In fact, all the way through the fossil record it's only shark teeth, dermal denticles, and vertebral centra (dorsal fins) – no bones. Therefore, as there are no fossilized shark bones found it's pretty safe to say that all sharks – and even their earliest ancestors – have had cartilaginous skeletons rather than bones.
Sharks do not have bones.
This category also includes rays, sawfish, and skates. Their cartilaginous skeletons are much lighter than true bone and their large livers are full of low-density oils, both helping them to be buoyant. Even though sharks don't have bones, they still can fossilize.
As you are probably already aware, sharks and their relatives don't have a skeleton in the traditional sense of the word. Instead, their skeleton is made of cartilage, the flexible connective tissue that lends shape to your nose and ears, as well as structural support throughout your body.
Cartilaginous skeleton
Unlike fishes with bony skeletons, a shark's skeleton is made out of cartilage. This is a flexible but strong connective tissue that's also found throughout the human body, in places like the nose, ears, and in joints between bones.
The fossil record suggests that sharks probably did have bones but evolved over the course of around a quarter of a billion years into the cartilaginous predators we know today.
Scientists believe that their ability to repair damaged DNA has helped them survive over the years. Their presence on the planet over millions of years have earned them the title of living fossil. Sharks also have a strong immune system that protects them from serious infection and illness.
So far we've only found teeth and vertebrae of megalodons. Like other sharks, most of their skeleton is made from cartilage which doesn't preserve well in the fossil record.
Fossil remains of megalodon have been found in shallow tropical and temperate seas along the coastlines and continental shelf regions of all continents except Antarctica.
Whale sharks (Rhincodon typus) are the largest shark, and indeed largest of any fishes alive today. They feed on plankton and travel large distances to find enough food to sustain their huge size, and to reproduce. Whale sharks are found in all the tropical oceans of the world.
Sharks keep ocean ecosystems in balance
Sharks limit the abundance of their prey, which then affects the prey of those animals, and so on throughout the food web. Because sharks directly or indirectly affect all levels of the food web, they help to maintain structure in healthy ocean ecosystems.
Global water temperature dropped; that reduced the area where megalodon, a warm-water shark, could thrive. Second, because of the changing climate, entire species that megalodon preyed upon vanished forever. At the same time, competitors helped push megalodon to extinction – that includes the great white shark.
The lost shark, Carcharhinus obsoletus, a native of the South China Sea and last recorded in 1934, may already be extinct as a result of overfishing in one of the most heavily trafficked marine regions on the planet, the report found.
Most fossil evidence of early sharks exists as fossil teeth along with a few skin impressions. The earliest known evidence of sharks are fossil scales that date over 420 million years ago during the early Silurian.
Rough and rigid placoid scales (dermal denticles) coat the skin of sharks, rays and cartilaginous fishes due to the absence of dermal bone.
So, can a shark bite through bone? Bull sharks and white sharks do seem to have a significantly stronger bite than a hyena, which is known to eat bones, so it's very safe to say that, yes, sharks can bite through bone.
The answer to the megalodon question is a resounding NO. Megalodon went extinct around 3.5 million years ago.
To give you a general price range for commercial grade (has some defects) Megalodon teeth. 2-3” teeth will typically be in the $20 to $60 range, 3-4” teeth will fall into the $50-100 range, 4-5” teeth the $100-200 range, 5-5 ½” teeth $200-400, etc.
They estimate its length to have been 30 feet. Some megalodons are estimated to have been much larger―as long as 50 feet. Using the data from this study, together with previous research, the researchers concluded that the potential lifespan of megalodons was 88-100 years.
The Megalodon weighs in at upwards of 50-70 tons, measuring a span of up to 60-70 feet in length. By contrast, the Blue Whale tips the scale at around 100-110 tons and tops lengths of up to 100 feet. Who Wins on Size? It's pretty obvious that the Blue Whale is the bigger apex predator in this fight.
The largest is the whale shark, which has been known to get as large as 18 meters (60 feet). The smallest fits in your hand. And the great white shark is somewhere in the middle.
“It's a great mystery,” Elizabeth Sibert, a paleobiologist and oceanographer at Yale University, told Science News. “Sharks have been around for 400 million years. They've been through hell and back. And yet this event wiped out (up to) 90% of them.”
In fact, sharks and their relatives were the first vertebrate predators on Earth. Shark fossils date back more than 400 million years – that means sharks managed to outlive the dinosaurs, survive mass extinctions, and continue to serve an important role near the top of underwater food chains.
Land walking is a more recent trend for the epaulette sharks, as only younger members of the species have been recorded doing it. Utilizing their fins as leg-like appendages, the sharks search for prey in reef regions where other sharks can not tread.
Slowly back away
Displace the least amount of water possible. Try not to thrash and splash around as you gradually swim backwards toward shore. "You must try and keep the animal in sight and very slowly and gently try and swim backwards and get into shallow water.