A sphenodon is a type of reptile that is sometimes called a 'tuatara'.
Sphenodons are interesting because they are very old and not like other reptiles.
Examples:
The sphenodon is a very old reptile.
I saw a sphenodon at the zoo.
The sphenodon has three eyes.
The sphenodon is not a dinosaur, but it's still very old.
The sphenodon is the coolest reptile in the world.
I want to see a sphenodon in real life.