feather-like structures on its head were used to rake plankton from the sea. The appendages had finely spaced spines, further divided by smaller spines, which would have been efficient traps for small plankton. And if there were filter feeders around, that means there must have been a lot of plankton living in the seas, which suggests there was a complex food web during the Cambrian. See a slideshow of more Cambrian creatures and view illustrations of the ancient seas over time.