Three prehistoric worlds where humans arrive just as the local megafauna is going extinct, and each episode follows the collision. In America's Serengeti, a Clovis child's people hunt caribou and mammoth across Montana while dodging Smilodon and the short-faced bear Arctodus simus. Sixty-five thousand years later in Australia, the first Aborigines land on a forested continent of giant marsupials, meeting the rhino-sized Diprotodon, the territorial bird Genyornis, and the giant monitor lizard Megalania. The final episode jumps to the 1200s, when Maori voyagers led by Kupe reach New Zealand and start hunting the giant moa, drawing the attention of Haast's eagle, a bird large enough to prey on people. The series tracks how fast each extinction moves once humans show up, and closes by noting the same pattern played out later on Hawaii and Easter Island. Produced by the BBC, it later aired on Animal Planet under the title Land of Lost Monsters. Reenactments carry the human story while the animals are rendered as CGI predators and prey.