No wolves on Fenris.

I just finished reading Prospero Burns, and in it (as well as in other books like Thousand Sons), the phrase “there are no wolves on Fenris” is stated several times. At one point, someone even stated there “were no wolves on fenris before the Space Wolves arrived (paraphrasing)”.

Im still not totally sure what this means. My interpretation is that all the actual wolves that accompany the space wolves are space wolves in an altered form? Im not even referring to the “Werewolf” space wolves that are hybrid, but the animal wolves.

Am I way off base?

Thanks