Intro

Hello and welcome to this episode of the podcast, "The Mnemonic Tree", where we add a single mnemonic leaf to our Tree of Knowledge.

I’m Jans, your Mnemonic Man, and today's episode will be on an evolution miracle, having survived five mass extinctions, the shark.

Sharks are an extremely diverse group of cartilaginous fish that have been in our oceans for about 450 million years, well before the dinosaurs.

They exist in all the oceans worldwide, from shallow waters where Bull sharks thrive, to the deep sea, where the Greenland shark is known to dive as deep as 2,200 metres.

Their cartilage skeleton helps them to be lighter, more buoyant, and flexible. While their skin is rough, with toothlike scales, which is a dull grey in colour. They also usually have an upturned tail, a pointed snout, and sharp triangular teeth.

They possess incredible senses that include smell, where they can detect tiny amounts of blood in the water up to 5 km away, vision, which is close to 360 degrees, and an ability to detect electrical signals through special organs.

They range in size from the giant Whale Shark, which can reach lengths of over 12 metres, to the tiny Dwarf Lantern Shark at around 20 cm.

They mature slowly and reach their reproductive age anywhere from around 12 to 15 years old.

The shark is represented strongly in cartoons and movies and some include my favourite, Jabberjaw, Kenny the Shark, Sharky the sharkdog, Sharky & George, and of course the mega franchise series by Steven Spielberg, Jaws.

With well over 500 species, unfortunately, nearly 40% are threatened with extinction due to overfishing, bycatch, habitat loss, and climate change. So, let’s hope conservation efforts, fishing regulations, and awareness can all help to preserve and enhance our marine environment.

Today’s mnemonic will be on the top seven types of sharks.

So, with that being said, we will begin with a summary from Wikipedia.

https://commons.wikimedia.org/wiki/File:Great_white_shark_south_africa.jpg

Wikipedia Summary

Sharks are a superorder of fish. This superorder is also known by its scientific name Selachimorpha.

Like other Chondrichthyes, sharks have skeletons made of cartilage instead of bone. Cartilage is a tough, rubbery material that is less rigid than bone. Cartilaginous fish also include skates and rays.

There are more than 350 different kinds of sharks, such as the great white and whale sharks. Fossils show that sharks have been around for 450 million years, since the late Ordovician. That is 200 million years before the dinosaurs.[2]

Most sharks are predators: they hunt and eat fish, marine mammals, and other sea creatures. However, the largest shark eats krill, like whales. This is the whale shark, the largest fish in the world. It is widely believed that sharks are "silent killers". However, a recent study shows that sharks emit a low growl from their throats, which resonates through their scales.

Some common kinds of shark are the hammerhead shark, the great white shark, the tiger shark, and the mako shark. Most sharks are cold-blooded but some, like the great white shark and the mako shark are partially warm-blooded.

Just a few million years ago, a giant shark called Megalodon swam in the seas. It was 18 meters long, twice as long as the closely related great white shark, and it ate whales. Megalodon died out 1.6 million years ago.

Much of what we understand about prehistoric sharks comes from the study of their fossils. While sharks have skeletons made of soft cartilage that can fall apart before fossilizing, their teeth are harder and easily fossilized.

Prehistoric sharks, like their modern descendants, would grow and shed many thousands of teeth over their lifetime. For this reason, shark teeth are one of the most common fossils.

Extracted from: [https://simple.wikipedia.org/wiki/Shark]

https://commons.wikimedia.org/wiki/File:Hammerhead_Shark_-_Marko_Dimitrijevic.jpg

Mnemonic

Sharks – Top 7 Types Mnemonic – WeT BaTH Great Mako

(Picture a miniature type of shark that is half Great White and half Mako that is perfectly suited to a bath situation)

1. Whale Shark

2. Thresher Shark

3. Bull Shark

4. Tiger Shark

5. Hammerhead Shark

6. Great White Shark

7. Mako Shark

Five Fun Facts

1. Sharks have been swimming in the oceans for more than 450 million years, since the late Ordovician Period, which predates the dinosaurs by around 200 million years and even predates trees.

2. Sharks are known for their fearsome teeth, and they have these in abundance. Over a shark’s life, they can shed more than 30,000 teeth. In a shark’s mouth, there are several rows of teeth behind the first row, which allows quick replacement when teeth are lost. They also don’t need to visit the dentist for cavities, as these teeth are coated in fluoride to protect them from decay.

3. Sharks are an extremely unique fish, and different species can give birth in three different ways. These ways are:

· Oviparous – where they lay eggs that are protected by an egg case, also known as a mermaid purse.

· Viviparous – where they carry their embryos to term and give birth to live shark pups

· Ovoviviparous – where the shark produces eggs, but instead of hatching outside, they hatch inside, and the shark pups will continue to develop inside the female until she gives birth

4. A shark’s skin or scales may look soft and smooth, but they are more like teeth than fish scales. They are called dermal denticles and are made up of an inner pulp cavity and an outside layer of dentine, which is an enamel-like material, that we have on our teeth. Along with this exterior protection, these dermal denticles decrease drag and turbulence and make them the stealthy predator they are known for.

5. Unlike dolphins, whales, and seals, sharks do not have vocal cords, though, as you heard in the Wikipedia article, a recent study now shows that sharks emit a low growl from their throats. Regardless of this, what they lack in sound, they make up for, with an additional sense. Sharks have an organ called the Ampullae of Lorenzini, which allows them to sense electrical stimuli. This is extremely helpful for them in hunting hidden prey, and why you often see sharks combing the ocean floor.

Now just before going onto the quiz. I was gill-tee of going to my favourite fish shop the other night. Anyway, I ordered my standard flake, but they also through in as a little bonus, a Clown Fish. Anyway, the flake was okay, but the Clown Fish tasted a little funny! So, I pushed them both aside and nailed the Hammerhead!