| Era | Prehistoric |
| Type | |
| Climate | Frosty landscapes |
| Key events | Late-period cold snap |
| Dominant fauna | Megatheria |
| Significant fauna | Megatheria • Stagbeetles • Spiketail dinosaurs • Bullwhip lizards |
| Distinctive features | Ecological dominance of megatheria • Giant insects like stagbeetles • Weaponized dinosaurs such as spiketail and bullwhip lizards |
| Prehistoric extinctions | Invasive predators |
The animals of the Prehistoric Period varied significantly from species to species and era to era. In this alternate timeline, notable differences from our world's prehistory include the prominence of elephant-like giantotherms called "megatheria", the existence of giant flightless insects known as "stagbeetles", and a higher prevalence of armed, weaponized dinosaurs.
The most dominant lineage of prehistoric animals were the megatheria, an order of large mammalian creatures resembling elephants but even larger. With size reaching up to 8 meters (26 ft) at the shoulder and weights over 20 tonnes (22 tons), these animals were among the largest terrestrial animals ever to exist in this alternate world.
Megatheria were native to the subarctic regions of the Northern Midlands, the Nuric Tundra, and the Four Corners. Their powerful tusks and thick, hairy hides made them formidable competitors for resources and respected by all other creatures who shared their ecosystems.
In this alternate timeline, flightless insects called stagbeetles (Megastomprus gigantalis) filled the niche occupied by pterosaurs and birds. Huge and powerful, these beetles had durable, armored wing casings they used for protection and as a means of flight.
Stagbeetles could reach sizes of up to 2 meters (6.56 feet) long and 1 meter (3.28 feet) tall, with massive mandibles and front legs they used for digging and burrowing. These creatures were herbivorous and thrived in humid, tropical, and subtropical climates.
Dinosaurs in this world were larger and more fearsome than in our reality, with many sporting an array of deadly weapons like spiketails, bullwhip lizards, and thunderbeasts. These highly specialized creatures dominated their ecosystems, preying on smaller animals and intimidating or outright terrorizing larger ones.
For example, the spiketail or Stygiosaurus (from the Stygiosaurus lineage) had a long, armored tail ended in a cluster of sharp spikes, while the bullwhip lizard or Venator ({Venator gaia} lineage) had a powerful, flexible tail it could whip at high speeds to kill or maim prey.
Compared to our known history, prehistoric animals in this alternate timeline saw different climatic events. The dominant land animal lineages survived relatively unchanged until a late-period global cooling event struck the planet around 67 million years ago.
This Late-Cenomanian Ice Age was caused by a sudden and drastic shift in the planet's orbit, reducing the amount of sunlight received and sending global temperatures plummeting. Glaciers formed in temperate regions, sea levels dropped, and ecosystems around the world were profoundly altered.
The Late-Cenomanian Ice Age marked the beginning of the end for the megafauna that dominated the previous epochs. As contact between ecosystems increased due to the shrinking of tropical regions, invasive predators like bullwhip lizards and other specially adapted species roamed far from their native habitats and decimated new populations of prey animals.
As a result of climate change and invasive predators, a mass extinction occurred that drastically altered the landscape and ecosystems of the planet. With the extinction of key species, new ecological niches opened up, setting the stage for the rise of modern mammals and birds.
Despite the profound changes, the fossil record still shows many familiar groups like mammoths, saber-tooth tigers and ancient horses, all of which continued to evolve in subtle ways shifted by their unique histories.
