在人類出現之前，地球是巨獸的天下。這個讓人大開眼界的特別節目，為觀眾細數地球曾經出現體型最大的動物，同時揭露這些超大物種不為人知的秘密生活。從翼展和飛機一樣長的大鳥，到體型和一架波音737噴射客機不相上下的恐龍，這部大量使用電腦動畫的節目，要尋找這些巨獸背後的真相，列舉其中最驚人的發現。帶觀眾見識剛出土、體型大過先前所有恐龍的恐龍骨頭，又分析七公尺巨鳥的飛行技術，揭開讓這些動物在世上興盛繁衍的特殊適應技能。
巨型動物是體重至少為 44 磅（20 公斤）的大型動物。 這些動物包括大象、犀牛、大猩猩和鯨魚等物種。 由於棲息地破壞、狩獵和其他人類活動，許多巨型動物物種被認為瀕臨滅絕或受到威脅。 巨型動物的一些例子包括：
大象：現存最大的陸生動物，大象重達 24 噸，分佈於非洲和亞洲。
犀牛：犀牛有五種，都是瀕危物種。 最大的是白犀牛，體重可達 8,000 磅。
大猩猩：大猩猩中體型最大的大猩猩，分佈於非洲中部和西部。 由於狩獵和棲息地破壞，它們瀕臨滅絕。
鯨魚：地球上最大的動物，鯨魚可以長到 100 英尺長，重達 200 噸。 有幾種鯨魚，包括藍鯨、座頭鯨和虎鯨。
巨型動物在其生態系統中發揮著重要作用，並且通常是關鍵物種，這意味著它們的存在或不存在會對生態系統的整體健康產生重大影響。
Megafauna are large animals that have a body mass of at least 44 pounds (20 kilograms). These animals include species such as elephants, rhinoceroses, gorillas, and whales. Many megafauna species are considered to be endangered or threatened due to habitat destruction, hunting, and other human activities. Some examples of megafauna include:
Elephants: The largest living land animals, elephants can weigh up to 24 tons and are found in Africa and Asia.
Rhinoceroses: There are five species of rhinoceros, all of which are endangered. The largest is the white rhinoceros, which can weigh up to 8,000 pounds.
Gorillas: The largest of the great apes, gorillas are found in central and western Africa. They are endangered due to hunting and habitat destruction.
Whales: The largest animals on Earth, whales can grow up to 100 feet long and weigh up to 200 tons. There are several species of whales, including blue whales, humpback whales, and killer whales.
Megafauna play important roles in their ecosystems and are often keystone species, meaning that their presence or absence can have a significant impact on the overall health of the ecosystem.
