"Racism" may not be the right word for the kind of prejudice exhibited by the dinosaurs in LBT. "Race" is usually used for variation within a species (e.g. Africans vs Europeans vs Indians vs Native Americans...ad naseum). Longnecks, threehorns, and fliers are clearly from different clades, never mind species. "Speciesism" or "cladism" would probably be more appropriate here.
And like you said, Pterano also displayed racism as well, believing that flyers are superior and how he should have been leader. This sense of superiority probably stems from the fact that he could fly and could travel faster than the other dinosaurs.
I know LBT treats paleontology the same way
300 treated history, but pterosaurs aren't dinosaurs, although both pterosaurs and dinosaurs belong to the archosaur clade (along with crocodiles and birds).
Racism is not limited to leaf-eaters, as sharpteeth seem to have a sense of racism as well. This we see very well in The Lonely Journey, when Chomper is constantly attacked by any sharptooth he encounters. Though these attacks may stem from more than just racism. Chomper was another sharptooth and posed a threat to the sharpteeth because it would mean another mouth to feed. So instead of just allowing Chomper to hunt down what little prey there was in the area, they decide to try to kill him instead.
What kinds of sharpteeth?