The wider variety of chacmool forms at Chichen Itza has also been used to support the development of the form there; no two possess identical form, dress and proportions. At Tula the chacmools have a standardised form with little variation in position or proportions. Miller has proposed that the chacmool developed out of Classic Maya iconography and underwent a transition into three dimensional sculpture at Chichen Itza, perhaps spurred by the influence of central Mexican sculptural forms. A chacmool from Costa Rica was dated by the excavators to approximately AD 1000.