ThePhaethontiformes/ˌfeɪ.ɪˈθɒntɪfɔːrmiːz/ are an order of birds. They contain one extant family, thetropicbirds (Phaethontidae), and one extinct familyProphaethontidae from the early Cenozoic. Several fossil genera have been described, with well-preserved fossils known as early as thePaleocene.[2] The group's origins may lie even earlier if the enigmatic waterbirdNovacaesareala from the latest Cretaceous or earliest Paleocene of New Jersey is considered a tropicbird.[3]
Many phaethontiform fossil taxa are known from the Paleocene andEocene, but the fossil record becomes much more scant after theOligocene. This suggests that around this time, the group may have moved out of the nearshore habitats where they were easier to fossilize and evolved thepelagic lifestyle that is still retained by the few surviving members today.[2]
The tropicbirds were traditionally grouped in theorderPelecaniformes, which contained thepelicans,cormorants and shags,darters,gannets and boobies andfrigatebirds; in theSibley-Ahlquist taxonomy, the Pelecaniformes were united with other groups into a large "Ciconiiformes". More recently this grouping has been found to be massively non-monophyletic (missing closer relatives of its distantly related groups) and split again. Microscopic analysis of eggshell structure by Konstantin Mikhailov in 1995 found that the eggshells of tropicbirds lacked the covering of thick microglobular material of other Pelecaniformes.[4]
Some early studies in the last decade suggested Phaethontiformes were distantly related toProcellariiformes,[5][6] but since 2004 they have been placed inMetaves, or in a lineage with no affinities with Procellariiformes, by the results of most recent molecular studies.[7][8][9][10] Jarvis,et al.'s 2014 paper "Whole-genome analyses resolve early branches in the tree of life of modern birds" aligns the Phaethontiformes most closely with thesunbittern and thekagu of theEurypygiformes, with these two clades forming the sister group of the "core water birds", theAequornithes, and the Metaves hypothesis abandoned.[11]
^Mikhailov, Konstantin E. (1995). "Eggshell structure in the shoebill and pelecaniform birds: comparison with hamerkop, herons, ibises and storks".Canadian Journal of Zoology.73 (9):1754–70.doi:10.1139/z95-207.
^Naish, D. (2012). "Birds." Pp. 379–423 in Brett-Surman, M.K., Holtz, T.R., and Farlow, J. O. (eds.),The Complete Dinosaur (Second Edition). Indiana University Press (Bloomington & Indianapolis).
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