When Spencer Milligan left the show after the second season, his absence was explained by having Rick Marshall disappear after he was trying to use one of the pylons to get home. Due to a contract dispute, Milligan refused to return for a third season. Rick's exit was filmed with producer Jon Kubichan in a wig, who kept his back turned to the camera throughout the scene.
The reason Cha-Ka speaks English during this final season was due to the Kroffts' new series, the hour-long The Krofft Supershow (1976) (which contained segments of three new programs), so trying to construct Cha-Ka's native dialog in the scripts was now deemed too time-consuming (which would also explain the disappearance of Cha-Ka's parents, who obviously wouldn't be speaking English).
The opening credits song is rewritten to accommodate the altered cast list, and the musical arrangement is different. The end credits song from seasons 1-2 is dropped completely, and replaced by an instrumental variation of the opening song.
First appearances of Uncle Jack and Lulu the two-headed lake monster.
When Uncle Jack asks rhetorically if the sun goes down, Will answers "Usually", a reference to The Longest Day (1975).