Sharks are some of the most interesting and misunderstood animals in the ocean.
Although best known for being the perfect predator, sharks should be better known for the extremely unique way their bodies work.
This shark is vastly more than just a killer.
They are the balancing force in their ecosystems.
How Many Bones Do Sharks Have?
Sharks do not have a single bone in their entire body.
Instead, sharks have cartilage, which is the same tissue that a human’s nose and ears are made of.
Cartilage is vastly lighter than bones, making it easier for sharks to zip around the water like a torpedo.
Human babies don’t have as many bones as adults because some of their bones start as cartilage.
This process is called endochondral osteogenesis.
Even as they age, sharks’ cartilage never truly ossifies (turns into bone).
A major difference between cartilage and bone is that bone has blood vessels while cartilage does not.
Red blood cells are formed in bone marrow, as well as white blood cells and platelets.
Sharks can’t live without blood and are known to bleed, so their blood cells have to be produced elsewhere.
Sharks have a special way of producing their blood cells.
These oceanic predators’ blood cells come from their spleen, epigonal organ, and Leydig’s organ.
The Leydig’s organ can only be found in fish that only have cartilage and no bones, or Chondrichthyes.
Not having any bones isn’t as bad as it would seem.
The cartilage that sharks have is vastly more beneficial to them than bones would be.
While strong bones may be needed to walk on land and to keep gravity from weighing you down, they’re nothing but a hassle in the water.
Bone is much heavier and firmer than cartilage.
In the water, cartilage is a much better skeletal structure.
Cartilage is lighter and much more flexible.
The flexibility of cartilage allows sharks to make sharp turns in the water and shake their prey wildly once they’ve caught it.
The shaking motion helps their teeth grind into the flesh of their prey and helps deplete the final burst of energy of the prey.
Are Sharks Vertebrates?
Yes, sharks are vertebrates, despite not actually having any bones.
Sharks’ skeletons may be made of cartilage, but they still have a spinal column, which earns them the classification of vertebrates.
There are nine different types of vertebrates and five of them are fish.
These classes are mammals, birds, reptiles, amphibians, Lobe-Finned fish, Ray-Finned fish, hagfish, lampreys, and Cartilaginous fish.
Their spinal columns are made up of two large, tube-like pieces of cartilage.
The upper piece of cartilage is where the neural arches are.
Below additional layers of cartilage, you’ll find the spinal cord.
The notochord is contained in the lower cartilaginous tube.
The shark’s notochord is their spine.
The difference between a notochord and a spine is that a notochord is made out of cartilage while a spine is made from bone.
Although sharks’ skeletal structures are completely made up of cartilage, that cartilage has multiple forms.
Each type of cartilage has its own level of density and use.
The skeletal structure of a shark is diverse and perfectly formed to its needs.
The most actively used cartilage that a shark has is around its spine and its jaw.
These sections of calcified cartilage are covered in calcium salts, which makes them incredibly rigid and strong.
The trade-off for having stronger cartilage is that it is not as flexible.
Flexibility in the jaw cartilage wouldn’t be as beneficial because it is those strong, snapping jaws that help make sharks such effective predators.
Sturdy cartilage around the notochord keeps the shark from getting spinal injuries.
A shark’s skull is also made out of an incredibly dense type of cartilage.
This helps keep its brain secure.
The cartilage in the shark’s snout is incredibly flexible and squishy.
It acts as a bumper for the shark.
Are Sharks Teeth Made Of Bone?
No, shark teeth are made of calcium phosphate, which is even stronger than bone.
A shark’s teeth are just as unique as the rest of its body.
Sharks’ teeth are planted in their gums, rather than their jaws like humans.
Sharks regularly shed their teeth in the same way that deer are known for shedding their antlers.
A shark will go through about 35,000 teeth in its lifetime.
In warmer months, sharks tend to hunt more often, which means they also lose more teeth.
On average, a shark will lose about a tooth per week.
Since the teeth are implanted in the gums rather than the jaw, this is a painless process for the shark.
Sharks’ teeth are just modified versions of their placoid scales that adhere to the dental membrane rather than the skin, like most other placoid scales.
Another name for placoid scales is denticles.
The shape of a shark’s tooth is based on its eating and hunting habits.
For example, the Great White shark has sharp, serrated teeth that are perfect for crunching and tearing up prey.
Meanwhile, the gentle Nurse shark has flat, conical teeth that are made for crushing up crustaceans
A lot of information can be derived from the shape and size of a shark’s tooth.
Most research on the Megalodon has been studied through their teeth.
Thanks to the shape of their fossilized teeth, we have been able to discover the diet of the average megalodon without ever having to see.
A shark’s teeth can tell us a lot about its life before it lost its tooth.
The color of the tooth can tell us the age.
The shape and serration of the tooth can help identify the species it came from, while location can determine what the shark was doing.
Shark’s Unique Scales
Every single part of sharks has evolved to be perfect for their unique situation and needs.
Their scales are no different.
A shark’s scales are unique to sharks and help them better navigate through the water effortlessly.
Shark scales are known as denticles or placoid scales.
These scales are coated in dentine, which can also be found in both shark and human teeth.
These scales are more closely related to teeth rather than skin.
A shark has two types of denticles.
Some denticles are thin and ridged, giving the shark some necessary drag reduction.
This helps sharks cut through the water like a hot knife through butter.
The second type of denticles is thicker and smoother.
These scales keep the shark from getting cut and make it harder for parasitic creatures to invade its body.
With neighbors like the sea lamprey, these denticles are necessary.
If you were to pet a shark, the surface of its body from its head to its tail would feel smooth.
Petting them in the opposite direction would be rough.
However, for safety reasons, it is best not to pet near sharks’ heads and to refrain from petting sharks that aren’t being handled alongside professionals.
Because shark skin is essentially covered in thousands of tiny teeth, their skin feels like sandpaper.
Occasionally, a shark will lose one of its scales and have to wait for a new scale to take its place.
Similar to shark teeth, the scales of a shark can tell you a lot about it, such as its species, age, and size.
The more we learn about the body of sharks, the better we can help them.
By learning about shark physiology, humans have been able to create better swimsuits.
Olympian swimsuit designers have taken inspiration from sharks in a form of biomimicry.
Using Sharks’ Bones To Determine Age
Just like a tree, you can tell how old a shark is by the rings on its vertebrae.
A set of seasonal rings represents one year of the shark’s life.
There are two factors that cause these rings to appear.
The first reason that these seasonal rings form on their vertebrae is that different resources are available each season.
The nutrients that the shark is getting are different each season, which results in different cartilage development.
Sharks have indeterminate growth patterns, which means that sharks never stop growing.
That’s the reason that the annual set of rings on the vertebrae continues to form every year.
Sharks will grow as big as their environments allow them to grow.
Not all species of sharks can have their age determined through this method.
The Greenland shark is the longest living species of vertebrate on the planet.
These sharks can easily live for 250 to 500 years.
After going through thousands of seasonal changes, all the rings on the Greenland shark’s vertebrae are distinguishable.
If marine biologists want to accurately determine the age of a Greenland shark, they must use another method.
Marine biologists have to use the eye tissue of Greenland sharks in order to determine their age.
Researchers also have the ability to use bomb radiocarbon to tell whether an animal was born before the 1960s and 1970s or later.
Animals that were born after the nuclear weapon testing of the 1960s and 1970s have a bomb pulse that can be seen in their skin tissue.
For this reason, most sharks aren’t tested for their age until after they die.
Both of the current aging methods would kill a live shark.
Most sharks that scientists study are tagged, which serves as a way to keep track of the individual shark.
The Giant Skeleton Of The Megalodon
The megalodon was the mightiest creature in the ocean, over 2.6 million years ago.
All scientists have left are the bones of these gigantic predators, but they have still managed to discover different parts of the megalodon’s daily life.
Megalodons were massive, making all modern sharks look like toys.
These prehistoric monsters of the deep were 50 to 60 feet long, which is only slightly smaller than a sperm whale.
Some scientists believe they could have been as large as 60 to 70 feet.
These sharks weren’t just long.
They were extremely heavy as well.
Megalodons are predicted to have weighed 60 tons, making them 20 times the weight of a Great White shark.
The megalodon had five rows of a collective 276 teeth.
Similar to modern day sharks, megalodons could grow these teeth back every 24 to 48 hours.
Adult megalodon teeth were about seven inches long while juvenile teeth were only a little longer than an inch.
Despite being extinct for 2.6 million years, it is not uncommon to find fossilized megalodon teeth.
The rarest types of megalodon teeth are the ones that are completely intact.
A fully intact megalodon tooth can sell for $50,000.
Even with as much as scientists have managed to learn about megalodon, the majority of the ancient shark’s features have been lost to time.
Only the strongest pieces of cartilage have managed to survive long enough to fossilize, which has only left us with the vertebrae, jaws, and teeth of the shark.
When creating models of megalodons for museums, the models are based on the megalodon’s last surviving relative, the mako shark.
There were once rumors that the megalodon was related to the Great White shark, but they bear little to no relation to one another.
The Sharks With Glowing Spines
There are many species of bioluminescent sharks, most of which make the deep sea their home.
The species that called the deep sea their home become stranger the deeper you go.
The velvet belly lanternshark is no exception.
You can dive anywhere from 65 feet to nearly 8,170 feet to find the velvet belly lanternshark.
The younger lanternsharks will stay near the surface while older lanternsharks will dive deeper as they age.
You can most commonly find them anywhere between 650 feet and 1,640 feet below sea level.
You’ll know you’ll have found one by their glowing spine and stomachs.
They use light-emitting photophores to light up their stomachs and spine.
The photophores are the organs that produce that bioluminescent glow.
Deep sea predators steer away from creatures with bioluminescent spines.
The dark, rock-like colors camouflage the rest of the shark.
Their spines shine bright blue like a neon light and work as it’s own form of counterillumination.
Most deep-sea creatures can’t handle light ever well, so when prey spark up their photophores, it blinds the predator.
This allows the velvet belly lanternshark to get away from predators.
The shark can also use its light to attract its prey, such as krill, shrimp, small bony fish, and even squid.
In order to keep itself afloat, the lanternshark has two organs that help in this task.
The first is the Leydig’s organ, which is found in most species of sharks.
The second way it stays afloat is all the oil in its liver.
Three-quarters of its liver is solely oil.
As the velvet belly lanternshark grows, there is not enough oil alone to keep them afloat, so it begins to sink.
On average, these sharks live for about 20 years.
Humans Have Learned From Shark Bodies
Oftentimes, the answer to a problem has already been solved in one form or another in the past.
Biomimicry is when humans attempt to create the same effect that nature has on a species to be used for the betterment of society.
Society has made many technological and medical advancements through the study of how sharks work.
We’ve done more from the study of sharks than just make great swimsuits.
We’ve created one of the most useful tools in modern medicine.
Dr. Anthony Brennan was studying how surface texture affects the growth of infections and bacteria.
While studying, Dr. Brennan found that sharks don’t grow the same fungi and bacteria on them as whales and other aquatic species do.
Brennan had found that microtextures of shark skin were what kept them from getting infected.
He then applied what he had learned about shark skin to catheters, which are thin tubes made for transferring body fluids.
Catheter infections can be lethal for medical patients.
They are used in multiple parts of the human body, including the heart.
By creating a safer and more effective catheter, the lives of catheter-users were saved and made better.
Sharks have taught humanity many lessons.
They’re elegant creatures who help keep our oceans balanced.
Without sharks, our oceans would become overpopulated, thus killing even more sea creatures.
Sharks are as crucial as they are deadly.NEXT: Why Are Train Drivers Paid So Much? (Top 10 Reasons)