Short answer: The good dinosaur in Pixar’s The Good Dinosaur is an Apatosaurus named Arlo. Details:

• Protagonist: Arlo, a young Apatosaurus, who provides the central perspective in the story. This species is a long-necked, herbivorous dinosaur from the Late Jurassic, depicted as gentle and protective in the film’s narrative.

• Other dinosaur species appear in supporting roles, such as Styracosaurus characters, but the main character is clearly identified as Apatosaurus Arlo.

• The film imagines an alternate history where non-avian dinosaurs did not go extinct, focusing on Arlo’s journey and growth alongside his human friend Spot.

If you’d like, I can summarize Arlo’s key traits and how the animation portrays Apatosaurus biology and behavior in the movie.