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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 ...
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Otodus megalodon (/ ˈ m ɛ ɡ əl ə d ɒ n / MEG-əl-ə-don; meaning "big tooth"), commonly known as megalodon, is an extinct species of giant mackerel shark that lived approximately 23 to 3.6 million years ago (Mya), from the Early Miocene to the Early Pliocene epochs.
The shark is among the 25 "most wanted lost" species that are the focus of Global Wildlife Conservation's "Search for Lost Species" initiative. [2] The Pondicherry has been spotted in rivers in India in the late 2010s. [3] A Pondicherry shark was caught in the Menik Ganga (river) in SE Sri Lanka in 2011. It was photographed and released alive.
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]
Older than dinosaurs and trees, sharks have endured a lot throughout their 450 million years on Earth. They’ve even survived five mass extinctions, including the asteroid that wiped out 75% of ...
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 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 ...