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Rising demands for shark products has increased pressure on shark fisheries, but little monitoring or management occurs of most fisheries. [7] Major declines in shark stocks have been recorded over the past few decades; some species had declined over 90% and population declines of 70% were not unusual by 1998. [8]
The first shark-like chondrichthyans appeared in the oceans 400 million years ago, [1] developing into the crown group of sharks by the Early Jurassic. [2] Listed below are extant species of shark. Sharks are spread across 556 described and 23 undescribed species in eight orders. The families and genera within the orders are listed in ...
In most oviparous shark species, an egg case with the consistency of leather protects the developing embryo(s). These cases may be corkscrewed into crevices for protection. The egg case is commonly called a mermaid's purse. Oviparous sharks include the horn shark, catshark, Port Jackson shark, and swellshark. [80] [82]
Otodus includes species that have not yet been formally described. One of these is Otodus debrayi, which is known to have lived in the Early Eocene and Middle Eocene epochs. This species has been found in Africa, North America, Central Asia, and Europe, dating from 47.8 to 38 milion years ago.
But many species of these aquatic apex predators are now in danger of dying out forever. Older than dinosaurs and trees, sharks have endured a lot throughout their 450 million years on Earth. They ...
The most widely known species still surviving is the frilled shark, known as a living fossil, along with the Southern African frilled shark, found along coastal areas of South Africa. Several extinct species are known. †Crassodontidanidae †Crassodontidanidae: 4 8 Extinct: Hexanchidae: Cow sharks: 3 extant 5 extinct 5 extant 31 extinct
The 8-year-old Lebanon, Pennsylvania, boy started digging in the soil, clay and gravel and pulled out a huge fossilized tooth from the long-extinct angustiden shark species, that was 22 million to ...