Sharks come in different shapes and sizes depending on their species. You may wonder why they are shaped this way and how their body supports their shape. So, do sharks have bones?
Sharks do not have bones. Instead, they have a cartilaginous skeleton that is lighter than bone. This cartilaginous skeleton provides them with flexibility and strength. Their livers are full of low-density oils, which help them with buoyancy. Though they have no bones, they have a backbone which is calcified cartilage that protects their spinal cords.
If you want to learn more about a shark’s structure, keep reading. We’ll go into more detail about their skeletons and their purposes.
Let’s dive in.
Do sharks have bones?
Sharks don’t have bones. Instead, they have a cartilaginous skeleton that is lighter and more flexible than a skeleton made of bone.
They are classified as Chondrichthyes, which means “cartilage fish.” Sharks also belong to the subclass Elasmobranchii, which includes other cartilage fish like rays, sawfish, and skates.
So, how does their cartilaginous skeleton work? It’s similar to a normal bone skeleton and has the same functions and support. It protects their organs and shapes their bodies.
Since it isn’t as dense and tough as bone, areas that need more protection are protected with calcified cartilage. This includes their spinal cord, jaw, and brain.
Is a Shark a vertebrate?
Sharks are classified as vertebrates even if though they don’t have one single bone. The calcified cartilage acts as a spine, making them vertebrates.
This calcified tissue is made from calcium salts and delivers many benefits for the shark. It only protects their vital organs, while strong and malleable cartilage supports the rest of the body.
Although sharks don’t have bones, they can still fossilize. They can do this with the tiny denticles on their skin composed of calcium phosphate.
This is the same mineral that enamel from teeth is made of, allowing them to become fossils. Some spines in their fins can also allow for fossilization.
Why do sharks not have bones?
Sharks have cartilage instead of bone because it makes it easier for them to swim. The lightweight properties of cartilage allow for a seamless swimming experience, making it easier to hunt and scavenge.
With a less dense structure, they can move more quickly and preserve energy. Pectoral fins along the gill slits lift the shark through the water, helping them to glide effortlessly.
Compared to bony fish, they have five to seven-gill slits on each side, while bony fish only have one. Gill silts allow for the filter of oxygen entering the organism.
They don’t need the density of a skeleton to keep themselves afloat. Their liver does that job for them and contains oils and fat keeping them buoyant. A shark’s liver makes up 25% of its body weight.
But, there are other factors at play and not just adaption. Studies suggest that a shark’s DNA sequence is responsible for its cartilaginous skeleton.
Before this research, it wasn’t clear whether sharks had lost the ability to form bone or never had it in the first place. Their DNA sequences reveal a missing single gene family that regulates the change from cartilage to bone.
Did ancient sharks have bones?
Sharks have been around for 450 million years, longer than trees and dinosaurs. So, it could make sense that modern sharks have evolved to no longer have bones.
The answer to this can be found by looking at previously fossilized sharks. There are fossilized scales, teeth, dorsal fins, and dermal denticles – but no bones.
This is evidence that even the earliest sharks had cartilaginous skeletons. Along with the research on their DNA sequences and fossilization records, it’s safe to say ancient sharks did not have bones.
Cartilage is lighter than bone and breaks down quicker, making it impossible to become fossilized. Parts of the jaw, vertebrate and dorsal fin can be recovered, but this is very rare. This cartilage is calcified and, therefore, can be fossilized.
The most commonly found shark fossil is their teeth. You may be familiar with shark teeth jewelry, weapons, and trinkets, as they are used for these purposes due to their strength.
They are prone to becoming fossilized as they are made of dentin, which is tougher than bone. They’re also plentiful, as sharks replace their teeth every two weeks.
The old teeth fall out of their mouths and onto the ocean floor. This means that billions of shark teeth have fallen onto the ocean floor over millions of years and are likely to be fossilized.
Do teeth count as bones in sharks?
Like human teeth, shark teeth do not count as bones. They are made from dentin which is calcified tissue stronger than bone.
Shark teeth contain a mineral called fluorapatite, which is fluorinated calcium phosphate. They are also coated with an outer layer of enameloid, making their teeth stronger.
Their jaws are also cartilage and don’t count as bone. They have a single set of oral jaws comprised of calcified tissue.
Sharks can open their jaws wider than animals with bone jaws. Some shark species have their jaws attached loosely to the skull, allowing for more expansion and extremely powerful bites.
What is shark skin made out of?
A shark’s skin is from dermal denticles, similar to tiny teeth structures. They are called dermal denticles because of their similarity to teeth, but also called placoid scales.
Their function is to prevent friction against the water when the shark is swimming. They point towards the tails and stick out, giving the skin a comparable texture to sandpaper.
It also prevents loss of speed and reduces drag, which makes them stealthy hunters. Their skins have inspired designs for Olympic swimsuits.
The shark’s skin also acts as an insulator; it generates necessary body heat and stores it. Its skin has to be very thick to retain it, with the whale shark having a skin thickness of 4 inches (10cm).
Often, sharks have darker skin on top to camouflage against the dark depths. This prevents prey that is above them from seeing them. When prey is below them, their lighter underside camouflages them against the lighter surface below.
A shark’s skin comprises three layers: a central pulp cavity, a dentine layer, and an outer layer of enamel. These layers protect the shark from injury and strengthen the skin.
Although this provides the shark with many benefits, it also makes them a target for poaching. It is used for luxury items such as shoes, handbags, and belts and can go for thousands of dollars.
Can shark skin cut you?
A shark’s skin is very rough and can cut human skin. Smaller animals with softer skin can be severely injured when coming in contact with shark skin.
Human injury isn’t as uncommon as you might think. Many people have been wounded after touching shark skin, with bull sharks being the main culprit. A cut from shark skin can be described as leaving a burning sensation.
Their skin is used as sandpaper and was used before sandpaper was invented. Their skin has been estimated to be around 80 to 220 grit that cuts in one direction and burnishes in the other.
Do sharks have tongues?
Sharks do have tongues, and they are referred to as basihyals. It is not muscle, so it cannot move like a human tongue.
For example, it cannot stick out its tongue. It is stuck to the floor of the shark’s mouth and cannot be pushed or stretched.
The functions of a shark’s tongue are limited, and it does not have taste buds. A basihyal is a large chunk of cartilage at the bottom of a shark’s mouth.
This may be an adaption to make its teeth more visible and dominant in the mouth. It makes us and other possible predators afraid of them, preventing predation.
The basihyal is said to protect the shark’s ventral aorta, a vital part of a shark’s anatomy. It prevents large pieces of food from harming the ventral aorta, which can harm the shark.
In most shark species, the basihyal cannot be moved and has no other function than protecting the ventral aorta. But in other sharks like the bull shark and carpet shark, it is used to suck up prey in coordination with strong neck muscles.
These muscular structures help with the intake of water after eating live food. This water cleans out any debris caught in the teeth and gills and provides oxygen for respiration.
In conclusion
Sharks don’t have bones. Instead, they have a cartilaginous skeleton that is lighter and more flexible than a skeleton made of bone.
Sharks have cartilage instead of bone because it makes it easier for them to swim. It makes it easier for them to hunt and scavenge.
Prehistorical sharks have always had no bones. There is proof of this in their DNA sequences and previous fossilized sharks.
Shark teeth are made from dentin which is calcified tissue stronger than bone. Sharks have tongues but cannot move and perform the same functions as human tongues.
Their skin consists of dermal denticles, which are similar to tiny teeth structures. A shark’s skin is very rough and can cut human skin.
