Dragon

A big, green, fire snortin' lizard. No, not that one.

Dragons are organic lifeforms native to the planet Earth. They appear to be reptilian in nature, are capable of flight, and can breathe fire. They are also tremendous in size, dwarfing both humans and averaged-sized Transformers. Although quite dangerous, they have been known to be driven off through the use of dragon's bane.

The Golden One, a wizard from the dimension of Menonia could also use magic to take on the form of a large, flying golden dragon.

When Megatron takes on the spark of the his Generation 1 namesake and is thrown into a lava his form mutates from a Tyranosaurus Rex to a large red fire-breathing dragon.

From Teletraan I: The Transformers Wiki, a Wikia wiki.