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 the living fossil which has existed for over 200 million years, the crocodile.

Existing on four continents the crocodile belongs to the order Crocodylia, which also includes alligators, caimans, and the gharial. They are large, carnivorous, apex, predators that feed mainly on fish, birds, and mammals. Known for their cunning ambush tactics and death roll they also have a more caring and maternal side. They build their nests on riverbanks and diligently guard these nests before escorting the hatchlings to the water where they continue to protect and guide.

Although crocodiles, alligators, and the gharial are in the same order they do belong to separate biological families. The alligator has only two species which are the American alligator and Chinese alligator, while the crocodile or Crocodylus has a total of 14 species according to Wikipedia.

The crocodile is well represented in literature, TV shows, movies and video games with some of the more popular characters being Tick-Tock from Peter Pan, Louis from the Princes and the Frog, Master Croc from Kung Fue Panda, King K. Rool from the video game Donkey Kong Country, Leatherhead from the Teenage Mutant Ninja Turtles, and all the way back to the Hanna-Barbera classic Wally Gator, from the Wally Gator show.

Today’s mnemonic will be on five types of crocodiles.

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

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

Wikipedia Summary

Crocodiles (family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to include all extant members of the order Crocodilia, which includes the alligators and caimans (family Alligatoridae), the gharial and false gharial (family Gavialidae) among other extinct taxa.

Although they appear similar, crocodiles, alligators and the gharial belong to separate biological families. The gharial, with its narrow snout, is easier to distinguish, while morphological differences are more difficult to spot in crocodiles and alligators. The most obvious external differences are visible in the head, with crocodiles having narrower and longer heads, with a more V-shaped than a U-shaped snout compared to alligators and caimans. Another obvious trait is that the upper and lower jaws of the crocodiles are the same width, and the teeth in the lower jaw fall along the edge or outside the upper jaw when the mouth is closed; therefore, all teeth are visible, unlike an alligator, which possesses in the upper jaw small depressions into which the lower teeth fit. Also, when the crocodile's mouth is closed, the large fourth tooth in the lower jaw fits into a constriction in the upper jaw. For hard-to-distinguish specimens, the protruding tooth is the most reliable feature to define the species' family.[1] Crocodiles have more webbing on the toes of the hind feet and can better tolerate saltwater due to specialized salt glands for filtering out salt, which are present, but non-functioning, in alligators. Another trait that separates crocodiles from other crocodilians is their much higher levels of aggression.[2]

Crocodile size, morphology, behaviour and ecology differ somewhat among species. However, they have many similarities in these areas as well. All crocodiles are semiaquatic and tend to congregate in freshwater habitats such as rivers, lakes, wetlands and sometimes in brackish water and saltwater. They are carnivorous animals, feeding mostly on vertebrates such as fish, reptiles, birds and mammals, and sometimes on invertebrates such as molluscs and crustaceans, depending on species and age. All crocodiles are tropical species that, unlike alligators, are very sensitive to cold. They separated from other crocodilians during the Eocene epoch, about 55 million years ago.[3] Many species are at the risk of extinction, some being classified as critically endangered.

Extracted from: [https://en.wikipedia.org/wiki/Crocodile]

https://commons.wikimedia.org/wiki/File:Crocodylus_acutus_05.jpg

Mnemonic

Crocodiles – 5 Types Mnemonic – SAND Marsh

(Picture a sand marsh next to the salt marsh where crocodiles would partially bury themselves and wait patiently before attacking unsuspecting prey)

1. Saltwater Crocodile

2. American Crocodile

3. Nile Crocodile

4. Dwarf Crocodile

5. Marsh Crocodile

Five Fun Facts

1. Crocodiles not only have an amazing history, but they are history, remaining relatively unchanged for around 200 million years. This makes them one of the oldest reptile lineages on the planet after the Hylonomus which was a lizard-like animal, 20 to 30 centimetres long and lived in swamps and originated 312 million years ago.

2. Now when it comes to the biggest crocodile that title goes to the Saltwater crocodile. It can reach lengths of up to six metres long, and weigh over 900 kilograms. They can also live for over 70 years.

3. Along with their incredibly powerful jaws which can exert a bite force of over several thousand pounds per square inch, the crocodile also contains a unique tooth replacement system. They have a specialised groove in their jaws that allows new teeth to grow to replace the lost and damaged ones. This could equate to thousands of teeth over the lifetime of a crocodile.

4. The crocodile also has a secret weapon on the skin of its snout. Here, they have tiny pits called "integumentary sensory organs" which are extremely sensitive to pressure changes in the water, both enabling the crocodile to detect prey, but also be aware of any threats.

5. Despite their clunky appearance crocodiles are excellent swimmers and can reach speeds of around 20 miles per hour, or in kilometres around 32. Interestingly they can swim at this speed and barely make a ripple at the surface. It is suggested that the bony ridges on the crocodile’s back produce destructively interfering wake patterns at the water's surface. To draw an analogy something like noise-cancelling headphones.