Sharks are magnificent creatures that are part of marine life.Sharks are predators of the ocean world. They have different body structures compared to many other aquatic species.There are over 500 shark species, each having varying sizes and distinctive features that set them apart from others. Some shark species are whale sharks, blue sharks, nurse sharks, gray or Greenland sharks, porbeagle sharks, and white sharks. The great white shark is the most famous and also the largest shark species in the world. Although most sharks are big and intimidating, they aren’t the largest fish in the ocean. This title belongs to the blue whale.The term ‘sharks’ has also been used to refer to other historical marine animals that were similar to sharks. Yet, the ancestors of modern sharks were way bigger and more fearsome. Even then, sharks are still feared by most animals living in the water, and even humans. Their sharp teeth can easily tear through skin and muscles. Like many species living in the water, a shark also has gills to help in performing the task of respiration. Sharks are able to extract oxygen from the seawater around them through the use of gills. A shark’s gills filter oxygen and clean the deoxygenated blood present in the body. Shark skin also has something called dermal denticles, which are made up of collagenous fibers that are flexible in nature. These dermal denticles help sharks to swing faster and more stealthily in the water. Sharks are considered to be predators at the top of the food chain due to various reasons. One of these reasons is their acute sense of smell. Sharks have great olfactory senses, which allow them to sense their prey easily.However, a shark’s body is made the same way as many other fish species. However, the body of the shark is slightly unique, which also makes it a skilled predator.Do sharks have bones?Unlike the human body that is made up of bones, sharks do not have bones in the actual sense of the word. You might then question, what is the shark skeleton we often see in a museum? Even though sharks don’t have bones, they still fossilize.Sharks do have bones such as the spinal cord, skull, teeth, fins, and jaws. But they aren’t the typical bones found in other organisms. Sharks do not have a rib cage. Because of the absence of rib cages, sharks can get crushed under their own weight while being on land.Most fish have skeletons that cover their entire bodies. However, a shark’s skeleton isn’t present on the lower part of the body at all.What do sharks have instead of bones?Although a shark doesn’t have actual bones, it does have something similar to bones. Sharks are cartilaginous fish which means they have cartilaginous skeletons. Shark cartilage is what shark bodies consist of.Cartilage is connective tissue. This connective tissue forms before the formation of bones. Soft bones in newborn human babies are these connective tissues. Cartilage provides the structure or the framework for a bone to ossify. Ossify means to harden. However, that does not mean that sharks have under-developed bones. In fact, this cartilaginous fish is in no way weak or easily killed.The distribution of cartilage in terms of density is also not proportional all over the body of a shark. While some areas of a shark’s body have denser cartilage, others have less cartilage density. In some areas of a shark’s body, the cartilage is exceptionally dense and strong, which can be considered as resembling bone. The skeleton of sharks has no muscles attached to it. It is only a bone skeleton. The skeleton includes the skull, spinal cord, teeth, fin bone, and jaws. The shark’s skull is known as chondrocranium. Here, the first part, ‘chondro’ refers to ‘cartilage’. The skull of sharks is also made up of cartilage and not bones. Similarly, the shark’s jaw is made up of cartilage.A shark’s jaw is not connected to the cranium, meaning the skull of the shark. This is because shark jaws have to be really strong to hold on to their prey. The jaws of sharks are covered with a layer of small hexagonal plates known as tesserae. The tesserae are calcium salts in the form of crystal blocks. They provide extra strength to the jaws. Most sharks have a total of eight fins. These consist of pectoral fins (two), dorsal fins (two), pelvic fins (two), anal fins (one), and caudal fins (one). Each fin helps sharks swim in the ocean and change directions when needed.However, a shark cannot move backwards in the tail-first direction, or even make a sudden stop. The fins of sharks are also supported by cartilage. Shark teeth bones are the only shark bones that are not made up of cartilage. Instead, similar to human teeth, shark teeth are made up of dentine, also spelled as dentin. The shark’s teeth are rooted in gums. They are also continuously replaced throughout their life.Due to the constant attack on the teeth during the process of catching and holding on to prey, a shark loses thousands of teeth in its lifetime. The shape of a shark tooth varies according to the diet and the hunting habits of sharks. Sharks that eat crustaceans or mollusks have teeth that are flat and dense, suitable for crushing. However, sharks that feed on other fish have sharp needle-like teeth and sharks that eat bigger fish and other mammals have serrated teeth, which help in sawing through the flesh of prey.Are sharks vertebrates?There are five types of vertebrates that belong to the category of fish. These are ray-finned fish, lobe-finned fish, lampreys, cartilaginous fish, and hogfish.The other vertebrates include reptiles, amphibians, mammals, and birds. Since sharks are cartilaginous fish, they are considered to be vertebrates too.A shark’s vertebrae are made up of calcified cartilage. The calcified tissue means that the vertebrae have hardened through calcium salts. Although the cartilage of the vertebrae is denser, it is still not considered to be bone. Interestingly by observing the vertebrae of the sharks, scientists used to determine the age of a shark. This was done by the count of the rings present in a shark’s backbone.Why don’t sharks have bones?A shark bone might not be bone in the true sense of the word. However, the absence of true bones isn’t a disadvantage to sharks. Instead, the cartilage of sharks benefits their image as apex predators of the oceans.Cartilage is more beneficial to sharks rather than bones. Since cartilage is less dense than bones and more on the lighter side, they help keep the body of a shark buoyant in the water. The buoyancy also comes from the absence of a swim bladder in sharks. This is common for species belonging to the Elasmobranchii group, which also includes sharks. This is also the reason a shark will sink if it stops swimming.While bones are rigid, cartilage is flexible. A shark is able to make sharp and agile turns in the water and also shake the prey caught in its mouth from side to side. Due to the flexibility and light body, a shark is able to do such things without using much of its energy. If sharks were to have bones instead of cartilage, they might not be so agile or even be deemed as a top predator in the marine food chain.You might still find the absence of bones a disadvantage as bones are known to support blood circulation. Bbones create very important red blood cells. You would think without bones, sharks might not have red blood cells, so how do they survive?It is true that cartilage is a tissue that does not contain any blood vessels. However, sharks still live, and this is because their blood is created in the spleen, which is an epigonal organ. It is also produced in a shark’s Leydig’s organ, which can only be found in a cartilaginous fish. So, they do not have bones like humans do, but they do not really need them.Did You Know…Often in the movies, it is shown that sharks are lured in by the smell of blood. This is absolutely true. They can not only sense blood through their olfactory senses, but they can also detect the direction of the smell. Even if the smell is at a great distance, they still sense it and pursue it.The depiction of shark fish in movies isn’t just an imaginative perspective. Sharks are really powerful marine predators and their body weight and body structure aid in making them seem so terrifying.Just like their sense of smell, a shark’s eyesight is also sharp. Its eyes are well adapted to the deep waters because of the tissue called tapetum lucidum present behind its retinas. This tissue reflects the light back to the retina, thereby making visibility better in the dark waters of the deep oceans.Sharks also have something called electroreception. Sharks have electroreceptor organs known as ampullae of Lorenzini, which detect the electromagnetic field produced by all living organisms. The ampullae of Lorenzini actually help sharks to find and hunt for their prey.
Sharks are magnificent creatures that are part of marine life.
