Animal Species/Other

Horn Eaters
Horn Eaters (ツノクイ, Tsuno Kui) are a type of creature featured prominently in the third One Piece movie. They are large herbivorous armadillo-like rhinos that will aggressively attack any horned creature within sight, even if said creature happens to have fake horns, as seen with Luffy (Usopp had him garbed in a ridiculous costume with antlers included). They are used by Butler to herd the various other horned animals on Crown Island in order to chop their horns off.

Trumpet Pig
Trumpet Pig is a weird pig living on the Crown Island.

Square Rhinos
Square Rhinos are animals with a rectangular form and loosely resemble rhinos that live on the Crown Island. When they lie on the ground, it is very easy to mistake them for rocks.

Dragon
Oda has mixed the Monsters story into the One Piece main story.

The powers and abilities of a dragon are so strong that not only can it destroy a single town (under the control of D.R. and Cyrano) and bring terror to the public, but killing one made Ryuma a legend, and stories about him are still passed down after generations.

Hogback remarked that Ryuma had slain a dragon, however Roronoa Zoro expressed skepticism toward this statement.