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Hexanchus Hookeri
The sixgill sharks are a genus, ''Hexanchus'', of deepwater sharks in the family Hexanchidae. These sharks are characterized by a broad, pointed head, six pairs of gill slits, comb-like, yellow lower teeth, and a long tail. The largest species can grow up to 8 m long and weigh over 600 kg (1320 lb). They are continental shelf-dwelling and abyssal plain scavengers with a keen sense of smell and are among the first to arrive at carrion, together with hagfish and rattails. They show a characteristic rolling motion of the head when feeding. They have been found at depths of up to . Though only two extant species (the bluntnose sixgill shark and the bigeyed sixgill shark) were originally known, a third, the Atlantic sixgill shark, was found to exist. Swimming behavior The bluntnose sixgill shark, ''Hexanchus griseus'', is relatively common to scientists. However, very little information exists about its distribution patterns, migrations and behavior. Data on occurrence ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sinemurian
In the geologic timescale, the Sinemurian is an age and stage in the Early or Lower Jurassic Epoch or Series. It spans the time between 199.3 ± 2 Ma and 190.8 ± 1.5 Ma (million years ago). The Sinemurian is preceded by the Hettangian and is followed by the Pliensbachian. In Europe the Sinemurian age, together with the Hettangian age, saw the deposition of the lower Lias, in Great Britain known as the Blue Lias. Stratigraphic definitions The Sinemurian Stage was defined and introduced into scientific literature by French palaeontologist Alcide d'Orbigny in 1842. It takes its name from the French town of Semur-en-Auxois, near Dijon. The calcareous soil formed from the Jurassic limestone of the region is in part responsible for the character of the classic Sancerre wines. The base of the Sinemurian Stage is at the first appearance of the ammonite genera ''Vermiceras'' and '' Metophioceras'' in the stratigraphic record. A global reference profile ( GSSP or golden spike) for ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stewart Springer
Stewart Springer (5 June 190623 August 1991) was an American ichthyologist and herpetologist. He was a world-renowned expert on shark behavior, classification (taxonomy), and population distribution. More than 35 species of sharks, skates, rays, and other creatures are either classified by or named after him. Education Springer was a field naturalist, mostly self-taught. In 1964, 35 years after he dropped out of Butler University, Springer obtained a baccalaureate from George Washington University after having already achieved success in his chosen field of ichthyology. Many colleagues and students addressed him as Dr. on the mistaken assumption that he must have a Ph.D. in biology or an allied field given his status in the world community of ichthyologists. His exceptional interest in animal behavior was apparent early in his life, when at age 22, he identified and described a new species of lizard, '' Cnemidophorus velox'', the plateau striped whiptail. His interest in the wh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List Of Prehistoric Cartilaginous Fish Genera
This list of prehistoric cartilaginous fish genera is an attempt to create a comprehensive listing of all genera that have ever been included in the class chondrichthyes ''and'' are known from the fossil record. This list excludes purely vernacular terms, genera that are now considered invalid, doubtful (nomina dubia), or were not formally published (nomina nuda), as well as junior synonyms of more established names, and genera that are no longer considered to be cartilaginous fish. It includes all commonly accepted genera. This list currently contains 804 generic names. * Extinct genera are marked by a dagger ( †). * Extant taxon genera are bolded. Naming conventions and terminology Naming conventions and terminology follow the International Code of Zoological Nomenclature. Technical terms used include: * Junior synonym: A name which describes the same taxon as a previously published name. If two or more genera are formally designated and the type specimens are later ass ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shark Teeth
Sharks continually shed their teeth; some Carcharhiniformes shed approximately 35,000 teeth in a lifetime, replacing those that fall out. There are four basic types of shark teeth: dense flattened, needle-like, pointed lower with triangular upper, and non-functional. The type of tooth that a shark has depends on its diet and feeding habits. Sharks are a great model organism to study because they continually produce highly mineralized tissues. Sharks continually shed their teeth and replace them through a tooth replacement system. Through this system, sharks replace their teeth relatively quickly with replacement teeth that are ready to rotate because their teeth often get damaged while catching prey. They will replace teeth that are broken and young sharks can even replace their teeth weekly. Although sharks constantly shed their teeth, factors such as water temperature affect the turnover rate. While warmer water temperatures produced faster rates, cold water temperatures slowe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
