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Enchanted Learning All About Sharks! |
 Geologic Time Chart |
| Introduction to Sharks | Introduction to Rays | Anatomy | Shark and Ray Species | Extreme Sharks | Extinct Sharks | Classification | Shark Glossary | Shark Index | Printables, Worksheets, and Activities |
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| NATURAL SELECTION Natural selection is the process in which some organisms live and reproduce and others die before reproducing. Some life forms survive and reproduce because they are better suited to environmental pressures, ensuring that their genes are perpetuated in the gene pool. |
 NAUTILOIDS Nautiloids are primitive, thick-shelled, carnivorous marine invertebrates, cephalopod. The shell is divided into chambers. The nautiloid head has well-developed eyes and tentacles that can grasp prey. They swim by jet-propulsion; they squirt water out from the body cavity. They evolved during the Silurian and are still around today, but are uncommon (only a single genus survives). They were most abundant during the Paleozoic Era, roughly 400 million years ago. Some Nautiloids evolved into Ammonoids. |
NEKTON Nektonic (nektos is Greek for "swimming") animals are those marine creatures that are able to swim against the current. Sharks and rays are nektonic. |
| NERETIC Pertaining to the shallow waters near the shore over the continental shelf. |
 NICARAGUA SHARK Carcharhinus leucas is also known as the Bull shark, the Ganges shark, the River shark, the Cub shark, the Zambezi shark, the Shovelnose shark, the Slipway gray shark, the Square-nose shark, 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. |
 NICTITATING MEMBRANE Some sharks (Carcharhiniformes) have a nictitating membrane, a type of eyelid that protects the eye during hunting. |
NORTHERN WHALER SHARK Carcharhinus plumbeus (also called the sandbar shark, brown shark, the thickskin shark, 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). |
NOSTRILS Sharks and rays have paired nostrils on the underside of the snout. Water continually flows through the nostrils, giving the shark olfactory (the sense of smell) information. Unlike humans, shark nostrils have nothing to do with breathing - they are not even connected to the mouth. |
 NOTHOSAURS Nothosaurs were reptiles with flipper-like limbs that lived both on land and in the water during the Triassic period. They were not dinosaurs. Nothosaurs include Nothosaurus, Lariosaurus, and Ceresiosaurus. |
NUMBFISH Numbfish are electric rays. They numb their prey with an electric current to disable it. |
 NURSE SHARK Ginglymostoma cirratum is a large, sluggish shark that is generally harmless unless provoked. It has very strong jaws, a stout body, and a wide head. They are dark gray on top, some with spots. They are nocturnal hunters that rest during the day in groups. Nurse sharks do well in captivity. |
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Shark Glossary |
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