Missing Episode: Not an episode, but there's a little bit of footage that most Dino Thunder fans would kill to see. On the day they were filming the video for Kira's song "Patiently," they were also filming some scenes with Mesogog. Latham Gaines says that the video filming ran long, so he's sitting around bored... until he had an idea. Somewhere, sitting on a dusty archive shelf, is footage of Gaines, in full Mesogog makeup, singing Kira's song "Patiently," and according to him, he was going full Celine Dion on the whole thing.
Throw It In: According to this interview, the scene in the teamup with Ninja Storm, with Rangers from both teams racing toward the battlefield, turned at some point into an actual race between the actors of each season.
According to some sources, Zeltrax's real identity was supposed to be Billy Cranston. Yes, THAT Billy. But they couldn't get David Yost to return, so they made up a new character and played Remember the New Guy with him.
Other sources take the above a step further by saying that Billy wasn't even the first choice the creators wanted to be Zeltrax's real identity. Wanna know who their first choice was? Jason. Arguably, this choice would have been the one with the most impact. Considering how close Tommy and Jason were in previousseasons. However, none of these have been confirmed as possibilities by the actual writers.
Devin was going to be the Triassic Ranger, but as Abaranger continued, it became apparent that rather than a separate hero it was just another Super Mode for Red, meaning these plans had to be discarded entirely.
Had Jason David Frank not returned for this season, the Black Ranger would have been named Edward Payne. Because little was changed outside of the name, this lead to the canon issue of Tommy becoming a Mad Scientist in seven years.
Word of God: The ZeoChristmas Episode showed Tommy and Katherine would be married in the future, but her not appearing in this season prompted fans to question that outcome (not that there hadn't been questioning for years prior to that, of course). When asked about this, though, Doug Sloan stated that Tommy and Kat getting married was still in-continuity.
While not officially stated in the show proper, Douglas Sloan has stated that Hayley has the same last name of Ziktor.