Sharks - By Tay
Sharks are ancient animals. They have been on earth for at least 420 million years. They are the top predators of the ocean's natural food chain. Even before dinosaurs roamed the earth, sharks hunted through the oceans. They are such good survivors that they have had little need to evolve in the last 150 million years. There are over 400 types of sharks. The lifespan of sharks is about 20 – 30 years.
Classification - Sharks belong to the class of fish, Chondrichthyes (cartilaginous fish). Chondrichthyes are fish with a skeleton made of cartilage, jaws, paired fins, and paired nostrils.
Appearance - Sharks, unlike most fish, do not have bones, but cartilage, which is a soft, strong substance. They have several rows of teeth and might have as many as 3,000 teeth in their mouth at one time. When one tooth falls out, another one moves forward to replace the broken tooth.
It is hard to see in the murky waters but sharks have excellent vision. A shark’s night vision is better than a cat’s or a wolf’s eyesight. A shark’s sense of smell is 10,000 times better than a human’s. Sharks can detect electrical impulses, including another fish’s heart beating.
Sharks typically have a tapering body (rounded and tapered at both ends). This shape reduces drag and requires a minimum amount of energy to swim.
Sharks are countershaded. Countershading is a type of camouflage in which the dorsal side is darker than the ventral side. The dark top of a countershaded shark blends in with the dark ocean depths when viewed from above. The light underside blends in with the light from the sun when viewed from below. The result is that predators or prey do not see a contrast between the countershaded animal and the environment.
Sharks range in size from 6 inches to 45 feet. For most shark species, females grow around 25% larger than males.
Habitat - Sharks have adapted to living in a wide range of aquatic habitats at various temperatures. While some species inhabit shallow, coastal regions, others live in deep waters, on the ocean floor and in the open ocean. Some species, like the bull shark, are even known to swim in salt, fresh and brackish waters.
Predators - Sharks are carnivores. Just about any animal in the ocean can be a meal to a shark. Great whites prey on California sea lions, wobbegongs eat shrimp, and tiger sharks feed on several species of sea turtles. As a group, sharks eat almost anything: fishes, crustaceans, mollusk, marine mammals, and other sharks.
While swimming, these animals reach at a speed of 5.0 mph. When foraging, they can escalate their speed to 12 mph.
Sources:
http://www.enchantedlearning.com
http://animalstime.com