Anomalocaridid
| Anomalocaridid Temporal range: Cambrian Stage 3–Early Devonian |
|
|---|---|
 |
|
| Model of Peytoia nathorsti measuring around 60 cm | |
| Scientific classification | |
| Kingdom: | Animalia |
| Class: | †Dinocaridida |
| Order: | †Radiodonta |
| Suborder: | †Anomalocarida |
| Family: |
†Anomalocarididae Raymond, 1935 |
| Genera | |
The Anomalocaridids comprise a group of very early marine animals known primarily from fossils found in Cambrian deposits in China, United States, Canada, Poland and Australia. They were long thought to be restricted to this Cambrian time range, but the discovery of large Ordovician specimens has extended this somewhat. The later Devonian Schinderhannes shows many anomalocaridid features. Although originally interpreted as an anomalocaridid-like arthropod, some recent studies suggest that it may represent an anomalocaridid: if so it would extend the group's record by some hundred million years: the non-mineralised anomalocaridid structure means they are absent from the intermediate fossil record.
Anomalocaridids are the largest Cambrian animals known—some Chinese forms may have reached 2 m (7 ft) in length—and most of them were probably active carnivores.
Anomalocaridids were flat, free-swimming, segmented animals that possessed two grasping appendages in front of their mouths (the "great appendages"). These consisted of a dozen or more jointed segments, which could be curled like fingers to grasp prey. Each segment bore a pair of spines, which were sometimes armed with smaller spinelets, that could be used to impale their food. The head was covered with a carapace formed by a series of chitinous plates, and the mouth was a circular structure resembling 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. The skeletons of Anomalocaridids were sclerotized but not mineralized—the great appendages, head, and jaws had a tough chitin exoskeleton like an insect's, but not the hard, calcium carbonate skeleton seen in arthropods such as trilobites and crabs. Anomalocaridids also had large compound eyes, a feature that they share with arthropods. The body was flanked with a series of flexible swimming lobes. On top of the back, there are a series of long, narrow, blade-shaped structures, which may have functioned as gills.
...
Wikipedia