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Facts about Sharks - Modern and Prehistoric


Facts about Sharks - Modern and Prehistoric

Shark Facts

This is a Hammerhead Shark from my dive trip in the Galapagos. I had to hold my breath to take this close-up shot, as these hammerheads tend to shy away from the bubbles coming from scubadivers.

Fast Facts about Sharks

This is a Whitetip Reef Shark that was cruising around while snorkeling in Tonga.

No Bones:
Sharks don't have bones! Instead, they have Cartilage.
Cartilage is firm but more flexible than bone. It is found in your nose and ears.
Fish that are made of Cartilage are called "chondrichthyes." This class of fish include Sharks, Skates, Rays, and Chimaeras.

Many Types of Sharks:
Sharks and Rays belong to the Elasmobranchii subclass.
This subclass contains 8 extant (living) orders, which contains over 600 species.
Over 400 of those species are sharks! Of the 400 species of sharks, how many can you name?

Sharks are Ancient:
Sharks first appear around 450 million years ago in the Ordovician time period.
Some of the very first shark fossils come from the Harding sandstone in Colorado.
The first sharks may not have had teeth or even jaws!
Here is an article about Shark Evolution.

The Largest Shark:
The largest shark is the Whale Shark. Whale sharks can reach lengths over 40 feet!
Don't worry, they are filter feeders, which means they eat mainly plankton, tiny fish, jellyfish, and shrimp.

The Largest Prehistoric Shark:
The largest prehistoric shark is called the Megalodon. Megalodon was like a GIANT Great White shark.
It could probably reach sizes over 60 feet in length, and ate whales
Luckily it wen't extinct around 2.5 million years ago!
Here is an article all about the Megalodon Shark

Sharks are unique in that they have rows of replacement teeth growing behind each tooth. When one falls out, another one simply replaces it.
A shark can go through 10,000 to 20,000 teeth in its lifetime!

Sharks have adapted to a wide range of conditions. Some live in tropical waters, others live in arctic waters. Some live near-shore, while others live in the open ocean. Some prefer very deep water, others prefer shallow water.
Some sharks, like the Bull shark and the River shark can even tolerate freshwater!

Sharks also come in a wide variety of shapes and sizes.
Most sharks are under 3 feet in length.
However, some sharks are quite large. The Basking shark can reach lengths of over 30 feet, while the Whale shark can reach lengths of over 40 feet!

Sense of Smell:
The Great White shark can smell a single drop of blood in an olympic sized pool!

Conservation Status: Although the total numbers of sharks are unclear, many sharks are threatened by overfishing and shark finning.
According to the IUCN, 25% of all shark and ray species are threatened with extinction.
110 species are listed as threatened and another 95 species are listed as near threatened.

Shark Attack... Not.

Althought the media wants you think otherwise, shark attacks are rare! Humans are not a food source for sharks, even the Great White. Consider the following:
On average there are less than 100 shark attacks per year. Of those, less than 10 are fatal.
When at the beach, your chances of being attacked by a shark are a mere 1 in 11.5 million.
To give you a perspective, here are some other averages:

In the United States:
There is less than 1 fatal shark attack each year
Vending machines kill 2 people per year
Snakes kill 5 people per year
Icicles kill 15 people per year
Horses kill 20 people per year
Cows kill 20 people per year
Lightning kills 49 people per year
Deer kill 130 people per year
700 people accidentally drown each year
Texting while driving kills 3,000 people per year
Global Averages
Sharks kill 10 people per year Jellyfish kill 30 people per year
Champagne corks kill 24 people per year
Coconuts kill 150 people per year
Elephants kill 500 people per year
Hippos kill 3,000 people per year
Snakes kill around 40,000 people per year!

Shark Anatomy - What do Sharks look like?

Sharks are a type of fish in the Chondrichthyes class, or the cartilaginous fish. This means sharks do not have a hard skeleton like us, instead their skeleton is made of a dense cartilage; similar to what the tip of your nose and ears are made of.

The chondrichthyes class not only includes sharks, but also skates, rays, and chimaeras as they also have a cartilaginous skeleton.

Specifically, sharks, skates, and rays belong to the Elasmobranchii subclass. This subclass contains 8 extant orders, which in itself contains over 600 species. The following shark pictures show the physical characteristics of a shark.

This shark picture shows the main body features of a shark. This picture was taken at Wolf Island in the Galapagos during one of my dive trips.

This shark picture shows detailed structures on the head of a shark, plus claspers, which are not present in the first picture. This picture was taken at the North Shore in Hawaii during a shark cage excursion.

Each shark order has a slightly different anatomy. Some orders have fin spines, some have one dorsal fin while other orders have two. The number of gill slits ranges from 5 to 7 depending on the order, some are torpedo shaped, some a very flat. There are a wide range of shapes and sizes of sharks.

Most of the terminology in the diagrams are self explanatory. Some shark terms that may be unfamiliar include the spiracles and the claspers. Claspers are found on male sharks. They are used to hold onto the female while mating (Hey, they don't have hands!). The spiracles are a bit more complicated. A spiracle is a hole behind the eye that leads to the mouth. When tracing the evolution, it use to be a gill in jawless fish. When jaws developed, the jaw bones isolated this gill slit from the rest, and could no longer be used. A remnant hole from this unused gill still remains in sharks. It's kind of like a tail bone on a person, we don't have a tail but still have a little bone there.

What is Shark Skin made of? Dermal Denticles

shark skin, showing the side view of shark dermal denticles

Shark dermal denticles - Top view

If you have ever touched shark skin, you have noticed it is quite different from other fish. When rubbing in one direction, it feels silky smooth. However, when rubbing in the opposite direction, it feels like coarse sandpaper! Some ancient cultures actuallly used shark skin as sand paper.

This sand paper like texture results from the sharks highly modified scales, called denticles. These denticles are very different from regular fish scales. They are very streamlined (hydrodynamic), and point away from the front of the shark. This lets water easily pass over the shark, allowing it to swim more efficiently.

Shark dermal denticles are very small, less than a millimeter in size. The images shows zoomed in sections on the tail of a shark, once zoomed in enough, you can start to see the denticles. They look like tiny diamonds, with small ridges on them.

Shark dermal denticles - Zoomed in view

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High Quality Shark Teeth by Fossilera

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