Anomalocaris canadensis

Anomalocaris was gigantic in comparison to contemporary animals. A complete specimen of A. canadensis, ROMIP 51211, is measured up to 20.5 cm (8.1 in) long (17.4 cm (6.9 in) long when excluding the frontal appendages and tail fan). The largest frontal appendage is measured up to 18 cm (7.1 in) long when extended, and this specimen of A. canadensis would have reached up to 34.2–37.8 cm (1.12–1.24 ft) in body length excluding the frontal appendages and tail fan.Dryad data 04 Previous body length estimation up to 1 m (3.3 ft) is unlikely based on the ratio of body parts (body length measured only about 2 times the length of frontal appendage in A. canadensis) and the size of largest frontal appendage. A. daleyae (formerly A. cf. canadensis or A. aff. canadensis) from the Emu Bay Shale of Australia is larger than A. canadensis, with the largest known appendage measuring up to 18.3 cm (7.2 in) long, which would have belonged to an individual between 34.8–51.2 cm (1.14–1.68 ft) long.

Anomalocaris propelled itself through the water by undulating the flexible flaps on the sides of its body. Each flap sloped below the one more posterior to it, and this overlapping allowed the lobes on each side of the body to act as a single "fin", maximizing the swimming efficiency. …

Specimens of Anomalocaris have been found worldwide spanning from Cambrian Stage 3 to the Guzhangian. Aside from the Burgess Shale and Emu Bay Shale, fossils have been found in the Chengjiang Biota, Hongjingshao Formation, Balang Formation and the Kaili Formation of China, as well as the Eagar Formation and Weeks Formation in the United States. Anomalocaris canadensis lived in the Burgess Shale in relatively great numbers. In the Burgess Shale, Anomalocaris is more common in the older sections, notably the Mount Stephen trilobite beds. However, in the younger sections, such as the Phyllopod bed, Anomalocaris could reach much greater sizes—roughly twice the size of its older, trilobite bed relatives. These rare giant specimens have previously been referred to a separate species, Anomalocaris gigantea; however, the validity of this species has been called into question, and is currently synonymized to A. canadensis. Other unnamed species of Anomalocaris live in vastly different environments. For example, Anomalocaris cf. canadensis (JS-1880) lived in the Maotianshan Shales, a shallow tropical sea or river delta in what is now Eastern Yunnan in modern China. Anomalocaris daleyae (Emu Bay Shale) lived in a comparable environment; the shallow, tropical waters of Cambrian Australia. …

From the start, Anomalocaris fossil was misidentified, followed by a series of misidentifications and taxonomic revisions. As Stephen Jay Gould, who popularised the Cambrian explosion in his 1989 book Wonderful Life, explained:[The story of Anomalocaris is] a tale of humor, error, struggle, frustration, and more error, culminating in an extraordinary resolution that brought together bits and pieces of three "phyla" in a single reconstructed creature, the largest and fiercest of Cambrian organisms.Anomalocaris fossils were first collected in 1886 by Richard G. McConnell of the Geological Survey of Canada (GSC). Having been informed of rich fossils at the Stephen Formation in British Columbia, McConnell climbed Mount Stephen on 13 September 1886. He found abundant trilobites, along with two unknown specimens. In August 1891, Henri-Marc Ami, Assistant Palaeontologist at GSC, collected many trilobites and brachiopod fossils, along with 48 more of the unknown specimens. The fifty specimens were examined and described in 1892 by GSC paleontologist Joseph Frederick Whiteaves. Whiteaves interpreted them as the abdomens of phyllocarid crustaceans, and gave the full scientific name Anomalocaris canadensis. …