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.

it would be d cause refers into the pargrapgh

cabeza de vaca was an spanish explorer and n his long exploration of 11,000.km. from florida to present-day mexico, he went through a series of calamities and setbacks that only added to his deeds. he applied his religious creed with the humanist idea, always current and universal, that all men were equal before god and destiny without any discrimination. as an explorer, he became a slave to the tipinoga, then his shaman pointer, later and after an operation of heart to an indian (from which both came alive) he achieved stardom and became a hero followed by a crowd that professed unusual respect and admiration.