The Land Before Time/WMG

The main characters die at the end of the first movie.
(This is not a new theory; it's been rumored since the movie came out and the existence of cut footage was revealed.) Littlefoot collapses in despair... and sees a ghost (his mother, in the clouds). Shortly after, he discovers Heaven The Great Valley, and all is happy again. Clearly, everyone dies at the end of the first movie; in all subsequent movies, everyone is in Purgatory. Or Heaven. After all, the dinosaurs had to die sometime. Every school child knows this story. That they don't almost seems like Executive Meddling.
 * By the 10th or 11th sequel, it became pretty clear that the viewers were the ones in purgatory.
 * WROOOONNG!
 * But if they're in Heaven, why are there still Sharp Teeth chasing them around? Are they all dead too? If they're really in Heaven, what could possibly hurt them - and why would anything even be allowed to hurt them?
 * They don't know their dead.
 * If they're in Heaven, why isn't Littlefoot's mother there?
 * And boom goes the dynamite.
 * Simple. Littlefoot's mother became an angel when she died. She helped lead her child and his friends to the Great Valley/Heaven, but couldn't stay there herself much due to other celestial duties.
 * Or... You know... they're not in heaven.
 * I have a good theory that'll fix everything...THE SEQUELS NEVER HAPPENED. There, does the theory make sense now?

The characters are in Hell
Though by the third sequel alone you can tell this is obvious.

The die-off that's happening is not the final extinction of the dinosaurs, but a more localized ecological disturbance.
It took the dinosaurs hundreds of thousands of years to die off - an eyeblink of geological time, but long enough, certainly, for this generation to prosper.
 * The Disney film Dinosaur had this same problem (among many, many others), with the added difficulty that the use of meteor showers as a plot element makes it pretty clear that this is in fact the lead-up to The Big Finish as far as the dinos are concerned. Seriously, people, if you're going to make a movie about cuddly dinosaur protagonists, don't set it at the end of the Cretaceous period. There's no way to avoid the depressing undercurrent of futility.
 * Another theory is that the sequels are an Elseworld showing what would have happened if they hadn't died. This has the advantage of making them non-canon.
 * This Troper always took the entire plot of the original films, and it's sequels, to mean that they were in something like the Lost World...an isolated enclave of dino-kind that survived the mass extinction and lives on, with mankind utterly ignorant of their continued survival. I kind of always felt it was quite ham-fisted in that implication, so much so I immediately groaned "Oh God, not another Lost World thing! So what, human explorers find them in the sequel?" when I heard about the movie as a kid.
 * The sequel "The Stone of Cold Fire" does have "rainbow faces," alien dinosaurs with UF Os and apparently magical powers.
 * Thing is, it looks nothing like the extinction of dinosaurs should had been, so I think it must have taken place somewhere in the middle of the Mesozoic, before the dinosaurs got prosperous again only to die from the asteroid.

They're Immortals, like in Highlander.
Title says it all.

The later movies take place in the alternate reality seen in the Super Mario Bros. movie.
This explains why the dinosaurs aren't extinct yet. Also, Koopa is Chomper's direct descendant.
 * What.

The main characters not only die at the end of the first movie, but they also die from an innocent looking plant turning out halluconogenic.
The rest of the movies are acid trips. This explains the singing.

Spike is a Shinigami.
Spike was Dead All Along; it's the late Cretaceous, and he's a stegosaur! We all know that the other characters end up dying. Spike was just a gentle psychopomp whose job was to help lead them to Dinosaur Heaven the Great Valley.
 * Spike was some variety of ankylosaur, varieties of which existed through almost all of the dinosaurs' reign. That Other Wiki disagrees, but he just doesn't look like a "stegosaur."
 * But there are adult stegosaurs in the first movie. On the other hand, the sauropods shouldn't have been around anymore, either.
 * Actually, sauropods did live at the end of the Cretaceous. They just were not very common.
 * I want to know what cut of the original "L.B.T." you saw, where there are any visible adult stegosaurs. The species we see in the Great Valley are the exact same ones we saw in the opening sequence. Interestingly, there is an adult ankylosaur (Rooter) so...
 * Or maybe Spike's a dravidosaur... Oh, wait.

Chomper grows up to be Barney.
Seriously, do you of any other purple T-Rexes?
 * Oh, Yes. Yeeeessss. Chomper probably is Megatron's beast template. He's even got red eyes.
 * Wait, if Chomper grows up to be Barney, but Chomper is also Megatron II's beast template, that means, by principle of "if A=B and B=C, then A=C", Megatron II's beast form is Barney.
 * Great going, you just ruined WesternAnimation/BeastWars for everybody.

Most of the dinosaurs died during the Earthquake from the first movie.
It was not a meteor that hit the earth, but an earthquake. It separated most of the dinosaurs; some died off, while others died searching for the Great Valley. This makes a bit of sense, since the meteor did not hit during the course of the movies.
 * An earthquake that spanned the entire world?
 * A major, rapid pole shift or some other global geological cataclysm, while not triggering a single Earthquake across the entire world, would probably cause all kinds of immensely powerful individual tremors, many in fact. To say nothing of, quoting a book on the subject, "terrifically powerful tsunamis and volcanism". Or basically, think about the disaster movies 10.5, Category 6, Japan Sinks and Supervolcano happening all at the same time.
 * So basically a prehistoric version of 2012, then?
 * Magnetic reversals don't cause earthquakes, and the dramatic, earthquake-causing pole shift idea was based on extremely faulty research from the early 20th century long before we really understood plate tectonics.

The first movie is an allegory to religion
Let's start off with the obvious: as someone else mentioned, the Great Valley is Heaven. The entire movie is about a quest to get in to heaven.
 * Littlefoot represents Christian faith. He believes that if you follow the path, no matter how difficult it may be, you will find heaven. Cera represents temptation. She too wants to get into heaven but doesn't want to have to work at it, and so is always looking for an "easy" way. These two spend much of the movie trying to convince Petrie, Duckie, and Spike to follow them. Cera's Heel Face Turn at the end represents the heroes overcoming temptation.
 * Petrie, Duckie, and Spike each represent a different type of follower. Petrie follows out of fear. Duckie follows out of innocence. Spike follows out of stupidity. All three are easily swayed and have to constantly be kept in line.
 * The Sharptooth, a mindless force of destruction, represents the sin that threatens to consume our heroes' souls should they ever stray from the path. Notice how when Sharptooth is presumed dead at the beginning of the movie, it is Cera (temptation) who finds and revives him. Notice also that Sharptooth normally only shows up if the heroes stray from the path. Symbolically, just before entering heaven they kill Sharptooth--killing Sin (in a pool of water, similar to a baptism ceremony, as it happens).
 * The tree-star represents a material possession, which keeps Littlefoot and his followers bound to their mortal coil. They are incapable of transcending the earthly realm while they are dependent on material possessions for comfort. Symbolically, it is destroyed at the halfway point of their journey.
 * Littlefoot's mother tells him that he can reach the Great Valley by following the sun. In many ancient religions, the Sun = God, so she's essentially saying to follow God. Littlefoot's mother herself could represent the Holy Mother (though combined with the fact that Littlefoot has no father, this interpretation turns Littlefoot into Jesus).
 * Technically, the 10th movie reveals he had a father, or are we just focusing on the first movie? It is true that nobody involved with the first film was still around by episode 10.
 * Oddly, I read an essay about Land Before Time ages ago in some weird book in college that argued essentially the same things, even going so far as to call it The Pilgrims Progress. With dinosaurs.

Disney's Dinosaur and The Land Before Time take place on the same prehistoric Earth
Furthermore, both herds arrived at the same Great Valley, however, at different points in time.

The real reason why Littlefoot doesn't talk about his mother

 * Okay, so in The Land Before, Littlefoot's mother dies and he's very sad, while in the sequels, he barely mentions her at all, right? Surely a case of Lighter and Softer, right? Wrong! In LBT 1, Littlefoot meets a dinosaur who tells him his mother will always be with him if he remembers the things she taught him. What did she teach him? That dinosaurs stick to their own kind. However, he chooses not to follow this rule and befriends dinosaurs of other species. By not remembering his mother's teachings, the memory of her has faded from his mind. Clearly this is all a complex, subtle metaphor for rebellion and rejection of parental ideals!
 * Mama Longneck never taught Littlefoot about segregation, she just told him it existed. She never followed it like Topsy did, it was just the nature of things at that time. She did save Cera from Sharptooth as well as Littlefoot.
 * I always felt that it's just easier for him to not talk about it. Most kids who've lost a mother, particularally in the violent manner Littlefoot did, don't like talking about it.

Tree-star leaves are like drugs to Pteranodons
It explains why pterosaurs eat the leaves despite clearly being carnivorous while the Microraptor in one of the sequels prefers to stick to insects

Petrie is Rodan

 * He grew up, then was preserved in volcanic ash until radiation mutated him.

The story takes place in modern times, under the premise of being an experiment.
Here's how it would work: scientists from our modern era find preserved dinosaur remains, but the method of death is unclear. Being heavily funded by the government to do research on survivalism and natural history, they re-clone these dinosaurs and keep them contained in a giant reserve of sorts. They build several oasises for the dinosaurs and several natural barriers, such as the big water and the vally of the mist, to encourage them to stay away from our part of the world. Most of the dillemas caused during the movies were based off theories scientists wanted to test eg. Starvation, an ice age, ect. The scientists change the Great Valley and the surrounding "Mysterious Beyond" to suit their current experiments.
 * The dinosaurs may have been given a stronger intellect from a previous experiment from the scientists.
 * Maybe they had the brain-boosting drugs on loan from NIMH.
 * Furthur they are being monitored secretly via hidden cameras and the results of the experiments are collected into records/documenteries on the project, hence the obvious yet unexplained prologues from our time.
 * The Land Before Time XVI: Jurassic Park

The Meteor already hit the earth but did not kill the dinosaurs.
Instead, it became the Great Valley.

The Meteor already hit the Earth and it did kill the dinosaurs.
They just aren't dead yet. Think about it, the extinction of the dinosaurs is described as being geologically instantaneous - which still means a quite lengthy time period from the viewpoint of individual animals. The whole movie is based on the premise that the region where those dinosaurs used to live has gotten barren, so they have to migrate somewhere else to get food. This is propably quite a likely scenario which happened during the times of the extinction of the dinousaurs. Still there might be some resorts where they can go and survive - like the Great Valley - but of course not forever. Also in the beginning there is a huge earthquake and volcanic eruptions, which also fits into the picture, as does - like the main page already mentions - the Super Persistant Predator behaviour of Sharptooth. And didn't at least one of the sequels involve the food running out even in the "Great Valley" so they have to migrate again? Okay, now I don't know if this is maybe too obvious to be WMG, as I've always interpreted the movie that way, even as a child, but I don't see it in the first sentence of the main article, so I've put it here ;)

Rooter is either clairvoyant or something more.
Take a look at that scene where he talks to Littlefoot about his mother again. He knows all of the horrible depressing things that poor Littlefoot has gone through so far and is able to give his little "Circle of Life" speech after hearing the following: "It's not fair! She shoulda known better! That ol' Sharptooth. It's all her fault! ...Mother's!" Seriously, what? Either Rooter is psychic or he is... God. Watching Littlefoot's story from an omniscient pose and narrating his life. (Come to think of it, the avatar of God from South Park bears more than a passing resemblance to Rooter...)
 * He's the Narrator. Of course he knows everything!

You can indirectly blame Petrie for Jar Jar Binks.
In 1988, Petrie was the Ensemble Darkhorse of the movie. Somehow George Lucas caught wind of this, and decided to give us the same character -- but more -- in the Prequels, and the rest is history.

The Next Land Before Time Sequel/Spin-off...
Won't even have a plot. It will just be hidden camera footage of Don Bluth sitting alone and nursing a strong drink, reflecting on what Universal is doing to his characters.

The reason that Red Claw is beaten so easily...
He's secretly scared of them. Think about it, how many Sharpteeth have been killed/beaten by Littlefoot and company throughout the series? Surely, at this point, they've probably got a reputation for beating them by now. Odds are Red Claw is just smart enough to realize that they'll be able to kick his butt for real if he's not careful. So he's not a coward, just being cautious, which does make him dangerous. Thus he goes by a 'live to fight another day' philosphy. Also, it could just be experience at taking them down on Littlefoot and company's part.

Littlefoot's dad is a prehistoric incarnation of Jack Bauer, and he himself is a prehistoric incarnation of John Connor.
This is just a silly theory based on the fact that the voice of Littlefoot for several of the sequels was Thomas Dekker, who played John Connor in the Sarah Connor Chronicles, and Brom, his dad, was voice by Kiefer Sutherland. Though when you think about it, Littlefoot is able to put him and his friends in perilous situations and escape from them without a scratch, and he does have a strained relationship with his father. So to this troper, having Littlefoot's dad being the most badass CTU agent ever, and he himself the future leader of the resistance against Skynet would explain alot.

The stone of cold fire was a Lavos seed.
The Rainbow Faces were not aliens, they were time travelers. They were there to destroy the seed, but the two fliers did it for them.

The narrator is Xenu.
Hattip to Diamanda Hagan.

Wait, what were we talking about again?

Petrie suffered some sort of brain damage from nearly being drowned by the Sharptooth in the original movie.
While it didn't immediately come up, it explains his poor grammar in the sequels (assuming, of course, you consider them canon).
 * He had bad grammar from the start.

Spike has brain damage from not being incubated properly as an egg.
Sort of a dumb analogue to how babies can suffer brain damage during the birthing process if their flow of oxygen is somehow cut off. He's supposed to have an Ambiguous Disorder, which is further supported by a claim on The Other Wiki: ""Spike was added to appeal to a growing number of mentally handicapped viewers who had in recent years become a significant portion of cartoon video consumers.""