Simon was a character originally created for the Renegade storyline. We scrapped him because there were too many characters to keep track of already and there was no need to introduce 2 new characters to the already existing crew. He is one of Kaeru's early experiments. He's based on a primitive kangaroo called procoptodon. They basically have a smooshed face and one giant toe.
Link
Bradypodidae
... one giant toe that looks like a heck of a weapon.
Well done!