|
Cyrtocerinida
Cyrtocerinida is an order of Ordovician nautiloid cephalopods. The order includes the families Cyrtocerinidae and Eothinoceratidae, as well as the genera '' Bathmoceras'' and '' Rummoceras''. Cyrtocerinids can be characterized by a broad siphuncle encased by very thick connecting rings with concave outer surfaces. Despite their thickness, the connecting rings are nautilosiphonate, meaning that their inner layer is a poorly-mineralized organic sheath (similar to modern nautiluses) rather than a porous calcified structure. There are various calcified endosiphuncular deposits such as collars and longitudinal ridges on the inner layer of the connecting ring. These deposits are discontinuous, reforming after each chamber. This differentiates them from the continuous endosiphuncular ridges found in other nautiloids, such as the related oncocerids. The overall shell shape is typically orthoconic (straight, pointed) or breviconic (stout). The body chamber is oncomyarian, meaning ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cyrtocerinidae
Cyrtocerinidae is a family of nautiloid cephalopods in the Order Cyrtocerinida Cyrtocerinida is an order of Ordovician nautiloid cephalopods. The order includes the families Cyrtocerinidae and Eothinoceratidae, as well as the genera ''Bathmoceras'' and '' Rummoceras''. Cyrtocerinids can be characterized by a broad siphunc ..., previously considered ellesmerocerids. Members of the family have slightly endogastric (inwardly curved) breviconic shells with ventral siphuncles that have connecting rings thickened as lobes that project straight into the interior. Cyrtocerinidae was established by Flower 1964 for the genus '' Cyrtocerina'' Billings 1865, found at various locations across North America. The shells are generally small, laterally compressed, and dorsum more narrowly rounded than the venter. References Prehistoric nautiloid families Ordovician first appearances Ordovician extinctions Ellesmerocerida {{paleo-nautiloidea-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Multiceratoidea
Multiceratoidea is a major subclass or superorder of Paleozoic nautiloid cephalopods. Members of this group can be characterized by nautilosiphonate connecting rings, with an organic inner layer and outer layer of calcitic spherules and blades, similar to the modern nautilus. The earliest-diverging multiceratoids have oncomyarian muscle scars (with numerous small muscle attachments ringing the body chamber), though several orders trend towards a ventromyarian condition (with muscle scar area concentrated at the bottom of the body chamber). Multiceratoid shells are generally short and curled, with a relatively small aperture (opening). Cameral deposits are never found among the multiceratoids, though several orders are known to bear endosiphuncular deposits within their siphuncles. When originally defined in 2013, Multiceratoidea included four nautiloid orders: Ellesmerocerida, Oncocerida, Discosorida, and Ascocerida. The order Tarphycerida was considered a potential member of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ellesmerocerida
The Ellesmerocerida is an order of primitive cephalopods belonging to the subclass Nautiloidea with a widespread distribution that lived during the Late Cambrian and Ordovician. Morphology The Ellesmerocerida are characterized by shells that are typically small, some even tiny, with close-spaced septa and relatively large ventral siphuncles. In some genera (e.g. '' Paleoceras''), the septa are uniformly spaced. Shells of ellesmerocerids are typically smooth and compressed and vary in form. They may be breviconic (short) or longiconic (elongate), straight (orthoconic) or curved (cyrtoconic). Cyrtoconic forms are usually endogastric, with longitudinally convex ventral margins. The apeces of straight forms typically have an endogastric curvature. Some may have grown to as much as 15 cm. Siphuncle segments are tubular or concave. Septal necks are short. Connecting rings which may appear layered are thick and typically wedge shaped with their maximum width at or near where ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bathmoceras
''Bathmoceras'' is a primitive cephalopod genus from the Middle and Upper Ordovician. It is a member of the order Cyrtocerinida and is the only genus in the family Bathmoceratidae. Derivation At one time ''Bathmoceras'' was thought to have possibly given rise to ''Polydesmia'', once thought to have been the ancestral actinocerid. Since then revision of actinocerid phylogeny and of Ordovician stratigraphy in east Asia have cast doubts on this hypothesis. ''Bathmoceras'' is most likely derived from ''Eothinoceras'' through lengthening of the septal necks and of the inward projections of the connecting rings in a forward direction. ''Eothinoceras'' differs in that the septal necks are vestigial rather than being somewhat long as in ''Bathmoceras'' and that the inward projections of the connecting rings point straight in rather than projecting forward. Both are straight shelled or slightly exogastric. Eothinoceras is also apparently more slender. Furnish and Glenister also include ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nautiloid
Nautiloids are a group of marine cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and '' Allonautilus''. Fossil nautiloids are diverse and speciose, with over 2,500 recorded species. They flourished during the early Paleozoic era, when they constituted the main predatory animals. Early in their evolution, nautiloids developed an extraordinary diversity of shell shapes, including coiled morphologies and giant straight-shelled forms (orthocones). Only a handful of rare coiled species, the nautiluses, survive to the present day. In a broad sense, "nautiloid" refers to a major cephalopod subclass or collection of subclasses (Nautiloidea ''sensu lato''). Nautiloids are typically considered one of three main groups of cephalopods, along with the extinct ammonoids (ammonites) and living coleoids (such as squid, octopus, and kin). While ammonoids and coleoids are monophyletic clades with exclusive ancestor-descendant re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eothinoceratidae
Eothinoceratidae is a family of Lower Ordovician nautiloid cephalopods included in the Cyrtocerinida Cyrtocerinida is an order of Ordovician nautiloid cephalopods. The order includes the families Cyrtocerinidae and Eothinoceratidae, as well as the genera '' Bathmoceras'' and '' Rummoceras''. Cyrtocerinids can be characterized by a broad si .... The family was originally established for the genus '' Eothinoceras''. Morphology The Eothinoceratidae as typified by ''Eothinoceras'' is characterized by slender slightly exogastric shells with a rather large siphuncle running along the convex ventral margin. Connecting rings are triangular in section and point straight into the interior of the siphuncle. Septal necks are short to absent. Genera In addition to the type genus ''Eothinoceras'' the family is said to include '' Conothinoceras'', '' Desioceras'', '' Margaritoceras'', '' Protothinoceras'', '' Sacerdosoceras'', and '' Saloceras'' summarized here. ''Desioceras'' Cecioni ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rousseau Flower
Rousseau Hayner Flower (1913–1988) was an extremely prolific 20th century paleontologist, known for his eccentric personality. Career Although trained as an entomologist, and a specialist in dragonflies and orthopterans, Flower began studying paleontology in the middle of the 1930s. He became an expert in North American cephalopods of the Devonian period as well as the stratigraphy of the early Paleozoic era. His main field was the nautiloids, which he studied intensely, often focusing on life habits and theoretical aspects of paleobiology, but he also penned many papers on fossil corals and other invertebrates. Flower described several hundred new fossil species and over 100 new genera. Eccentricities In the paleontology community, Flower's colorful behavior earned him admirers and enemies—whom he would occasionally "thank" in the acknowledgement sections of his papers or, in one case, in the name of a fossil species. His antics included mocking the alleged low-s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oncocerida
The Oncocerida comprise a diverse group of generally small nautiloid cephalopods known from the Middle Ordovician to the Mississippian (early Carboniferous; one possible member is known from the Early Permian), in which the connecting rings are thin and siphuncle segments are variably expanded (Flower, 1950). At present the order consists of some 16 families, a few of which, such as the Oncoceratidae, Brevicoceratidae, and Acleistoceratidae contain a fair number of genera each while others like the Trimeroceratidae and Archiacoceratidae are represented by only two or three (Sweet, 1964). Physical characteristics The shells of oncocerids are primarily somewhat compressed cyrtoconic brevicones. More advanced forms include gyrocones, serpenticones, torticones, and elongate orthocones and cyrtocones, reflective of the different families and genera (Flower, 1950; Sweet, 1964). The siphuncle in the Oncocerida is commonly located at or near the ventral margin. Connecting rings are mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prehistoric Nautiloids
Prehistory, also known as pre-literary history, is the period of human history between the use of the first stone tools by hominins 3.3 million years ago and the beginning of recorded history with the invention of writing systems. The use of symbols, marks, and images appears very early among humans, but the earliest known writing systems appeared 5000 years ago. It took thousands of years for writing systems to be widely adopted, with writing spreading to almost all cultures by the 19th century. The end of prehistory therefore came at very different times in different places, and the term is less often used in discussing societies where prehistory ended relatively recently. In the early Bronze Age, Sumer in Mesopotamia, the Indus Valley Civilisation, and ancient Egypt were the first civilizations to develop their own scripts and to keep historical records, with their neighbors following. Most other civilizations reached the end of prehistory during the following Iron Age. T ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clade
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, the equivalent Latin term ''cladus'' (plural ''cladi'') is often used in taxonomical literature. The common ancestor may be an individual, a population, or a species (extinct or extant). Clades are nested, one in another, as each branch in turn splits into smaller branches. These splits reflect evolutionary history as populations diverged and evolved independently. Clades are termed monophyletic (Greek: "one clan") groups. Over the last few decades, the cladistic approach has revolutionized biological classification and revealed surprising evolutionary relationships among organisms. Increasingly, taxonomists try to avoid naming taxa that are not clades; that is, taxa that are not monophyletic. Some of the relationships between org ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Monophyly
In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic groups are typically characterised by shared derived characteristics ( synapomorphies), which distinguish organisms in the clade from other organisms. An equivalent term is holophyly. The word "mono-phyly" means "one-tribe" in Greek. Monophyly is contrasted with paraphyly and polyphyly as shown in the second diagram. A ''paraphyletic group'' consists of all of the descendants of a common ancestor minus one or more monophyletic groups. A '' polyphyletic group'' is characterized by convergent features or habits of scientific interest (for example, night-active primates, fruit trees, aquatic insects). The features by which a polyphyletic group is differentiated from others are not inherited from a common ancestor. These definitions have tak ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Body Chamber
The body whorl is part of the morphology of the shell in those gastropod mollusks that possess a coiled shell. The term is also sometimes used in a similar way to describe the shell of a cephalopod mollusk. In gastropods In gastropods, the body whorl, or last whorl, is the most recently formed and largest whorl (or revolution) of a spiral or helical shell, terminating in the aperture. It is called the "body whorl" because most of the body of the soft parts of the animal fits into this whorl. The proportional size of the body whorl in gastropod shells differs greatly according to the actual shell morphology. For shells in which the rate of whorl expansion of each revolution around the axis is very high, the aperture and the body whorl are large, and the shell tends to be low spired. The shell of the abalone is a good example of this kind of shell. The opposite tendency can sometimes create a high spire with very little whorl increase per revolution. In these instances, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
