| Pelagornis | |
|---|---|
 | |
| Reconstruction of aP. miocaenus skeleton at theNMNH. | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | †Odontopterygiformes |
| Family: | †Pelagornithidae |
| Genus: | †Pelagornis Lartet, 1857 |
| Type species | |
| †Pelagornis miocaenus Lartet, 1857 | |
| Species | |
†P. miocaenusLartet, 1857 | |
| Synonyms | |
seetext | |
Pelagornis is an extinctgenus ofprehistoricpseudotooth birds, a group of extinct seabirds. Species span from theOligocene to theEarly Pleistocene. Members ofPelagornis represent among the largest pseudotooth birds, with one species.P. sandersi, having the widest wingspan of any bird known.
Fourspecies have been formally described, but several other namedtaxa of pseudotooth birds might belong inPelagornis too. Thetype speciesPelagornis miocaenus is known fromAquitanian (Early Miocene) sediments – formerly believed to be ofMiddle Miocene age – ofArmagnac (France). The original specimen on whichP. miocaenus was founded was a lefthumerus almost the size of a human arm. Thescientific name – "the most unimaginative name ever applied to a fossil" in the view ofStorrs L. Olson[1] – does in no way refer to the bird's startling and at that time unprecedented proportions, and merely means "Miocenepelagic bird". Like many pseudotooth birds, it was initially believed to be related to thealbatrosses in the tube-nosedseabirds (Procellariiformes), but subsequently placed in thePelecaniformes where it was either placed in thecormorant andgannetsuborder (Sulae) or united with other pseudotooth birds in a suborder Odontopterygia.[2]
WhileP. miocaenus was the first pseudotooth bird species to be described scientifically, itscongenerPelagornis mauretanicus was only named in 2008. It was a slightly distinct and markedly younger species. Its remains have been found in 2.5 MaGelasian (Late Pliocene/Early Pleistocene,MN17) deposits atAhl al Oughlam (Morocco).[3]
Additionalfossils are placed inPelagornis, usually without assignment to species, mainly due to their large size and Miocene age. From the United States, such specimens have been found in the Middle MioceneCalvert Formation ofMaryland andVirginia, and the contemporaryPungo River Formation of theLee Creek Mine inNorth Carolina (though at least one other pelagornithid is probably represented among this material too).USNM 244174 (atarsometatarsus fragment) was found nearCharleston, South Carolina and assigned toP. miocaenus, and the slightly smaller left tarsometatarsal middletrochlea USNM 476044 might also belong here. A broken but fairly completesternum probably of this genus, specimenLHNB (CC-CP)-1, is known from theSerravallian-Tortonian boundary (Middle toLate Miocene) nearCosta da Caparica inPortugal. Contemporary are certain specimens[4] from theBahía Inglesa Formation ofChile, while other material from this formation[5] as well as remains from thePisco Formation of Peru are from the Late Miocene toEarly Pliocene.[6]
It is not clear whether theSouth American fossils – of similar size and age and not including directly comparable bones – are from one or two species. A very worn sternum and some other remains from the Miocene ofOregon as well as roughly contemporary material fromCalifornia are sometimes assigned toPelagornis, but this appears to be an error; if not of the contemporaryNorth PacificOsteodontornis, the specimen is better regarded as indeterminable. Given the distance in space and time involved, allPacific material may well have been a species different fromP. miocaenus or even from birds closer toOsteodontornis. Indeed, some of the older Bahía Inglesa Formation remains[7] tentatively referred toPelagornis were at first assigned to the mysteriousPseudodontornis longirostris in error, and aproximal (initially misidentified asdistal) humerus piece (CMNZ AV 24,960), from theWaiauan (Middle-Late Miocene) cliffs near the mouth of theWaipara River (North Canterbury, New Zealand) seems to differ little from eitherO. orri orP. miocaenus. The Pisco Formation specimens – which may be from the same species as the Bahía Inglesa ones, or from its direct descendant – on the other hand seem to be well distinct fromOsteodontornis. It must be remembered, however, that theIsthmus of Panama had not been formed yet during the Miocene.[8]
Pelagornis sandersi was described in July 2014, whose fossil remains date from 25 million years ago, during theChattian age of theOligocene.[9][10] The only known fossil ofP. sandersi was first uncovered in 1983 atCharleston International Airport,South Carolina, discovered by James Malcom, while working construction building a new terminal there. At the time the bird lived, 25 million years ago, global temperatures were higher, and the area where it was discovered was an ocean.[11][12] After excavation, the fossil ofP. sandersi was catalogued and put in storage at theCharleston Museum, where it remained until it was rediscovered bypaleontologist Dan Ksepka in 2010.[13][14] The bird is named after Albert Sanders, the former curator of natural history at the Charleston Museum, who led the excavation ofP. sandersi.[15] It currently sits at the Charleston Museum, where it was identified as a new species by Ksepka in 2014.[10]
A humerus from theMuséum d'Histoire naturelle de Bordeaux was labelled "Pelagornis Delfortrii 1869". Though the name from the label had been listed in thesynonymy ofP. miocaenus, neither does it seem to be a validly establishedtaxon nor was the specimen compared withP. miocaenus remains. It seems to refer to one of thesyntypes of the procellariiformPlotornis delfortrii – found atLéognan (France) and also of Aquitanian age – from which that species was described in the 1870s byAlphonse Milne-Edwards: when thenomen nudum "Pelagornis delfortrii" is listed in the synonymy ofP. miocaenus, the pseudotooth bird is claimed to be known from the Léognan deposits also, whereas it has not actually been found there.Pseudodontornis, meanwhile, is a generallyPaleogene genus of huge pseudotooth birds. All its species are not uncommonly consideredsynonymous with earlier-described taxa. The (probably)Eo-Oligocenetype speciesPseudodontornis longirostris might belong inPelagornis, though given its uncertain age and provenance a comparison with undisputedPelagornis material – which is currently lacking – would seem to be necessary before such a step is taken. In that respect,Palaeochenoides mioceanus was also hypothesized to includeP. longirostris, and would need to be compared withPelagornis to see whether it does not belong here too.[16]
There has been little dedicated study of the relationships ofPelagornis, for while quite a lot of remains are known from the present genus, those of most other pseudotooth birds are few and far between and direct comparisons are further hampered by the damaged state of most remains. The largeGigantornis eaglesomei from theMiddle Eocene Atlantic was established based on a broken but not too incompletesternum and might actually belong inDasornis. InGigantornis thearticular facet for thefurcula consists of a flat section at the very tip of thesternal keel and a similar one set immediately above it at an outward angle, and thespina externa is shaped like anOld French shield in cross-section. The slightly smaller LHNB (CC-CP)-1 has a less sharply protruding sternal keel, the articular facet for the furcula consists of a large knob at the forward margin, and the spina externa is narrow in cross-section. While these differences are quite conspicuous, the two fossils are clearly of closely related hugedynamically soaringseabirds, and considering the 30 million years or so that separateGigantornis and LHNB (CC-CP)-1, the Paleogene taxon may be very close to the Miocene bird's ancestor nonwithstanding their differences.[17]
In any case, thefamily name of the pseudotooth birds, Pelagornithidae, as thesenior synonym has widely replaced the once-commonly used Pseudodontornithidae. It may be thatPseudodontornis belongs to a distinct lineage of these birds, and then the family name would perhaps be revalidated. Also, the presumed similarity betweenDasornis[18] and the smallerOdontopteryx seems to be asymplesiomorphy that is not informative regarding their relationships to each other and withPelagornis. Rather, it is likely that the huge pseudotooth birds form aclade, and in this case, Pseudodontornithidae like Cyphornithidae and Dasornithidae is correctly placed in the synonymy of Pelagornithidae even if several families were accepted in the Odontopterygiformes.[19]
The sole specimen ofP. sandersi has awingspan estimated between approximately 6.06 and 7.38 m (19.9 and 24.2 ft),[9] giving it the largest wingspan of any flying bird yet discovered, twice that of thewandering albatross, which has the largest wingspan of any extant bird (up to 3.7 m (12 ft)).[20] In this regard, it supplants the previous record holder, the also extinctArgentavis magnificens. The skeletal wingspan (excluding feathers) ofP. sandersi is estimated at 5.2 m (17 ft) while that ofA. magnificens is estimated at 4 m (13 ft).[15][21]
Thefossil specimens show thatP. miocaenus was one of the largest pseudotooth birds, hardly smaller in size thanOsteodontornis or the olderDasornis. Its head must have been about 40 cm (16 in) long in life, and its wingspan was probably more than 5 m (16 ft), perhaps closer to 6 metres (20 ft).
Like all members of thePelagornithidae,P. sandersi had tooth-like or knob-like extensions of the bill's margin, called "pseudo-teeth," which would have enabled the living animal to better grip and grasp slippery prey. According to Ksepka,P. sandersi's teeth "don’t have enamel, they don’t grow in sockets, and they aren’t lost and replaced throughout the creature’s life span."[11] Unlike in its contemporaryOsteodontornis but like in the olderPseudodontornis, between each two ofPelagornis's large "teeth" was a single smaller one. Thesalt glands inside theeye sockets were extremely large and well-developed inPelagornis.
Pelagornis differed fromDasornis and its smaller contemporaryOdontopteryx in having nopneumatic foramen in thefossa pneumotricipitalis of thehumerus, a single longlatissimus dorsi muscle attachment site on the humerus instead of two distinct segments, and no prominentligamentum collaterale ventrale attachment knob on theulna. Further differences betweenOdontopteryx andPelagornis are found in thetarsometatarsus: in the latter, it has a deepfossa of thehallux'first metatarsal bone, whereas its middle-toetrochlea is not conspicuously expanded forward. From the humerus pieces of specimenLACM 127875, found in theEo-OligocenePittsburg Bluff Formation nearMist, Oregon (United States),P. miocaenus differs in anexternal tuberosity that is not as much extended towards shoulder and that is separated from theelbow end by a wider depression. The head of the humerus is turned more to the inward side and the large protuberance found there is not as far towards the end. The Waipara River humerus mentioned above agrees withP. miocaenus in that respect. If the Oregon fossils are related toCyphornis and/orOsteodontornis, and if the traits as found inP. miocaenus and the New Zealand specimen areapomorphic, the latter two may indeed be very close relatives.[22]
P. sandersi had short, stumpy legs, and was probably only able to fly by hopping off cliff edges.[21] This is supported by its location being near coasts. Originally, there were controversies over whether or notP. sandersi would be able to fly. Previously, the assumed maximum wingspan of a flying bird was 5.2 m (17 ft), because it was hypothesized that above 5.2 m, the power required to keep the bird in flight would surpass the power capacity of the bird's muscles. However, this calculation is based on the assumption that the bird in question stays aloft by repeatedly flapping its wings, whereasP. sandersi more likely glided on ocean air currents close to the water, which is less power-intensive than reaching high altitudes.[14][23] It has been estimated that it was able to fly at up to 60 km/h (37 mph).[21]P. sandersi's long wingspan and gliding power would have enabled it to travel long distances without landing while hunting.[12] Due toP. sandersi's size, the bird likelymolted all of itsflight feathers at once, similarly to agrebe, since larger feathers take longer to regrow.[12]P. sandersi is theorized to have glided and traveled similarly to a modern albatross, however, according to Dan Ksepka, its closest modern relatives are chickens and ducks.[13]
Some scientists expressed surprise at the idea that this species could fly at all, given that, at between 22 and 40 kg (48 and 88 lb), it would be considered too heavy by the predominant theory of the mechanism by which birds fly.[24] Dan Ksepka of theNational Evolutionary Synthesis Center inDurham, North Carolina, who identified that the discovered fossils belonged to a new species, thinks it was able to fly in part because of its relatively small body and long wings,[25] and it spent much of its time over the ocean, like the albatross.[11] Ksepka is currently focused on solving howP. sandersi evolved and what caused the species to go extinct.[13]
Fossils ofPelagornis have been found in:[26]
.jpg)
