I mean, it is a children's film. Paleontologists stubbornly refuse to accept the work of several notable Gallifreyan scholars on the subject, including the work of the only Gallifreyan known to have worked under both Time Lord and human scholarly conditions (the Doctor, of course--how anyone could possibly disagree with the Doctor's scholarly work is beyond me. The man's very name proves his methodology--he was born with a PhD for Christ's sake!). However, Gallifreyan scholarship has consistently shown that dinosaur communities were both vastly more intelligent than paleontologists would believe, but also vastly more discriminatory. Given the enormous biodiversity of the period and the clear lines of relations that could be easily drawn from pure observation of related species, it should not strike us as particularly surprising that dinosaur society was not particularly egalitarian. Indeed, the divisions between periods of the Mesozoic increasingly seem to fall along periods of intense civil unrest and, dare I suggest it, genocide. The egalitarianism of The Land Before Time is quite demonstrably anachronistic--the Doctor has shown in his recent paper, Civil Conflict of the Late Cretaceous, that as food supplies ran short and the climate turned against the dinosaurs in the late Cretaceous (the setting of the film, of course), violence among dinosaur societies merely increased. We know directly of several herds or communities that experienced forms of civil war. Most notable is of course Aladar's herd, the subject of the 2000 Disney documentary Dinosaur, where multi-species interests erupted under the stress of migration, predatory attacks, and individual ambition

The last couple of decades have seen an explosion of time travel documentaries, mostly thanks to the efforts of the Discovery Channel and the BBC. As these documentaries make plain, the vast majority of dinosaur interactions were ferocious and bloody in highly dramatic fashion.

However, an important subset of dinosaurs were sentient, as seen in The Land Before Time, and these were much more likely to exhibit compassion and other recognizably human emotions. This is taken to the extreme in the Dinosaur Train timeline.

I feel that the real question here is, how can we be sure that it was before time? What did we use to measure it's relation to the beginning of time?

I believe this belongs in /r/paleontology

While some brief intermixing of herds would be expected, much like you would see in the modern African savanna, the film is correct in that Longnecks and Three-horns do not generally belong together.

I can’t think of any reputable source that denies the existence of some cooperation, but that doesn’t mean everything was welcome. What evidence we have shows that large and complex interspecies civilization tended only to include herbivorous and omnivorous species - with carnivores generally confined to jungle ghettos. For a general overview, I’d point you to Steven Spielberg’s seminal documentary on the Isla Nublar Civilization, which was made with close involvement from the Dr. Emmet Brown Institute for Temporal Studies.

Real universal inter-species cooperation wasn’t really established until the signing of the Omnivorous Accords near the beginning of the last Ice Age, with Diego the Tiger signing on behalf of carnivores, and with no dinosaur signatories present.

Like any film, The Land Before Time took its fair share of historical liberties. It's important to note that the dinosaurs depicted in the film are paid actors, not the real thing and their dialogue and interactions were done for our convenience to tell a story

In real life, while there was a fair amount of cohabitation in certain areas, interaction between species was fairly limited for the simple reason that most of the dinosaurs simply would not have understood each other! Long-Necks typically speak Brachioese (often incorrectly called Brontoese by laymen), Three Horns speak Tricertopian, Flyers speak Pterodactylician, etc. This isn't to say there would not have been a few dinosaurs who were multilingual in any community. Just that it was uncommon. While all the dinosaurs were attracted to the resources and freedom offered by major dinopolises like the Great Valley, when they actually got there they tended to stick to their own communities, with some being better off than others and most interaction highly discouraged. Spiketails for instance, were often consigned to the poorest parts of the valley (I'd recommend reading up on the Spiketail Ghetto if you're interested in this).

In terms of interaction between species, as I said, it certainly did happen. The Flyers were especially well known for this and it wasn't uncommon for them to act as merchants of sort, trading leaves and roots amongst the various dinosaur populations. Unfortunately, this also led to them having sort of unsavory reputation as greedy or untrustworthy.

In the end, I would say that as a film, The Land Before Time is not a bad picture. The Great Migration to the Great Valley is a well documented event and while the film may have exaggerated when it comes to the friendships between the dinosaurs, I would not say the events were impossible, just implausible. I guess to sum things up, open the door, get on the floor, everybody walk the dinosaur.

Sources: Boom Boom Acka Lacko Boom Boom, Was (Not Was), 1987

Doctor Ross Gellar did a pretty extensive study on this. His insights are pretty profound. In my person opinion he is the greatest paleontologist of our time.

There is a rather large documentary addressing this exact topic. It goes into how the different dinosaur species coexisted and all the different problems they had. Including relationships, jobs, and general friendships. Its done a bit differently,10 seasons of episodic segments, each around 20 minutes long. Its portrayed as a classic sitcom but anyone who knows anything about paleontology can clearly see what it is really about.

Honestly, this is quite a charged question, but this documentary in particular seems to answer your question quite succinctly while sidestepping the obvious political undertones of the period's immigration policy.

The concept of aversion to interspecies miscegenation, or even mixed communities among proto-avians is unfortunately a contemporary reimagining of historical sources. The so-called documentaries that you may have seen in elementary school or even, sadly, on National Geographic today are based on faulty, or even outright fabricated evidence that was collected during the tumultuous Bone Wars (Master Naturalist : Life and Letters of Edward Drinker Cope, With a Bibliography of His Writings, Osborne). This 'evidence' was fabricated during the late 19th and early 20th centuries by leading eugenicists of the time. The idea was to perpetuate the incompatibility of the difference racial groups, by creating the idea that segregation was natural and scientifically-sound.

Perhaps this is better suited for /r/AskScience, but evidence such as fossils of snakes eating a clutch of Titanosaurs are often cited as examples of interspecies predation during the Cretaceous Period, when in-fact, it is actually a tragic example of both ethical norms of the time, a shocking display of violence from an otherwise peaceful era, and a flagrant violation of the interspecial treaty that had been in effect at the time.

We have evidence of the treaty in the fossil record, dating back to 250MYA. The 'Rosetta Boulder' (named after its excavation site near present-day Boulder, Colorado), clearly states in the codified vernacular of the time, that "no dinosaur species may cause bodily or psychological harm to another, on the penalty of imprisonment". We have reason to believe that this treaty was later iterated in later revisions and updates, given its early appearance in the Triassic Period, although no newer examples have been found as of yet. The fear is that they may have been excavated and immediately destroyed due to prevailing thoughts at the time.

The Land Before Time series was created as a way to right our past sins towards prehistoric history. Land Before Time sidesteps the controversy and simply accepts the Rosetta Boulder as fact, and depicts stories of friendship and adventure set during the Golden Age of interspecial cooperation that existed during the Triassic and Cretaceous Periods.

Not a dinosaur guy but I'll give the best analysis you've ever seen. The films were historically accurate in every way besides the lack of stovepipe hats which were present during the late Edo era.

Everyone looked like they got along very nicely in the diorama I saw at the Creation Museum.

Unfortunately, no. Massive divides existed in these eras. Dinosaurs were discriminated against for everything; their size, their features, etc. Lynching was all too common. Carnivores would team up on herbivores for sport. Any remote idea of peace are really only manifested in these lynch gangs. Prejudices violence was so rampant it occurred over different periods; fossil records show dinosaurs from the Jurassic period hurting those from the Cretaceous period.

Sources:

Alvin W. West - "The Truth Behind Jurassic Park, revised edition."

Thomas Ryan-Eberts Xavierson - "Small Arms Still Hold Pitchforks - Anecdotes of Pre-historic Violence and Conflict."

Yep yep yep!

Dinosaurs have feathers. Don't ever forget that! A Land Before Time and all other movies about dinosaurs are trying to hide the fact from all mammals that birds once ruled the world!