Is fossil fighters champions the sequel of fossil fighters

yes and no. it is a sequel in many occasions, like some of the people you talk to are either related to a person before or the person them selves but they don't reconize you (ex. Rosie after beating the game, and the Chieftan during the story who is related to the girl with the mask), the durainians are there and the two legendary vivosaurs etc.

and no because it is not on the same island, the rest of the story does not correspond to the first one, new friends, no Dr. Diggins ( there is no mention of him in the game, NONE!) no Mr.Richmond ( again no mention!) and a new owner of the fossil industry, Joe Wildwest.

So in all the game is a balance of both games new people, old rivals, new fighting styles, old vivosours/new ones...........hoped this helped.