I just finished reading The Hobbit, and the riddles Bilbo and Gollum ask one another seem much more difficult than the common ones today, yet Tolkien references that the reader would know the answers to some of the riddles, particularly the teeth and fish riddle. Were these riddle common during the time of publishing or was Tolkien trying to recreate medieval style riddles. Here is a list of the riddles if you don't have the book handy.
Riddles are part of traditional European folklore. From Anglo-Saxon (i.e. Old English) sources, it is clear that riddle games were popular before 1066 and the Norman conquest. Tolkien (1892-1973) was drawing on a time-honored tradition, and he even drew on traditional sources for inspiration when he wrote the riddle game between Bilbo and Gollum in The Hobbit (1937).
Riddle games are by no means universal. My mentor, Sven S Liljeblad (1899-2000), who was one of the first to conduct comprehensive language and folklore collecting among the Northern Paiutes and Shoshone of the Great Basin, documented how foreign and alien the riddle game was to these people. He told me that he once told a riddle to one of his oldest informants at Fort Hall, Idaho. He recited to him the traditional European riddle, "Box without lid, gold within. What am I?" The man said he did not know, so Sven told him the answer was "an egg." The man's reply was, "Well, why didn't you just say so?" That is a response from a culture that has no tradition of the riddle game.
Folklorists were able to document riddle telling in pre-industrial/pre-modern European cultures, but Tolkien was not attempting to depict recent European culture. Rather, he was drawing on early medieval documentation of this aspect of Northern European oral tradition.