Lepidocaris rhyniensis is an extinct species of crustacean. It is the only species known from the order Lipostraca, and is the only abundant animal in the Pragian-aged Rhynie chert deposits. It resembles modern Anostraca, to which it is probably closely related, although its relationships to other orders remain unclear. The body is 3 mm (0.12 in) long, with 23 body segments and 19 pairs of appendages, but no carapace. It occurred chiefly among charophytes, probably in alkaline temporary pools.
Lepidocaris Temporal range:
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Class: | Branchiopoda |
Order: | †Lipostraca Scourfield, 1926 |
Family: | †Lepidocarididae Scourfield, 1926 |
Genus: | †Lepidocaris Scourfield, 1926 |
Species: | †L. rhyniensis
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Binomial name | |
†Lepidocaris rhyniensis Scourfield, 1926
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All the known specimens of Lepidocaris rhyniensis have been excavated from the Rhynie chert deposits in Aberdeenshire, Scotland, which is a famous Lagerstätte, or site of exceptional preservation. Lepidocaris is the only abundant animal in the deposits,[1] and is likely to be responsible for many of the frequent coprolites found in the rocks.[2]
Lepidocaris was first described by D. J. Scourfield in a 1926 paper in the Philosophical Transactions of the Royal Society B.[3] Scourfield could not accommodate his new genus in the same order as its closest relatives – the Anostraca – so he erected a new family and order for Lepidocaris alone: Lepidocarididae and Lipostraca, respectively.[4] Until 2003, when Castracollis was described, Lepidocaris was the only crustacean known from the Rhynie chert.[5][6]
Lepidocaris rhyniensis is a segmented animal with 23 body segments.[7] The whole body measures around 3 millimetres (0.12 in) long.[4] The head has two pairs of antennae, the second of which is used for swimming.[7] As in Anostraca, there is no carapace.[7] There are eleven pairs of appendages on the thorax and abdomen, of which the first three pairs are phyllopodia, or leaf-like limbs, as seen in other branchiopods such as Triops, while the last eight pairs are similar to the swimming limbs of copepods.[7] The tail ends in a pair of caudal furcae.[8]
Lepidocaris is one of the earliest preserved freshwater crustaceans.[8] It is frequently found in association with the charophyte Palaeonitella (Characeae); if the ecology of Palaeonitella resembled that of its modern relatives, the water would have been alkaline.[8] Similarly, Lepidocaris is thought to have had a similar ecology to extant members of the Anostraca and the Notostraca such as Artemia and Triops, inhabiting shallow, temporary pools.[8]
The phylogenetic position of Lepidocaris in relation to other orders of crustaceans is uncertain.[9] In his original description of the species, Scourfield noted that Lepidocaris could not be accommodated in the existing order Anostraca, and even suggested that a position outside the Branchiopoda was not unthinkable.[4] In 1986, Frederick Schram considered Lipostraca to be the sister group to Brachypoda, with the two orders together making up the Cephalocarida.[10] In 1997, Dieter Walossek considered Lepidocaris and Rehbachiella to be stem-group anostracans, outside the extant Euanostraca.[9] In 2001, Schram and Koenemann considered Lepidocaris and Rehbachiella to be stem-group lineages basal to the whole Branchiopoda.[9]
This is the first new crustacean described from the chert since Lepidocaris rhyniensis (Scourfield 1926, 1940c).