In the fourth episode, Dromaeosaurs stalk a hadrosaur herd as they cross a freezing river. Male Ornithomimus raid rival nests to bolster their own. Olorotitan raise their offspring on fertile volcanic fields but contend with biting mosquitoes. Troodontids hunt mammals flushed out by a forest fire. A juvenile Antarctopelta scours the forest for a new winter den. Within the snow-covered forest, a tense standoff develops between ancient rivals, Pachyrhinosaurus and Nanuqsaurus.
A Tyrannosaurus and two Quetzalcoatlus fight over an Alamosaurus carcass. A shoal of Sphenodiscus are ambushed by a Globidens, intent on surplus killing them. At an evaporating lake, juvenile Pectinodon hunt flies while their father hunts Styginetta. Male Triceratops fight and display for the right to mate. A female Nanuqsaurus hunts Ornithomimus to feed herself and her offpsring.
Troodontids hunt mammals flushed out by a forest fire. A juvenile Antarctopelta scours the forest for a new winter den. Within the snow-covered forest, a tense standoff develops between ancient rivals, Pachyrhinosaurus and Nanuqsaurus.