It may have started out as a time-travel mystery starring dinosaurs, but Fox television now appears to be repositioning its pricey new "Terra Nova" series as a family adventure.

The opening two-hour premiere of the ambitious and much-delayed TV series, executive produced by Steven Spielberg, has been tweaked and partly re-shot ahead of its debut in September to put more emphasis on character, producers say.

"If we don't get (lead character) Jim Shannon and his family right, we don't have a show. It's about story and keeping it strong," director Jon Cassar told TV reporters on Friday last week at a gathering of critics.

"If you don't tune in and love this family in the first hours, it doesn't matter how good the dinosaurs look," Cassar added.

"Terra Nova", shot entirely on location in Australia, is the most expensive first-year show ever for Fox. Executives have declined to give figures, but according to some reports the two-hour opener on September 26 cost more than $15 million.

Set in 2149 on an overdeveloped and polluted planet, the series follows a group of "pilgrims" who are transported back 85 million years to a prehistoric Earth -- complete with dinosaurs -- through a time fracture.

A year ago, producers were touting "Terra Nova's" high-tech special effects, strong environmental themes and sci-fi mystery. Another major plot strand to lure viewers was humanity being given a second chance to save Earth by going back in time to avoid mistakes and reverse the future's course.

That is no longer part of the plot, producers said while promoting the upcoming show. "They are not going back to change history," said executive producer and writer Brannon Braga, who wrote for both "24" and the "Star Trek" TV shows and movies.

EPIC FAMILY ADVENTURE

Getting dinosaurs and other prehistoric creatures looking good enough for prime time has proved challenging in the faster time frame required for a TV series than a movie, leading to some delays in broadcasting the series.

The T-Rexs are still there, but Braga said that "finding a believable family you can fall in love with was more challenging than creating the dinosaurs."

"Life on Mars" actor Jason O'Mara and British-born Shelley Conn play the husband and wife in the family of five that makes the journey to Terra Nova.

Fox is now describing "Terra Nova" as "an epic family adventure" and hoping it will be watched by more than just sci-fi fans and passionate followers of TV shows like "Lost" and the blockbuster movie "Avatar"

"This show has a very broad appeal in that regard. It is really about a family. There is a little something for everybody in this show," Braga said.

"Terra Nova" is a big risk for Fox in a fall season heavy with scores of new dramas, comedies and reality shows vying for the attention of an increasingly dwindling amount of viewers willing to watch programs on a traditional TV set.

"Is 'Terra Nova' a big bet? Yes it is...But every drama is a big bet. There is no inexpensive drama on television," Fox entertainment president Kevin Reilly said.

Reilly said that although "Terra Nova" cost more to produce upfront, especially expenses for the pilot, "over the course of 13 episodes, it's not that much of a bigger bet." He said the series had already sold well internationally.

But he added; "The thing I like best about it, for all of the spectacle, is the cast...This is a very talented group of people. So I think we have a real shot."