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Chondrichthyes is a class of jawed fish that contains the cartilaginous fish or chondrichthyians, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or bony fish, which have skeletons primarily composed of bone tissue. Chondrichthyes are aquatic vertebrates with paired fins, paired nares, placoid scales, conus arteriosus in the heart, and a lack of opecula and swim bladders. Within the infraphylum Gnathostomata, cartilaginous fishes are distinct from all other jawed vertebrates.
Galeocerdo is a genus of ground shark. Only a single species, G. cuvier, the tiger shark is extant. The earliest fossils date back to the early Eocene epoch, (Ypresian), around 56–47.8 Million years ago. While historically considered a member of the requiem shark family Carcharhinidae, it is currently considered to be the only member of the family Galeocerdonidae. While this genus was historically considered diverse, including 21 extinct species, morphometric analysis conducted in 2021 suggested that the diversity of the genus included only 5 extinct species much lower than previously assumed. The oldest fossils of the extant G. cuvier date to the middle Miocene.
Chimaeras are cartilaginous fish in the order Chimaeriformes, known informally as ghost sharks, rat fish, spookfish, or rabbit fish; the last three names are not to be confused with rattails, Opisthoproctidae, or Siganidae, respectively.
Elasmobranchii is a subclass of Chondrichthyes or cartilaginous fish, including sharks, rays, skates, and sawfish. Members of this subclass are characterised by having five to seven pairs of gill clefts 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.
Holocephali, sometimes given the term Euchondrocephali, is a subclass of cartilaginous fish in the class Chondrichthyes. The earliest fossils are of teeth and come from the Devonian period. Little is known about these primitive forms, and the only surviving group in the subclass is the order Chimaeriformes.
An egg case or egg capsule, often colloquially called a mermaid's purse, is the casing that surrounds the eggs of oviparous sharks, skates and chimaeras. Egg cases typically contain one embryo, except for big skate and mottled skate egg cases, which contain up to 7 embryos. Oviparity is completely absent in the superorder Squalomorphii.
The Australian ghostshark is a cartilaginous fish (Chondrichthyes) belonging to the subclass Holocephali (chimaera). Sharks, rays and skates are the other members of the cartilaginous fish group and are grouped under the subclass Elasmobranchii. Alternative names include elephant shark, makorepe, whitefish, plough-nose chimaera, or elephant fish. It is found off southern Australia, including Tasmania, and south of East Cape and Kaipara Harbour in New Zealand, at depths of 0–200 m (0–656 ft). Despite several of its names, it is not a shark, but a member of a closely related group.
Ischyodus is an extinct genus of chimaera. It is the most diverse and long-lived chimaera genus, with over 39 species found worldwide spanning over 140 million years from the Middle Jurassic to the Miocene. Complete specimens of I. quenstedti from the Late Jurassic of Germany most closely resemble the genus Callorhinchus amongst living chimaera genera. It is sometimes placed in the "Edaphodontidae" a unclearly defined group of chimaera with an uncertain position within the clade. While other authors place it into Callorhinchidae along with Callorhinchus.
The ptyctodontids ("folded-teeth") are placoderms of the order Ptyctodontida, containing the family Ptyctodontidae. With their big heads, big eyes, reduced armor and long bodies, the ptyctodontids bore a superficial resemblance to modern day chimaeras (Holocephali). Their armor was reduced to a pattern of small plates around the head and neck. Like the extinct and related acanthothoracids, and the living and unrelated holocephalians, most of the ptyctodontids are thought to have lived near the sea bottom and preyed on shellfish.
Edaphodon was a fish genus of the family Callorhinchidae. As a member of the Chimaeriformes, Edaphodon was a type of rabbitfish, a cartilaginous fish related to sharks and rays. The genus appeared in the Aptian age of the Lower Cretaceous and vanished in the Pliocene. It was most prominent during the Late Cretaceous. Many Edaphodon species were found in the Northern Hemisphere, but species from the Southern Hemisphere are also known.
Harriotta is a genus of cartilaginous fish in the family Rhinochimaeridae.
Chimaera is the type genus of the cartilaginous fish family Chimaeridae.
The Edestidae are a poorly known, extinct family of shark-like eugeneodontid holocephalid cartilaginous fish.
Chondrenchelys is an extinct genus of cartilaginous fish and the earliest member of Holocephali known from complete skeletons. Chondrenchelys would have been quite a relatively medium-sized fish with an elongated body up to 18 cm (0.59 ft)in length, it had a dorsal fin which was indeed long and a body which tapered to a point. Chondrenchelys had one large pair, one middle-sized pair, and three small pair of tooth plates in each jaw.
Edaphodon mirificus is a species of Edaphodon, which was found by Joseph Leidy in 1856, in Hornerstown, New Jersey.
The Eastern Pacific black ghostshark is a species of fish in the family Chimaeridae. Despite its name, it does not belong to the clade Selachii used for the modern classification of sharks. It is, however, distantly related to the sharks in the sense that both are Chondrichthyes.
Chimaera bahamaensis, commonly known as the Bahamas ghost shark, is a species of fish in the family Chimaeridae. It is found in North Atlantic Ocean around the Bahamas, specifically it has been found east of Andros Island. Chimaera bahamaensis is known to inhabit marine waters from a depth range of 1,483 metres (4,865 ft) – 1,506 metres (4,941 ft). It is one of the most recently described members of the genus Chimaera and to date only a single specimen has been found.
Dwykaselachus is an extinct genus of symmoriiform, a cartilaginous fish that lived in what is now South Africa during the Permian period around 280 million years ago. It was first discovered in the 1980s, in a nodule of sediments from the Karoo Supergroup. Dwykaselachus was named based on Dwyka Group, the group of sedimentary geological formation in the southeastern part of Africa. It represents the place where the type species Dwykaselachus oosthuizeni was found.
Ptyctodus is an extinct armour-plated fish of the late Devonian. Ptyctodus belongs to the family Ptyctodontidae and is of the class Placodermi. They share a close resemblance to modern day chimaeras (Holocephali). Fossils of this armour-plated fish have been found in locations such as in Russia, the Michigan Basis, and Arizona, United States.
Amylodon is an extinct genus of chimaera. It consists of four described species. A. karamysh is known from the latest early Campanian of Russia, the name being derived from the Karamysh River which runs near the type locality. In the Eocene, two species are known. A. venablesae and A. eocenica are both known from the Ypresian-aged London Clay of England. A mandibular plate originally ascribed to the latter was found in the Bartonian of the Barton Beds of England, though later found not to fit with any described species. A. delheidi is known from the Rupelian-aged Boom Clay of Belgium. All species are known mainly from isolated mandibles. They show a slow progressing towards increased shearing ability. Amylodon was considered to be a member of Chimaeridae in Nessov and Averianov, 1996 but other studies have either been assigned to the "Edaphodontidae", or to the Rhinochimaeridae.
References
- ↑ Angielczyk, Ken (April 25, 2012). "A Curious Tooth Collection". New York Times. Archived from the original on April 28, 2012. Retrieved January 1, 2018.
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