"Forests" opens in South America, with the Brazilian titanosaur Austroposeidon magnificus. One thing I really like about this sequence is that it emphasizes just how small even the largest dinosaurs were when compared to plants. In fact, this episode has multiple moments that show the diversity and even competitiveness of plant life in a way that acknowledges them as living things, rather than simply background material. After this brief opening, Prehistoric Planet returns to Triceratops, one of the most famous dinosaurs that had thus far been relegated to the role of T. Rex breakfast. There are actually two known species of Triceratops, and the relative shortness of the nasal horn and the lengthy brow horns help identify these as Triceratops horridus, as opposed to Triceratops prorsus. Recent studies of the stratigraphy of the Hell Creek formation show that Triceratops prorsus appeared later than Triceratops horridus, leading to the hypothesis that T. Horridus evolved into T. Prorsus via anagenesis. The use of clay licks has been observed in macaws, and the trip through the cave by the Triceratops seems an intentional callback to another BBC documentary on elephants that travel through caves for salt, once again showing how Prehistoric Planet utilizes documented animal behavior to make their dinosaurs more realistic. Returning to South America, Prehistoric Planet treated its viewers to a speculative mating display by Carnotaurus sastrei. Darren Naish, the show's lead scientific consultant, gave an interview breaking down the potential for display in the arms of Carnotaurus, and what's seen here is an adaptation of artist John Conway's depiction in All Yesterdays: Unique and Speculative Views of Dinosaurs and Other Prehistoric Animals, that Conway and Naish put together with artist C. M. Kosemen. Given that Prehistoric Planet takes place at the end of the Cretaceous Period, it did come as a bit of a surprise that the show didn't recount the famous K-Pg extinction event. That said, the choice to end the story of this prehistoric world as if it was going to last forever comes off as refreshing, allowing viewers to bask in the beauty without suffering the apocalypse. It's a fitting way to end the exploration of life in Prehistoric Planet.