Wings are attested in Mesopotamian art, appearing in every major category (human, bull, lion, etc.), except for the fish and the snake. Simple addition of wings to an otherwise land-bound creature radically enhances its mobility (adding flight or at least speed), without further physical modification. Dog, ibex, and scorpion-based hybrid always have wings. Humans, bulls, and lions do not always have wings may be because they are capable or powerful enough without them. Four wings are at least optional in some cases as on the Human-Figured Ūmu-apkallu, Bird-of-Prey-Headed, Winged Apkallu, Human Headed Bovine, and Demon. Thus, all can possess the flight capability of four wings also have human elements, to varying degrees of dominance. The addition of wings to anthropomorphic figures begins later and gains ground slowly until the second half of the second millennium, when it becomes a common practice.