Background Extinctions
Background extinctions are those extinctions that occur continually throughout time. These extinctions are caused by small changes in climate or habitat, depleted resources, competition, and other changes that require adaptation and flexibility. Most extinctions (perhaps up to 95 per cent of all extinctions) occur as background extinctions.

Bamboo sharks
Bamboo sharks belong to a family (Family Hemiscylliidae) of Orectolobiformes sharks. These bottom-dwelling sharks have flattened body. They have an anal fin, 5 gill slits on either side of the head, 2 dorsal fins, no fin spines, and the mouth is well in front of the eyes. The bamboo sharks include the Bluespotted bambooshark (Chiloscyllium caerulopunctatum), the Grey bambooshark (Chiloscyllium griseum), the slender bambooshark (Chiloscyllium indicum), the whitespotted bambooshark (Chiloscyllium plagiosum), and the Brownbanded bamboo shark (above, Chiloscyllium punctatum). Classification: Order Orectolobiformes, Family Hemiscylliidae (bamboo sharks).

Basking Shark
Cetorhinus maximus is a large, sluggish, harmless filter feeder that swims either alone, in pairs, or in large schools. It is the second largest fish.

Bala shark
The Bala shark, also called the Silver shark or tricolor shark (Balantiocheilus melanopterus, is not really a shark - it is a type of minnow. It belongs to the order Cypriniformes (algae-eating minnows), and is a type of bony fish that is much more closely related to goldfish than to sharks. These common pets are originally from south-east Asia, and may be an endangered species in the wild. These fish grow to about 8 inches (20 cm) long, but is usually smaller. Its native habitat is rivers in Borneo, Sumatra, and Thailand. These "sharks" can be found at most pet stores.

Barbel
Barbels are sensory projections near the nostrils and mouth of some sharks (e.g., the nurse shark). These barbels are whisker-like feelers used to taste and feel.

Basihyal
A shark's tongue is called a basihyal. A basihyal is a small, thick, relatively immovable piece of cartilage that is found on the floor of the mouth of sharks and fishes. The basihyal seems to be useless for most sharks, except for the cookiecutter sharks, who use it to rip "flesh-cookies" out of their prey (Shirai and Nakaya, 1992).

Benthic Feeders
Benthic feeders are organisms (plants and animals) that live in or on the bottom of a body of water. Some sharks, like angel sharks, frilled sharks, wobbegongs, and saw sharks are benthic, living on the ocean floor.

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Bigeye Thresher Shark
The Bigeye Thresher Shark, Alopias superciliosus, is a large, charcoal-colored shark with a huge, asymmetrical caudal fin (the top of the tail is much longer than the bottom) and large, green eyes. The Bigeye Thresher Shark hunts in packs; these predators cooperates in rounding up a school of fish, using their long tials to stun or kill the prey. This shark averages 15 feet (4.6 m) long; males are larger than females. Classification: Order Lamniformes (Mackerel sharks), Family Alopiidae (Thresher sharks), Genus and species Alopias superciliosus

Birdbeak Dogfish Shark
The Birdbeak Dogfish Shark, also known as Thompson's Shark and the Shovelnosed Shark (Deania calcea) is a pale-gray, bottom-dwelling shark about 3-3.5 ft (80-90 cm) long. Males and females have different types of teeth.

Blacktip Reef Shark
Carcharhinus melanopterus is a common shark with distinctive black markings on the ends of its fins and a blunt snout. It also has a white streak on its side. (It is NOT the same as the blacktip shark.) It has long, thin, serrated teeth suited for its diet of reef fish. It can grow to be about 6' (1.6 m) long and is a potentially dangerous predator, but it's not very aggressive. It is very common in the coral reefs and shallow lagoons of the tropical Indian and Pacific Oceans. Some have recently entered the Mediterranean (via the Suez canal). These sharks are viviparous and have litters of 2-4 pups after a 16 month gestation period.

Bigeye sixgill shark
The Bigeye sixgill shark (also known as the Calf shark and the Lesser sixgill shark) lives in warm temperate seas, usually living on the bottom. It averages about 6 feet (1.8m) long. The skin ranges from dark gray to light gray. Classification: Order Hexanchiformes (frilled and cowsharks), Family Hexanchidae (cowsharks, sixgilled and sevengilled sharks), Genus and species Hexanchus vitalus (Springer and Waller, 1969) or Hexanchus nakamurai (Teng, 1962) - the latter is preferred.

Bignose shark
The bignose shark (Carcharhinus altimus) is also known as Knopp's shark. This bottom dweller isfound in warm-temperate and tropical seas. It is up to about 10 ft (3 m) long. The skin is ash-colored, but is lighter on the belly; the fins have dark tips. Bony fish is the mainstay of the diet (mackerel is a favorite). . The bignose is viviparous; litters contain from 3 to 11 pups. Newborns are 27 to 35 inches (70-90 cm) long. It was named by Springer in 1950.

Blacknose shark
The blacknose shark Carcharhinus acronotus is a common shark in inshore and moderately deep waters of the western Atlantic Ocean (North Carolina to the Bahamas to southeastern Brazil). This requiem shark averages about 4 feet (1.2 m) long, but can grow to 6 1/2 feet (2 m) long. It has gray skin above (and white skin below) and the snout is dark; some of these sharks have spots that fade with age. The fins are darker at the edges. When threatened, it exhibits a "hunch" display: this shark arches its back, raises its head, and lowers its tail. The blacknose is harmless to people - it is fished as game. The blacknose eats small fish; it is eaten by larger sharks and people. It is viviparous (it has a yolk-sac placenta to nourish the embryos). There are 3 to 6 pups in each litter; the gestation period is 8 to 9 months long. Newborns are 10-19 inches (25.5 to 48.5 cm) long. Classification: Order Carcharhiniformes (ground sharks), Family Carcharhinidae (requiem sharks), Genus Carcharhinus, Species C. acronotus [named by Poey in 1860].

Blacktip Shark
Carcharhinus limbatus (also known as the spinner shark) is a common shark with black marking on the tips of the dorsal and pectoral fins. It is grayish on top and white underneath, with a white stripe running along the side of the body. It has a very long snout and is about 9 feet ( 2.8 m) long. It is harmless to people (unless provoked or while they are eating). It is found in the western and eastern Atlantic Ocean, and the central, western, and eastern Pacific Ocean. Spinner sharks live at the surface and in shallows, and they migrate along the coasts. Their diet consists mostly of small fish, squid, and crustaceans. They have been seen jumping out of the water during feeding. Females give birth to 4-8 live young (10 inches or 25 cm long) after a gestation period of about 10 to 11 months.

Bluntnose sixgill shark
The Bluntnose sixgill shark Hexanchus griseus is a distinctive shark that has six gills on each side of the body (most sharks have five). These sharks (also known as the Cow shark, the Grey shark, the mud shark and the Bulldog shark) have a single (and small) dorsal fin near the end of the body. They are gray-brown in color and are paler underneath. The Bluntnose sixgill is a common shark about 16 ft (4.8 m) long. It has a toxic liver but edible flesh. It eats large fish, crabs and squid. It lives in dark waters at depths down to 5900 ft (1800 m). It has litters of up to 100 pups. Classification: Order Hexanchiformes, Family Hexanchidae, Genus Hexanchus, Species griseus.

Bonnethead Shark
Sphyrna tiburo (also known as the shovelhead) is a small hammerhead shark with a smooth, rounded head. It has small, sharp teeth in the front of the mouth (for grabbing soft prey) and flat, broad molars in the back (for crushing hard-shelled prey). It is a common, harmless, timid shark averaging about 3.3 feet (1 m) long. It is gray-brown above and lighter on the underside with short pectoral fins Large schools migrate to warm water in the winter and cooler water in the summer. Females are mature at 2.5 feet (75 cm) long and give birth in shallow bays to 8 to 16 pups about 14 inches (35 cm) long. Bonnetheads are found in the western Atlantic and eastern Pacific Oceans, in the surf zone, reefs, on sandy bottoms and in estuaries.

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Bronze Whaler
Carcharhinus brachyurus is a very common, dangerous shark that is bronze-colored (brownish-red/yellow) on top and off-white on the belly. It has a subtle white stripe running along its side from the to the pelvic fin. The second dorsal fin is very small and the upper part of the tail is elongated. It is up to 10 feet (3 m) long. This requiem shark lives in warm temperate to subtropical waters, usually by reefs and in shallow bays, but migrates seasonally to higher latitudes, perhaps in search of food. Bronze whalers eat other sharks, rays, squid and sea snakes and hunt during the day. The teeth are sharp and pointed and have tiny serration's. Females give birth to 13-20 live young. Order Carcharhiniformes.

Brown Shark
Carcharhinus plumbeus (also called the sandbar shark, thickskin shark, the northern whaler, and the ground shark) is a common shark with a very tall dorsal fin. They have mouse-gray skin, with paler skin below; the head is wide and flat. They largest found was about 8 ft (2.4 m) long; on average, females are 6 ft (1.8 m) long and males are 3.2 ft (1 m) long. Sandbar sharks are found from very shallow waters to deep waters, generally staying on the bottom. They also frequent estuaries and harbors. Sandbar sharks have a growth rate of about 1.7 inches (43 mm) per year, a slow growth rate for sharks. The thick skin is used for leather. These strong swimmers migrate over 1550 miles (2500 km). Their diet is mostly fish, including menhaden, eels, other sharks, skates, squid, and also crustaceans. Females are mature at 16 years and give birth to 8-12 live young after a gestation period of 9-12 months. Pups are about 8.5 inches (22 cm) long at birth. Classification: Order Carcharhiniformes, Family Carcharhinidae (requiem sharks).

Bull Shark
Carcharhinus leucas is also known as the Cub shark, the Ganges shark, the River shark, the Nicaragua shark, the Zambezi shark, the Shovelnose shark, the Slipway gray shark, the Square-nose shark, the Swan River Whaler, and Van Rooyen's shark. It is a large, fierce predator that eats fish, including other sharks, ray, and just about anything else. It has been known to attack people and will venture into fresh water.

Blue Shark
Prionace glauca, the blue shark, is a large, indigo-colored shark. It is a sleek shark with long, pointed fins and a pointed snout. It has large eyes and grows to be up to 12.5 feet (3.8 m) long. Its diet consists mostly of squid, but it will eat almost anything. It is found worldwide, but is endangered due to over fishing.

Bonito
Bonito is another name for the short finned mako shark (Isurus oxyrinchus), which has a conical snout and long gill slits. It is the fastest swimming fish.

Broadnose sevengill shark
The broadnose sevengill shark (Notorynchus cepedianus) is a distinctive and rare shark that has seven gills (most sharks have five). This unusual shark also has a single (and small) dorsal fin. The broadnose sevengill grows to be up to 10 ft (3 m) long, is speckled and silvery; this shark has small eyes, and a wide head. These aggressive sharks eat fish (including other sharks, rays, and bony fish), seals, and scavenged prey (including human corpses). Broadnose sevengill sharks live in temperate seas on continental shelves (to a depth of 450 ft (135 m). The upper teeth are jagged and multi-cusped (except the center tooth). The lower teeth are comb-shaped. These sharks bear live young in shallow bays. Litters of up to 80 pups have been found. Pups are about 16-18 inches (40-45 cm) long. It was named by Peron in 1807. Classification: Order Hexanchiformes, Family Hexanchidae. It is also called the ground shark, the cow shark, the broad snout shark and the spotted sevengill shark.

Brownbanded bamboo shark
The Brownbanded bamboo shark (also known as the brown-spotted cat shark) is a sluggish shark with distinctive vertical brown and tan markings (juveniles have dark spots). This common shark averages about 3.5 ft (104 cm) long. This bottow-dwelling shark is often found in ports and reefs. It can survive for a while out of water. These sharks are oviparous; they lay oval-shaped eggs on the sea floor. They range from the Indian Ocean to the Western Pacific Ocean. Classification: Order Orectolobiformes, Family Hemiscylliidae, Genus Chiloscyllium, Species C. punctatum (named by Müller and Henle, 1838).

Bullhead Sharks
Known as the Heterodontiformes, this order of sharks has an anal fin, 5 gill slits 2 dorsal fins, and dorsal fin spines.

Buoyancy
Buoyancy is the ability to keep afloat. Sharks are buoyant because of the oil contained in their over-sized livers.



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