There are two creatures situated below the angels and above the demon on the holy water font seen just inside the entrance to Sauniere's church, that seem to be the mythical Basilisks.
Holy Water Font from Sauniere's Mary Magdalene Church
The Two Basilisks
What is a Basilisk?
1 - Classical Mythology . a creature, variously described as a serpent, lizard, or dragon, said to kill by its breath or look.
2 - Any of several tropical American iguanid lizards of the genus Basiliscus, noted for their ability to run across the surface of water on their hind legs.
I imagine it is the 1st description that is to be given to Sauniere's creatures.
A frame taken from a video taken inside Sauniere's church, reveals that the heads were missing. Perhaps loose and to prevent them from being stolen, they were removed for safe keeping. They have now been glued in place.
Missing Basilisk Head