A variety of animals have historically been used in acts. While the types of animals used vary from circus to circus, big cats, elephants, horses, birds, sea lions, bears and domestic animals are the most common.
The earliest involvement of animals in circus was just the display of exotic creatures. Going as far back as the early eighteenth century, exotic animals were transported to North America for display, and menageries were a popular form of entertainment. The first true animals acts in the circus were equestrian acts (source: Wikipedia).