What you don't know about Sharks

shark | Attacks, Types, & Facts
shortfin mako shark
The whale shark (Rhincodon typus) and the basking shark (Cetorhinus maximus), both of which may weigh several tons, are harmless giants that subsist on plankton strained from the sea through modified gill rakers. Whale sharks may grow up to 18 metres (59 feet) in length, whereas basking sharks may reach 14 metres (46 feet) fully grown. All other sharks prey on smaller sharks, fish, squid, octopuses, shellfish, other invertebrates, and, in some species, trash. The largest among the more predatory species is the voracious 6-metre (20-foot) white shark, which attacks seals, dolphins, sea turtles, large fish, and occasionally people. The more sluggish Greenland shark (Somniosus microcephalus) of cold deep waters feeds on seals, large fish, and even swimming reindeer; they may also scavenge whale carcasses.

Whale shark (Rhincodon typus).
Whale shark (Rhincodon typus). © Jeffrey L. Rotman
reef shark; nurse shark.
Normally, sharks feed on fish, often attacking in schools. Open-ocean species such as the mackerel (Lamna), mako (Isurus), and thresher (Alopias) sharks frequently feed near the surface and are much sought after with rod and reel for sport. Beautifully streamlined and powerful swimmers, those open-ocean sharks are adept at feeding on fast tuna, marlin, and the like. Bottom-feeding species of sharks are stout, blunt-headed forms that tend to have more-sluggish habits. The shellfish eaters among them have coarse, pavementlike, crushing teeth.

grey reef shark
grey reef sharkLearn about the grey (or gray) reef shark, including its mating behaviours.Contunico © ZDF Enterprises GmbH, MainzSee all videos for this article
Fertilization in sharks is internal. The male introduces sperm into the female by using special copulatory organs (claspers) derived from the pelvic fins. The young in many species hatch from eggs within the female and are born alive. Other species may lay eggs or nurture their young in the uterus with a placental attachment to the mother, like humans. Some species may even consume their siblings before they are born.
Study the life cycle and fossilization of Carcharocles megalodon from the Miocene and Pliocene epochs
Study the life cycle and fossilization of Carcharocles megalodon from the Miocene and Pliocene epochsThe natural history of the megalodon (Carcharocles megalodon), a gigantic predatory shark that plied tropical and temperate seas during the Miocene and Pliocene epochs.Encyclopædia Britannica, Inc.See all videos for this article
The origin of sharks is obscure, but their geologic record goes back at least to the Devonian Period (419.2 million to 358.9 million years ago). Fossil sharklike fish appeared in the Middle Devonian Epoch and became the dominant vertebrates of the Carboniferous Period (358.9 million to 298.9 million years ago). Modern sharks appeared in the Early Jurassic Epoch (201.3 million to 174.1 million years ago.
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