Eutreptodactylus itaboraiensis gen. et sp. nov., an early cuckoo (Aves: Cuculidae) from the Late Paleocene of Brazil

Eutreptodactylus itaboraiensis from Late Paleocene karst deposits of eastern Brazil is the oldest and most primitive member of the Cuculidae known to date. It is one of the oldest fossils that can be placed in a modern family of birds. The zygodactyl condition, characterising the cuculids, is present in Eutreptodactylus, but the relative rotation of the trochlea metatarsi IV is slight in comparison with that in extant cuculids, suggesting that this bird may not have been an obligate zygodactyl form. Since zygodactyly had developed within the Cuculiformes by the Late Paleocene, it follows that the other family in this order, the Musophagidae, must have diverged by the early part of the Cainozoic.