As early as in the Shang Dynasty (17th – 11th century BC), many characters related to animals appeared in scripts on tortoise shells and animal bones. At the first beginning, these characters were all pictographs such as 
(ox), 
(goat), 
(dog), 
(fish), 
(bird) and so on.
Besides these animal-related independent pictographic characters, quite a few compound characters that are combined by two or more elements also indicate animals such as 
(wolf), 
(bear), 
(fly), 
(sparrow) and so on.
The Shuowen Jiezi defines over 60 independent characters related to animals as radicals in many Chinese compound characters. These independent characters include 
(worm), (bird), 
(horse), (fish), (dog), 
(seashell), (ox), (goat), 
(deer), 
(tiger), 
(rat), 
(rabbit) and so on. Those compound characters with the above-mentioned independent characters as radicals are in a great number. From this we can see that the emergence of animal-related radicals indicates ancient people’s knowledge about animals entered a new stage.
（Source: chinaculture.org）
