From Creatures Wikia
Like their namesakes, Reptile Norns are cold-blooded and so cannot adjust their own temperatures. This means that it is positively dangerous to leave one in a cold environment - after a while, they will become tired, fall asleep, and eventually die (although they are protected from damage by a form of antifreeze which is produced while they sleep).
On the other hand, Reptile Norns do not require as much food as warm-blooded creatures, and they can survive longer underwater - usually a little over three to four minutes. They love the Desert Terrarium. Like Draconian Norns, they also have a longer-than-usual lifespan.
The Reptile Norns bring their favourite fodder with them: small crickets and other insects. These breed in regions of grass, weeds or plants (fruit, seeds, carrots and other sorts of food do not count). These are very nutritious for all creatures, and can vary their brightness.
The Reptile Norns require Toxic Norn and Banshee Grendel sprites - if these breeds are not installed, then other sprites will be used. They are not laid by Muco or at the Hatchery, but must be injected using the agent injector. They can be downloaded at Mummy's Creatures.