Alpha lived over half a century in Dredd's future, and the crossover was accomplished by having Alpha time-travel back to Dredd's era. An example of the second kind is the Judge Dredd story "The Cursed Earth," which featured a dinosaur called Satanus who was described as the clone of the offspring of the female dinosaur which had appeared in most episodes of the earlier series Flesh.
Alpha lived over half a century in Dredd's future, and their journey to his past involved time travel. The Judge Dredd story "The Cursed Earth" is an example of this crossover, featuring a dinosaur named Satanus who was described as the clone of a female dinosaur from an earlier series called Flesh.