They resembled baby gargoyles, hence their moniker, and their small stature (2 feet tall/long) allowed them to hide in the wizard's posessions, ready to fly out and strike if they sensed a presence in the room it was guarding that wasn't it's creator or one of the 5 people it could be programmed to not attack. Greater guardgoyles tended to be between 4-6 feet tall and lacked the ability to fly, they were also much more expensive to create and required much more powerful magic to animate them.