The "albatross" designation comprises between 13 and 24 species (the number is still a matter of some debate, with 21 being the most commonly accepted number) in four genera. These genera are the
great albatrosses (
Diomedea), the
mollymawks (
Thalassarche), the
North Pacific albatrosses (
Phoebastria), and the
sooty albatrosses or sooties (
Phoebetria). The North Pacific albatrosses are considered to be a
sister taxon to the great albatrosses, while the sooty albatrosses are considered closer to the mollymawks. Though a case was made for the simplification of the family (particularly the nomenclature), the classification was based on the morphological analysis by
Elliott Coues in 1866, and paid little attention to more recent studies and even ignored some of Coues's suggestions. While some agree on the number of genera, fewer agree on the number of species. Historically, up to 80 different taxa have been described by different researchers; most of these were incorrectly identified juvenile birds. Based on the work on albatross genera, Robertson and Nunn went on in 1998 to propose a revised taxonomy with 24 different species, compared to the 14 then accepted. This expanded taxonomy elevated many established
subspecies to full species, but was criticised for not using, in every case,
peer reviewed information to justify the splits. Since then, further studies have in some instances supported or disproved the splits; a 2004 paper analysing the mitochondrial DNA and
microsatellites agreed with the conclusion that the
Antipodean albatross and the
Tristan albatross were distinct from the
wandering albatross, per Robertson and Nunn, but found that the suggested
Gibson's albatross,
Diomedea gibsoni, was not distinct from the Antipodean albatross. For the most part, an interim taxonomy of 21 species is accepted by
ITIS and many other researchers, though by no means all—in 2004 Penhallurick and Wink called for the number of species to be reduced to 13 (including the lumping of the
Amsterdam albatross with the
wandering albatross), although this paper was itself controversial.
Sibley and Ahlquist's molecular study of the
evolution of the bird families has put the
radiation of the
Procellariiformes in the
Oligocene period 35–30 million years ago (Mya), though this group probably originated earlier, with a
fossil sometimes attributed to the order, a seabird known as
Tytthostonyx, being found in late
Cretaceous rocks (70 Mya). The molecular evidence suggests that the storm petrels were the first to diverge from the ancestral stock, and the albatrosses next, with the procellarids and diving petrels separating later. The earliest fossil albatrosses were found in
Eocene to Oligocene rocks, although some of these are only tentatively assigned to the family and none appear to be particularly close to the living forms. They are
Murunkus (Middle Eocene of
Uzbekistan),
Manu (early Oligocene of
New Zealand), and an undescribed form from the Late Oligocene of
South Carolina. The oldest widely accepted fossil albatross is
Tydea septentrionalis from the early Oligocene of Belgium.
Diomedavus knapptonensis is smaller than all extant albatrosses and was found in late Oligocene strata of Washington State, U.S.
Plotornis was formerly often considered a petrel but is now accepted as an albatross. It is from the Middle
Miocene of
France, a time when the split between the four modern genera was already underway as evidenced by
Phoebastria californica and
Diomedea milleri, both being mid-Miocene species from
Sharktooth Hill,
California. These show that the split between the great albatrosses and the North Pacific albatrosses occurred by 15 Mya. Similar fossil finds in the Southern Hemisphere put the split between the sooties and mollymawks at 10 Mya. The fossil record of the albatrosses in the Northern Hemisphere is more complete than that of the Southern, and many fossil forms of albatross have been found in the North
Atlantic, which today has no albatrosses. The remains of a colony of
short-tailed albatrosses have been uncovered on the island of
Bermuda, and the majority of fossil albatrosses from the North Atlantic have been of the genus
Phoebastria (the North Pacific albatrosses); one,
Phoebastria anglica, has been found in deposits in both
North Carolina and
England. Due to
convergent evolution in particular of the leg and foot bones, remains of the prehistoric
pseudotooth birds (Pelagornithidae) may be mistaken for those of extinct albatrosses;
Manu may be such a case, and quite certainly the supposed giant albatross
femur from the
Early Pleistocene Dainichi Formation at
Kakegawa,
Japan, actually is from one of the last pseudotooth birds.
Aldiomedes angustirostris was a uniquely narrow-beaked species from the Pliocene of New Zealand. == Morphology and flight ==