Anomalocaris ("unlike other shrimp", or "abnormal shrimp") is an extinct genus of radiodont, an order of early-diverging stem-group arthropods. The first fossils of Anomalocaris were discovered in the Ogygopsis Shale of the Stephen Formation in British Columbia, Canada by Joseph Frederick Whiteaves, with more examples found by Charles Doolittle Walcott in the Burgess Shale unit of the Stephen Formation. Other closely related fossils have been found in the older Emu Bay Shale of Australia, as well as possibly elsewhere. Originally several fossilized parts discovered separately (the mouth, frontal appendages and trunk) were thought to be three separate creatures, a misapprehension corrected by Harry B. Whittington and Derek Briggs in a 1985 journal article. With a body length close to 40 centimetres, A. canadensis is thought to be one of the earliest examples of an apex predator, though others have been found in older Cambrian lagerstätten deposits.

Anomalocaris has been misidentified several times, in part due to its makeup of a mixture of mineralized and unmineralized body parts; the mouth and frontal appendage was considerably harder and more easily fossilized than the delicate body. Anomalocaris fossils were first collected in 1886 or 1888 by Richard G. McConnell of the Geological Survey of Canada. The specimens were described and named in 1892 by GSC paleontologist Joseph Frederick Whiteaves. The specimens are now known to represent isolated frontal appendages, but Whiteaves interpreted them as the abdomens of phyllocarid crustaceans. Noting its unusual anatomy for the abdomen of a crustacean, Whiteaves gave it the name Anomalocaris, meaning "unlike other shrimps". In 1928, Danish paleontologist Kai Henriksen proposed that Tuzoia, a Burgess Shale arthropod which was known only from the carapace, represented the missing front half of Anomalocaris. The artists Elie Cheverlange and Charles R. Knight followed this interpretation in their depictions of Anomalocaris.

The interpretation of Anomalocaris as an active predator is widely accepted throughout the history of research, as its raptorial frontal appendages and mid-gut glands strongly suggest a predatory lifestyle. In the case of A. canadensis, its outstanding size amongst Burgess Shale fauna also making it one of the first apex predators known to exist.

Anomalocaris canadensis lived in the Burgess Shale in relatively great numbers, though comparable fossils have been found elsewhere, suggesting a more expansive range over the Laurentian continent. 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.

Anomalocaris: Earth's First Predator :hex-crab:

When Giant 'Shrimps' Ruled the Earth :hexcrab-party:

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    • Cromalin [she/her]
      ·
      2 years ago

      if they've given you their pronouns and you use they instead that can definitely be misgendering. back before :melon-musk: a lot of people who didn't want to get banned from twitter on the off chance someone decided to enforce tos would refer to binary trans women (and men, but mostly women) with they/them pronouns. it can be a way of avoiding using the persons preferred pronouns even when clearly stated.