Anomalocaris

Anomalocaris ("abnormal shrimp") is an extinct genus of anomalocaridid, which are, in turn, thought to be closely related to the 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 famed Burgess Shale. Anomalocaris has two known species: A. canadensis and A. daleyae.

The recently discovered species A. daleyae is known from the somewhat older Emu Bay Shale of Australia. Since the original description in the late 19th century, the frontal appendages were the only known fossilized parts and misidentified as the body parts of other creatures.

Description

Anomalocaris lived in the Cambrian period, which was a long time before dinosaurs. This makes Anomalocaris very old, so their body parts haven't evolved to be as detailed as modern animals.

 Physical appearance 
Anomalocaris still had compound eyes which were very big and complex compared to other animals in the earlier parts of the Cambrian, and also had segmented (has many sections) front appendages which were used to grasp its prey like arms. So while Anomalocaris was around the size of a small lobster, it still was a very good apex predator for its time.

 As a different animal 
Anomalocaris was misidentified many times, as the mouth, front appendages and trunk (the rest of its body) were discovered separately multiple times, leading scientists to think for a while that these parts of Anomalocaris were, in fact, of three different animals, with the mouth thought to be a jellyfish, the front appendages thought to be a shrimp and the trunk thought to be a sea cucumber or sponge.

 Size comparison 
Anomalocaris was huge in comparison to other animals. A complete specimen of A. canadensis, called ROMIP 51211, measures 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 newly discovered A. daleyae from the Emu Bay Shale is larger than A. canadensis, with the biggest appendage measuring up to 18.3 cm (7.2 in) long, which belongs to an individual measuring between 34.8–51.2 cm (1.14–1.68 ft) long.

 Discovery and identification 

 Early misidentifications 
Anomalocaris was misidentified after its discovery, followed by a series of misidentifications and taxonomic revisions.

An excerpt from Stephen Jay Gould's 1989 book Wonderful Life describing Anomalocaris:

"[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."

 Early discovery 
Anomalocaris fossils were first collected in 1886 by Richard G. McConnell of the GSC) Geological Survey of Canada). McConnell climbed Mount Stephen on 13 September 1886. He found two unknown specimens.
In August 1891, Henri-Marc Ami collected 48 more unknown specimens. The fifty specimens were examined and described in 1892 by GSC paleontologist Joseph Frederick Whiteaves.
Whiteaves thought they were the abdomens of phyllocarids, and made the name Anomalocaris canadensis. He describes the things:

"Body or abdominal segments, which, in all the specimens collected, are abnormally flattened laterally, a little higher or deeper than long, broader above than below, the pair of ventral appendages proceeding from each, nearly equal in height or depth to the segment itself... The generic name Anomalocaris (from ανώμαλος, unlike,—καρίς, a shrimp, i.e., unlike other shrimps) is suggested by the unusual shape of the uropods or ventral appendages of the body segments and the relative position of the caudal spine."

 A. daleyae 
In 2011, compound eyes of Anomalocaris were found from a dig at Emu Bay Shale on Kangaroo Island, Australia; with compound eyes; proving that Anomalocaris was really an arthropod. This was later identified in 2023 as a newly discovered species of the genus, A. daleyae.
Behaviour

Anomalocaris lived in the sea, like most of the plants (which were really small algae in the Cambrian) and animals back then. Recently, people now think that Anomalocaris didn't hunt trilobites and other benthic animals that lived on the sea floor, but instead swam after nekton like basal chordates (animals that can control how they move underwater, unlike plankton). 

Related pages

Category:Fossils
Category:Arthropods
Category:Cambrian life

 Opabinia—a related genus to Anomalocaris
 Cambroraster

 Sources 


 Other websites 

 The anomalocaris homepage featuring swimming animation
 https://undsci.berkeley.edu/this-is-not-the-shrimp-youre-looking-for/