Were dinosaurs better left extinct? Fox executives will start grappling with that question after this evening, when the network airs a two-hour season finale for "Terra Nova," the much-ballyhooed sci-fi drama whose ratings performance hasn't quite matched the hype accorded it for the last year or so.

Averaging a total viewership of about 10.1 million season to date as of December 11, according to Nielsen, "Terra Nova" is notable not just for its outsize subject matter, but the production talent behind it. "Terra Nova" packs a lot of stuff into a 60-minute TV program -- you've got time-traveling futurists journeying back to the past, a struggle for survival, dinosaur attacks and even a little sci-fi mystery. Why, it's as if someone decided to take Sid and Mary Kroftt's "Land of the Lost" and mix in a little green environment talk and a few ideas from ABC's "Lost." Whipping up this souffle are none other than film impresario Steven Spielberg and former News Corp.honcho Peter Chernin.

Many broadcast networks would salivate over 10 million viewers. That's more than the average viewership this season of such prime-time veterans as NBC's "Law & Order: SVU," Fox's own "Glee," and ABC's "Private Practice." Still, that 's not in the same league as TV's biggest drama hitters, such as CBS's "NCIS," which snares around 21 million, or even another family-focused program, ABC's "Modern Family," which has won around 15.9 million this season so far.

More telling, perhaps, is the number of viewers aged 18 to 49 watching "Terra Nova." According to Nielsen, the show has won over just 4.6 million members of advertising's most coveted demographic -- that 's more than the numbers won over by ABC's "Castle," but fewer than the Disney network's fantasy-themed "Once Upon A Time ."

The allure of "Terra Nova," which Fox has been hinting at since 2010, came from the ambitious plot, the dinosaur effects and the echoes of Mr. Spielberg's "Jurassic Park" movies. In short, it was the amount of money being invested in "Terra Nova" that got people excited. Yet without the ratings that will help Fox gain more money from advertisers and give it the momentum to resell "Terra Nova" in syndication and on DVD (not to mention the show's costly production process), the network may have to think twice about whether the show is worth further investment for next fall.

To be fair, Fox has hedged its bets. By capping the first season of "Terra Nova" at 13 episodes, Fox is only investing in half of a traditional TV season. Cable networks create "seasons" of series that run for as little as 10 episodes per year -- a move that keeps costs down and creates the illusion of scarcity for the program's original episodes.

A Fox spokeswoman indicated the network has not yet made a decision about whether "Terra Nova" will continue. While the show's enemy "Sixers" and oddball mix of barter economics and future gadgetry hasn't caught on universally, only Fox's economic needs will truly determine whether the dinosaurs of "Terra Nova" still need to walk this earth.

~ ~ ~

Tuning In is an ongoing series of commentaries by Ad Age TV Editor Brian Steinberg on the TV schedule, the ads it carries and changes within the industry. Follow him on Twitter.