Can different species of reptiles be aggressive to each other?

I know there are certain species that you can't house together because they will be a danger to each other (only example I can think of is Kingsnake with anything including other kings) I would imagine that you couldn't safely keep a large (or aggressive) carnivore with a meek animal of any kind. But I think it is kind of a matter of the actual animal themselves too. I was always told a large iguana would be unsafe to be loose with my bearded dragon...and now they are "best buds" and even hang out on the back of my chair together...yesterday I let Scar (the iguana) bathe in the tub and put Pancake (bearded) in to see what she would do...they were perfectly fine until Kash (the DOG) decided she wanted to swim too...