Trogon - Evolution and Taxonomy

Evolution and Taxonomy

The position of the trogons within the class Aves has been a long-standing mystery. A variety of relations have been suggested, including the parrots, cuckoos, toucans, jacamars and puffbirds, rollers, owls and nightjars. More recent morphological and molecular evidence has suggested a relationship with the Coliiformes. The unique arrangement of the toes on the foot (see morphology and flight) has led many to consider the trogons to have no close relatives, and to place them in their own order, possibly with the similarly atypical mousebirds as their closest relatives.

The family is thought to have an Old World origin (but see Moyle (2005) for an alternative theory), notwithstanding the current richness of the family, which is more diverse in the Neotropical New World. The earliest formally described fossil specimen is a cranium from the Fur Formation lover-eocene in Denmark (54 mya). Other trogoniform fossils have been found in the Messel pit deposits from the mid-Eocene in Germany (49 mya)., in Oligocene rocks from Switzerland and Miocene France. The oldest New World fossil of a trogon is from the comparatively recent Pleistocene. DNA evidence seems to support an African origin for the trogons, with the African genus Apaloderma seemingly basal in the family, and the other two lineages, the Asian and American, breaking off between 20-36 million years ago. The trogons are split into three subfamilies, each reflecting one of these splits, Aplodermatinae is the African subfamily and contains a single genus, Apaloderma; Harpactinae is the Asian subfamily and contains two genera, Harpactes and Apalharpactes. Apalharpactes, consisting of two species in the Java and Sumatra, has only recently been accepted as a separate genus from Harpactes.

The remaining subfamily, the Neotropical Trogoninae, contains the remaining four genera, Trogon, Priotelus, Pharomachrus and Eupilotis. The two Caribbean species of Priotelus were formerly different ones (Temnotrogon on Hispaniola), and are extremely ancient. The two quetzal genera, Pharomachrus and Eupilotis are possibly derived from the final and most numerous genus of trogons in the Neotropics, Trogon. A 2008 study of the genetics of Trogon suggested the genus originated in Central America and radiated into South America after the formation of the Isthmus of Panama (as part of the Great American Interchange), thus making trogons relatively recent arrivals in South America.