All these sentences use the word "so" correctly except:
A dinosaur egg is a fossil, and so is petrified wood.
A dinosaur egg is a fossil; so is petrified wood.
A dinosaur egg is a fossil. So is petrified wood.
A dinosaur egg is a fossil, so is petrified wood.
A dinosaur egg is a fossil, and so is petrified wood.
A dinosaur egg is a fossil; so is petrified wood.
A dinosaur egg is a fossil. So is petrified wood.
A dinosaur egg is a fossil, so is petrified wood.