Size of course! In this case, Amadeus, a beautiful bearded dragon, (say that 5 times fast), may look like a lizard. And he is, sort of. He's two years old, and if he isn't walking on the ceiling of his habitat, he's hanging out on the warm rocks below. His guardian likes to take him out to hold him, but Amadeus prefers to get a bird's eye view by climbing up on his shoulder instead.
It's not every library that can claim it has dragons - except in books.