Ellie and Alan, Paleontologists

{T}, Exile a creature card from your graveyard: Discover X, where X is the mana value of the exiled card. Activate only as a sorcery. (Exile cards from the top of your library until you exile a nonland card with that mana value or less. Cast it without paying its mana cost or put it into your hand. Put the rest on the bottom in a random order.)

Cresting Mosasaurus

Emerge {6}{U} (You may cast this spell by sacrificing a creature and paying the emerge cost reduced by that creature's mana value.)
When this creature enters, if you cast it, return each non-Dinosaur creature to its owner's hand.

Ghalta, Primal Hunger

This spell costs {X} less to cast, where X is the total power of creatures you control.
Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)

Jurassic Park

(Transforms from Welcome to ....)
Each Dinosaur card in your graveyard has escape. The escape cost is equal to the card's mana cost plus exile three other cards from your graveyard. (You may cast cards from your graveyard for their escape cost.)
{T}: Add {G} for each Dinosaur you control.

Welcome to . . .

(As this Saga enters and after your draw step, add a lore counter.)
I — For each opponent, up to one target noncreature artifact they control becomes a 0/4 Wall artifact creature with defender for as long as you control this Saga.
II — Create a 3/3 green Dinosaur creature token with trample. It gains haste until end of turn.
III — Destroy all Walls. Exile this Saga, then return it to the battlefield transformed under your control.

Welcome to . . . // Jurassic Park

Life Finds a Way

Whenever a nontoken creature you control with power 4 or greater enters, populate. (Create a token that's a copy of a creature token you control.)