2015 isn't just the first year with two Pixar movies. It's also the first time that their movies haven't opened at No. 1.

"Inside Out" missed that brass ring this summer -- only due to the unexpected staying power of "Jurassic World." Now, "The Good Dinosaur" has underperformed over Thanksgiving weekend, a frame that Disney and Pixar have all but owned over the past two decades.

By most standards, the estimated $39.2 million opening weekend "Dinosaur" enjoyed would be cause for celebration. Indeed, Disney is touting the $55.6 million the film has earned since it premiered last Wednesday as the fourth-biggest five-day Thanksgiving weekend debut ever. ("Frozen" is tops, followed by "Toy Story 2" and "Tangled.")

But Pixar movies have traditionally done much better -- opening on average above $60 million. In fact, "Dinosaur" saw the lowest three-day wide-release debut for a Pixar picture since "A Bug's Life" earned $33.3 million back in 1998, when tickets were a lot cheaper.

Advance tracking for "Dinosaur" was already soft by Pixar standards, with most analysts expecting the movie to open between $50 and $53 million from Friday to Sunday, and from $60 to $75 million over the five-day holiday weekend. Why did the movie fail to reach even those relatively-modest expectations? Here are five possible reasons:
1. The Movie's Troubled Production History
"Dinosaur" was initially scheduled for release a year ago, but due to story problems, the studio replaced the film's director and pushed back its release date. "Dinosaur" is hardly the first Pixar film to have to go back to the drawing board -- even "Toy Story" ran into similar problems -- but it's possible this time that not everything that was wrong got fixed. For example:

2. Too family-oriented
Usually, this is a plus for an animated movie, but one key to Pixar's success has been its ability to appeal to adults as well as kids. By most accounts, however, "Dinosaur" has lots of kid appeal but little to interest grown-ups. In fact, Disney is reporting that only 17 percent of the "Dinosaur" audience was adults.

3. Less-than-stellar Reviews
A 77 percent "fresh" rating at Rotten Tomatoes isn't bad, but original-premise Pixar films and movies in the "Toy Story" franchise typically rate at a 96 or higher. At least the word-of-mouth has been top-notch, with viewers giving the movie an "A" CinemaScore, but you have to get them into theaters to see it first. The weaker-than-usual reviews may have kept adults away from this movie.

4. No Star Power
This shouldn't matter much when it comes to a film where you can't even see the stars, and where the target audience is kids too young to care much who's doing the voice work. In practice, however, most of Pixar's movies have relied upon big-name talent for at least the lead characters (think Tom Hanks for the "Toy Story" movies).

But the "Dinosaur" cast is led by unknowns Raymond Ochoa and Jack Bright. Arguably, the biggest names in the cast are Anna Paquin and Frances McDormand. None of these are box office draws.
5. Stronger-than-expected Competition
Last week saw the weakest-ever opening for a "Hunger Games" movie, but "Mockingjay -- Part 2" held on better than expected, losing just under 50 percent of its business to take in an estimated $51.6 million over the three-day weekend and remain in first place.

Boxing drama "Creed" (above) was widely expected to open in the low-to-mid twenties, but it slugged its way to an estimated $30.0 million from Friday to Sunday and $42.6 million over the five-day holiday. Strong reviews, excellent word-of-mouth, and the "Rocky" nostalgia factor all helped "Creed" attract an older, predominantly male audience. By contrast, "Dinosaur" not only skewed young, but also female, with 53 percent of the audience. To the extent that it was trying to appeal to all ages and to equal numbers of men and women, both "Mockingjay" and "Creed" bit into the potential "Dinosaur" audience.

Disney and Pixar have held themselves to lofty standards. Not only have Pixar's movies typically done better, but so has Disney at Thanksgiving, where eight of the top-10 turkey holiday five-day weekend debuts of all time belong to the Mouse House.

Given how good Disney's marketing machine is at selling original-premise cartoons at this time of year, especially Pixar offerings, it seems that someone is badly off their game.