Sharks - Evolution And Classification, Overview Of Shark Groups, Structural And Functional Adaptations, Locomotion And Buoyancy

Sharks - Evolution And Classification

Sharks are often described as "primitive" animals, and little changed in millions of years of evolution. It is true that the first sharks evolved in the oceans more than 300 million years ago, in the Devonian era. However, the earliest species of sharks are all extinct. The species living in the oceans today evolved only 70-100 million years ago. The fact that the general body plan o…

Sharks - Overview Of Shark Groups

There are eight orders of living sharks. The Angelshark order includes the angelsharks and sand devils. These sharks are flattened like rays and tend to live on the ocean bottom in water depths to 4,200 ft (1,300 m). They are found in most oceans, except the central Pacific and Indian Oceans and the polar areas. There are thirteen species, most of which are less than 60 in (1.5 m) long. The Dogfis…

Sharks - Structural And Functional Adaptations

Sharks - Locomotion And Buoyancy

Sharks swim by moving their caudal fin from side to side in a sweeping motion, which propels them forward through the water. The large upper lobe of the caudal fin of most sharks provides most of the forward thrust. Sharks, like makos, which sometimes need to swim at high speed, also have a well-developed lower caudal fin lobe for greater thrust. As a shark moves through the water, it angles the p…

Sharks - Temperature Regulation

Sharks are "cold-blooded" (poikilothermic) animals, meaning their body temperature is the same as that of the water in which they live. The term cold-blooded is misleading, however, because sharks living in warm water are "warm-blooded" in actual temperature. Some fast-swimming sharks in the Mackerel shark order (for example the mako and white sharks) can actually raise…

Sharks - Respiration

Sharks - Water And Salt Balance

Sharks - Sensory Systems

Sharks have the same five senses of sight, hearing, smell, taste, and touch that humans have. Moreover, some of these senses are more acute in sharks. Sharks also have an additional sense; they can detect weak electric fields in the water. Sharks are known to possess a complex visual system, and can even see color. A problem for sharks is that, if they are in deep or murky water, the light level i…

Sharks - Feeding And Diet

All sharks are carnivorous, meaning that they only eat other animals. The range of prey eaten by sharks is extremely broad, from snails to sea urchins, crabs, fish, rays, other sharks, seals, and birds. Some sharks eat carrion (animals that are already dead), but most only eat live prey. Sharks eat relatively little for their size, compared to mammals, because they do not use energy to maintain a …

Sharks - Reproduction And Growth

Sharks have fascinating reproductive systems, with some advanced features for such an ancient group of organisms. Unlike bony fish, sharks have internal fertilization. The male shark uses projections from his pectoral fins, called claspers, to anchor himself to the female. He then transfers packets of sperm into the female's urogenital opening, using pulses of water. The sperm fertilize the…

Sharks - Conservation

Historically, sharks have been fished for their meat and for liver oil, which was the best source of vitamin A until the 1940s. Shark fin soup is a traditional Asian delicacy and shark meat has recently gained popularity; these are greatly increasing the killing of sharks in marine fisheries. In addition to their food value, many sharks are caught and killed for sport by individuals and in specifi…