Dinosaurs and other prehistoric creatures still roam Caspak, as do various tribes of people representing different stages of human evolution.
Death is common, yet there are no children.
The facts of life on Caspak are very different. That Time Forgot was first published as a three-part magazine serial in 1918, then in book form in 1924. Each of the linked stories follows a different hero while gradually revealing the mystery of Caspak's biology. When Lys disappears into the jungle, abducted by a cave man or perhaps a German, Tyler goes off in search of his lady love. He has many brushes with death and falls in love with a native girl.