|
Agassizodontidae
Helicoprionidae (sometimes referred to as Agassizodontidae) is an extinct family of holocephali, holocephalans within the order (biology), order Eugeneodontida. Members of the Helicoprionidae possessed a "whorl" of Crown (tooth), tooth crowns connected by a single Tooth root, root along the midline of the Mandible, lower jaw. While historically considered Elasmobranchii, elasmobranchs related Shark, sharks and Batomorphi, rays, the closest living relatives of the Helicoprionidae and all other eugeneodonts are now thought to be the ratfishes. The anatomy of the tooth-whorls vary between taxa, with some possessing highly specialized, coiling spirals (such as those of the namesake genus ''Helicoprion''), while others such as ''Sarcoprion'' and ''Parahelicoprion'' possessed shorter whorls''.'' References External linksPalaeos Vertebrates 70.100 Chondrichthyes: Eugnathostomataat paleos.comJSTOR: Journal of PaleontologyVol. 70, No. 1 (Jan., 1996), pp. 162-165 [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Helicoprion
''Helicoprion'' is an Extinction, extinct genus of shark-like Chondrichthyes, cartilaginous fish in the order Eugeneodontiformes. Almost all ''Helicoprion'' Fossil, fossils consist of spirally-arranged clusters of fused teeth, called "tooth whorls", which in life were embedded in the Mandible, lower jaw. With the exception of the Palatoquadrate, upper and lower jaws, the Cartilage, cartilaginous skeleton of ''Helicoprion'' is unknown. The closest living relatives of ''Helicoprion'' (and other eugeneodonts) are the chimaeras, though their relationship is very distant. The unusual tooth arrangement is thought to have been an adaption for feeding on soft-bodied prey, and may have functioned as a deshelling mechanism for hard-bodied cephalopods such as nautiloids and Ammonoidea, ammonoids. In 2013, study of the genus ''Helicoprion'' via morphometric analysis of the tooth whorls found that the genus contained only the species ''H. davisii, H. bessonowi'' and ''H. ergassaminon''. Fossi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Agassizodus
''Agassizodus'' is an extinct genus of eugeneodont holocephalian from the Carboniferous. It belongs to the family Helicoprionidae, which is sometimes called Agassizodontidae. Like other members of its family, it possessed a symphyseal tooth whorl, which was likely present at the tip of the lower jaw and associated with lateral crushing toothplates. The type species, ''A. variabilis'', was originally named ''Lophodus variabilis'' until the name "Lophodus" was determined to be preoccupied. ''A. variabilis'' was originally based on tooth fragments from the Pennsylvanian of Illinois, but the authors who named the genus (St. John and Worthen, 1875) also referred a massive jaw from Osage County, Kansas Osage County is a county located in the U.S. state of Kansas. Its county seat is Lyndon, and its most populous city is Osage City. As of the 2020 census, the county population was 15,766. The county was originally organized in 1855 as We .... The Osage jaw shared some simil ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Toxoprion
''Toxoprion'' (Ancient Greek for "bow saw") is an extinct genus of eugeneodont holocephalans whose fossils are found in marine strata from the Early Carboniferous until the Late Permian near Eureka, Nevada. Description ''Toxoprion'' was one of the many Carboniferous eugeneodonts which bore a palatoquadrate fused to its skull or reduced in other forms, and had its heavily serrated teeth grow outwards on the symphysis of the lower jaw similar to a rounded saw. Despite its jaw showing similarities to another eugeneodont, ''Helicoprion'', the tooth row of ''Toxoprion'' does not coil back on itself, as seen in ''Helicoprion,'' but instead forms a downward curved tooth whorl similar to '' Campyloprion'', '' Lestrodus'', and ''Edestus''. As in most members of eugeneodontida, the smaller teeth found near the anterior end of the whorl represent the oldest teeth, which the animal grew as a juvenile and the larger and younger teeth found near the back of the whorl represent teeth gro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Parahelicoprion
''Parahelicoprion'' is an Extinction, extinct genus of shark-like Chondrichthyes, cartilaginous fish that lived during the Early Permian. The genus contains two species: ''P. clerci'' from the Artinskian, Arta Beds of the Ural Mountains of Russia, and ''P. mariosuarezi'' from the Copacabana Formation of Bolivia. Members of the genus possessed a row of large Crown (tooth), tooth crowns on the midline of the lower jaw, known as a tooth whorl. The characteristics of this whorl are unique to fishes of the order Eugeneodontida, and more specifically the family Helicoprionidae to which ''Parahelicoprion'' belongs. The genus name refers to ''Helicoprion,'' another eugeneodont from the Ural Mountains that bore a similar midline tooth arrangement. The holotype of ''Parahelicoprion clerci'', which consists only of tooth fragments, was badly damaged by mining and is broken into several pieces. That of the Bolivian ''P. mariosuarezi'' similarly consists of only nine partial teeth, the outer e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sarcoprion
''Sarcoprion'' (from the Ancient Greek, "flesh saw") is an extinct genus of eugeneodont holocephalan from the Permian of Greenland. Similar to other helicoprionids such as ''Agassizodus'' and ''Helicoprion ''Helicoprion'' is an Extinction, extinct genus of shark-like Chondrichthyes, cartilaginous fish in the order Eugeneodontiformes. Almost all ''Helicoprion'' Fossil, fossils consist of spirally-arranged clusters of fused teeth, called "tooth whor ...'', it possessed tooth whorls on the symphysis of the jaw as well as flattened, pavement-type teeth. It is distinguished from other members of its family by the presence of sharp, symphyseal teeth on both the upper and lower jaws. The tooth whorl on the lower jaw bore sharp, compact tooth crowns, while a row of backward facing, triangular teeth was present on the roof of the mouth. The preserved material does not show evidence of a distinct upper jaw, implying it may have been fused to the cranium, reduced, or lost entirely. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sinohelicoprion
''Sinohelicoprion'' (meaning "Chinese spiral saw" or "Chinese ''Helicoprion''") is an extinct genus of helicoprionidae, helicoprinid eugeneodontida, eugeneodontid fish that lived during the late Permian and possibly the Early Triassic, from 254 to 251 million years ago. It was first named and classified by H. T. Liu and M. N. Chang in 1963. References Agassizodontidae Permian fish of Asia {{paleo-holocephalan-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crown (tooth)
In dentistry, the crown is the visible part of the tooth above the gingival margin and is an essential component of dental anatomy. Covered by Tooth enamel, enamel, the crown plays a crucial role in cutting, tearing, and grinding food. Its shape and structure vary depending on the type and function of the tooth (incisors, Canine tooth, canines, premolars, or Molar (tooth), molars), and differ between Deciduous teeth, primary dentition and Permanent teeth, permanent dentition. The crown also contributes to facial aesthetics, speech, and oral health. Anatomical crown vs clinical crown The anatomical crown refers to the portion of the tooth covered by enamel, regardless of whether it is visible. The clinical crown is the part of the tooth that is visible in the mouth. In a healthy young adult, the gums typically follow the contour where enamel meets the root, so the clinical and anatomical crowns are similar in size. However, with age or periodontal disease, this may change. Te ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ratfish
Chimaeras are cartilaginous fish in the order Chimaeriformes (), known informally as ghost sharks, rat fish (not to be confused with rattails), spookfish, or rabbit fish; the last two names are also applied to Opisthoproctidae and Siganidae, respectively. At one time a "diverse and abundant" group (based on the fossil record), their closest living relatives are sharks and rays, though their last common ancestor with them lived nearly 400 million years ago. Living species (aside from plough-nose chimaeras) are largely confined to deep water. Anatomy Chimaeras are soft-bodied, shark-like fish with bulky heads and long, tapered tails; measured from the tail, they can grow up to in length. Like other members of the class Chondrichthyes, chimaera skeletons are entirely cartilaginous, or composed of cartilage. Males use forehead denticles to grasp a female by a fin during copulation. The gill arches are condensed into a pouch-like bundle covered by a sheet of skin (an opercul ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Batomorphi
Batomorphi is a division of cartilaginous fishes, commonly known as rays, this taxon is also known as the superorder Batoidea, but the 5th edition of ''Fishes of the World'' classifies it as the division Batomorphi. They and their close relatives, the sharks, compose the subclass Elasmobranchii. Rays are the largest group of cartilaginous fishes, with well over 600 species in 26 families. Rays are distinguished by their flattened bodies, enlarged pectoral fins that are fused to the head, and gill slits that are placed on their ventral surfaces. Anatomy Batomorphs are flat-bodied, and, like sharks, are cartilaginous fish, meaning they have a boneless skeleton made of a tough, elastic cartilage. Most batomorphs have five ventral slot-like body openings called gill slits that lead from the gills, but the Hexatrygonidae have six. Batomorph gill slits lie under the pectoral fins on the underside, whereas a shark's are on the sides of the head. Most batomorphs have a flat, mantle-l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shark
Sharks are a group of elasmobranch cartilaginous fish characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the Division (taxonomy), division Selachii and are the sister group to the Batoidea, Batomorphi (Batoidea, rays and skate (fish), skates). Some sources extend the term "shark" as an informal category including Extinction, extinct members of Chondrichthyes (cartilaginous fish) with a shark-like morphology, such as hybodonts. Shark-like chondrichthyans such as ''Cladoselache'' and ''Doliodus'' first appeared in the Devonian Period (419–359 million years), though some fossilized chondrichthyan-like scales are as old as the Ordovician, Late Ordovician (458–444 million years ago). The earliest confirmed modern sharks (Selachii) are known from the Early Jurassic around , with the oldest known member being ''Agaleus'', though records of true shar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Elasmobranchii
Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including modern sharks ( division Selachii), and batomorphs (division Batomorphi, including rays, skates, and sawfish). Members of this subclass are characterised by having five to seven pairs of gill slits opening individually to the exterior, rigid dorsal fins and small placoid scales on the skin. The teeth are in several series; the upper jaw is not fused to the cranium, and the lower jaw is articulated with the upper. The details of this jaw anatomy vary between species, and help distinguish the different elasmobranch clades. The pelvic fins in males are modified to create claspers for the transfer of sperm. There is no swim bladder; instead, these fish maintain buoyancy with large livers rich in oil. The definition of the clade is unclear with respect to fossil chondrichthyans. Some authors consider it as equivalent to Neoselachii (the crown group clade including modern sharks, rays, and all o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
