Year 225 million BC. Something wonderful is happening: a new evolutionary branch of reptiles are starting to populate the planet. We’re in the middle of the period between the Permian-Triassic and the Triassic-Jurassic extinction events. With more place to grow from the last extinction, tetrapods have diversified greatly. Right now the dinosaurs aren’t that big in size, but by the end of 220 million BC the vegetation will be dominated by seed-producing Gymnosperms, poor in nutrients, which will make herbivores grow to huge sizes just so they can digest the plants. There are two species of trees from that period that have survived until today: Ginkgo biloba and Sequoia.
Fast forward to 200 million BC. The 4th mass extinction in the history of Earth just took place, killing off half of the living species in just 10.000 years. Not long after, the single continent Pangaea starts to break apart. In the aftermath, dinosaurs rule the world. Entire herds of Brachiosaurus and Diplodocus fill the fern prairies. Towards the end of Jurassic we can see a lot of flying dinosaurs starting to emerge. Predators like Allosaurus are at the top of the food chain. The rise of sea levels would bring an even larger diversity of species, as the continents separated and drifted away from each other. Not only the dinosaurs, but also the mammals are prospering, thought remaining comparatively small in size.
Cretacious started with a major increase in waterways. As the continents drift further and further away, there’s one specie that managed to get on every single one of them and prosper: the Iguanodon. There are some dinosaurs used to islands that evolved and adapted to the coastal shallows of ancient Europe, like Eustreptospondylus. Others take advantage of the new environmental conditions to thrive, like Carcharodontosaurus and Spinosaurus. The seasons are starting to be felt more and more, specially around the poles, but dinosaurs still inhabit those areas, like the Muttaburrasaurus which roamed the polar forests. Flying dinosaurs increase in size to compensate for the longer distances they need to travel.
Along with the late stage of Cretaceous, the climate begins to change. Beyond the tropics seasonal weather starts to drastically vary. Ichthyosaurus became extinct a bit earlier, but land dinosaurs still thrive as new species such like the Tyrannosaurus, Ankylosaurus, Triceratops and Hadrosaurs dominate the food chains. Pterosaurs are not that prolific and will soon face extinction, instead we can see more and more birds flying around. As we go towards the end of Cretaceous, volcanic eruption, namely the Deccan Traps, are releasing poisonous gas into the atmosphere. As this is continuing, it is thought that a large meteor smashed into Earth 65 million years ago in what today is the Gulf of Mexico, impacting the climate all over the planet for several decades in what will be the fifth and most recent mass extinction event. Almost 75% of life on earth became extinct, including all non-avian dinosaurs. Everything over 10 kilograms became extinct. Somewhere at the start of Paleogene, the last remnant of the dinosaurs, Triceratops, would eventually also die off. The age of the dinosaurs was over.