Anomalocaris canadensis

Anomalocaris ("abnormal shrimp") is an extinct genus of anomalocaridid, a family of animals thought to be closely related to ancestral arthropods. The first fossils of Anomalocaris were discovered in the Ogygopsis Shale by Joseph Frederick Whiteaves, with more examples found by Charles Doolittle Walcott in the Burgess Shale. Originally several fossilized parts discovered separately (the mouth, feeding appendages and tail) were thought to be three separate creatures, a misapprehension corrected by Harry B. Whittington and Derek Briggs in a 1985 journal article.

Anomalocaris has been misidentified several times, in part due to its makeup of a mixture of mineralized and unmineralized body parts; the mouth and feeding appendage was considerably harder and more easily fossilized than the delicate body. Its name originates from a description of a detached 'arm', described by Joseph Frederick Whiteaves in 1892, as a separate crustacean-like creature due to its resemblance to the tail of a lobster or shrimp. The first fossilized anomalocaridid mouth was discovered by Charles Doolittle Walcott, who mistook it for a jellyfish and placed it in the genus Peytoia. Walcott also discovered a second feeding appendage, but failed to realize the similarities to Whiteaves' discovery and instead identified it as feeding appendage or tail of the extinct Sidneyia. The body was discovered separately and classified as a sponge in the genus Laggania; a mouth was found with the body, but was interpreted by its discoverer Simon Conway Morris as an unrelated Peytoia that had through happenstance settled and been preserved with Laggania. Later, while clearing what he thought was an unrelated specimen, Harry B. Whittington removed a layer of covering stone to discover the unequivocally connected arm thought to be a shrimp tail and mouth thought to be a jellyfish. Whittington linked the two species, but it took several more years for researchers to realize that the continuously juxtaposed Peytoia, Laggania and feeding appendage actually represented a single, enormous creature. The two genera are now placed into the family Anomalocaridae. Because Peytoia was named first, it became the correct name for the entire animal. The original feeding arm, however, came from a larger species distinct from Peytoia and "Laggania", which retains the name Anomalocaris. In 2011, six fossils of compound eyes, the first for Anomalocaris, were recovered from an paleontological dig at Emu Bay on Kangaroo Island, Australia, proving that Anomalocaris was indeed an arthropod as.