The Isle of KPG

Sure, let's imagine this scenario: Taking up more than twice the size of New Zealand in total land mass, the island is known as Paleo-Isle on Earth. This island showcases a variety of environments, from lush forests and expansive swamps to vast, open fields. The tropical climate dominates much of the island's landscape while temperate climates influence the outer regions. On Paleo-Isle, while the KPG mass extinction event did ravage the mainland, it had a considerably reduced impact. As such, animals that went extinct elsewhere flourished here, evolving in intriguing ways that were not witnessed elsewhere on the planet. Tyrannosaurs, the apex predators of Paleo-Isle, grew bulkier and more agile to adeptly navigate the varied landscape. Dromaeosaurs developed sharper, serrated teeth to enable easier consumption of the robust species endemic to the island. Therizinosaurs, with their long necks and claws, became arboreal, feeding on the multitude of tree-dwelling ferns, veggies, and bark. The omnivorous oviraptorosaurs took advantage of enlarged brain capacity with advanced tool usage, while alvarezsaurids became both ground and tree dwellers to optimize food sources. Ornithomimosaurs played the role of agile scavengers and quick hunters in open fields. Titanosaur sauropods grew to be even larger due to an abundance of food and lack of significant predation, becoming the equivalent of Earth's elephants. Thescelosaurids incorporated swimming and fishing to their behaviors, thriving in the verdant swamps. Hadrosaurs evolved brightly colored crests for mating displays. Pachycephalosaurs turned into Island's forest guardians, using their thick skulls for territorial disputes. Ceratopsians developed larger frills and horns for defense, while ankylosaurs developed intricate armor patterns for bodily protection. Meanwhile, pterosaurs evolved to fill the roles similar to our modern birds, becoming improved fishers, hunters and seed spreaders. Cretaceous crocodiles grew to substantial sizes in warm swamps, rivalling the tyrannosaurs in size. Champsosaurs evolved into a cross between crocodiles and whales, becoming amphibious marine predators. The polyglyphanodontian lizards developed more intricate patterns to blend into the unique flora of the island, acting as one of the essential links in the food chain. This untouched paradise would continue its evolutionary path throughout the Cenozoic, until eventually being discovered by hominids during the late Pleistocene or early Holocene. The arrival of humans would add extra pressures to this already unique ecosystem, but perhaps they would also come to realize the incomparable treasure that was Paleo-Isle. It would become a living museum, showcasing a world where dinosaurs never went extinct and continued to evolve in isolation from the rest of the world.