“That was the Grand Canyon as we know it today, but it wasn't always that way. Quiet now, as we travel back in time, back to the fantastic Primeval World, land of the dinosaurs!”
―Announcer in the California version of the attraction after passing the Grand Canyon Diorama (pre-2017 revamp)
It is based on the Rite of Spring segment of the 1940 Disney animated feature film Fantasia.
In Disneyland, it comes immediately after the Grand Canyon Diorama between the Tomorrowland and Main Street stations. In Tokyo Disneyland, it is located in a mining shaft behind Big Thunder Mountain Railroad, heralded by a Triceratops skeleton at the entrance to the tunnel.
At the Primeval World, guests see a many dinosaurs (a large number of dinosaurs) in a supposed natural habitat after traveling back in time. This includes a forest inhabited by Edaphosaurus, a swamp with a feeding herd of Brontosaurus (plural: Brontosauri) and Pteranodons perched upon rocks and waterfalls, a Triceratops couple and a nest of baby Protoceratops, a group of Gallimimus at a small watering hole in a scorching desert, and a Tyrannosaurus battling a Stegosaurus in a volcanic landscape. The Tokyo version merges the Pteranodon and Gallimimus vignettes into one scene and utilizes figure molds created for the Universe of Energy to depict its brontosaur herd.
Disneyland's diorama is accompanied by the theme for the 1961 film The Mysterious Island, while Tokyo's diorama uses the original Ford Magic Skyway soundtrack.
On the ride, guests will encounter ten species of prehistoric animals (counting dinosaurs and other prehistoric reptiles --although Edaphosaurus and Pteranodon are not dinosaurs):
Edaphosaurus - Actually a synapsid (a mammal-like reptile) that became extinct before the dinosaurs existed, though this is a common mistake. They are among the first creatures shown, and have characteristic glowing red eyes.
Gallimimus - A small herd of these ornithomimids are seen at a watering hole in a desert. They may not actually be Gallimimus, as names are not mentioned on the ride.
Multiple/countless paleontological mistakes are found in the diorama. This can be forgiven by the fact that it was created in the 1960s and was predominately rooted in an animated sequence that was created in the 1940s.
They are seen chewing plants like cows. This is known to be incorrect, as it/they swallowed its/their food whole and it was broken down by gizzard stones (gastroliths).
They did not have spines.
They did not drag its/their tail on the ground.
They were proven incapable of eating (or resting/snuggling) with its/their body submerged under water due to the pressure's impact on its/their internal organs.
Its tail should be more elevated and it has five or six tail spikes (with the fifth spike --out of the five-- being on the tip of the tail). (The real dinosaur Stegosaurus only had four spikes on the tail.)
They are shown standing on their hind legs with their wings spread out like a vulture, when they should be on all fours with their wings folded like a vampire bat.
They (like all pterosaurs) were supposed to have fur and lack bat wings.
Despite not living at the same time as Brontosaurus --as Brontosaurus was around in the Jurassic period and Pteranodon lived in the Cretaceous period-- Pteranodon --even though it was not a dinosaur-- it (like all pterosaurs) lived at the same time as the dinosaurs.
So the Brontosaurus and Pteranodon living at the same time (living in the Mesozoic era --age of dinosaurs-- overall) could be seen correct, as pterosaurs lived at the same time as the dinosaurs. (The Pteranodons near the Brontosaurus are a correct seeing, as pterosaurs were around at the same time as the dinosaurs.)
Edaphosaurus went extinct before the dinosaurs existed. And (since it was a mammal-like reptile and related to mammals) it should have naked mammal-like skin instead of scales.
The Tyrannosaurus Rex near the end has a number of anatomical faults:
The head is wrong shape.
There are three fingers on the hand (three fingers like an Allosaurus or Giganotosaurus). The real dinosaur (Tyrannosaurus Rex) had two.
It did not have pronated arms.
It is standing upright, which has been determined wrong.
Tyrannosaurus Rex (when it was young) had feathers along its back, neck, and head. This however was not definitively proven until the 21st century so the mistake is understandable.
Trivia
The Triassic period is not ignored. And since Plateosaurus lived in the Triassic, it appears as a skeleton (near the end of the attraction). Said dinosaur is no exception.
The theme song is from the 1961 film Mysterious Island was played.
The battle between the Tyrannosaurus Rex and the Stegosaurus was based on the battle scene between the two dinosaurs from The Rite of Spring segment of Fantasia.
