This is the model of the strange animal, Anomalocaris that lived during the Cambrian Period about 500 million years ago. Fossils of Anomalocaris are best known from the famous Burgess Shale of Western Canada but they also occur in some other countries such as Australia and China.
During the Cambrian Period the only animals on earth lived in the oceans and Anomalocaris was the largest of these and it was a fierce predator.
We didn’t always know that Anomalocaris looked like this. The first fossils that were found were only of these two large limbs at the front of the head. Partly because of their size they were thought to be the body of a shrimp-like animal, and the rows of spines along the lower edge of the fossil were thought to be the legs. That explains the origin of the name Anomalocaris, which means unusual shrimp.
The body of Anomalocaris behind the head is made up of a number of segments. At the sides these segments had a series of flap-like lobes that were partly overlapping. These lobes were flexible and by moving them in a wave-like motion, the animal could swim through the water. The mouth of Anomalocaris is a strange disk-like structure that’s unlike that of any animal living today. The first fossils of the mouth part that were found were separate from the rest of the body and they were thought to belong to a totally separate animal – they were interpreted as jellyfish. It wasn’t until 1985 that a more complete specimen was found and the complete body of Anomalocaris was described.
Anomalocaris was the largest animal that we know of from the Cambrian period. It reached lengths of a half a metre or more. It was the top predator of its time and it would have eaten mainly soft body shrimp-like animals. It probably could have also preyed on animals with a hard shell such as trilobites. We know this because we found fossils of trilobites with injuries that could have been caused by Anomalocaris.
It was during the Cambrian period that for the first time on earth there were large, active predators. Anything that prey could do to avoid being eaten such as moving faster or hiding or acquiring a hard external shell, gave them a better chance at survival. In that way, the interaction between predator and prey was a driving force for evolution.