Though there are 440 known types of sharks, all sharks share the same basic anatomical characteristics. These characteristics are what makes sharks different from fish or whales, and define sharks as their own unique aquatic species.
Shark anatomy is highly developed as a result of over 450 million years of evolution and has made sharks an incredibly successful species. Here is an overview of the unique anatomical characteristics that make sharks unique.
The key differentiating anatomical characteristics between sharks and other marine life like fish or whales is that they have a skeletal structure made of cartilage. Cartilage is the same material make our noses and ears. Cartilage is extremely flexible and much lighter than bone which helps sharks stay afloat and move through the water with less energy. It also helps them swim faster and make sharp turns. Cartilaginous bones make shark skeletons more efficient than the skeletons of bony fish.
Another unique anatomical characteristics that makes sharks different from fish is that fish skin is covered in scales, while shark skin is covered in denticles. Denticles are tiny teeth that feel almost like sandpaper. Denticles reduce drag in the water, making it easier for sharks to swim faster. Denticles range in size among sharks, as some types of sharks have denticles so large they are used as defensive spikes. Furthermore, denticles make shark skin thick and tough, making it harder for sharks to suffer injury from attacks.
A shark’s teeth are essentially another form of denticle. Sharks are born with a full mouth of teeth, lined in multiple rows. Sharks continuously lose and regrow their teeth throughout their lives. Sharks are predators with quick, aggressive eating habits, so they constantly break and lose teeth. So they regrow these teeth so they can continue to be effective hunters. In a single lifetime, a shark can lose and regrow 30,000 teeth.
Sharks have massive oily livers that help them store food and maintain a neutral buoyancy. A shark’s liver can weigh up to a 25% of the total weight of the shark and can store enough oil that some sharks can go up to a year between feedings. Shark livers also help them stay afloat. Unlike fish, sharks do not have swim bladders to maintain their buoyancy, instead the dense oils contained in the liver help them maintain buoyancy.
The lateral line is a unique sensory quality found in all types of shark. The lateral line is a type of sense that helps sharks detect the movement of their prey in the water. The lateral line helps them in two ways. First, it helps them detect vibrations to identify where both potential prey and competing predators are in the water. Secondly, it helps detect electrical currents in the water which helps them both locate prey and navigate the ocean.
Powerful Sense of Smell
Sharks have an impressive sense of smell. In fact, nearly two-thirds of a shark’s brain weight is comprised of olfactory lobes, lobes that help detect and interpret smell. Sharks can smell blood in the water of up to one to ten billion parts water from miles away. Sharks smell by inhaling water into their nasal sacs over millions of tiny sensory folds known as olfactory lamellae. These sensory folds then send a signal to the brain letting them know what is in the water.
Sharks have sharp efficient fins that help them swim fast and efficiently. Sharks usually have a pair of pectoral fins that steer and guide lift. A pair of pelvic fins and either one or two dorsal that help them stabilize and stay upright. Some types of shark have an anal fin that also helps stabilize them. Finally, they have caudal or tail fins that help propel the shark forward. Sharks’ fins help them swim fast, efficiently, and flexibly.
Shark coloration is in a pattern known as countershading. Countershading means the skin on top of the shark is darker than the skin on the bottom. The dark skin on top helps hide their presence from predators and prey above them. When looking down on a shark they blend into the color of the darker seafloor. The light skin on bottom helps hide their presence from predators and prey below them, because the lighter skin blends with the sunlight coming through the surface of the ocean. Countershading helps sharks stay camouflaged in the water.
Most bony fish only have one gill, however sharks have five to seven gills depending on the species. Water passes over the gills from the mouth either through ram filtering or from pumping water from their mouths, providing the shark’s body with oxygen. Shark gills also do not have gill covers like the gills of bony fish. The extra gills and the lack of gill cover makes it easier for sharks to breath and helps them continue to move through the water.
Sharks have a range of different body types, depending on the species. However all sharks have arrow dynamic bodies. They all have round bodies that taper at both the front and the back. This makes them extremely aerodynamic, so they can move through the water quickly without expending extra energy.
Sharks have two types of extremely powerful muscles. The first type, red muscle, is found under their skin and works to break down the fats and oils in the body to produce energy. Red muscle provides a steady stream of energy and helps sharks continuously cruise through the water. The second types of muscle is white muscle which breaks down sugars to produce energy. White muscle is used when the shark is either attacking or dodging predators, because it gives them an extra burst of quick energy and movement. Having two sets of muscles reduces the energy needs of a shark, making them more efficient, stronger swimmers.
All of these unique anatomical characteristics make sharks an amazing species. Between the efficiency of cartilaginous bones, oily liver, and aerodynamic bodies using two sets of muscles, and the incredible defense of denticles, regenerative teeth, and countershading, it’s no wonder sharks have outlived even the dinosaurs.