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Anomalocarids (meaning "unusual shrimp") are a group of very early marine animals known from fossils found in Cambrian deposits in China, North America, and Australia. Anomalocarids are the largest Cambrian animals known (some Chinese forms grew up to 2 m, around 6 feet, in length), and most of them were probably active carnivores (although recent thought posits one genus, Laggania, as a plankton-eating animal).
Characteristics
Anomalocarids were flat free-swimming segmented animals, which in front of their mouths had two appendages that look like the bodies of shrimps. The mouth is a peculiar circular structure like a pineapple slice, but with a ring of hard sharp teeth in the central orifice. The mouth was more rectangular than round, and the teeth did not meet in the middle. This would still let it crack open shells of small arthropods and other like animals, such as trilobites. Indeed, many trilobites have been found with bite marks on them. Anomalocarids also had large eyes and a body half-flanked with a series of swimming lobes.
Compared with many of the other sea-dwelling creatures of its time, anomalocarids were extremely agile. The flaps along its body could be moved in a wave-like formation, allowing it to move at great speeds or to 'hover'. The shell of the anomalocarids was more flexible than those of its prey, allowing it easier movement.
After death this large organism tended to disintegrate and fall apart into separate chunks; the same happened with its moulted skins. Completely intact fossil remains of it are very rare. When the fossils were originally described, the jointed arms in front of the mouth were classified as separate arthropods (a large mystery before the fossils were fully reassembled was why these fossils, mistaken as "shrimps", were always found without "heads"), the mouth was thought to have been a fossilized jellyfish called "Peytoia", and the body, thought to be a sponge named "Laggania" was not associated with either. Since the pieces were reassembled in the 1980s, a number of genera and species have been described that differ in the details of the grasping appendages, as to whether a tail is present, mouth location, and other features. Curiously enough, when fully assembled they do strongly resemble (in outside appearance) a gigantic brine shrimp with a pair of finger-like appendages near its mouth.
The name Anomalocaris originally referred to the detached arms (which were the first part to be named), and was later used for the whole animal because of the biological name priority rules.
The anomalocarids thrived in the Early and Mid Cambrian and then apparently died out.
Classification
Three genera of anomalocarids are known: Anomalocaris, Laggania, and Amplectobelua. A variety of other related animals including Parapeytoia, Pambdelurion and Kerygmachela are sometimes classified as anomalocarids, but probably belong to different clades.
Compared with Anomalocaris species, Laggania species lack any kind of tail structures and sport a considerably enlarged head with the eyes placed behind (instead of in front of) the mouth, an adaptation which would be disadvantegous in active hunting. As a result some scientists have characterised this animal as a cruising plankton feeder. Amplectobelua species, by contrast, are compact and display a much wider front body than Anomalocaris with the eyes placed lateral to the mouth.
The only plausible close relatives of the anamalocarids are the opabinids, another group of enigmatic early forms. The anomalocarids and opabinids are usually considered to be allied to the arthropods, but they clearly are not crown group arthropods. In some taxonomies they are placed as stem group arthropods; in others they are given their own phylum, Dinocarida.
Anomalocarids in popular culture
- The Pokémon Anorith and Armaldo are based on anomalocarids.
- The BBC documentary Walking with Monsters features Anomalocaris as the top predator in the Cambrian sea. It is shown to catch Trilobite by flexing the Trilobite's armor. Two are also shown fighting, with the loser getting nibbled on by a school of Haikouichthys.
- Episode 10, "Woke Up With a Monster", of the anime Bubblegum Crisis Tokyo 2040 features an enormous Anomalocaris-like monster, said to have been created using biotechnology "based on an ancient life form from the Cambrian period".
- The Cthulhu Mythos-inspired novelette A Colder War suggests that anomalocarids may be extraterrestrial in origin.
References
- Briggs, Derek; Collier, Frederick; Erwin, Douglas. The Fossils of the Burgess Shale. Smithsonian Books, 1995.
- James W. Valentine. On the Origin of Phyla. University Of Chicago Press, 2004.
- Tom Haines & Paul Chambers. The Complete Guide to Prehistoric Life. BBC Books, 2005.
External links
"Anomalocarid"