Anomalocarididae

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Anomalocarididae
Reconstruction of Laggania cambria

Reconstruction of Laggania cambria

Temporal occurrence
Cambrian to Devonian
540 to 400 million years
Locations
Systematics
Bilateria
Primordial mouths (protostomia)
Molting animals (Ecdysozoa)
Panarthropoda
Order : Radiodonta
Family : Anomalocarididae
Scientific name
Anomalocarididae
Raymond , 1935

The Anomalocarididae ( Greek ἀνώμαλος anomalos and καρίς karis ( Gen .: καρίδος) "unusual shrimp") are a group of very early marine animals known mainly from fossils from the Cambrian deposits in China , the USA , Canada , Poland and Australia . Although "Anomalocarida" or "Anomalocarid" are often used colloquially, the term Anomalocarididae or "Anomalocarididen" is the technically correct expression.

For a long time it was assumed that the Anomalocarididae became extinct at the end of the Cambrian, but the discovery of a large specimen from Morocco has shown that representatives of the Anomalocarididae survived at least into the Ordovician . The discovery of the early Devonian Schinderhannes bartelsi , an arthropod with large appendages and a number of anomalocaridid ​​features, extended the period of the fossil record of the anomalocaridids by 100 million years to the early Devonian 400 million years ago. The unmineralized body structure of the animals means that no fossils have been preserved in the geological layers in between. Anomalocaridids were the largest known animals of the Cambrian - some Chinese species were believed to be two meters in length - and most of the forms were possibly active predators .

features

The anomalocaridids swimming in the open water had flat, segmented bodies, which were equipped with two spiked arms in front of the mouth, the shape of which is reminiscent of the body of shrimp . The mouth opening had a circular structure and resembled a pineapple slice . The mouth was covered with a ring of sharp plates which, however, did not touch in the middle, since the mouth opening was more rectangular than round. It has been suggested that these teeth enabled some anomalocaridids to feed on hard-shelled trilobites . Anomalocaridids had large eyes and their bodies were flanked on the sides by a series of movable lobes-like appendages, which were used to move in the water.

Laggania cambria mouth opening (model)

Parapeytoia yunnanensis , which presumably belongs to the Anomalocarididae (whether Parapeytoia belonged to the real Anomalocarididae or rather was more closely related to Yohoia or Haikoucaris , is disputed in science) could have had legs.

Compared to many other sea-dwelling creatures of its time, the anomalocaridids were very agile. The flap-like appendages (lobes) on the body flanks could probably be moved in waves, so that the animals were able to move quickly or to float in the water. This type of locomotion is comparable to that of modern rays or cuttlefish . The outer skin (cuticle) of the anomalocaridids was not mineralized . As a result, it was more flexible than that of its prey and allowed greater freedom of movement.

Complete fossil of Anomalocaris from the Burgess Shale in the Canadian Rockies

After death, the organism tended to fall apart into several parts. Fully preserved fossils are therefore rare. In the first description of the fossils of Anomalocaris was initially classified the articulated gripper arms as a separate species of arthropods . Before the fossils could be put together correctly, the fact that the supposed shrimp were always found without their heads caused astonishment. The round mouth was thought to be a fossil jellyfish , which was given the generic name Peytoia . The body was also assigned to the sponges under the name Laggania . It was not until the 1980s that the three different fossils were put together correctly. Since then, a number of genera and species have been described within the Anomalocarididae, which differ mainly in the structure of the grasping arms, the presence of a tail, the position of the mouth opening, etc.

Tentacle of Anomalocaris canadensis in the Natural History Museum Vienna

The name Anomalocaris originally only referred to the grasping arms, which were mistakenly mistaken for a species of shrimp, but was later extended to the entire animal according to the rules of biological nomenclature , since the fossil grasping arms were the first to be described.

The anomalocaridids flourished in the early and middle Cambrian , fossil records from younger rock strata are rarer, but this can also be explained by the lack of suitable deposits from later times, as the soft bodies of the anomalocaridids were only preserved under special circumstances.

classification

There are eleven genera within the Anomalocarididae, most of which are known only with one species:

Some other related genera are sometimes placed in the Anomalocarididae, but may belong to other clades :

The Anomalocarididae, already known from the earliest Cambrian faunas in Poland, were widespread during the Cambrian and occurred before the trilobites .

Compared to the species of the genus Anomalocaris , Laggania lacked a tail structure. The latter also had a larger head in which the eyes were placed behind instead of in front of the mouth opening, which would have been a disadvantage when hunting. Because of these characteristics, some scientists have referred to Laggania as a plankton eater . Amplectobelua species, unlike anomalocaris, were smaller and had a wider body with the eyes placed sideways to the mouth.

The Anomalocarididae appear to be closely related to the Opabinididae and fall somewhere in the arthropod parent group . The discovery of a Devonian anomalocarid suggests that the group is paraphyletic and includes the arthropods . In the meantime, however, a species from the Ordovician has also been discovered.

literature

  • 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.
  • Tim Haines & Paul Chambers. The Complete Guide to Prehistoric Life . BBC Books, 2005.
  • Conway Morris, Simon. The Crucible of Creation . Oxford University Press, 1998.

Individual evidence

  1. ↑ Xianguang, H .; Bergström, J .; Jie, Y. (2006): "Distinguishing Anomalocaridids from Arthropods and Priapulids", in: Geological Journal 41, 3-4, p. 25.
  2. ↑ a b Van Roy, P .; Briggs, DEG (2011): "A giant Ordovician anomalocaridid", in: Nature 473 (7348), pp. 510-513.
  3. ↑ a b Kühl, G .; Briggs, DEG; Rust, J. (Feb 2009): "A Great-Appendage Arthropod with a Radial Mouth from the Lower Devonian Hunsrück Slate, Germany", in: Science 323 (5915), pp. 771-3.
  4. ↑ http://www.trilobites.info/species2.html The Anomalocaris Homepage
  5. ↑ Jakob Vinther, Martin Stein, Nicholas R. Longrich, David AT Harper. A suspension-feeding anomalocarid from the Early Cambrian. Nature , 2014; 507 (7493): 496 DOI: 10.1038 / nature13010
  6. ↑ Budd, Graham E. / Peel, John S. (1998): A New Xenusiid Lobopod from the Early Cambrian Sirius Passet Fauna of North Greenland, in: Palaeontology 41, pp. 1201-1213. (PDF; 3.54 MB)
  7. ↑ Dzik, J. and Lendzion, K. 1988. The oldest arthropods of the East European Platform, in: Lethaia 21, pp. 29-38.
  8. ↑ Anomalocarid trunk limb homology revealed by a giant filter-feeder with paired flaps [1]

Web links

Commons : Anomalocarididae  - collection of images, videos and audio files