We might see rats the size of sheep in a horror movie. However, scientists in England say that in the future, they could be real. Giant rats could be as big as sheep and weigh 80kg. Rats are now all over the Earth. They are the strongest animals on many small islands. One reason for this is that they travel on ships and move to places that never had rats before. Another reason is that larger animals are becoming extinct. There are fewer animals that might kill rats. Researcher Dr Jan Zalasiewicz said rats could probably grow to become the world's largest rodent.

Dr Zalasiewicz said rats are an example of a species that humans spread around the world. They have adapted well to many of their new environments. He said: "There will be future thin rats, future fat rats, slow and heavy rats, fast and [fierce] rats, probably future aquatic rats." After the dinosaurs died, many small animals grew bigger. The same thing could happen with rats if there were no animals left that hunt and kill them. Dr Zalasiewicz said "super-rats" would kill other species to make them extinct. This will damage food chains. He did not say what humans would do about giant rats.