The level of photorealism in The Good Dinosaur is so convincing that it’s not entirely clear this is a computer-animated picture until the dinosaurs themselves — who are given cartoonish features and human voices — show up. Unfortunately, from what follows, it’s also not entirely clear this is a Pixar film. In concept, if not always execution, The Good Dinosaur is simplistic, aimed primarily at young children and not their parents (as the best Pixar movies are). The plot is a standard-issue, lost-heroes-must-find-their-way-home affair, as a skittish dinosaur named Arlo gets separated from his family and learns to survive with the help of a feral caveboy. Vague lessons about bravery follow, thinly linking a series of busy and mildly comic vignettes. What’s missing is any sense of unified purpose or vision. Still, there are magical moments, including one in which Arlo and the (nonverbal) caveboy share their life stories by using twigs to represent family members. The sticks that are laid on their side and covered with sand represent those who died. There’s a flicker of Pixar here — it’s creative, visual and authentically emotional — but not enough elsewhere to bring The Good Dinosaur fully to life.