Before there were filter-feeding baleen whales, basking sharks or whale sharks, the earth's ancient oceans were trolled by a large shelled creature that sported two broom-like flaps protruding from its head to sweep plankton and other small organisms plying the waters.

So says a new study from the University of Bristol in the United Kingdom, which says fossils unearthed about five years ago in northern Greenland are those of the Tamisiocaris borealis, which lived an estimated 520 million years ago, during the Early Cambrian, a period when scientists believe all the major animal groups and complex ecosystems appeared in a relatively short amount of time.

Reaching a length of about 28 inches or so, the Tamisiocaris might not sound big by today's standards, but during the Cambrian period it was one of the largest creatures around.

The Tamisiocaris belonged to a group of animals called anomalocarids, early arthropods that swam using flaps extended along the sides of their bodies and had large appendages in front of their mouths that they most likely used to capture prey such as trilobites, although the latest discovery, say researchers, shows the creatures evolved into being able to capture small crustaceans and other creatures as small as half a millimeter.

The transition by Cambrian animals from active predators to passive sweep feeders is similar to evolutionary changes identified during other periods in the planet's history, the study's lead author, Jakob Vinther, a lecturer in macroevolution at Bristol, said in a school news release.

"These primitive arthropods were, ecologically speaking, the sharks and whales of the Cambrian era," said Vinther. "In both sharks and whales, some species evolved into suspension feeders and became gigantic, slow-moving animals that in turn fed on the smallest animals in the water."

To better understand how the Tamisiocaris likely used its front-mounted appendages to feed, Vinther and his colleagues developed a 3D computer model that simulated the range of movements the creature could have made (see 3D simulation video here).

"This is a rare instance when you can actually say something concrete about the feeding ecology of these types of ancient creatures with some confidence," asserted Martin Stein of the University of Copenhagen, who created the computer animation.

The fossil discovery, said Vinther, demonstrates how diverse life was during the Cambrian period, with very different species and planet ecosystems evolved at that time.

"We once thought that anomalocarids were a weird, failed experiment," said co-author Nicholas Longrich from the University of Bath.

"Now," he said, "we're finding that they pulled off a major evolutionary explosion, doing everything from acting as top predators to feeding on tiny plankton."