Sharks have vertebrae, but their structure is different from that of mammals. Indeed, sharks have cartilaginous vertebrae instead of bony vertebrae, which makes them more flexible and suited to marine life.
In sharks, the skeleton is mainly made of cartilage, a flexible and strong material, very different from the calcified bones found in most other fish or mammals. This cartilage offers an ideal combination of lightness and flexibility, allowing sharks to make quick and fluid movements in the water. Their internal structure is reinforced in places by deposits of calcium, but not to the extent of creating true bony vertebrae. Instead, they have sort of cartilaginous rings that protect the spinal cord without forming a traditional backbone. These assembled cartilaginous elements also provide the effective muscular support needed for nonstop swimming, as many sharks must constantly be in motion.
The skeleton of sharks is made of cartilage, a material that is much lighter and more flexible than solid bone. Thanks to this flexibility, sharks can absorb impacts and easily navigate through the water without weighing themselves down unnecessarily. Another nice advantage: cartilage grows faster and repairs more easily than bone, a real bonus for these predators regularly faced with muscular fights or occasional injuries. Its lower density also provides buoyancy, allowing them to expend less effort to stay level in the water, thus saving their energy for hunting and navigation.
Sharks are part of the chondrichthyans, primitive fish that emerged about 400 million years ago. At that time, a rigid bony skeleton was not yet widespread among aquatic creatures. The development of a cartilaginous skeleton was more than sufficient for their needs: flexible, lightweight, easy to produce and regenerate. Throughout evolution, this type of skeleton has perfectly met the constraints of sharks, which are often predatory and fast fish. Since cartilage already provided them with all the necessary rigidity without burdening them with excessive weight, the emergence of true bony vertebrae has never constituted a real evolutionary advantage for them. They have therefore retained this ancestral characteristic, while fish with bony skeletons (osteichthyans) have followed a different evolutionary path, gradually developing hard and heavy bones. This is why sharks still have cartilage today rather than bony vertebrae.
Sharks have a skeleton made of cartilage, which is much lighter and more flexible than the bones of vertebrate animals. As a result, they float better and swim without expending too much energy. In animals with bony vertebrae, the skeleton is solid, heavy, and rigid, ideal for supporting the body out of water but less suited for fluid underwater movements. Cartilage allows for better shock absorption and more flexibility in tight and fast turns—useful when chasing prey. Conversely, a cartilaginous skeleton somewhat limits brute strength, precise movements on land, and support for heavy weights out of the water.
Thanks to a cartilaginous skeleton, sharks are lighter and more flexible. This lightness allows them to float easily and conserve energy during movement. Less rigid than bone, cartilage provides ideal elasticity, giving sharks the ability to make tight turns and accelerate quickly. This combination of flexibility and lightness makes the shark a fearfully agile and efficient swimmer. Cartilage also absorbs shocks better related to sudden changes in direction, making it ideal for hunting or quickly fleeing danger. However, the downside is that without true bones, sharks must always keep moving to maintain good buoyancy.
Shark teeth are not anchored in a bony jaw but are embedded in the skin and are regularly replaced throughout their lives, allowing some sharks to lose and replace up to 30,000 teeth during their lifetime.
Although sharks do not have true bony vertebrae, some species do have calcified mineral layers on their cartilage, giving them enough rigidity to reach high speeds.
Cartilage being lighter than bone allows sharks to maintain a reduced weight, which facilitates their buoyancy in water and helps them avoid wasting precious energy to stay submerged.
Complete shark fossils are rare precisely because cartilage does not fossilize easily, which complicates the paleontological study of the evolution of these fascinating marine creatures.
No, cartilage decomposes quickly after death, making shark skeleton fossils very rare. Generally, only their teeth, which have a more mineralized composition that is more resistant to decomposition, are frequently found fossilized.
Sure! Here’s the translation: "Yes, sharks, and more generally chondrichthyans, have retained a primarily cartilaginous skeleton for about 400 million years. This provides them with lightness and flexibility, allowing them to thrive as marine predators."
Not necessarily. Although cartilage is less solid than bone, its flexibility offers advantages, including better maneuverability. Additionally, sharks compensate for their lack of vertebrae with powerful musculature that provides them with strength and resilience.
Sure! Here’s the translation: "Yes. Some fish, such as sturgeons or rays, have skeletons that are primarily cartilaginous with limited ossified elements. They represent a sort of intermediate stage between strictly cartilaginous fish (sharks) and fully bony fish."
Shark cartilage is less innervated than true bone, but sharks still possess a nervous system that allows them to feel pain. The difference lies more in the way cartilage transmits signals compared to a bony skeleton.
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