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All About Sharks!
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Radioisotope dating is used to find out how old fossils are.
RAGGED TOOTH SHARK
Ragged tooth sharks (Eugomphodus taurus) are also known Sandtigers, the grey nurse shark, the sand shark, and the spotted ragged-tooth shark. They are widespread Mackerel sharks (Lamniformes) that range from gray to brown and are about 10-12 feet (3-3.7 m) long. They are fish-eaters that have long, sharp teeth in a narrow snout. They eat and migrate in groups; their activity peaks at night. They are found mostly near coastlines, from the surface down to depths of 3,900 ft (1,200 m). At birth they are about 3 ft (1 m) long. Classification: Order Lamniformes (Mackerel sharks), Family Odontaspididae (Sandtiger sharks).
The rainbow shark, Epalzeorhynchus (Labeo) frenatusis not a real shark - it is a type of algae-eating minnow (a cyprinid) that superficially resembles a shark (and is often confused with the red-finned shark - another non-shark). The rainbow shark can be an aggressive fish and will eat smaller or weaker fish (although it is mostly an algae eater). The rainbow shark is a popular home aquarium fish. It grows up to 6 inches (15 cm) and is native to Thailand and Indochina.
Ratfish (or chimaeras) are cartilaginous fish that have compressed bodies and rodent-like teeth (hence their name). Ratfish are closely related to sharks and rays (in the class Chondrichthyes), but ratfish have bigger heads and eyes, the mouth is more towards the front of the head, the skin is smooth, most species have a whip-like tail, and the four gills have gill covers and are located under the skull. Male ratfish are smaller than the females. Ratfish are also called elephantfish (the family Callorhynchidae) or ghost sharks. Ratfish evolved during the Devonian (about 340 million years ago). There are three families of ratfish and about 35 species of ratfish alive today; they all live in cold water and are oviparous (they lay eggs on the ocean bottom).
Rays are fish that have a flat body, a tail, and cartilage instead of bones. Rays evolved from sharks.
Ray-finned fish (class Actinopterygii) are the largest group of fish. These bony fish evolved during the very end of the Silurian, about 408 million years ago. These fish dominate the seas today. Sharks are not ray-finned fish.
The red-tailed shark, Epalzeorhynchus (Labeo) bicoloris not a real shark - it is a type of minnow (a cyprinid) that superficially resembles a shark (and is often confused with the rainbow shark - another non-shark). The red-tailed shark can be an aggressive fish and will eat smaller or weaker fish (although it is mostly an algae eater). The red-tailed shark is a popular home aquarium fish. It grows up to about 5 inches (13 cm) and is native to Thailand.
Remora (family Echeinidae) are small fish that live on and around sharks. They eat stray bits of food left by the shark and tiny shrimp-like parasites that live on the shark's skin. They have sucker-like disks on their heads with which they attach to the shark. Both the shark and the remora benefit from the pairing, but the remore benefits much more; this is commensalism. Remora are also known as sucker fish or shark sucker.
Reptiles are a group of animals that have scales, breathe air, are cold-blooded, and usually lay egg. Lizards, snakes, turtles and dinosaurs are reptiles.
Requiem sharks (Family Carcharinidae) are a type of large Carcharhiniformes sharks. with 5 gill slits, two dorsal fins, an anal fin, no fin spines, the mouth behind the eyes, and nictitating eyelids. There are 48 species of carcharinidae including the tiger shark, Dusky shark, Bull shark, Galapagos shark, Sandbar shark, and many others.
A rostrum is the beak-like upper jaw of a whale.
Roughsharks (Oxynotidae) are a group of small sharks that are mostly bottom-dwellers. They have a stout, laterally-compressed body, no anal fin, and a prominent ridge along the abdomen. Their lower teeth point backwards and the upper teeth are larger in the back of the mouth. The roughsharks include the prickly dogfish (humantin), the Caribbean roughshark, the angular roughshark, and the sailfin roughshark (sharp-back shark). Classification: Order Squaliformes
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