Evolution and systematics

The fossilized remains of woodhoopoe-like birds have been found from Eocene and more recent Miocene deposits in Europe, but modern woodhoopoes are now confined to Africa. Woodhoopoes occur in two main forms, based on studies of their anatomy, DNA-DNA hybridization, and nuclear DNA. The two groups are usually separated as subfamilies, sometimes even as families, the true woodhoopoes, Phoeniculinae (genus Phoeniculus), which live in groups and breed cooperatively, and the smaller scimitarbills, Rhinopo-mastinae (genus Rhinopomastus), which live and breed only as pairs. The separation occurred about 10.2 million years ago, based on estimation from a molecular clock.

Woodhoopoes are most closely related to the more widespread hoopoe (Upupa epops), family Upupidae, with which they share a unique stirrup-like structure of the inner ear bone. The hoopoe feeds mainly while walking on the ground, whereas woodhoopoes feed mainly by hopping about on tree branches. Molecular and anatomical evidence suggests that woodhoopoes and hoopoes are close relatives of hornbills (family Bucerotidae), which lack the stirrup-like stapes but have their own unique neck vertebrae, and also have terres trial and arboreal members. Still more distant relatives are other members of the order Coraciiformes.

Three species of woodhoopoe are recognized in each subfamily. All species can be divided further into clearly recognizable subspecies that, in the widespread and variable green woodhoopoe (P. purpureus), are sometimes even treated as separate species, the violet woodhoopoe (P. damarensis) and the black-billed woodhoopoe (P. somaliensis).

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