Writing Credits: Mark Edens
First Aired: October 17, 1989
Title reference: A mashup of "prehistoric pet" referring to Steggy and "hysterical"
Episode Number: 32
Production Number: CDRR 1219
The episode begins at a dig for dinosaur bones. Hearing an explosion, the scientists find a large "dinosaur egg." This egg is actually a working spacecraft piloted by a small creature (Steggy) resembling a dinosaur. The scientists take the egg back to the museum and Steggy gives chase. Back at Ranger HQ, Dale brings home another pet and is chided by the others for his irresponsible nature. Various adventures bring Dale and Steggy together, with Dale wanting to keep Steggy as his pet. Dale at first hides Steggy, but he is eventually discovered by the other Rangers.
Steggy then sees his egg/spacecraft on TV and leaves to attempt to retrieve it. After the Rangers rescue him from a tar covered new road, he reveals that he can speak their language. As they return to RRHQ, Steggy tells the Rangers about his civilization and how he has come to Earth to find out what happened to his ancestors. They all go to the local museum where Steggy finds that his ancestors became large and dumb before going extinct. He shows signs of the same effect himself.
Dale attempts to hide Steggy while the other Rangers look for his spacecraft, hoping to find a way to reverse the effect. The craft is still thought to be an egg by Dr. Piltdown and he plans to examine it soon. The Rangers manage to get into the craft and Gadget flies it out of the examining room. After various mishaps by both groups, they meet back up. By this time, Steggy is almost fully animal like. However, after eating food packets from his homeworld, he immediately reverts to his small and intelligent state. The Rangers surmise that eating Earth food must have had this effect on the dinosaurs. The group escapes in the craft and returns to HQ.
Steggy prepares to leave and states that he would like to bring Dale with him, but he is not allowed to have pets.
The Rescue Rangers
Dr. Piltdown: Careful with that egg, men. It's millions of years old. I can't wait to write a 50-page research paper about it.
Dale: I can't help it that animals like me.
Chip: Like the goldfish that followed you home?
Steggy: (to Dale) I'd like it very much if you'd come and live with me on my planet...
Dale: Oh, yeah?
Steggy: ...but I'm not allowed to have any pets.
Dale: (after Steggy takes off) Well, maybe he couldn't handle the responsibility.
- Near the beginning, there is a scene where we get a panoramic view of the Ranger's entrance/living room, where the tire slide, TV & couch, table, and both doors are visible together.
- Steggy appears to be a stegosaurus 
- In one scene, The Ranger's front door is shown from the inside to lack the usual domino steps.