Some scientists argue that Torosaurus was actually not a distinct dinosaur, but simply the adult form of Triceratops, meaning that the episode's depiction of juvenile Torosaurus would be erroneous. However this theory still hasn't been widely accepted (since for one, Torosaurus was actually smaller), and of course hasn't been proposed at the time of this show's production, so it doesn't count as an error.
The Quetzalcoatlus is a modified version of the Ornithocheirus animation from the fourth episode. It even makes the same sounds as Ornithocheirus.
The program's depiction of the Ankylosaurus and Quetzalcuatlus have both been based on models that by now have become outdated. These are not considered errors, since new discoveries have been made since the series had been finished, however it does mean that slowly all of the animal designs that appear in the series are becoming obsolete. The Ankylosaurus didn't have that many plates on its back, for instance, but had fewer, larger plates. Whereas the Quetzalcoatlus had a much, much longer neck, a differently shaped head with a different crest on its skull, and no teeth. It also walked more upright, when on the ground.
Anatotitan, one of the featured dinosaurs in the program, may actually be re-classified as a species of a similar dinosaur named Edmontosaurus. In the Walking with Dinosaurs book, Edmontosaurus also appear in this story, but are viewed as a separate animal.
The program shows two Torosaurus bulls engaging in combat by interlocking their horns, much like modern-day deer do with their antlers. Recent studies however indicate these animals couldn't have fought this way, since their horns were too fragile. Indeed, the fight does end with one of the Torosaurus' horns breaking off, yet confrontations like this most likely didn't take place in real life.