The Phaethontiformes are an order of birds. They contain one extant family, the
tropicbirds (Phaethontidae), and one extinct family
Prophaethontidae from the early Cenozoic. Several fossil genera have been described, with well-preserved fossils known as early as the
Paleocene
The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...
.
The group's origins may lie even earlier if the enigmatic waterbird ''
Novacaesareala'' from the latest Cretaceous or earliest Paleocene of New Jersey is considered a tropicbird.
Many phaethontiform fossil taxa are known from the Paleocene and
Eocene
The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
, but the fossil record becomes much more scant after the
Oligocene
The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...
. This suggests that around this time, the group may have moved out of the nearshore habitats where they were easier to fossilize and evolved the
pelagic
The pelagic zone consists of the water column of the open ocean and can be further divided into regions by depth. The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or water column between the sur ...
lifestyle that is still retained by the few surviving members today.
The tropicbirds were traditionally grouped in the
order
Order, ORDER or Orders may refer to:
* A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
...
Pelecaniformes, which contained the
pelican
Pelicans (genus ''Pelecanus'') are a genus of large water birds that make up the family Pelecanidae. They are characterized by a long beak and a large throat pouch used for catching prey and draining water from the scooped-up contents before ...
s,
cormorants and shags,
darters,
gannets and boobies and
frigatebirds; in the
Sibley-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
In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria:
# the grouping contains its own most recent co ...
(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.
Some early studies in the last decade suggested Phaethontiformes were distantly related to
Procellariiformes
Procellariiformes is an order (biology), order of seabirds that comprises four family (biology), families: the albatrosses, the Procellariidae, petrels and shearwaters, and two families of storm petrels. Formerly called Tubinares and still call ...
,
but since 2004 they have been placed in
Metaves, or in a lineage with no affinities with Procellariiformes, by the results of most recent molecular studies.
[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).] 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 the
sunbittern and the
kagu
The kagu or cagou (''Rhynochetos jubatus'') is a crested, long-legged, and bluish-grey bird endemism, endemic to the dense mountain forests of New Caledonia. It is the only surviving member of the genus ''Rhynochetos'' and the family Rhynoche ...
of the
Eurypygiformes, with these two clades forming the sister group of the "core water birds", the
Aequornithes, and the Metaves hypothesis abandoned.
References
{{Taxonbar, from=Q12765692
Bird orders
Seabirds