Author/Creator: Edgar Rice Burroughs
First appearance: Tarzan the Terrible
Media: Novel
Year: 1921
Located: Zaire, Africa
Plot/Premise: In a frantic search for Jane Tarzan has tracked her to a hidden valley called Pal-ul-don, which means "Land of Men." In Pal-ul-don Tarzan finds a real world filled with dinosaurs, notably the savage Triceratops-like Gryfs, which unlike their prehistoric counterparts are carnivorous. The lost valley is also home to two different races of tailed human-looking creatures, the Ho-don (hairless and white skinned) and the Waz-don (hairy and black-skinned). Tarzan befriends Ta-den, a Ho-don warrior, and Om-at, the Waz-don chief of the tribe of Kor-ul-ja.

First appearance: The Face in the Abyss
Author/Creator: Abraham Merritt
Media: Novel
Year: 1931
Located: Among the Andes
Plot/Premise: Treasure seekers discover a million-year-old Atlantian civilization ruled over by the Snake Mother, Adana, the last of a race of superintelligent serpent people whose servants, the Old Race, are immortal. Humans, the Yu Atlanchians, share this land with ancient lizard men and Xinli, small predatory dinosaurs that roam in large hunting packs and which are used by the Yu-Atlanchi in sport and as war-steeds.

Rodney Matthews

Author/Creator: Robert Moore Williams
First appearance: Jongor of the Lost Land
Media: Novel
Year: 1940
Located: Inland Australia
Plot/Premise: Isolated from the world by mountains, valleys and desert, the Lost Land has undergone a unique evolution. Many dinosaurs dwell here along with various monsters and human civilizations. It is in this world a Tarzan-like hero, Jongor (John Gordon) has many adventures.
Sequels/Other appearances: The Return of Jongor (1946), Jongor Fights Back (1951)

First appearance: "4-Color" #595, Dell Publishing
Author/Creators: Rex Maxon, Matthew H. Murphy, Gaylord Du Bois and Paul S. Newman
Media: Comic
Year: 1954
Located: A deep canyon in the Carlsbad area of New Mexico that perhaps leads to a prehistoric sub-universe
Plot/Premise: Turok was a brave Kiowa warrior living some time in the 1800's before the arrival of white men. He and a young companion, Andar, wander into a savage prehistoric land they call Lost Valley and find themselves cut off from their homeland and people. They wander around Lost Valley, encountering cavemen and hungry dinosaurs (which they call "honkers"), searching for a way out. Fortunately, on their journeys, they discover a poisonous plant with highly toxic berries. They smear the tips of their arrows with these berries and now even the biggest, nastiest honker is no longer a threat.
Sequels/Other appearances: Turok (1993, Valiant Comics)
Adaptations: Turok: Dinosaur Hunter (1997, Video Game), Turok (rebooted premise)

First appearance: The Valley of Gwangi
Author/Creator: Willis H. O'Brien, Ray Harryhausen, James O'Connolly, William E. Bast and Julian More
Media: Film
Year: 1969
Located: Deep in the Mexican desert
Plot/Premise: The Forbidden Valley is an almost impenetrable valley deep in the Mexican desert where dinosaurs (through very few plants) still flourish. Chief among its inhabitants is the huge carnivorous dinosaur dubbed "Gwangi" which escapes and wreaks havoc when it is captured in a travelling Wild West show.
Sequels/Other appearances: "Gwango's Lonesome Trail" (Children's book, 2006)
Adaptation: Dell Comic, 1969