''Scenella'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

invertebrate animal which is generally considered to be a mollusc; at various times it has been suggested that this genus belongs with the gastropods, the

monoplacophora Monoplacophora , meaning "bearing one plate", is a polyphyletic superclass of molluscs with a cap-like shell inhabiting deep sea environments . Extant representatives were not recognized as such until 1952; previously they were known only from ...

ns, or the

helcionellid Helcionellid or Helcionelliformes is an order of small fossil shells that are universally interpreted as molluscs, though no sources spell out why this taxonomic interpretation is preferred. These animals are first found about in the late Nem ...

s, although no firm association with any of these classes has been established. An affinity with the hydrozoa (as a flotation device) has been considered, although some authors oppose this hypothesis. A gastropod affinity is defended on the basis of six pairs of internal muscle scars, whilst the serially-repeated nature of these scars suggests to other authors a monoplacophoran affinity. However the specimens showing this scarring have not been convincingly shown to belong to the genus ''Scenella''. A similarity to the Ediacaran '' Ovatoscutum'' has also been drawn.

Description

The shell of ''Scenella'' is elongated along its anterior-posterior axis, and comprises concentric rings around a conical central peak. Radial and concentric corrugations exist in some species. Some specimens are preserved as organic films, others appear to have been infilled with calcite. They are usually preserved point-upwards, with their long axes consistently oriented; this probably represents their most stable position under their depositional current. Soft parts have never been reported in association with ''Scenella'', suggesting that the preserved fragments separated quickly from the associated tissue prior to burial.

Fossil occurrence

''Scenella'' lived from the

Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ag ...

to the

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. ...

. Its remains have been found in

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest co ...

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an ...

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located enti ...

, and North America. Individual fossils are common throughout the Burgess shale, where they often occur in dense aggregations. Where they overlap, specimens deform as by draping. Specimens are sometimes cracked or torn, with margins often damaged by folding or "tattering". 1206 specimens of ''Scenella'' are known from the Greater Phyllopod bed, where they comprise 2.29% of the community.

Taxonomy

''Scenella'' is the only genus in the family Scenellidae. This family has no subfamilies and ''Scenella'' is the

type genus In biological taxonomy, the type genus is the genus which defines a biological family and the root of the family name. Zoological nomenclature According to the International Code of Zoological Nomenclature, "The name-bearing type of a nomina ...

of the family Scenellidae. The taxonomy of the Gastropoda by Bouchet & Rocroi, 2005 categorizes Scenellidae in the superfamilia Scenelloidea within the Paleozoic molluscs of uncertain systematic position.

Species

Species in the genus ''Scenella'' include:''Scenella''
Paleobiology Database, accessed 16 August 2009.

References

External links

*
''Scenella''
at the

Field Museum The Field Museum of Natural History (FMNH), also known as The Field Museum, is a natural history museum in Chicago, Illinois, and is one of the largest such museums in the world. The museum is popular for the size and quality of its educational ...

's Evolving Planet {{Taxonbar, from=Q3951822 Burgess Shale fossils Scenellidae Prehistoric mollusc genera Cambrian invertebrates Ordovician invertebrates Extinct animals of Antarctica Paleozoic animals of Asia Prehistoric animals of Europe Paleozoic animals of North America Cambrian Series 2 first appearances Late Ordovician extinctions Paleozoic life of Ontario Paleozoic life of Newfoundland and Labrador Paleozoic life of Quebec Taxa named by Elkanah Billings