Caprona (also known as Caspak) is a fictional island in the literary universe of Edgar Rice Burroughs' Caspak Trilogy, including The Land That Time Forgot, The People That Time Forgot, and Out of Time's Abyss.^[1] They were published as serial novels in 1918, and collected in book form in 1924.

In the first novel, Caprona is described as a land mass near Antarctica and was first reported by the (fictitious) Italian explorer Caproni in 1721, the location of which was subsequently lost. The island is ringed by high cliffs, making it inaccessible to all but the most intrepid explorers. (The people who first explore the island access it by taking a submarine through a tunnel.)^[2] It has a tropical river teeming with primitive creatures extinct elsewhere and a thermal inland sea, essentially a huge crater lake, whose heat sustains Caprona's tropical climate.

Burroughs postulates a unique biological system for his lost world, in which the slow progress of evolution in the world outside is recapitulated as a matter of individual metamorphosis. This system is only hinted at in The Land That Time Forgot; presented as a mystery whose explication is gradually worked out over the course of the next two novels, it forms a thematic element serving to unite three otherwise rather loosely linked stories. Dinosaurs, prehistoric mammals, and primitive humans coexist on the island.^[3]

The island is also called "Caspak" by its native humanoid inhabitants – thus the name of the trilogy.^[4]

Unlike Pellucidar which is actually a huge melting pot of earth's various ages where all types of ancient fauna and flora intermix, the fauna and flora of Caprona is organized into different zoogeographic zones where fauna from the different respective ages are confined.

• Giant amphibians, insects such as the giant dragonfly-like Meganeura, and Mammal-like reptiles such as the Gorgonopsid and Dimetrodon are confined to the southern extremity of the island.
• Reptiles and dinosaurs dominate slightly further north.
• The lagoon in this region is infested with water-living creatures like huge aquatic saurians such as Plesiosaurus and the Sea serpent-like Mosasaurus, "a veritable Mesozoic nightmare", according to Bowen Tyler's journal.
• Pterodactyls of all kind fly the misty skies and dinosaurs, such as Allosaurus, Diplodocus, and Stegosaurus from the Jurassic, and Iguanodon, Styracosaurus, Triceratops, Tyrannosaurus rex, and Velociraptor from the Cretaceous periods overrun the land.
• Further north, the mammals begin to dominate, beginning with the most primitive types, and upward through the late Pleistocene fauna, including the Aurochs, Mastodon, Woolly mammoths, Woolly rhinoceros, and Megatherium, preyed upon by cave lions, the cave bear, Smilodon, and giant panthers.
• Primates are numerous throughout the island, including "monkeys of all sizes and shades", and a variety of apes and man-like creatures.

Caprona is home to various tribes. Virtually all of them are different types of human that actually existed during the earth's past from upright walking apes to advances species like Neanderthals and Cro-Magnons.

The following tribes are found on Caprona:

• Ho-lu – A tribe of apes with the ability to "walk upright" (resembling the real-life Australopithecus afarensis).
• Bo-Lu – A tribe of Neanderthals whose name means "Club Men" because they wield clubs.
• Band-Lu – A tribe of Cro-Magnons whose name means "Spear Men".
• Sto-Lu – A tribe of missing links whose name means "Hatchet Men".
• Kro-Lu - A tribe of humans whose name means "Bow Men" because they are good archers. They can domesticate cows and goats. In addition, they can domesticate wolf-like dogs to guard their livestock.
• Galu – A tribe of educated humans whose name means "Rope Men". They are experts at cloth-weaving and have been shown to domesticate horses.
• Weiroo – A tribe of winged humans. Because there are mostly male Weiroo, they often abduct female Galu for breeding purposes.

• Pellucidar
• Savage Land