Artist's reconstruction of an anomalocarid hunting a trilobite.

Anomalocarids [AN-ohm-ah-low-kar-id] (meaning "odd 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 meters [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). Reconstruction of Anomalocaris in its marine habitat, hunting a trilobite. ... Reconstruction of Anomalocaris in its marine habitat, hunting a trilobite. ... Orders Agnostida Redlichiida Corynexochida Lichida Phacopida Proetida Asaphida Harpetida Ptychopariida doubtful order Nektaspida Trilobites are extinct arthropods in the class Trilobita. ... Superfamilies and families Alpheoidea Alpheidae - snapping shrimps Barbouriidae Hippolytidae Ogyrididae Atyoidea Atyidae Bresilioidea Agostocarididae Alvinocarididae Bresiliidae Disciadidae Mirocarididae Campylonotoidea Bathypalaemonellidae Campylonotoidae Crangonoidea Crangonidae Glyphocrangonidea Galatheacaridoidea Galatheacarididae Nematocarcinoidea Eugonatonotidae Nematocarcinidae Rhynchocinetidae Xiphocarididae Oplophoroidea Oplophoridae Palaemonoidea Anchistioididae Desmocarididae Euryrhynchidae Gnathophyllidae Hymenoceridae Kakaducarididae Palaemonidae Typhlocarididae Pandaloidea Pandalidae Thalassocarididae Pasiphaeoidea Pasiphaeidae Procaridoidea Procarididae Processoidea... The Cambrian is a major division of the geologic timescale that begins about 542 Ma (million years ago) at the end of the Proterozoic eon and ended about 488. ... World map showing North America A satellite composite image of North America. ... A carnivore (KAR-nih-vohr) meaning meat eater (Latin carn = flesh + vorare = to devour) is an animal that eats a diet consisting solely of meat, whether it comes from live animals or dead (scavenging). ... Photomontage of plankton organisms For the Spongebob SquarePants character, see Sheldon J. Plankton. ...

Anomalocarids were flat, free swimming, segmented animals with two shrimp-like appendages forward of the mouth. Their mouth is a peculiar structure resembling a pineapple slice with multiple layers of hard, sharp teeth in the central orifice. The mouth was actually more rectangular than round, and the teeth did not meet in the middle. This would still allow it to 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. Orders Agnostida Redlichiida Corynexochida Lichida Phacopida Proetida Asaphida Harpetida Ptychopariida doubtful order Nektaspida Trilobites are extinct arthropods in the class Trilobita. ...

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 not as rigid as those of its prey, allowing it easier movement.

After death this large organism tended to disintegrate and fall apart into separate chunks, and completely intact fossil remains 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 "shrimp", were always found without "heads"), the mouth was thought to have been a fossilized jellyfish, and the body was not associated with either. Since the pieces were re-assembled 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 (cosmetically) gigantic brine shrimp. Orders Stauromedusae Coronatae Semaeostomeae Rhizostomae Jellyfish are marine invertebrates belonging to the Scyphozoa class, and in turn the phylum Cnidaria. ...

The anomalocarids thrived in the Early and Mid Cambrian and then apparently died out. The Cambrian is a major division of the geologic timescale that begins about 542 Ma (million years ago) at the end of the Proterozoic eon and ended about 488. ...

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. Subphyla and Classes Anomalocaridae - Anomalocarids, extinct     Genus Anomalocaris     Genus Laggania     Genus Parapeytoia Opabinidae - Extinct     Genus Opabinia Unclassified anomalocarid-like specimens     Genus Kerygmachela     Genus Pambdelurion Anomalocarids (meaning odd shrimp) are a group of very early marine animals known from fossils found in Cambrian deposits in China, North America, and Australia. ...

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. Opabinia is a curious animal found in early Cambrian fossil deposits. ... Subphyla and Classes Subphylum Trilobitomorpha Trilobita - trilobites (extinct) Subphylum Chelicerata Arachnida - spiders, scorpions, etc. ... The Crown Group started life in 1978 as a well-formed collection of highly trained and qualified chefs. ... In palaeontology, a stem group is a systematic grouping that is required to accommodate fossils in the classification of organisms. ... Phylum (plural: phyla) is a taxon used in the classification of animals, adopted from the Greek phylai the clan-based voting groups in Greek city-states. ... A group of creatures regarded as the sister phylum to arthropods. ...

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

• The Anomalocaris Homepage