| Skania Temporal range: | |
|---|---|
 | |
| Illustration of Skania fragilis | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | † Marrellomorpha |
| Order: | † Acercostraca |
| Genus: | † Skania Walcott, 1931 |
| Species | |
| |
Skania is a Cambrian fossil arthropod. The type species, S. fragillis, is known from the Burgess Shale of British Columbia, Canada. A second possible species "S." sundbergi is known from the Kaili Formation of China, [1] but its placement within the genus has been questioned. [2]
Specimens of S. fragillis range in length from 7.5 to 13.5 millimetres (0.30 to 0.53 in) The cordiform dorsal shield/carapace covers the entire body, with its midline having a raised keel. The shield curls around the front to form a doublure, with the posterior edge of the doublure having a pair of lateral spines. A pair of spines is also present on the posterior of the dorsal shield. A hypostome was present on the underside of the head. There are two sets of appendages, the first 5 pairs of appendages are elongate, the first one of which is described as an antenna and has small subquadrate segments/podomeres, while the others have elongate subrectangular segments. These appendages are somewhat curved and extend beyond the shield. In contrast, the trunk appendages are shorter (not extending beyond the shield) and are less curved, and the segments are not preserved. There was a diverticular (digestive) network running through the carapace, along with a central gut tract. [2]
Specimens of "S." sundbergi are on average 7.92 millimetres (0.312 in) in length. The midline keel is more strongly pronounced in "S." sundbergi. The spines present in S. fragillis are either more weakly developed or absent. [1] [2]
While previously enigmatic, it is now thought to be a marrellomorph, with both species, regardless of generic placement, belonging to Acercostraca. [2] The resemblance with the Ediacaran organism Parvancorina, to which Skania had previously been suggested to be closely related as part of the proposed clade "Parvancorinomorpha", [1] is superficial and they are probably not related. [2]
Redlichiida is an order of trilobites, a group of extinct marine arthropods. Species assigned to the order Redlichiida are among the first trilobites to appear in the fossil record, about halfway during the Lower Cambrian. Due to the difficulty to relate sediments in different areas, there remains some discussion, but among the earliest are Fallotaspis, and Lemdadella, both belonging to this order. The first representatives of the orders Corynexochida and Ptychopariida also appear very early on and may prove to be even earlier than any redlichiid species. In terms of anatomical comparison, the earliest redlichiid species are probably ancestral to all other trilobite orders and share many primitive characters. The last redlichiid trilobites died out before the end of the Middle Cambrian.
Marrella is an extinct genus of marrellomorph arthropod known from the middle Cambrian Burgess Shale of British Columbia. It is the most common animal represented in the Burgess Shale, with tens of thousands of specimens collected. Much rarer remains are also known from deposits in China.
Sidneyia is an extinct arthropod known from fossils found from the Early to the Mid Cambrian of China and the Burgess Shale formation of British Columbia. 144 specimens of Sidneyia are known from the Greater Phyllopod bed, where they comprise 0.27% of the community.
Yohoia is an extinct genus of megacheiran arthropod from the Cambrian period that has been found as fossils in the Burgess Shale formation of British Columbia, Canada. It has been placed among the arachnomorpha, a group of arthropods that includes the chelicerates and possibly the trilobites. Fossils range in size from 7 to 23 mm. 711 specimens of Yohoia are known from the Greater Phyllopod bed, where they comprise 1.35% of the community.
Anomalocaris is an extinct genus of radiodont, an order of early-diverging stem-group arthropods. It is best known from the type species A. canadensis, found in the Stephen Formation of British Columbia, Canada. Other closely related fossils have been found in the older Emu Bay Shale of Australia, as well as possibly elsewhere. Originally several fossilized parts discovered separately were thought to be three separate creatures, a misapprehension corrected by Harry B. Whittington and Derek Briggs in a 1985 journal article. Like other radiodonts, Anomalocaris had swimming flaps running along its body, large compound eyes, and a single pair of segmented, "frontal appendages", which in Anomalocaris were used to grasp prey. With a body length close to 40 centimetres, A. canadensis is one of the largest animals of the Cambrian, and thought to be one of the earliest examples of an apex predator, though others have been found in older Cambrian lagerstätten deposits.
Canadaspis is an extinct genus of bivalved Cambrian arthropod, known from North America and China. They are thought to have been benthic feeders that moved mainly by walking and possibly used its biramous appendages to stir mud in search of food. They have been placed within the Hymenocarina, which includes other bivalved Cambrian arthropods.
Amplectobelua is an extinct genus of late Early Cambrian amplectobeluid radiodont, a group of stem arthropods that mostly lived as free-swimming predators during the first half of the Paleozoic Era.
Olenoides was a trilobite from the Cambrian period. Its fossils are found well-preserved in the Burgess Shale in Canada. It grew up to 10 cm long.
Habelia is a genus of extinct arthropod from the Middle Cambrian, thought to be one of the earliest known relatives of chelicerates. Its fossils have been found in the Burgess Shale in British Columbia, Canada. Fifty-four specimens of Habelia are known from the Greater Phyllopod bed, where they comprise 0.1% of the community.
A number of assemblages bear fossil assemblages similar in character to that of the Burgess Shale. While many are also preserved in a similar fashion to the Burgess Shale, the term "Burgess Shale-type fauna" covers assemblages based on taxonomic criteria only.
Sarotrocercus is a small Cambrian arthropod known from Burgess shale, reaching a centimetre or two in length (0.39–0.79 in). Sarotrocercus is only known from 7 specimens. It may lie in the arthropod crown group, and a recent study has revised some points of its original description.
Haikoucaris is a genus of megacheiran arthropod that contains the single species Haikoucaris ercaiensis. It was discovered in the Cambrian Chengjiang biota of China.
Isoxys is a genus of extinct bivalved Cambrian arthropod; the various species of which are thought to have been freely swimming predators. It had a pair of large spherical eyes, and two large frontal appendages used to grasp prey.
Primicaris is genus of Cambrian arthropod from the Chengjiang biota of China and the Burgess Shale of Canada. It contains a single described species, P. larvaformis.
Marrellomorpha are an extinct group of arthropods known from the Cambrian to the Early Devonian. They lacked mineralised hard parts, so are only known from areas of exceptional preservation, limiting their fossil distribution. The best known member is Marrella, with thousands of specimens found in the Cambrian aged Burgess Shale of Canada. The group is divided up into two major orders, Marrellida and Acercostraca. Marrellida is recognised by the possession of head shields with two or three pairs of elongate spine-like projections, and three pairs of uniramous appendages on the cephalon, while Acercostraca generally have large ovoid carapaces that cover the entire upper half of the body, and five pairs of uniramous cephalic appendages. Both groups have unbranched antennules and a segmented trunk with biramous appendages. Recent research has suggested the previously enigmatic Cambrian trliobite-like arthropods Skania and Primicaris belong to this group. Their phylogenetic position is uncertain, various studies have alternatively placed them within in the Arachnomorpha as relatives of Artiopoda, as stem-group Mandibulata, or as stem group euarthropods.
Molaria is a genus of Cambrian arthropod, the type species M. spinifera is known from the Middle Cambrian Burgess Shale. 144 specimens of Molaria are known from the Greater Phyllopod bed, where they comprise 0.27% of the community. A second species M. steini was described from the Sirius Passet in Greenland in 2017.
Stanleycaris is an extinct, monotypic genus of hurdiid radiodont from the middle Cambrian (Miaolingian). The type species is Stanleycaris hirpex. Stanleycaris was described from the Stephen Formation near the Stanley Glacier and Burgess Shale locality of Canada, as well as Wheeler Formation of United States. The genus was characterized by the rake-like frontal appendages with robust inner spines.
Kiisortoqia soperi is an extinct species of arthropod from the Early Cambrian Sirius Passet Lagerstätte in Greenland. While it had a superficially trilobite-like bodyform, it also possessed large frontal appendages similar to those of radiodonts.
Squamacula is an extinct artiopodan arthropod from the Cambrian Series 2. The type species S. clypeata was described in 1997 from the Chengjiang biota of Yunnan, China. At the time of description there were only two known specimens of S. clypeata, but now there are at least six known specimens. In 2012 a second species S. buckorum was described from the Emu Bay Shale of Australia.
Erratus is an extinct genus of marine arthropod from the Cambrian of China. Its type and only species is Erratus sperare. Erratus is likely one of the most basal known arthropods, and its discovery has helped scientists understand the early evolution of arthropod trunk appendages. Some of the stem-arthropods like radiodonts did not have legs, instead they had flap like appendages that helped them swim. Erratus on the other hand had not only flaps but also a set of primitive legs. It also supported the theory that the gills of aquatic arthropods probably evolved into the wings and lungs of terrestrial arthropods later in the Paleozoic.
 | This prehistoric arthropod-related article is a stub. You can help Wikipedia by expanding it. |