From Halopedia, the Halo wiki

There is more information available on this subject at Porcupine on the English Wikipedia.
The porcupine in Halo: Reach.

A Porcupine is a species of small rodent with sharp spines. It is native to Earth.

A similar animal resembling its Earth namesake was intended to appear in Halo: Reach as part of the planet's ambient life, but an error in its AI saw it cut from the final game by the Zero-bug release.[1]