The entire special is framed around "Big Al", an Allosaurus skeleton with many preserved injuries, and tries to show how this animal may have gotten them. Over the course of the show, Big Al is hurt in various ways from hunting, fighting, and accidentally tripping. Toward the end he is shown to be battered and sickly. Some viewers may find this depressing/sad.
In one scene multiple dinosaurs get stuck in a mud pit and slowly die of exhaustion. This may also upset some viewers.