Sharks - Lamniformes

Lamniformes, also known as Mackerel Sharks, is one of the most well-known groups as it includes famous species and feared hunters, like the Great White Shark, Basking Shark, Mako (Shortfin and Longfin) and Megamouth. This group has a particularly large mouth, ideal for seizing and immobilising large prey as well as for tearing off chunks of meat from hapless victims. The Megalodon, now extinct, was also part of this fascinating group. Other members include the Goblin and Thresher sharks.

Lamniformes have two dorsal fins, neither of which is spined. They also have an anal fin, five gill slits and small spiracles (in most species), which are situated behind the eyes. The eyes have no nictitating membrane, and usually roll back in the case of frontal impact in order to protect them.

The mouths of these sharks are large, with jaws extending far back to allow them to open as widely as possible, gulping down large prey and chunks of flesh. These jaws are filled with lamnoid teeth, characterised by very large anterior teeth, followed by increasingly smaller intermediate teeth and large lateral teeth and then a row of small posterior teeth. The Basking Shark and the Megamouth sieve plankton through bristle-like structures in their mouths.

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Lamniformes are ovoviviparous. Eggs are fertilised and hatched internally. However, this group also displays a phenomenon known as oophagy, which dictates that the first pup to hatch in the oviduct should devour the other unfertilised eggs in the oviduct. This pup is born strong, beable and with trained killer instincts in preparation for its independent life in the open waters.

Lamniformes only live in saltwater, and cannot survive in freshwater rivers or lakes. Different species are able to live in the shallower, warmer coastal areas or the deeper, colder waters of the open seas. They also withstand varying temperatures to make them one of the most prolific and abundant known shark groups. The smallest lamnoid is the Crocodile Shark, which reaches about 1.1 metres in length. The largest is the Basking Shark, growing to an impressive length of approximately 9.8 metres.

Interestingly, Lamniformes have a special adaptation. This involves their circulatory system and allows them to retain heat generated by cellular metabolic processes. This is in contrast to other cold-blooded sharks and fish and allows them to spend energy on hunting and travelling rather than on trying to maintain a beable body temperature as the water temperature around them cools.

For more information please view: http://www.pbs.org

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