Giant Megarat

Giant megarat is a future descendant of brown rats in North America that grew much bigger, about the size of a Gambian pouched rat. They are more bulkier than stronger than their ancestors. They are omnivores that feed on just about any food they could find edible. Nothing else changed about this species of rodent.

Evolution
After the Late Holocene ended, humans are now gone, but they have failed to eradicate brown rats due to their fast reproduction and adaptibility to tolerate human activities and developments. Their numbers may have diminished due to no more man-made food, but they survived and repopulate after finding abundant food in the wild and less predators than during the Holocene. Eventually, some brown rats grew much bigger and stronger, as well as becoming more aggressive species. These brown rats had evolved into giant megarats.