Now, bear with me.
IIRC, all the dinosaurs of each time were part of the main characters' herd—that is, all the duckbills were Duckie's herd, all the Longnecks were Littlefoot's herd, and so on and so forth.
Herds are basically family. Meaning when they grow up, they inbreed to keep their species going.
Eventually, dinosaurs (possibly Littlefoot's clan, since he's the only one who didn't
have to inbreed) invented technology and television—we know this, because an episode of Eek the Cat
clearly demonstrates that the dinosaurs went extinct due to sitcom addiction.
Now, my theory:
The Land Before Time sequels actually existed in prehistoric times. They were not
produced by MGM or whoever, but actually by Duckie's retarded incest babies!
Prove me wrong!