Pictures of Sharks

For millions of years sharks have lived in our seas in all parts of the world. Over the years there have been mixed feeling about the interaction with sharks and humans. I know as a child growing up after seeing the movie jaws it scared the crap out of me. Sharks are not man eaters as some people may believe. The cases of most shark attacks on humans are simple cases of mistaken identity. Many surfing attacks happen because sharks swimming below think the surfer is a sea turtle or a sea lion which are some of the main food sources for sharks.

The nine known species of hammerhead range from 0.9 to 6 m long (3 to 20 feet). All the species have a projection on each side of the head that gives it a resemblance to a flattened hammer. The shark's eyes and nostrils are at the tips of the extensions.

The hammer shape of the head was once thought to act as a wing, aiding in close-quarters maneuverability and allowing the shark to execute sharp turns without loss of stability. However, it was found that the special design of its vertebra allowed it to make the turns correctly, more than its head. But as a wing the hammer would also provide lift; hammerheads are one of the most negatively buoyant of sharks. Like all sharks, hammerhead have electrolocation sensory pores called ampullae of Lorenzini. By distributing the receptors over a wider area, hammerheads can sweep for prey more effectively.[1] These sharks have been able to detect an electrical signal of half a billionth of a volt. The hammer-shaped head also gives these sharks larger nasal tracts, increasing the chance of finding a particle in the water by at least 10 times as against the ability of other 'classical' sharks.

Wider spacing between sensory organs better enables an organisms to detect gradients and therefore the location of a gradient source such as food or a mate. The peculiar head of this shark can be thought of as analogous to the antennae of an insect.

The great white shark, Carcharodon carcharias, also known as white pointer, white shark, or white death, is an exceptionally large lamniforme shark found in coastal surface waters in all major oceans. Reaching lengths of about 6 metres (20 ft) and weighing up to 2,250 kilograms (5,000 lb), the great white shark is the world's largest known predatory fish. It is the only known surviving species of its genus, Carcharodon.

Taxonomy

Carolus Linnaeus gave the great white shark its first scientific name, Squalus carcharias in 1758. Sir Andrew Smith gave it the generic name Carcharodon in 1833 and in 1873, the generic name was identified with Linnaeus specific name and the current scientific name Carcharodon carcharias was finalised. Carcharodon comes from the Greek words karcharos, which means sharp or jagged, and odous, which means tooth.

Related species

The great white is classified as a mackerel (Lamnidae) shark. There are four other living species in this family, two mako and two Lamna sharks.
Megalodon tooth with two great white shark teeth and a 25 cent coin for size comparison
Megalodon tooth with two great white shark teeth and a 25 cent coin for size comparison

Dental features and the extreme size of both the Great White and the prehistoric Megalodon lead many scientists to believe they were closely related, and the name Carcharodon megalodon was applied to the latter. At present there is considerable doubt about this hypothesis, and other scientists would place the megalodon and white shark as distant relatives - sharing the family Lamnidae but no closer relationship.

Megalodon is only known from its teeth and from a few cartillage remains, and probably reached sizes of 12 metres (40 ft) or more, considerably larger than even the largest great white sharks. From time to time it is suggested that megalodon might still exist. Megalodon teeth have supposedly been found from as recently as 10,000 to 12,000 years ago, but these results appear to be based on misinterpretation of the evidence.[2] However, while megalodon fossils are widespread and plentiful, no evidence has surfaced that the species is anything but extinct.

Other evidence suggests that the great white shark is more closely related to the mako shark than to the megalodon.[3] Accoding to this theory, Carcharodon orientalis[verification needed] and the broad tooth mako Isurus hastalis are fossil sharks that are considered ancestral to the Great White.