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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 ...
In reefs, where visibility is high, species of sharks from the family Carcharhinidae have smaller olfactory bulbs. [58] Sharks found in deeper waters also have larger olfactory bulbs. [59] Sharks have the ability to determine the direction of a given scent based on the timing of scent detection in each nostril. [60]
Sharks are split into eight orders: Carcharhiniformes: ground sharks, the largest order of sharks, including requiem sharks, catsharks, swellsharks, houndsharks, weasel sharks and hammerheads; Heterodontiformes: bullhead sharks; Hexanchiformes: cow sharks and frilled sharks; Lamniformes: mackerel sharks, including thresher sharks
In particular, harvesting young sharks before they reproduce severely impacts future populations. Sharks generally reach sexual maturity only after many years and produce few offspring in comparison to other fish species. [9] Conservationists estimate that up to 100 million sharks are killed by commercial and recreational fishing every year.
These species of bigger, more-lengthy sharks can include great whites, bull sharks, big tiger sharks, great hammerheads, scalloped hammerheads, lemon sharks, spinner sharks, sandbar sharks and ...
In addition, coastal features like rip tides and strong currents pose a greater risk to beachgoers than sharks. The odds of being killed by a shark in the U.S. are 4,332,817 to 1.
Ground sharks, like this blacknose shark, have a nictitating membrane which can be drawn over the eye to protect it. Carcharhiniformes / k ɑːr k ə ˈ r aɪ n ɪ f ɔːr m iː z /, commonly known as ground sharks, are the largest order of sharks, with over 270 species. They include a number of common types, such as catsharks, swellsharks, and ...
During the Cretaceous Period, a genus of sharks roamed the sea with rows of unusual teeth. Mostly large and rounded, these chompers were not meant to slice through their prey, but to grind and ...