Lost World Bestiary — Hollow Earth & Lemuria

Travellers look over the hidden prehistoric valleys, ancient inland sea and glowing fungal caverns of the Lost World

The Lost World Bestiary gathers prehistoric survivors, deep-cavern inhabitants and colossal creatures for expeditions through Hollow Earth, Lemuria and other hidden regions. Browse by environment: an inland sea, a sealed valley and a fungal cavern offer very different dangers.

Hollow Earth’s Old-Earth Wilds preserve different ages in separate refuges. Lemuria’s drowned ruins connect ancient communities, marine habitats and passages into deeper regions. The lists below lead to individual creatures and their rules; the complete Bestiary A–Z covers the wider world.

Choose an environment

Old-Earth Wilds

A basin’s inhabitants matter as much as its predators. Herds migrate between mineral-lit forests and river valleys; armoured herbivores close trails; giant hunters take advantage of the movement. Different basins preserve different periods of prehistory. The lists below separate genuine dinosaurs from earlier land animals and extinct mammals.

Dinosaurs A–L56 linked entries

True dinosaur lineages, from armoured browsers to giant theropods, listed alphabetically by name.

Dinosaurs M–Z66 linked entries

The remaining linked dinosaur genera. Pterosaurs and marine reptiles are listed separately.

Pterosaurs and early flyers6 linked entries

Flying reptiles are not dinosaurs. Early birds are treated separately where their identity requires it.

Early land animals: amphibians, synapsids and ancient reptiles43 linked entries

Aetosaurs, synapsids, early amphibians and related ancient land animals. Some predate dinosaurs by many millions of years.

Extinct mammals, giant birds and other land animals80 linked entries

Prehistoric mammals and giant terrestrial survivors, including mammoths, giant sloths and other extinct creatures.

Ancient Seas and Rivers

Inland seas and black rivers divide the Inner World. Travel hazards range from giant predatory fish and crocodilians to marine reptiles, primeval invertebrates and creatures that investigate the hull of a passing vessel. Some favour shallow channels; others require open water.

Ancient seas, coasts and waterways32 linked entries

Marine reptiles, ancient fish, shelled invertebrates and predators of rivers and shallows.

Deep-Earth Caverns and Fungal Forests

Below the passages used by ordinary miners lie fungal forests, vast karst basins and flooded caverns. Some animals are true prehistoric survivors; others are fantasy creatures adapted to darkness, warm stone or isolated ecosystems. A cautious flumph can warn travellers of danger; a cave fisher simply needs prey.

Older than the caverns. A shaft can also break into an abandoned Elder Thing laboratory. The engineered Shoggoths that once worked in such places rebelled during the Middle Permian; isolated descendants still inhabit some buried installations. These are not native Hollow Earth animals, and a passage into an ancient laboratory does not automatically lead into the Inner World. The distinction matters when choosing guides, supplies and an exit.

Great arthropods and cavern invertebrates32 linked entries

Giant ant colonies, ancient arthropods and other oversized invertebrates.

Subterranean beasts and living hazards29 linked entries

Cave fishers, oozes, underground predators and other inhabitants of deep caverns.

Primordial Colossi

A colossus can close a strait, destroy a settlement or force an entire expedition to turn back. These entries distinguish kaiju, gargantuas, elemental behemoths and ancient giants. Their habitats and origins differ; their individual entries describe the territories and powers that make each dangerous.

Kaiju in known history. In 1274, Mizuchi-no-Arashi overturned withdrawing Eastern Fang ships and damaged Japanese coastal settlements. The second invasion in 1281 brought a storm in which Raijin, Susanoo and coastal kami acted, while the war also awakened Mogaru. His advance devastated invading shipping and nearby settlements alike. The chronicle of the two invasions records these separate interventions.

Peoples, Kingdoms and Ancient Guardians

Hollow Earth has its own states: Agartha is only one of them. Derro warrens on the approaches, independent illithid city-complexes and other subterranean societies have politics and borders. Surface accounts that treat all deep-dwellers as a single primitive tribe are wrong.

Using This Bestiary in Play

Choose the environment first, then decide how inhabitants respond to a trespass. An expedition might need to cross a feeding ground, negotiate passage through a settlement, wait out a migration, or learn why a dormant colossus has begun to move. Not every encounter should become a fight.

Hollow Earth is a physical Inner World, not another plane. Reaching the real Inner World normally requires passage beyond mines and Deep-Earth caves through rare thresholds. The Hollow Earth gazetteer explains known regions, entrances and current conflicts.

Historical Images and Further Reading

Lost World Bestiary illustration: prehistoric marine reptiles battling at sea
Plesiosaurus battling Temnodontosaurus (Oligostinus), John Martin’s frontispiece for Thomas Hawkins’s The Book of the Great Sea-Dragons (1840). This historical interpretation predates modern reconstructions. Image source and credit.

Further viewing: MythKeeper — Pathfinder Creature Feature: Megafauna; AJ Pickett — D&D dinosaur lore. The first surveys Pathfinder megafauna; the second explores dinosaurs in D&D.

Explore more: Dinosaur Bestiary · Kaiju · Complete Bestiary A–Z.

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