You don't choose whether to reveal a Dinosaur card from your hand until the triggered ability of Priest of the Wakening Sun resolves. You may respond to the triggered ability by taking an action to get a Dinosaur card into your hand, such as activating its second ability.

While resolving Priest of the Wakening Sun's triggered ability, you can't reveal multiple Dinosaur cards to gain more life.

You can reveal the same Dinosaur card for multiple Priests of the Wakening Sun or for the same one over multiple turns.

If an effect refers to a "[subtype] spell" or "[subtype] card," it refers only to a spell or card that has that subtype. For example, March of the Drowned is a card that benefits Pirates and features Pirates in its illustration, but it isn't a Pirate card.