The precise affinities of the Trogons are difficult to determine but all the evidence derived from their anatomy seems to show that they must be regarded as having split off from the very base of the stem which gave rise, eventually, to the Caprimulgi, Cypseli, Colii, and Striges. The fact that they have ranged from the Old into the New World shows them to be a very ancient group. Furthermore, it is significant that remains of a fossil Trogon have been found in the upper Eocene of Southern France.
The Trogons differ from all other birds in the structure of the feet. The first and second digits are turned backwards and are supplied by the flexor longus hallucis, whilst the third and fourth digits are directed forwards and connected with the flexor perforans digitorum. The two flexor tendons are united by a vinculum.