Pelecaniformes
| Pelecaniformes Fossil range: Late Cretaceous - Recent |
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 Blue-footed Booby
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Anhingidae |
The Pelecaniformes are an order of medium-sized and large waterbirds found worldwide. They are distinguished from other birds by the possession of feet with all four toes webbed (totipalmate). They all have a bare throat patch (gular patch). The nostrils have evolved into dysfunctional slits and unlike other birds, they breathe through their mouths. There are some 50-60 living species, depending on which families are placed in this group.
They feed on fish, squid or similar marine life. Nesting is colonial, but individual birds are monogamous. The young are altricial, hatching from the egg helpless and naked.
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Systematics and evolution
Sibley and Ahlquist's landmark DNA-DNA hybridisation studies (see Sibley-Ahlquist taxonomy) led to them placing the families traditionally contained within the Pelecaniformes together with the grebes, cormorants, ibises and spoonbills, New World vultures, storks, penguins, albatrosses, petrels, and loons together as a sub-group within a greatly expanded order Ciconiiformes, a radical move which by now has been all but rejected: their "Ciconiiformes" merely assembled all early advanced land- and seabirds for which their research technique delivered insufficient phylogenetic resolution.
Recent research strongly suggests that the similarities between the Pelecaniformes as traditionally defined are the result of convergent evolution rather than common descent, and that the group is paraphyletic[1]. All families in the traditional or revised Pelecaniformes except the Phalacrocoracidae have only a few handfuls of species at most, but many were more numerous in the early Neogene. Fossil genera and species are discussed in the respective family or genus accounts; one little-known prehistoric pelecaniforms, however, cannot be classified accurately enough to assign them to a family. This is "Sula" ronzoni from Early Oligocene rocks at Ronzon (France), which was initially believed to be a sea-duck and possibly is an ancestral pelecaniform.
The "pelecaniform" lineages appear to have originated around the end of the Cretaceous. Monophyletic or not, they appear to belong to a close-knit group of "higher waterbirds" which also includes groups such as penguins and Procellariiformes. It is interesting to note that there are quite a lot of fossil bones from around the K–Pg boundary which cannot be firmly placed with any of these orders and rather combine traits of several of them. This is of course only to be expected, if the theory that most if not all of these "higher waterbird" lineages originated around that time is correct. Of those apparently basal taxa, the following show some similarities to the traditional Pelecaniformes:
- Lonchodytes (Lance Creek Late Cretaceous of Wyoming, USA)
- Torotix (Late Cretaceous)
- Tytthostonyx (Late Cretaceous/Early Palaeocene)
- Cladornis (Deseado Early Oligocene of Patagonia, Argentina)
- "Liptornis" - a nomen dubium
The proposed Elopterygidae - supposedly a family of Cretaceous Pelecaniformes - are neither monophyletic nor does Elopteryx appear to be a modern bird[2]. Argilliornis from the Early Eocene of England (London Clay) may be a pelagornithid.
List of Pelecaniformes families
- Fregatidae: frigatebirds. A group of five closely related large birds with black and white plumage, very long wings, and parasitical hunting habits. Red throat patches are inflated in display.
- Pelecanidae: pelicans. Very large birds with throat pouches in which they catch and store fish while hunting.
- Pelagornithidae: pseudotooth birds. A family of gigantic seabirds that looked similar to albatrosses, but had a large bill with tooth-like projections that enabled them to pick up slippery prey like fish or squids more easily.
- Plotopteridae: plotopterids or diving-"boobies". An extinct group of penguin-like seabirds. Possibly link penguins and (some?) pelecaniforms. Depending on how the remaining Pelecaniformes would be split up, the plotopterids might have to be placed in a monotypic order.[3].
The following families are now consider to be part of this group due to recent DNA study. They were all once consider to be closley related to storks.
- Ardeidae: herons and their kin
- Balaenicipitidae: Shoebill stork
- Scopidae: Hammerkop
- Threskiornithidae: Spoonbills and their kin
These birds are long legged, slender birds that hunt (or scavenge) their prey near rivers and lakes.
The following four families can be united as suborder Sulae:
- Sulidae: gannets and boobies. Medium to large species which hunt by diving from the air into the sea (plunge diving). Long wings and bills, often coloured feet.
- Phalacrocoracidae: cormorants and shags. Medium to large with hooked bills and usually black or similar dark plumage. Plumage is not fully waterproof.
- Anhingidae: darters. Another small closely related group of four species, with long bills, snake-like necks and the ability to swim with their body submerged. Plumage is not fully waterproof.
- Protoplotidae: an extinct family which apparently is derived from the same ancestor as the darters, but is very badly known.
Former members
The tropicbirds (Phaethontidae) and their prehistoric relatives, the Prophaethontidae, were traditionally placed in the Pelecaniformes, but molecular and morphological studies indicate they have no close relatives and do not form part of the order. They have been placed in their own order Phaethontiformes. They are medium-sized birds, adapted to a matrine lifestyle similar to frigatebirds. The adults have long central tail feathers, no gular patch and normal nostrils. Hatchlings are covered in down. Apparently closer to Procellariiformes[4]
The shoebill and the hammerkop, which make up the monotypic families (Balaenicipitidae and Scopidae, respectively) usually placed with the traditional Ciconiiformes, may be very distinct pelecaniform lineages instead.
Footnotes
References
- Bourdon, Estelle; Bouya, Baâdi & Iarochene, Mohamed (2005): Earliest African neornithine bird: A new species of Prophaethontidae (Aves) from the Paleocene of Morocco. J. Vertebr. Paleontol. 25(1): 157-170. DOI: 10.1671/0272-4634(2005)025[0157:EANBAN]2.0.CO;2 HTML abstract
- Mayr, Gerald (2003): The phylogenetic affinities of the Shoebill (Balaeniceps rex). Journal für Ornithologie 144(2): 157-175. [English with German abstract] HTML abstract
- Mortimer, Michael (2004): The Theropod Database: Phylogeny of taxa. Retrieved 2008-AUG-14.
External links
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