Ancient sea creatures filtered food like modern whales

Ancient, giant marine animals used bizarre facial appendages to filter food from the ocean, according to new fossils discovered in northern Greenland. The new study, led by the University of Bristol and published today in Nature, describes how the strange species, called Tamisiocaris, used these huge, specialized appendages to filter plankton, similar to the way modern blue whales feed today.

The animals lived 520 million years ago during the Early Cambrian, a period known as the 'Cambrian Explosion' in which all the major animal groups and complex ecosystems suddenly appeared. Tamisiocaris belongs to a group of animals called anomalocarids, a type of early arthropod that included the largest and some of the most iconic animals of the Cambrian period. They swam using flaps down either side of the body and had large appendages in front of their mouths that they most likely used to capture larger prey, such as trilobites.

However, the newly discovered fossils show that those predators also evolved into suspension feeders, their grasping appendages morphing into a filtering apparatus that could be swept like a net through the water, trapping small crustaceans and other organisms as small as half a millimetre in size.

The evolutionary trend that led from large, apex predators to gentle, suspension-feeding giants during the highly productive Cambrian period is one that has also taken place several other times throughout Earth's history, according to lead author Dr Jakob Vinther, a lecturer in macroevolution at the University of Bristol.

Dr Vinther said: "These primitive arthropods were, ecologically speaking, the sharks and whales of the Cambrian era. 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."

In order to fully understand how the Tamisiocaris might have fed, the researchers created a 3D computer animation of the feeding appendage to explore the range of movements it could have made.

"Tamisiocaris would have been a sweep net feeder, collecting particles in the fine mesh formed when it curled its appendage up against its mouth," said Dr Martin Stein of the University of Copenhagen, who created the computer animation. "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."

The discovery also helps highlight just how productive the Cambrian period was, showing how vastly different species of anomalocaridids evolved at that time, and provides further insight into the ecosystems that existed hundreds of millions of years ago.

"The fact that large, free-swimming suspension feeders roamed the oceans tells us a lot about the ecosystem," Dr Vinther said. "Feeding on the smallest particles by filtering them out of the water while actively swimming around requires a lot of energy -- and therefore lots of food."

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