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.

### 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

- Opabinia—a related genus to _Anomalocaris_
- Cambroraster

## Other websites

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