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Helcionellidae
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 Nemakit-Daldynian age, which is the earliest part of the Cambrian period. A single species persisted to the Early Ordovician. These fossils are component of the small shelly fossils (SSF) assemblages. These are thought to be early molluscs with rather snail-like shells, although they lack any compelling molluscan synapomorphies and thus may not belong to the group. They have been alleged to represent ancestors of the modern conchiferans, a group that includes all the well-known modern classes – gastropods, cephalopods and bivalves. They have also been considered to represent direct ancestors to the cephalopods. Parkhaev (2006, 2007) considers these animals to be crown-group gastropods. Previous to the 2006 classification by Parkh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Latouchella
''Latouchella'' is an extinct genus of marine invertebrate animal, that is considered to be a mollusk and which may be a sea snail, a gastropod. It is a helcionellid from the Tommotian epoch of what is now Siberia. Its tightly coiled, spiral shell contains a number of low "walls" running up the front surface of the interior; these would have directed water currents within its shell. Between these walls are a series of furrows, parallel to the shell's aperture, giving casts of the internal structure the appearance of a railway line, with sleepers (created by furrows) tying together paired rails that run towards the apex of the shell. Description This genus had a curved, segmented shell, and it is often reconstructed as a snail A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class G ... ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Helcionelliformes
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 Nemakit-Daldynian age, which is the earliest part of the Cambrian period. A single species persisted to the Early Ordovician. These fossils are component of the small shelly fossils (SSF) assemblages. These are thought to be early molluscs with rather snail-like shells, although they lack any compelling molluscan synapomorphies and thus may not belong to the group. They have been alleged to represent ancestors of the modern conchiferans, a group that includes all the well-known modern classes – gastropods, cephalopods and bivalves. They have also been considered to represent direct ancestors to the cephalopods. Parkhaev (2006, 2007) considers these animals to be crown-group gastropods. Previous to the 2006 classification by Parkh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Helcionellidae
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 Nemakit-Daldynian age, which is the earliest part of the Cambrian period. A single species persisted to the Early Ordovician. These fossils are component of the small shelly fossils (SSF) assemblages. These are thought to be early molluscs with rather snail-like shells, although they lack any compelling molluscan synapomorphies and thus may not belong to the group. They have been alleged to represent ancestors of the modern conchiferans, a group that includes all the well-known modern classes – gastropods, cephalopods and bivalves. They have also been considered to represent direct ancestors to the cephalopods. Parkhaev (2006, 2007) considers these animals to be crown-group gastropods. Previous to the 2006 classification by Parkh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Helcionelloida
Helcionelloida is an extinct group of ancient molluscs (phylum Mollusca). These are the oldest known conchiferan molluscs, that is, they had a mineralised shell. Some members of this class were mistaken for Monoplacophorans. The class was erected by Peel in 1991. Anatomy These animals were untorted and they had a coiled, cone-shaped shell. The majority of species were small (shells being about two millimeters in length and or diameter). Modern reconstructions depict them as resembling snails. The shells of some genera, particularly '' Yochelcionella'', also possessed a " snorkel"-like opening which was most likely used for breathing. 2005 taxonomy The taxonomy of the Gastropoda by Bouchet & Rocroi, 2005Bouchet P. & Rocroi J.-P. (Ed.); Frýda J., Hausdorf B., Ponder W., Valdes A. & Warén A. 2005. ''Classification and nomenclator of gastropod families''. Malacologia: International Journal of Malacology, 47(1-2). ConchBooks: Hackenheim, Germany. . ISSN 0076-2997. 397 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Small Shelly Fauna
The small shelly fauna, small shelly fossils (SSF), or early skeletal fossils (ESF) are mineralized fossils, many only a few millimetres long, with a nearly continuous record from the latest stages of the Ediacaran to the end of the Early Cambrian Period. They are very diverse, and there is no formal definition of "small shelly fauna" or "small shelly fossils". Almost all are from earlier rocks than more familiar fossils such as trilobites. Since most SSFs were preserved by being covered quickly with phosphate and this method of preservation is mainly limited to the late Ediacaran and early Cambrian periods, the animals that made them may actually have arisen earlier and persisted after this time span. Some of the fossils represent the entire skeletons of small organisms, including the mysterious '' Cloudina'' and some snail-like molluscs. However, the bulk of the fossils are fragments or disarticulated remains of larger organisms, including sponges, molluscs, slug-like halkierii ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 in amber, hair, petrified wood and DNA remnants. The totality of fossils is known as the ''fossil record''. Paleontology is the study of fossils: their age, method of formation, and evolutionary significance. Specimens are usually considered to be fossils if they are over 10,000 years old. The oldest fossils are around 3.48 billion years old to 4.1 billion years old. Early edition, published online before print. The observation in the 19th century that certain fossils were associated with certain rock strata led to the recognition of a geological timescale and the relative ages of different fossils. The development of radiometric dating techniques in the early 20th century allowed scientists to quantitatively measure the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Yochelcionella Water Flow
''Yochelcionella'' is an extinct genus of basal molluscs which lived during the Tommotian epoch, the first epoch of the Cambrian period. This genus is often reconstructed to resemble snails. ''Yochelcionella'' is the type genus of the family Yochelcionellidae. Description This genus of molluscs possessed shells which were shaped like curved caps, with an exhaust pipe shaped " snorkel" emanating underneath where the apex (point of the shell) curves over. It is believed that the "snorkel" was used in breathing, allowing waste water to flow away from the gills. Taxonomy When they were first discovered, they were originally thought to be monoplacophorans. Their snorkel may represent a move towards a tubular shell, such as is seen in the modern scaphopods. It has also been interpreted as a precursor to the cephalopod funnel or siphuncle. The taxonomy of the Gastropoda by Bouchet & Rocroi, 2005Bouchet P. & Rocroi J.-P. (Ed.); Frýda J., Hausdorf B., Ponder W., Valdes A. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stenothecidae
Stenothecidae is an extinct family of fossil univalved Cambrian molluscs which may be either gastropods or monoplacophorans. The name of this taxon should not be confused with that of the class Stenothecoida, a group of problematic Cambrian invertebrates that have a bivalved (dorsal and ventral) shell. Morphology The group comprises conical laterally compressed shells that may be smooth or ornamented with folds or ribs. The shells are broadly limpet-like, which led to their initial consideration as monoplacophoran molluscs. Taxonomy The taxonomic position of the group is unclear; it has been classified as a Yochelcionelloid or Helcionelloid. It is not obviously in the stem group of any modern molluscan class, and has been referred to the monoplacophora, although the monoplacophora are no longer considered to be a clade, and thus that classification means little more than "primitive mollusc". Genera The family Stenothecidae consists of two subfamilies and the fol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Yochelcionellidae
''Yochelcionella'' is an extinct genus of basal molluscs which lived during the Tommotian epoch, the first epoch of the Cambrian period. This genus is often reconstructed to resemble snails. ''Yochelcionella'' is the type genus of the family Yochelcionellidae. Description This genus of molluscs possessed shells which were shaped like curved caps, with an exhaust pipe shaped " snorkel" emanating underneath where the apex (point of the shell) curves over. It is believed that the "snorkel" was used in breathing, allowing waste water to flow away from the gills. Taxonomy When they were first discovered, they were originally thought to be monoplacophorans. Their snorkel may represent a move towards a tubular shell, such as is seen in the modern scaphopods. It has also been interpreted as a precursor to the cephalopod funnel or siphuncle. The taxonomy of the Gastropoda by Bouchet & Rocroi, 2005Bouchet P. & Rocroi J.-P. (Ed.); Frýda J., Hausdorf B., Ponder W., Valdes A. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trenellidae
''Trenella'' is the sole genus in the Trenellidae, an extinct family of paleozoic Yochelcionellids. 2005 taxonomy The taxonomy of the Gastropoda by Bouchet & Rocroi, 2005Bouchet P. & Rocroi J.-P. (Ed.); Frýda J., Hausdorf B., Ponder W., Valdés Á. & Warén A. 2005. ''Classification and nomenclator of gastropod families''. Malacologia: International Journal of Malacology, 47(1-2). ConchBooks: Hackenheim, Germany. . . 397 pp. http://www.vliz.be/Vmdcdata/imis2/ref.php?refid=78278 categorizes Trenellidae in the superfamilia Yochelcionelloidea within the Paleozoic molluscs of uncertain systematic position. This family has no subfamilies. 2006-2007 taxonomy According to P. Yu. Parkhaev, the family Trenellidae is in the superfamily Yochelcionelloidea Runnegar & Jell, 1976 within the order Helcionelliformes Golikov & Starobogatov, 1975, subclass Archaeobranchia Parkhaev, 2001, class Helcionelloida Peel, 1991. Genera Genera in the family Trenellidae include: * ''Trenella ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
