- Narrator: All six Animorphs
A nuclear explosion sends the Animorphs back to the time of the dinosaurs.
Tropes
- Artistic License – Biology: Broccoli was apparently brought over to Earth by the Mercora, and carrots existed in the Cretaceous Period. Both of these vegetables were bred into existence by humans and their wild form barely resembles their domesticated form.
- Artistic License – Paleontology: Tobias addresses this in the last page of the book, where he admits that most of the dinosaurs depicted were separated by vast time periods.Tobias: <So who are you going to believe? Me, or a bunch of scientists with some old fossils?>
- Somewhat less excusable, though, is the fact that many of the descriptions of the dinosaurs themselves disagree with what is known from fossils, even at the time the book was written. For example, Spinosaurus is portrayed as a sail-backed carnosaur instead of the crocodile-headed fish-eater it actually was, and the Deinonychus are scaly rather than feathered. The fact that the dinosaurs in question come from different places as well as different times also goes unmentioned.
- Colony Drop: After being kicked off the planet, the Nesk redirect a comet towards Earth, causing the K-T extinction event and closing the Sario Rip.
- Covers Always Lie: A promotional poster showed Jake morphing into an Oviraptor, Marco into a Deinonychus, Cassie into a Hadrosaur, and Rachel into a Stytracosaurus. In the book, the dinosaur morphs acquired are a T-Rex (Jake, Marco, Cassie, Ax) and Deinonychus (Rachel and Tobias).
- Cutting the Knot: Marco dodges the T-Rex by going around a tree. After a few seconds of this, the Big Rex gives up on running around and just chews through the tree itself.
- The Day the Dinosaurs Died: The Animorphs accidentally Time Travel to the late Cretaceous and get embroiled in a war between two alien races colonizing the prehistoric Earth, the Mercora and the Nesk. They help the Mercora drive the Nesk off the planet, only for the Nesk to be Sore Losers and deorbit a comet that was going to miss. Tobias realizes this is probably the Chicxulub impactor, and makes Ax sabotage the Mercora attempt to deflect it. The impact then reverses the time travel.
- Death World: The Cretaceous Period not a safe place for four humans, one hawk, and one Andalite. None of the morphs they have at their disposal are able to avoid predators forever, at least until they acquire some period-appropriate animals.
- Drama-Preserving Handicap: For some unexplained reason, morphing doesn't fix Tobias' broken wing, keeping him and Rachel separate from the rest of the team for longer than they could have been.
- Dramatic Slip: Marco inconveniently trips on a tree root while fleeing from a T-Rex.
- Eaten Alive:
- Tobias and Rachel are Swallowed Whole by a Kronosaurus while in dolphin morph.
- Jake is eaten by a Tyrannosaurus while trapped under a Saltasaurus that the Big Rex had just killed.
- Foreshadowing: The Animorphs noticed a comet in the sky, and Tobias figures out they're in the Cretaceous period (the final period before the dinosaurs extinction). Readers who knows about how the dinosaurs died can figure out that the comet is the Chicxulub asteroid that killed the dinosaurs (though it needed a push in the right direction by the Nesk).
- It Can Think: According to Marco, the T-Rex didn't become an apex predator by being stupid. The T-Rex morph's instincts are overwhelming because of how smart they really are; Cassie, who is normally the one who has the easiest time controlling morphs, loses herself to the T-Rex's mind while still being able to talk to the others like she's an actual T-Rex.
- Mundane Utility: Ax is surprised by the fact that the bomb was nuclear, as Andalites use nuclear fusion in children's toys.Marco: So the Andalite Toys ‘R’ Us must be a wild place, huh?
- Psychic Radar: A literal example in the form of the Nesk building a device to detect thought-speech, allowing them to know if there were any Mercora in their base.
- Raptor Attack: While they're at least called Deinonychus instead of Velociraptor, in all other respects the book's raptors follow this trope to a T, being scaly, intelligent pack-hunters.
- Regret Eating Me:
- Rachel's response to being eaten by a Kronosaurus is to morph to grizzly bear and rip her way into its lungs for air.
- Jake is nearly swallowed by a T-Rex, but begins morphing in its throat. This incapacitates the Big Rex long enough for him and the others to acquire it.
- Super-Persistent Predator: The first T-Rex kills a baby Saltasaurus and then goes after the Animorphs instead of enjoying its meal. Marco morphing to an osprey, a bird not even bite-sized to the Big Rex, does nothing to stop it from pursuing him. Marco notes that a sufficiently worked-up predator stops caring about food or hunger, and will kill out of sheer stubborn pride.
- Tastes Like Chicken: Subverted at one point. The Animorphs manage to kill a t.rex and decide to cook and eat part of it. Jake says that it tastes like swordfish, of all things.
- Terrifying Tyrannosaur: The Tyrannosaurus Rex predictably makes its appearance in this book. The first one encountered is so unbelievably powerful compared to the Animorphs that all they can do is run, while the second one makes a mistake that allows Jake, Cassie, Marco, and Ax to acquire it.Cassie's narration: More than forty feet from head to tail: the length of a bus. Eighteen feet tall: the height of a two-story house. Seven tons of bone and muscle: the weight of five cars.
Power and speed and destruction made flesh. Power the world had never seen before and would never see again.
I had become Tyrannosaurus rex.
King of the dinosaurs. - Too Good for This Sinful Earth: The Mercora are a peaceful species who only want to start a new life on Earth. So of course, they go extinct along with the dinosaurs.
- Worf Had the Flu: Ax kills a T-Rex with his tail blade. He flatly says it's because the Big Rex was distracted by trying to eat Marco in osprey morph; in direct combat, the Big Rex would have bitten him in half. To drive the point home, the T-Rex retaliates before it bleeds out, sending Ax flying across the jungle.
- The Worm That Walks: The Nesk are alien ants that can bundle together to make bodies that can build laser weapons and spaceships, and even learn to speak English in a few hours.
