Here is how The Spinosaurus kills T-Rex in Thomas and Twilight Sparkle visit Jurassic Park III
Alan: It's okay, it's dead.
Rarity: Ew! Gross!
(Then a T-Rex appears)
Mako: But he isn't!
Mane 6: Gasp!
Luke: Oh My!
The Cutie Mark Crusaders: Gasp!
Sir Handel: Oh, no! I know that dinosaur!
Steam Claw D.: It's the T-Rex!
Alan: Nobody move a muscle.
Duncan: AAH! No! Help me! AAAAH!
Mucker: HEY! HE SAID "DON'T MOVE!"
(then, the Spinosaurus appears)
Alan and Rarity: [screaming]
(Spinosaurs and T-Rex go into battle)
(the Spinosarus bites the T-Rex's neck)
(Then the Spinosaurus snaps the T-Rex's neck and falls to the ground])
(after the team escape)
Rainbow: What the hay was that thing?!
Willy: That... was a Spinosaurus.
Pinkie: What's a Spinosarus?
Mucker: Next to the T-Rex, the Spinosarus is a deadly giant but not as deadly as the T-Rex.