"Away from the flood-zones and out of the forest exist the open prairie environments of the floodplain. These areas are not as frequently subject to waterlogging and are instead formed from disturbances of other types, most commonly forest fires or overgrazing from megaherbivorous dinosaurs. The palmetto-like Sabalites is frequently the tallest tree here, arising among a ground cover of primarily forked ferns (Gleicheniaceae). This provides an abundance of fodder for Triceratops and ankylosaurs that roam these areas."
― Saurian encylopedia
Hatchling Triceratops with its adult herd, alongside a Tyrannosaurus corpse, in a fern prairie's edge
The Fern Prairie is the most open terrestrial space of the game, as the rest of the map is mostly composed either by dense forest or water. This biome is home for the largest land animals in the game, like Triceratops, Anatosaurus and Tyrannosaurus, a biome where they can be found often. Ornithomimids, Denversaurus, Thescelosaurus and Pachycephalosaurus are also not rare here. Acheroraptor and Dakotaraptor are, however, less common, as they prefer more bushy areas, though Pectinodon will more promptly explore more open areas during the night. Ankylosaurus may sometimes visit this biome, from the forested edges of the map. Basilemys can be found here in occasion. This area is also plentiful in lizard population, as this is both a common place to find Chamops as well as to find the deadly Palaeosaniwa. Didelphodon can also be found here often. As for plant life, this is a biome that is abundant in ferns (as suggested by the name). Blechnacean and osmundacean ferns are abundant, as well as Symplocarpus, cannabaceans and Zingiberopsis.
In real life, ferns appear to have had a spike of abundance after the K-Pg extinction event, but prior to the extinction event, ferns were not very abundant in Hell Creek, and open areas, when they were present, were dominated by herbaceous angiosperms instead.
Concept art of a fern prairie with a herd of Anatosaurus in the background
Chris Lomaka's rendition of the fern prairie biome
Dakotaraptor in the new fern prairie rendition