Marine predator from the Cambrian era, fossils of which have been found in the Burgess shale and similar deposits in China and Australia. A. canadensis, the best-known member of the family, was about 2m long, making it the largest known animal alive at the time.
Anomalocaris and related species are distinguished by a pair of long, segmented grasping claws, an almost circular mouth, protruding, bulbous eyes, and a flat, oval body superficially similar to that of a cuttlefish but lacking an internal skeleton. This has only been determined fairly recently, however, as complete fossils only appeared in the late 70s and various parts of the animal had previously been identified as separate species.
The first sections to be studied were the grasping claws, which had frequently been appearing in the Burgess Shale in the late 19th Century and were initially identified as the tail and abdomen of a form of shrimp with unsegmented legs (the name Anomalocaris, which was applied to these claws long before the shape of the full creature was known, literally means "unusual shrimp"). The hard mouthparts were originally identified as a jellyfish and named Peyotia because their shape resembled the Peyote cactus. Imprints made in the shale by the soft abdomen were believed to be the remains of a sea
cucumber. The clues that these were all in fact part of the same creature were not all put together until Harry Whittington and Dennis Briggs published a complete description of Anomalocaris nathorsti (later renamed Laggania cambria) in 1985.
Anomalocaris, Laggania and five or six other related genera are grouped together to form the family Anomalocaridae, all of which share the same general plan described above but differ in details such as the shapes of the tail fins and and grasping claws. They are usually considered (due to the jointed claws, although some biologists dispute this) to be Arthropods, but of an extinct class and order which have yet to be formally named.
Fossils of trilobites bearing marks similar in shape to Anomalocarid mouths suggest that these creatures made up a large part of Anomalocaris' diet, confirming its reputation as one of the earliest known predators.
The Anomalocaridae became extinct at the end of the Cambrian and have no extant descendants.
Complete fossil of an Anomalocaris:
http://www.fossa.de/Trilobita/Lebensweise_II/Anomalocaris/anocaris.jpg
Reconstruction of an Anomalocaris:
http://www.grafikhuset.dk/Urhavet/DKA Anomalocaris.jpg