Thylacocephala
Extinct group of arthropods / From Wikipedia, the free encyclopedia
The Thylacocephala (from the Greek θύλακος or thylakos, meaning "pouch", and κεφαλή or cephalon meaning "head") are group of extinct probable mandibulate arthropods,[1] that have been considered by some researchers as having possible crustacean affinities. As a class they have a short research history, having been erected in the early 1980s.[2][3][4]
Thylacocephala | |
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Restoration of Clausocaris, a Concavicarida | |
Reconstruction of Thylacares, once considered to be the earliest known thylacocephalan | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Clade: | Mandibulata |
Class: | †Thylacocephala Pinna et al., 1982 |
Orders | |
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They typically possess a large, laterally flattened carapace that encompasses the entire body. The compound eyes tend to be large and bulbous, and occupy a frontal notch on the carapace. They possess three pairs of large raptorial limbs, and the abdomen bears a battery of small swimming limbs.
Inconclusive claims of thylacocephalans have been reported from the lower lower Cambrian (Zhenghecaris),[5] but later study considered that genus as radiodont or arthropod with uncertain systematic position.[6] The oldest unequivocal fossils are Upper Ordovician and Lower Silurian in age.[7][8] As a group, the Thylacocephala survived to the Santonian stage of the Upper Cretaceous, around 84 million years ago.[9][10]
Beyond this, there remains much uncertainty concerning fundamental aspects of the thylacocephalan anatomy, mode of life, and relationship to the Crustacea, with whom they have always been cautiously aligned.