The book revolves around an alternative timeline where the earth did not suffer from the Cretaceous-Paleogene mass extinction event, and as a result, the non-avian dinosaurs alongside other organisms that had perished in the event, remained in place. as the predominant groups of the terrestrial biosphere but that eventually had to face the following geographical, ecological and climatic changes through the Cenozoic and evolve to adapt to such changes, which as a result has created an interesting new variety of fauna throughout the planet. Dinosaurs have had a new wave of diversity from part of small sized clades, being the most successful several theropods descendants of the Coelurosaurs which have diversified into different niches, from the arboreal dwellers called Arbrosaurs, small scavengers, and some heavy carnivores, and several Thescelosaurs and Hypsilophodonts that have taken several herbivorous niches. Other groups including megafauna such as Hadrosaurs, Iguanodonts, Pachicephalosaurs, Tyrannosaurs, Megalosaurs, Ankylosaurs, Ceratopsids and Titanosaurs are still present, some preserving a certain aspect of their Cretaceous forms and some with varied new derivative forms. Of course, not all groups survived during the new era, being mentioned Camarasaurids, Dromeosaurids, Therizinosaurs, Diplodocids, Stegosaurs, Short-Frilled Ceratopsids, Spinosaurids, Oviraptorosaurs and Ornithomimids the ones that perished though the Cenozoic.
Mammals due to the presence of non-avian dinosaurs are still in the margin as small creatures with some species of peculiar behavior, with the three clades still existing, Monotremes, Marsupials and Placenta (even though there is only one representative of the placentary mammals). Other groups of reptiles such as Pterosaurs remained as the dominant group of flying animals and even evolving various flightless forms, while in the oceans the Plesiosaurs such as Elasmosaurs and Pliosaurs are still present, with the latter adopting filter feeding lifestyle. Other clades such as Squamata (mosasaurs, lizards and snakes), Crocodiles and Turtles exist but there is not mention of their diversity, as well as several clades of fish or other organisms that lack a description of their status in this alternative world, except for the ammonite cephalopods that show two representatives in the book.
Earth still keeps the same continental arrangement as in our timeline, but with a different biogeography due to the different fauna diversity, the book groups these in zoogeographical realms, which are:
- The Palearctic Realm (Eurasia and North Africa)
- The Nearctic Realm (North America)
- The Neotropical Realm (Central and South America)
- The Ethiopian Realm (Sub-Saharan Africa and Madagascar)
- The Oriental Realm (India and Southeast Asia)
- The Australasian Realm (Australia, Papua New Guinea, and New Zealand)
- The oceans
- Coconut Grab, Nuctoceras litureperus, an ammonite that crawls onto land to grab coconuts, similar to our robber crab. The Coconut Grab can even climb trees (Oceania).
- Kraken, Giganticeras fluitarus, a massive floating ammonite with a shell 13 feet in diameter. Its tentacles are covered with poisonous barbs like those of a jellyfish. These deadly tentacles spread out in an area of 67 feet in diameter. The kraken only fears the pelorus, who is immune to its poisonous stings.
- Balaclav, Nivesaurus yetiforme, a large mountain-dwelling thescelosaur (an American relative of hypsilophodonts). It feeds mostly on the sparse vegetation along mountain slopes (North America).
- Bricket, Rubusaurus petasus, a furry hadrosaur (Eurasia).
- Cutlasstooth, Caedosaurus gladiadens, a saber-toothed predatory dinosaur (South America).
- Coneater, Strobofagus borealis, a large social hypsilophodont with an elongated snout to store large batteries of cheek teeth (Eurasia).
- Crackbeak, Fortirostrum fructiphagum, an arboreal hypsilophodont that evolved specialized perching feet. They use their beaks for cracking seeds and fruit (Africa, Asia, and Australia).
- Cribrum, Cribrusaurus rubicundus, a flamingo-like predatory dinosaur with slender teeth for straining soda lakes for microorganisms (Australia).
- Debaril, Harenacurrerus velocipes, a small running and hopping hypsilophodont (Eurasia).
- Dingum, Velludorsum venenum, a meter-long predatory dinosaur with sexual dimorphism. Males are partially quadrapedal with a sail atop its back. The rays in this sail are tipped with venomous barbs, containing poisons from consumed desert plants. Females are larger and look more like a typical predatory dinosaur (Australia).
- Dip, Harundosaurus montanus, a fish-eating mountain-dwelling predatory dinosaur (South America).
- Flurrit, Labisaurus alatus, a gliding predatory dinosaur (Asia).
- Footle, Currerus elegans, an agile squirrel-like two-legged arboreal predatory dinosaur (North America).
- Gestalt, Formisaura delacasa, a colonial pacheyocephalosaur. They build fortresses in trees where the queen sits on eggs. Males serve as soldiers in the colonies (Eurasia).
- Gimp, Melexsorbius parvus, a nectar-sipping arboreal predatory dinosaur (South America).
- Glub, Lutasaurus anacrusus, an aquatic hypsilophodont with no back legs (Asia).
- Gourmand, Ganeosaurus tardus, a scavenging tyrannosaur with detachable jaws and no front limbs (South America).
- Gwanna, Gryllusaurus flavus, a kangaroo-like relative of Iguanodon. It inhabits grasslands and deserts. It has two movable fingers with two stationary ones and a thumb spike (Australia).
- Hanuhan, Grimposaurus pernipes, a fleet-footed rock-dwelling hypsilophodont (Asia).
- Jinx, Insinusaurus strobofagoforme, a sickle-clawed predatory dinosaur that imitates the coneaters. It looks and smells like its prey so packs can wander into coneater herds and attack (Eurasia).
- Lumber, Elephasaurus giganteus, a large sauropod with a short tapir-like trunk (South America).
- Megalosaur, Megalosaurus modernus, a surviving carnosaur from the Mesozoic. It survives on an island off the coast of Africa and spends most of its life scavenging. A species of dwarf megalosaur inhabits small islands (Madagascar).
- Monocorn, Monocornus occidentalis, a furry one-horned ceratopsian dinosaur(North America)
- Mountain Leaper, Montanus saltus, an agile mountain-dwelling predatory dinosaur (North America).
- Nauger, Picusaurus terebradens, a woodpecker-like arboreal predatory dinosaur (North America).
- Northclaw, Monuncus cursus, a predatory dinosaur with a claw on its arm used for killing (North America).
- Numbskull, Sphaeracephalus riparus, a mountain-dwelling pacheyocephalosaur (Asia).
- Pangaloon, Filarmura tuburostra, a pangolin-like predatory dinosaur (South America).
- Pouch, Saccosaurus spp., a duck-like predatory dinosaur with webbed feet, a stiff tail, and a transparent throat pouch like that of a pelican (Australia).
- Rajaphant, Gregisaurus titanops, a socially-sophisticated sauropod (Asia).
- Sandle, Fususaurus foderus, a burrowing mole-like predatory dinosaur (Africa).
- Scaly Glider, Pennasaurus volans, an arboreal predatory dinosaur with a fan of plates along its sides for gliding (South America).
- Springe, Necrosimulacrum avilaquem, a predatory dinosaur that attracts its prey by playing dead, then stabbing it with its sickle toe claws (North America)
- Sprintosaur, Family Sprintosauridae, antelope-like hadrosaurs. They come in two types: short-tailed crested sprintosaurs and long-tailed sprintosaurs without crests (North America).
- Taddey, Multipollex moffati, a panda-like hypsilophodont (Asia).
- Taranter, Herbasaurus armatus, a desert-dwelling ankylosaur (Eurasia).
- Titanosaur, Altosaurus maximus, one of the few sauropod dinosaurs on Earth. It survives on a large island off the coast of Africa, as well as some dwarf species on various small islands(Madagascar)
- Tree Hopper, Arbrosaurus bernardi, an arboreal leaping predatory dinosaur (Africa).
- Treepounce, Raminsidius jacksoni, an agile marten-like arboreal predatory dinosaur (North America).
- Treewyrm, Arbroserpens longus, an arboreal snake-like predatory dinosaur with a slender neck and no front legs (Asia).
- Tromble, Gravornis borealis, a massive flightless grazing bird from the Arctic regions (Eurasia).
- Tubb, Pigescandens robustus, a slow-moving koala-like hypsilophodont with a pot belly and short legs. Its tail is shorter than its ancestors. It eats mostly eucalyptus leaves (Australia)
- Turtosaur, Turotosaurus armatus, an armored sauropod (South America).
- Waspeater, Vespaphaga parma, a thick-scaled anteater-like predatory dinosaur that eats wasps (Africa).
- Watergulp, Fluvisaurus hauristus, a manatee-like hypsilophodont (South America)
- Whiffle, Adescator rotundus, a flightless insect-eating bird (Eurasia).
- Wyrm, Vermisaurus perdebracchius, a snake-like predatory dinosaur with no arms, thick belly scales, and an armored head used as a shield when burrowing (Africa).
- Zwim, Naremys platycaudus, a swimming placental mammal (Eurasia).
- Flarp, Vexillala robusta, a flightless grazing ostrich-like pterosaur (Africa).
- Harridan, Harpyia latala, a large condor-like pterosaur (South America).
- Kloon, Perdalus rufus, a small flightless moa-like pterosaur with no wings and flexible feet (New Zealand).
- Lank, Herbafagus longicollum, a flightless giraffe-like pterosaur (Africa).
- Paraso, Umbrala solitara, a solitary heron-like pterosaur (Asia).
- Plunger, Pinala fusiforme, a penguin-like pterosaur.
- Shorerunner, Brevalus insularis, a small mobile island-dwelling pterosaur that behaves like a gull, beachcombing and eating the corpses of any animal stranded on shore.Although it's wings are slightly atrophied,it is still capable of true flight (Oceania).
- Sift, Pterocolum rubicundum, a fine-toothed heron-like pterosaur (North America).
- Soar, Cicollum angustualum, an albatross-like pterosaur. (Coasts)
- Wandle, Pervagarus altus, a giant flightless moa-like pterosaur that lives in high altitude plains in small groups (New Zealand).
- Birdsnatcher, Raperasaurus velocipinnus, a large bird-eating elasmosaur with an elongated neck. (Oceans).
- Pelorus, Piscisaurus sicamalus, a fish-shaped pliosaur that eats fish. It also hunts the kraken and is one of the few predators that is immune to the kraken's venom. (Oceans).
- Whulk, Insulasaurus oceanus, a large whale-like plankton-eating pliosaur. (Oceans).