Dinosaurs, and other prehistoric creatures such as pterodactyls were trapped alive in tree sap in the abandoned mines in the Gravity Falls Forest. The summer heat is causing the tree sap to melt, slowly releasing the dinosaurs and others from the sap.
In "The Time Traveler's Pig," when Blendin Blandin's wrist-worn device malfunctions, a scene from Land Before Swine with dinosaurs trapped in tree sap is shown on his jacket. Later, when Dipper and Mabel go back to the past, they are attacked by a Tyrannosaurus.
In "Land Before Swine," the pterodactyl escapes in the tree sap and begins terrorizing the town and ends up stealing Waddles. It retreats to the Abandoned mines, where other dinosaurs are seen trying to escape. It also had an egg which hatched into a baby pterodactyl that ate Old Man McGucket.
Mabel gave Dipper a dinosaur sticker saying "Ext-Roar-Dinary" in "The Golf War".
A number of dinosaur species are seen trapped in tree sap in the abandoned mines. They are all from different periods of the Mesozoic. Some of them are:
- Pterosaur (Although a flying reptile not a dinosaur)
- Tyrannosaurus Rex
- Unknown dinosaur (only its tail was visible, it was possibly a Spinosaurus)
- Intro: "Gravity Falls Main Title Theme"
- Mystery Shack Mystery (mentioned)
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