The large Cambrian predator with a circular, tooth-lined mouth that exceeded a meter in length was Anomalocaris. Its name means “unlike other shrimp,” an early misinterpretation caused by researchers initially mistaking separate body parts for different animals.
Anomalocaris belonged to Radiodonta, an extinct group of stem-arthropods. It had two grasping frontal appendages, a flexible body with lateral flaps for swimming, and a distinctive circular mouth made from overlapping plates. The mouth and appendages identify it as one of the major predators of Cambrian seas, although its feeding mechanics and the hardness of its mouthparts remain subjects of scientific discussion.
Fossils of Anomalocaris are especially associated with the Burgess Shale of British Columbia, Canada, which dates to about 508 million years ago. Some specimens reached around a meter or more in length, making the animal enormous compared with many other Cambrian organisms. It was not a trilobite, mollusk, or segmented worm. The name is sometimes used broadly for related radiodont fossils, and modern studies have revised the classification of several specimens once assigned to Anomalocaris.