"Sharks are a large group of fish that have inhabited the oceans for over 400 million years, even before dinosaurs populated our planet. They belong to the superorder Selachimorpha, and modern sharks have specific characteristics like a cartilaginous skeleton, five or six pairs of gills and several rows of teeth." -sharks-world.com

From the Smithsonian's Ocean Portal:
​What makes a Shark a Shark?

1. Their Cartilage
"No matter their size, all sharks have similar anatomy. Like other elasmobranchs (a subclass of animals that also includes rays and skates), sharks have skeletons made of cartilage—the hard but flexible material that makes up human noses and ears. This is a defining feature of elasmobranchs, as most fish have skeletons made of bone. Cartilage is much lighter than bone, which allows sharks to stay afloat and swim long distances while using less energy."
2. Their Teeth! 
"Every shark also has several rows of teeth lining its jaws. Unlike people, which have a limited number of teeth in their lifetime, sharks are constantly shedding their teeth and replacing them with new ones."
​3. Their Gill Slits
"Another defining feature of sharks is their array of gill slits. Unlike bony fishes, which have one gill slit on each side of their bodies, most sharks have five slits on both sides that open individually (and some shark species have six or seven)."

Where Sharks Live

Concept Planner

Sharks 101 from Nat Geo

"Sharks can rouse fear and awe like no other creature in the sea. Find out about the world's biggest and fastest sharks, how sharks reproduce, and how some species are at risk of extinction." www.nationalgeographic.com/animals/fish/group/sharks/

Shark Senses from Discovery's Sharkopedia

"A shark's main missions in life are to eat and survive. But finding food in the ocean takes an arsenal of finely tuned senses, even some we don't have. Find out how sharks are hardwired to hunt their prey." sharkopedia.discovery.com

Shark Teeth

On Animal Planet's series "Fooled by Nature," we learn about the most famous teeth on Earth: shark teeth. Sharks have a massive bite, with rows of teeth. They even have teeth on the surface of their skin.

Words to Know

Cartilage strong connective tissue that supports the body and is softer and more flexible than bone
Denticles- The teeth-like scales that cover sharks’ skin which help them to swim quickly.
Dorsal Fin an unpaired fin on the back of a fish or whale, e.g., the tall triangular fin of a shark or killer whale.
Ecosystem a biological community of interacting organisms and their physical environment.
 Electroreception a shark's "sixth" sense; electroreception is the ability to sense electrical signals/
Gill Slits any of a series of openings between the gill arches of a fish, through which water passes from the pharynx to the exterior, bathing the gills in the process.
Habitat The natural home or environment of an animal, plant, or other organism.
Plankton tiny plants and animals that float in the ocean
Pectoral Fin each of a pair of fins situated on either side just behind a fish's head, helping to control the direction of movement during locomotion. They correspond to the forelimbs of other vertebrates.
Predator an animal that naturally preys on others.
Pup a young shark.
Species a group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding.
 Temperate being of mild temperature: neither extremely hot nor extremely cold.

Additional Resources

Shark Research Institute (SRI), a multi-disciplinary nonprofit scientific research organization, was created to sponsor and conduct research on sharks and promote their conservation. sharks.org
The Ocean Portal from the Smithsonian National Museum of Natural History offers in depth info and resources for educators. ocean.si.edu
Educator resources from Florida's official Natural History Museum located at the University of Florida. flmnh.ufl.edu
The Discovery Channel's interactive one stop shop for Shark information, videos and activities. sharkopedia.discovery.com

Want more in depth content knowledge? 
Go to the National Science Teachers Association for articles, books and free online modules. you do not need to be a member to access many of the resources.