In ancient China, people connected natural animals with the sky and earth, and with the theory of yin-yang. Animals in the yang group symbolized the sky and the sun. The unification of "yang" animal from the sky with "yin" animals of earth meant a connection of the sky and earth, or the unity of yin-yang. Among Chinese totem animals and legendary animals, the tiger, the ox, the goat, the bird, the bear, the boar, the dog and the cock were of the sky and yang group; the dragon, the snake, the turtle, the fish and the frog were yin group and
symbols of earth and water. The dragon, with his head on earth but mating in heaven, was a totem of both worlds (Dragon was originally earth and water animal, but later went to heaven to become the king, and phoenix, an animal in heaven was the queen.) This is rather unique. For example, dragon, being an earth and water totem symbol, later became a cultural symbol of the entire nation in the confluence of multiple national cultures. People integrated the dragon into their own totem animal which turned into the dragon with a boar head in Liaohe basin; or the dragon with a tiger head in the middle-upper stream of the Yellow River; the dragon with a bird head in middle-lower stream of the Yellow River and the Yangtze River; and the dragon with an ox head in middle-upper stream of the Yangtze River. It is also quite common to see "fish with a tiger head" or "fish with a cock head" in Chinese folk art. When two animals are combined into one, it was a cultural symbol that heaven and earth connect, male and female mate. Other example like "cock holding a fish in the mouth" and "bird holding a fish in the mouth" also implied the connection of heaven and earth, yin and yang. It was a cultural code originated in the communal philosophy in primitive society.