 It has also been theoretized that tyrannosaurids had such protofeathers . However , rare skin impressions from adult tyrannosaurids in Canada and Mongolia show pebbly scales typical of other dinosaurs . While it is possible that protofeathers existed on parts of the body that have not been preserved , a lack of insulatory body covering is consistent with modern multi @-@ ton mammals , such as elephants , hippopotamus , and most species of rhinoceros . As an object increases in size , its ability to retain heat increases due to its decreasing surface area @-@ to @-@ volume ratio . Therefore , as large animals evolve in or disperse into warm climates , a coat of fur or feathers loses its selective advantage for thermal insulation and can instead become a disadvantage , as the insulation traps excess heat inside the body , possibly overheating the animal . Protofeathers may also have been secondarily lost during the evolution of large tyrannosaurids , especially in warm Cretaceous climates . A precedent can be seen in other dinosaur groups such as ornithischians , in which filamentous structures were lost , and scales reappeared . 
