On a prehistoric Earth, the T-Rex Norrannosaurman and his lackeys pursued the weakling Pteranodon Pter Ptarker. Just as Norrannosaurman bit Ptarker, both were hit by a meteorite containing alien spiders. When they awoke, the two found that they switched bodies, which now also were clad in colorful costumes. Norrannosaurman once more attacked Ptarker for the theft of his body, but Ptarker fought off Norrannosaurman and his lackeys with his new Spider-Powers. Now powerful and confident, Ptarker swung away, but the tree branch broke and he fell down, crushing both Norrannosaurman and two innocent dinostanders. Horrified by the result of his recklessness, the Amazing Spider-Rex learned the power of responsibility.^[1]

• The reality's designation is seemingly a reference to a period dinosaurs died out, which is generally accepted to be at least 66 million years ago.
• A Spider-Dinosaur previously made a cameo appearance in Spider-Geddon #4. The Appendix to the Handbook of the Marvel Universe assigned that character to the reality of Earth-19760. It remains to be seen whether that was intended to be the first appearance of Spider-Rex.