"Prehistoric Sonic" is the fifty-first episode of the Adventures of Sonic the Hedgehog television series. Despite it being produced as the fifty-first episode, it originally aired as the fortieth episode during the show's original run. This episode is the fourth and final part of the "Quest for the Chaos Emeralds" saga.
Picking up where the previous episode, "Robotnik's Pyramid Scheme" left off; Dr. Robotnik, Scratch and Grounder are in the middle of a battle during WWI. The trio quickly use their time machine to travel back to prehistoric times to obtain the Chaos Emerald of Life. Robotnik explains that with it, he could bring anything to life. Scratch is excited because he could become a real life chicken. Grounder does not know what he is, so he is confused to become a real life whatever he is.
Robotnik, Scratch and Grounder find the Volcano where the Chaos emerald of Life had emerged from. Sonic and Tails follow them, not far behind. Scratch and Grounder are attacked by a pack of Cave Bears. Dr. Robotnik uses his Robot-Transmogrifier Ray on a T-rex to take care of the primitive fuzzies. Sonic and Tails comes to their aid, but that just makes Robotnik sic the T-rex on them instead. Sonic gets on the T-rex's back and rides it like a horse. He uses the dinosaur to chase Robotnik, Scratch and Grounder, but they escape by zapping a pterodactyl with the Robot-Transmogrifier Ray and flying it back to the volcano. Robotnik finds the Emerald, but it is stuck in the rock. Magma the Volcano God emerges from the lava and says Robotnik must make a sacrifice to him before he can have the emerald. Robotnik sacrifices Scratch and Grounder just as Sonic and the Cave Bears arrive to stop him.
Robotnik obtains the emerald and commands the lava to come to life and form into Lava Monsters. The lava monsters catch Sonic, Tails and the Cave Bears and throw them all in the lava (Robotnik ties Tails' tails together so he can't fly). Sonic does a spin along the walls of the volcano and rescues Tails and all the Cave Bears. Scratch and Grounder crawl out of the lava and reveal it is really only volcanic mud. Robotnik picks up the two Badniks in his pterodactyl and they fly away with the Chaos Emerald.
Robotnik travels back to Mobigypt and Sonic and Tails follow close behind. Inside the tomb of Robotnikhotep, Dr. Robotnik finds his ancestor in one piece again, sleeping with the Chaos Emerald of Immortality around his neck once again. Sonic and Tails arrive and Robotnikhotep wakes up and declares that he hates Hedgehogs. Robotnik says he'll take the emerald and Robotnikhotep can take the hedgehog. Robotnik escapes in his time machine and Sonic Spin Dashes Robotnikhotep into nothing. The heroic duo decide to go to King Arfur's castle next.
Finally Robotnik and his goons show up at Shark Island where they dig up the Chaos Emerald of Invisibility. Robotnik brings the treasure chest to life, making it into a Treasure Chest Crab creature. He leaves the chest to deal with Sonic while he returns to his lair in the present.
Back at his lair, Robotnik places all four Chaos Emeralds around his neck and transforms into the Supreme High Robotnik, master of the universe. Sonic and Tails arrive, Robotnik attempts to finish off his nemeses once and for all by sending them back in time to the Big Bang. The duo narrowly escape, and then gather four versions of themselves from earlier points in the timeline and successfully defeat Robotnik. Afterwards, the four extra Sonics and Tailses use Robotnik's time machine to return the Emeralds to their proper owners, and also to destroy the time machine afterwards.
Tails is fiddling with the Time Traveling Skateboard trying to modify it so it goes faster. Sonic tells Tails not to try and fix electrical appliances on his own. Robotnik steals the board and gets electrocuted.
Let's make like an orange and juice!
I always hear that volcanic mud baths are good for your skin.
We'll be lucky if we have any skin when we get this junk off.