A small subset of shark species that spend their life constantly swimming, a behavior common in pelagic (open ocean) sharks, have lost the ability to pump water through their gills.
Sharks also have a sharp sense of hearing and can hear prey many miles away.
Some sharks can lie on the bottom while actively pumping water over their gills, but their eyes remain open and actively follow divers.
Some sharks, if inverted, enter a natural state of tonic immobility—researchers use this condition for handling sharks safely (Pratt et al.
The teeth of carnivorous sharks are not attached to the jaw, but embedded in the flesh, and in many species are constantly replaced throughout the shark's life.
Sharks belong to the superorder Selachimorpha in the subclass Elasmobranchii in the class Chondrichthyes.
Sharks have even been known to engage in playful activities (a trait also observed in cetaceans and primates).
The tails (caudal fins) of sharks vary considerably between species and are adapted to the lifestyle of the shark.
The effectiveness of the tissue varies, with some sharks having stronger nocturnal (nighttime) adaptations.
Part of the buoyancy problem is addressed by the fact that sharks have skeletons made of cartilage, which is lighter than bone.
Sharks have been a popular recreational target, with a reputation as a good fighting fish (such as the shortfin mako sharks and blue shark).
Some sharks have a modified slit called a spiracle located just behind the eye, which is used in respiration (Gilbertson 1999).
Despite the importance of sharks, their reputation and location makes them difficult to conserve.
Despite the common view that sharks are simple, instinct-driven "eating machines," recent studies have indicated that many species are more complex, possessing powerful problem-solving skills, social complexity, and curiosity.
The fossil record of sharks extends back over 450 million years—before land vertebrates existed and before many plants had colonized the continents (Martin 2007a).
Nelson (1994) notes that there is growing acceptance of the view that sharks and rays form a monophyletic group (superorder Euselachii), and sharks without rays are a paraphyletic group.
Cross-species social hierarchies exist with oceanic whitetip sharks dominating silky sharks of comparable size when feeding.
Other sharks are hunted for food (Atlantic thresher, shortfin mako, and others) (FAO 1998).
Instead of bones, sharks have cartilagenous skeletons, with a bone-like layer broken up into thousands of isolated apatite prisms.
Many scientists believe this is one of the reasons sharks have spiracles.
From the number of teeth found in any one place it is most likely that Cladoselache did not replace its teeth as regularly as modern sharks.
The cartilage and oil-filled liver only addresses part of the problem, so sharks also employ dynamic lift to maintain depth, by moving and utilizing their large pectoral fins and upward curved tail.
Migration patterns in sharks may be even more complex than in birds, with many sharks covering entire ocean basins.
The smaller catsharks often mate with the male curling around the female.
The author of Jaws, Peter Benchley, had in his later years attempted to dispel the image of sharks as man-eating monsters.
When approached too closely, some sharks will perform a threat display to warn off the prospective predators.
Sharks and their relatives, skates and rays, have skeletons made from rubbery cartilage, which is very light and flexible.
The porbeagle sharks, like some tunas, can elevate body temperatures in excess of 20°C above ambient water temperatures.
Mostly only the fossilized teeth of sharks are found, although often in large numbers.
From about 300 to 150 million years ago, most fossil sharks can be assigned to one of two groups.
Some species, such as nurse sharks, have external barbels that greatly increase their ability to sense prey.
Different tail shapes have evolved in sharks adapted for different environments.
Modern sharks began to appear about 100 million years ago (Martin 2007c).
Sharks are hunted in commercial fisheries and for recreational purposes.
Sharks are a common seafood in many places around the world, including Japan and Australia.
The Elasmobranchii are sometimes divided into two superorders, Selachimorpha (sharks) and Batoidea (rays, skates, sawfish).
All of these sharks have been filmed in open water, without the use of a protective cage.
Sharks have eyelids, but they do not blink because the surrounding water cleans their eyes.
Certainly, wherever the teeth of large sharks have been found, there has also been an abundance of marine mammal bones, including seals, porpoises, and whales.
Contrary to popular belief, only a few sharks are dangerous to humans.
Until the sixteenth century, sharks were known to mariners as "sea dogs" (Marx 1990).
Like other fish, sharks extract oxygen from seawater as it passes over their gills.
Due to a short history of shark attacks on humans, most sharks inspire fear in many people.
Sharks have keen olfactory senses, with some species able to detect as little as one part per million of blood in seawater, up to a quarter of a mile away.
The Squatiniformes (angel sharks) have a ray-like body (Nelson 1994).
The majority of the modern sharks can be traced back to around 100 million years ago (Martin 2007c).
Porbeagle sharks have been seen repeatedly rolling in kelp and have even been observed chasing an individual trailing a piece behind them (Martin 2007f).
The extant (living) orders of Elasmobranchii that are typically considered sharks are Hexanchiformes, Squaliformes, Squatiniformes, Pristiophoriformes, Heterodontiformes, Orectolobiformes, Lamniformes, and Carchariniformes (Nelson 1994; Murch 2007).
In 1987, near Smitswinkle Bay, South Africa, a group of up to seven great white sharks worked together to relocate the partially beached body of a dead whale to deeper waters to feed (Martin 2007e).
At the same time, transportation techniques have improved and now provide a way for the long distance movement of sharks (MCS 2005).
Some sharks can be highly social, remaining in large schools, sometimes up to over 100 individuals for scalloped hammerheads congregating around seamounts and islands, e.g.
The brain mass to body mass ratios of sharks are similar to those of mammals and other higher vertebrate species (Martin 2003).
Until recently, only a few benthic species of shark, such as hornsharks, leopard sharks, and catsharks could survive in aquarium conditions for up to a year or more.
Among the most ancient and primitive sharks is Cladoselache, from about 370 million years ago (Martin 2007b), which has been found within the Paleozoic strata of the U.S. states of Ohio, Kentucky, and Tennessee.
Sharks have a different reproductive strategy from most fish.
The oceanic currents moving in the magnetic field of the Earth also generate electric fields that can be used by the sharks for orientation and navigation.
Humans kill between 100 million and 200 million sharks each year, while human deaths are about five per year.
Sharks are long-lived apex predators with comparatively small populations, which make it difficult for them to breed rapidly enough to maintain population levels.
The meat of dogfishes, smoothhounds, catsharks, skates, and rays are in high demand in some locations.
All sharks have multiple rows of teeth along the edges of their upper and lower jaws.
The evidence that sharks are resistant to cancer is mostly anecdotal and there have been few, if any, systematic scientific studies that have shown sharks to have heightened immunity to this disease (Handwerk 2003).
Some sharks can lose 30,000 teeth in a lifetime.
There have been cases where hundreds of de-finned sharks were swept up on local beaches.
They eat a lot of fish and there is some evidence that they ambush sleeping seals, but some scientists believe they are primarily scavengers. Some strange things have been found in Greenland sharks' stomachs, including the remains of polar bears, horses, moose, and in one case an entire reindeer.Feb 3, 2014
Several populations of skilled orcas around the world have learned how to overcome sharks using a combination of superior brain power and brute force. The Great White and Mako are just two of at least nine species of shark known to be eaten by some orca families.Nov 27, 2009
Secondary consumers include fish, whales and the friendly basking, and whale sharks. They are the animals in the middle of the food chain. they eat plankton, shrimp and mollusks, which are primary consumers (see: primary consumers). They are eaten by the tertiary consumers, which, I will tell you about in minute.
Hammerhead sharks are voracious predators and their mallet-shaped heads boost their ability to find that which they like to eat. The wide expanse of head allows for a broader spread of highly specialized sensory organs that they use to find food. And beyond smell and vision, these sensory organs are rather high-tech.Aug 13, 2012
Unlike many fish, hammerheads do not lay eggs. A female gives birth to live young. One litter can range from six to about 50 pups. When a hammerhead pup is born, its head is more rounded than its parents'.
Hammerhead Shark FactsKingdom: Five groups that classify all living thingsAnimaliaMain Prey:Fish, Squid, OctopusPredators: Other animals that hunt and eat the animalTiger Shark, Great White Shark, Killer WhaleSpecial Features:Broad, flat head and large eyes21 more rows
Humans are the #1 threat to all species of Hammerhead Sharks. Attacks on humans are extremely rare. Only 3 of the 9 Hammerhead species (Great, Scalloped, and Smooth Hammerheads) have ever attacked a human. The vast majority of the time, these sharks are safe for divers in open waters.
As the apex predators of the oceans, the role of sharks is to keep other marine life in healthy balance and to regulate the oceans. ... Sharks play a vital role at the top of the food chain by maintaining balance in the oceans. Destroying shark populations could destroy our oceans and our life support system.
Not only are shark's teeth razor sharp but they are also constantly regrown throughout life, gradually replaced like a conveyor belt of rows of teeth, and not just when they are worn down or fall out. ... Sharks don't actually regrow teeth one by one but have multiple rows inside their jaw that are constantly regrown.Aug 5, 2016