Anomalocaris

Anamalocarids are a group of very early animals found in Cambrian deposits in China, North America, and Australia. Anamalocarids were large (for the time) carnivores. They are thought to be arthropods or possibly an extinct phylum closely related to the arthropods. They were flat, free swimming, predatory, segmented animals with two arthropod-like appendages forward of the mouth. They were as much as 17cm in length. Their mouth is a peculiar structure somewhat like a pineapple slice with multiple layers of hard sharp teeth in the central hole. Originally, the jointed arms were classified as arthropods, the mouth was thought to be a fossilized jellyfish, and the body was not associated with either. Since the pieces were assembled in the 1980s, a number of genera and species have been identified differing in the details of the grasping appendages, whether a tail is present, mouth location, and other features. The only plausible close relative of the Anamalocarids is another enigmatic early form known as Opabinia.

The Anamalocarids thrived in the Early and Mid Cambrian and then apparently died out.