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The Pelagornithidae, commonly called pelagornithids, pseudodontorns, bony-toothed birds, false-toothed birds or pseudotooth birds, are a prehistoric family of large . Their fossil remains have been found all over the world in rocks dating between the Early Paleocene and the Pliocene-Pleistocene boundary.Bourdon (2005), Mayr, G. (2008), Boessenecker and Smith (2011)Gerald Mayr, G. et al.. (2019) Oldest, smallest and phylogenetically most basal pelagornithid, from the early Paleocene of New Zealand, sheds light on the evolutionary history of the largest flying birds.
Most of the common names refer to these bird most notable trait: tooth-like points on their beak edges, which, unlike true teeth, contained Volkmann's canals and were outgrowths of the and mandible bones. Even "small" species of pseudotooth birds were the size of ; the largest ones had estimated at 5–6 metres (15–20 ft) and were among the largest flying birds ever to live. They were the dominant seabirds of most oceans throughout most of the Cenozoic, and modern apparently missed encountering them only by a tiny measure of time: the last known pelagornithids were contemporaries of Homo habilis and the beginning of the history of technology.Hopson (1964), Olson (1985: pp. 199–201), Bourdon (2005), Geraads (2006), Mayr (2009: pp. 55,59), Mlíkovský (2009)
The Pelagornithidae had extremely thin-walled bones widely pneumatized with the air sac extensions of the bird lung. Most limb bone fossils are very much crushed for that reason. In life, the thin bones and extensive pneumatization enabled the birds to achieve large size while remaining below critical . Though 25 kg/m2 (5 lb/ft2) is regarded as the maximum wing loading for powered bird flight, there is evidence that bony-toothed birds used dynamic soaring flight almost exclusively: the proximal end of the humerus had an elongated diagonal shape that could hardly have allowed for the movement necessary for the typical flapping flight of birds; their weight thus cannot be easily estimated. The attachment positions for the muscles responsible for holding the upper arm straightly outstretched were particularly well-developed, and altogether the anatomy seems to allow for an ability of holding the wings rigidly at the glenoid joint unmatched by any other known bird. This is especially prominent in the Neogene pelagornithids, and less developed in the older Paleogene forms. The sternum had the deep and short shape typical of dynamic soarers, and bony outgrowths at the sternal keel's forward margin securely anchored the furcula.Meunier (1951), Hopson (1964), Olson (1985: p. 200) Mayr (2008, 2009: p. 58) The legs were proportionally short, the feet probably webbed and the hallux was vestigial or entirely absent; the tarsometatarsi (anklebones) resembled those of while the arrangement of the front toes was more like in . Typical for pseudotooth birds was a second toe that attached a bit kneewards from the others and was noticeably angled outwards. The "teeth" were probably covered by the rhamphotheca in life, and there are two furrows running along the underside of the upper beak just inside the ridges which bore the "teeth". Thus, when the bill was closed only the upper jaw's "teeth" were visible, with the lower ones hidden behind them. Inside the of at least some pseudotooth birds – perhaps only in the younger species – were well-developed .Woodward (1909): pp. 86–87, Hopson (1964), Olson (1985: p. 142), Bourdon (2005), Mayr (2009: p. 58), Mayr et al. (2008)
Altogether, almost no major body part of pelagornithids is known from a well-preserved associated fossil and most well-preserved material consists of single bones only; on the other hand the long occurrence and large size makes for a few rather comprehensive (though much crushed and distorted) remains of individual birds that were entombed by as they lay dead, complete with some fossilized . Large parts of the skull and some beak pieces are found not too infrequently. In February 2009, an almost-complete fossilized skull of a presumed Odontopteryx from around the Chasicoan-Huayquerian boundary c. 9 million years ago (Ma) was unveiled in Lima. It had been found a few months earlier in Ocucaje District of Ica Province, Peru. According to paleontologist Mario Urbina, who discovered the specimen, and his colleagues Rodolfo Salas, Ken Campbell and Daniel T. Ksepka, the Ocucaje skull is the best-preserved pelagornithid cranium known as of 2009.Olson (1985: pp. 194–195), Mayr (2008), GG 2009
Thus, direct competition for food between bony-toothed birds and cetaceans or pinnipeds cannot have been very severe. As both the birds and pinnipeds would need level ground near the sea to raise their young, competition for breeding grounds may have affected the birds' population. In that respect, the specializations for dynamic soaring restricted the number of possible nesting sites for the birds, but on the other hand upland on islands or in coastal ranges could have provided breeding grounds for Pelagornithidae that was inaccessible for pinnipeds; just as many today nest in the uplands of islands (e.g. the Galápagos or Torishima). The bony-toothed birds probably required strong for takeoff and would have preferred higher sites anyway for this reason, rendering competition with pinniped rookeries quite minimal. As regards breeding grounds, giant eggshell fragments from the Famara mountains on Lanzarote, , were tentatively attributed to Late Miocene pseudotooth birds. As regards the Ypresian London Clay of the Isle of Sheppey, wherein pelagornithid fossils are not infrequently found, it was deposited in a shallow epicontinental sea during a very hot time with high . The presumed breeding sites cannot have been as far offshore as many seabird rookeries are today, as the region was hemmed in between the Alps and the Grampian and Scandinavian Mountains, in a sea less wide than the Caribbean is today.
Neogene pseudotooth birds are common along the Americas coasts near the Appalachian and mountains, and these species thus presumably also bred not far offshore or even in the mountains themselves. In that respect the presence of medullary bone in the specimens from Lee Creek Mine in North Carolina, United States, is notable, as among birds this is generally only found in laying females, indicating that the breeding grounds were probably not far away. At least Pacific islands of volcanic island would be erosion away in the last millions of years however, obliterating any remains of pelagornithid breeding colonies that might have once existed in the open ocean. Necker Island for example was of significant size 10 million years ago, when Osteodontornis roamed the Pacific.Olson (1985: pp.195–199), del Hoyo et al. (1992), Olson & Rasmussen (2001), Price & Clague (2002), Mlíkovský (2002: pp.81–83, 2003), Rincón R. & Stucchi (2003), Sluijs et al. (2006), Mayr (2009: pp. 6,56) There is no obvious single reason for the pseudotooth birds' extinction. A scenario of general ecological change – exacerbated by the beginning ice age and changes in due to plate tectonic shifts (e.g. the emergence of the Antarctic circumpolar current or the closing of the Isthmus of Panama) – is more likely, with the pseudotooth birds as remnants of the world's Paleogene fauna ultimately failing to adaptation. In that respect it may be significant that some lineages of cetaceans, like the primitive dolphins of the Kentriodontidae or the Squalodon, flourished contemporary with the Pelagornithidae and became extinct at about the same time. Also, the modern diversity of pinniped and cetacean genera evolved largely around the Mio-Pliocene boundary, suggesting that many emerged or became vacant. In addition, whatever caused the Middle Miocene disruption and the Messinian Salinity Crisis did affect the trophic web of Earth's oceans not insignificantly either, and the latter event led to a widespread extinction of seabirds. Together, this combination of factors led to Neogene animals finally replacing the last remnants of the Paleogene fauna in the Pliocene. In that respect, it is conspicuous that the older pseudotooth birds are typically found in the same deposits as plotopterids and , while younger forms were sympatric with , albatrosses, penguins and Procellariidae – which, however, underwent an adaptive radiation of considerable extent coincident (and probably caused by) with the final demise of the Paleogene-type trophic web. Although the fossil record is necessarily incomplete, as it seems and were very rarely found in association with the Pelagornithidae.Warheit (1992, 2001), Olson & Rasmussen (2001), Geraads (2006), Chávez et al. (2007), Mayr (2009: pp. 217–218), GG 2009, Mlíkovský (2009)
Irrespective of the cause of their ultimate extinction, during the long time of their existence the pseudotooth birds furnished prey for large predators themselves. Few if any birds that coexisted with them were large enough to harm them while airborne; as evidenced by the Early Eocene Limnofregata, the coevolved with the Pelagornithidae and may well have harassed any of the small species for food on occasion, as they today harass albatrosses. From the Middle Miocene or Early Pliocene of the Lee Creek Mine, some remains of pseudotooth birds which probably fell victim to while feeding are known. The large members of the abundant Lee Creek Mine shark fauna that hunted near the water's surface included the broadnose sevengill shark ( Notorynchus cepedianus), Carcharias sand tiger sharks, Isurus and Cosmopolitodus , Carcharodon white sharks,The huge megalodon shark ( Carcharocles megalodon) would probably have found even the largest pseudotooth bird to be not worth the effort of hunting. the snaggletooth shark Hemipristis serra, ( Galeocerdo), Carcharhinus whaler sharks, the lemon shark ( Negaprion brevirostris) and ( Sphyrna), and perhaps (depending on the bird fossils' age) also Pristis sawfishes, Odontaspis sand tiger sharks, and Lamna and Parotodus mackerel sharks. It is notable that fossils of smaller diving birds – for example auks, and – as well as those of albatrosses are much more commonly found in those shark pellets than pseudotooth birds, supporting the assumption that the latter had quite low population densities and caught much of their food in mid-flight.Olson & Rasmussen (2001), Purdy et al. (2001)
A study on Pelagornis' flight performance suggests that, unlike modern seabirds, it relied on thermal soaring much like continental soaring birds and Pteranodon.
If the pseudotooth birds are Galloanseres, phaeomelanins might be more likely to have occurred in their feathers, but it is notable that the most basal lineages of Anseriformes are typically grey-and-black or black-and-white. Among ocean-going birds in general, the upperside tends to be much darker than the underside (including the underwings) – though some are dark grey all over, a combination of more or less dark grey upperside and white underside and (usually) head is a widespread colouration found in and may either be for "higher waterbirds" or, perhaps more likely, be an adaptation to provide crypsis, in particular against being silhouetted against the sky if seen by prey in the sea. It is notable that at least the primary remiges, and often the other too, are typically black in birds – even if the entire remaining plumage is completely white, as in some or in the Bali starling ( Leucopsar rothschildi). This is due to the fact that will , making all-black feathers very robust; as the largest encountered by bird feathers affect the flight feathers, the large amount of melanin gives them better resistance against being damaged in flight. In soaring birds as dependent on strong winds as the bony-toothed birds were, black wingtips and perhaps tailsShort-tailed waterfowl and "higher waterbirds" often have light or white tails: del Hoyo et al. (1992) can be expected to have been present.
As regards the bare parts, all the presumed close relatives of the Pelagornithidae quite often have rather bright reddish colours, in particular on the beak. The phylogenetic uncertainties surrounding them do not allow to infer whether the bony-toothed birds had a throat sac similar to pelicans. If they did, it was probably red or orange, and may have been used in . Sexual dimorphism was probably almost nonexistent, as it typically is among the basal Anseriformes and the "higher waterbirds".
Historically, the disparate bones of the pseudotooth birds were spread across six groups: a number of genera described from leg bones was placed in a family Cyphornithidae, and considered close allies of the pelican family (Pelecanidae). They were united with the latter in a Taxonomic rank Pelecanides in suborder Pelecanae, or later on (after the endings of were fixed to today's standard) Pelecanoidea in suborder Pelecani. Subsequently, some allied them with the entirely spurious "family" "Cladornithidae" in a "pelecaniform" suborder "Cladornithes". Those genera known from skull material were typically assigned to one or two families ( Odontopterygidae and sometimes also Pseudodontornithidae) in a "pelecaniform" suborder Odontopteryges or Odontopterygia. Pelagornis meanwhile, described from wing bones, was traditionally placed in a monotypic "pelecaniform" family Pelagornithidae. This was often assigned either to the gannet and cormorant suborder Sulae (which was formerly treated as superfamily Sulides in suborder Pelecanae), or to the Odontopterygia. The sternum of Gigantornis was placed in the albatross family (Diomedeidae) in the order of tube-nosed seabirds (Procellariiformes).Lanham (1947), Wetmore (1956: pp. 12–14), Brodkorb (1963: pp. 241,262–264), Hopson (1964), Olson (1985: pp. 195–199), Mlíkovský (2002: p. 81), Mayr (2009: p. 59)
The most extensive taxonomic and systematics confusion affected Dasornis. That genus was established based on a huge skull piece, which for long was placed in the Gastornithidae merely due to its size. Argillornis – nowadays recognized to belong in Dasornis – was described from wing bones, and generally included in the Sulae as part of the "Elopterygidae" – yet another invalid "family", and its type genus is generally not considered a modern-type bird by current authors. Some additional tarsometatarsus (ankle) bone fragments were placed in the genus Neptuniavis and assigned to the Procellariidae in the Procellariiformes. All these remains were only shown to belong in the pseudotooth bird genus Dasornis in 2008.Lanham (1947), Brodkorb (1963: pp. 248–249, 1967: p. 141-143), Olson (1985: p. 195), Mlíkovský (2002: pp. 78,81–83), Mayr (2008, 2009: p. 59)
The most basal known pelagornithid is Protodontopteryx.
In 2005, a cladistic analysis proposed a close relationship between pseudotooth birds and waterfowl (Anseriformes). These are not part of the "higher waterbirds" but of the Galloanserae, a basal lineage of neognath birds. Some features, mainly of the skull, support this hypothesis. For example, the pelagornithids lack a crest on the underside of the palatine bone, while the Neoaves – the sister clade of the Galloanserae which includes the "higher waterbirds" and the "higher landbirds" – have such a crest. Also, like ducks, geese and swans pelagornithids only have two and not three condyles on the Mandible process of the quadrate bone, with the middle condyle beakwards of the side condyle. Their basipterygoid articulation is similar to that of the Galloanseres. At the side of the parasphenoid , there is a wide platform as in Anseriformes. The bony-toothed birds' attachment of the coronoideal part of the external mandible adductor was located at the midline, the rostropterygoid process had a support at its base and the mesethmoid bone had a deep depression for the caudal concha, just as in waterfowl.Bourdon (2005), Mayr (2008), Mayr (2009: p. 59)
As regards other parts of the skeleton, the proposed of pelagornithids and waterfowl are found mainly in the arm- and handbones: the ulna had a strongly upper backside at its elbow end – at the handward end of which the scapulotricipital muscles attached –, a point-tipped dorsal cotyle and only a shallow depression to house the meniscus between ulna and radius; towards the elbow, the intercondylar sulcus of the ulna becomes wide and is bordered by a long winding ridge on the belly side. The radius, meanwhile, has a convex ventral border to the humeral cotyle, which prominently continues the hind edge of the knob where the biceps brachii muscle attaches; towards the upper side of the radius bone the surface becomes flat and triangular handwards of the articular surface for the ulna. The carpometacarpus of both Anseriformes and pseudotooth birds has a prominent pisiform process, which extends from the carpal Tarsometatarsus far fingerwards along the bone's forward side. On the carpometacarpus' underside, there is a long but narrow symphysis of the distal , with the large metacarpal bone having a mid-ridge that at its outer end curves tailwards, and the thumb joint has a well-developed knob on the hind side of its articular surface. The leg and foot bones, as is to be expected from birds not as specialized for swimming as waterfowl are, show less similarities between Anseriformes and pseudotooth birds: on the tibiotarsus there is a wide incision between the condyles and the middle condyle is narrower than the side condyle and protrudes forwards; the tarsometatarsus has a low distal Vascular tissue with recessed opening on its plantar surface and a middle toe trochlea that is elongated, slightly oblique, projects to the underside of the foot and is pointed at the tip.Bourdon (2005)
It is unclear what to make of these supposedly uniting Anseriformes and bony-toothed birds, for on the other hand, the sternum, distal humerus, leg and foot bones of pelagornithids seem to show apomorphies typical of "higher waterbirds". While details of the braincase bones are held to be very informative , the skull features in which the two groups are similar are generally related to the point where the bill attaches to the skull, and thus might have been subject to the selective forces brought about by skimming food from the upper water layer. The apparent non-neoavian traits distinguishing pelagornithids could just as well be retained or atavistic ; as the "higher waterbirds" are very ancient Neoaves and none of the suspected basal members of their radiation (see also "Graculavidae") were included in the analysis, it is not known for sure when the derived conditions typical of modern Neoaves were acquired. Footbone traits are notoriously prone to selection forces in birds, with convergent evolution known to inhibit or even invalidate cladistic analyses; however, the apparent autapomorphies of the lower arm and hand bones are hard to explain by anything else than an actual relationship. The location of the inside the of Osteodontornis, Pelagornis (and probably others) shows that whatever their relationships were, the pelagornithids adaptation to an oceanic habitat independently from penguins and tubenoses, which instead have supraorbital salt glands. Their missing or vestigial hallux – like in ducks but unlike in pelicans which have all four toes fully developed and webbed – was held against a close relationship with pelicans. But as is known today, pelicans are closer to storks (which have a hallux but no webbing) than to pseudotooth birds and evolved their fully webbed toes independently. With both a webbed and a hypotrophied hallux being and paraphyletic, its absence in pseudotooth birds does not provide much information on their relationship.Wetmore (1917), Hopson (1964), Olson (1985: pp. 199–200), González-Barba et al. (2002), Bourdon (2005), Christidis & Boles (2008: pp.100,105), Mayr (2008, 2009: p. 59), Mayr et al. (2008), TZ 2009
While giant Galloanserae were common and diverse in the Paleogene in particular, these ( Gastornis and ) were flightless terrestrial birds; it is perhaps significant though that the only other "bone-toothed" birds known so far are the two species of the moa-nalo genus Thambetochen, extinct giant flightless from the Hawaiian Islands. In any case, the 2005 cladistic analysis uses a representative sample of Procellariiformes and recovers them as strongly supported clade in agreement with the current consensus. The presumed close relationship between bony-toothed birds and tubenoses can thus be disregarded after all. As regards "Pelecaniformes", the analysis does not recover the correct phylogeny and does not include the shoebill ( Balaeniceps rex, a "missing link" between pelicans and storks) either; clearly, the adaptive radiation of the pelican-stork lineage is misleading the analysis here. In addition, the Galloanserae are not recovered as monophyletic. In 2007, a far more comprehensive cladistic analysis of bird anatomy including some fossil forms (though not the crucialIn particular the enigmatic Laornis edvardsianus: Mayr (2009: p. 21) Late Cretaceous taxa, which are usually known only from fragmentary remains) resolved the "higher waterbird" radiation somewhat better; still, the problem of leg and foot traits confounding the analysis was noticeable.Bourdon (2005), Livezey & Zusi (2007), Mayr (2009: p. 59)
As their relationships are still unresolved between Galloanserae and "higher waterbirds", the pseudotooth birds are here placed in the distinct order Odontopterygiformes as a compromise, rather than in a pelecaniform/ciconiiform or anseriform suborder Odontopterygia or even a family of the Anseriformes, Ciconiiformes or Pelecaniformes. Such a treatment is unlikely to be completely wrong in either case, as the pseudotooth birds are well distinct from the Presbyornithidae and Scopidae, today generally regarded as the very basal divergences of, respectively, the Anseriformes and the pelican-stork group. It also provides leeway should the proposed separation of the Pelagornithidae into several families turn out to be appropriate. It is perhaps notable that when Boris Spulski established the Odontopterygia in 1910, he did this partly because he noted some of the similarities between pseudotooth birds and waterfowl listed above. Dasornis was long mistaken for a Gastornithidae, now strongly suspected to be very close indeed to the Anseriformes. Also, the pelagornithid Palaeochenoides mioceanus was initially mistaken for an anseriform, and the same might hold true for the supposed Oligocene swan Guguschia nailiae. In the former case, however, a "much the more convincing"Stone (1918) analysis for a placement outside the Galloanseres was published the year after its description already. Most unrecognised pelagornithid bones were initially assigned to "higher waterbird" families however, typically to the (then-paraphyletic) "Pelecaniformes", but in particular the tarsometatarsus was typically mistaken for that of a procellariiform. The Odontopterygiformes were first proposed when Osteodontornis was described from the first – and still the only known – reasonably complete skeleton of one of these birds. Hildegarde Howard found that, no matter that some of its features resembled other birds, the combination was quite unlike any neognath known.Howard (1957), Hopson (1964), Brodkorb (1967: p. 142), Wetmore (1917), Bourdon (2005), Mayr (2008, 2009), Mayr et al. (2008), TZ 2009
While the authors claim it is beyond the paper's scope, the study describing Protodontopteryx suggests that the proposed pro-galloansere traits might actually be plesiomorphic in relation to Aves. It also notes "striking" similarities between pelagornithids and Ichthyornis in terms of jaw anatomy, but still classifies them as neognaths due to the well-developed hypotarsal crests, a supratendineal bridge on the distal tibiotarsus and the caudally closed ilioischiadic foramen. The actual phylogenetic tree depicts them in a polytomy with both Galloanserae and Neoaves.
It has been suggested at times that the "teeth" of pelagornithids were homologous with true teeth on an at least molecular level, being derived from the same programs responsible for the formation of teeth in other dinosaurs. This might have an importance to their actual phylogenetic position.
A 2022 paper described Janavis, an ichthyornithine (advanced stem-bird) with a pterygoid bone similar to that of galloanserans. This implies that a galloanseran-like pterygoid is ancestral for crown-group birds as a whole, rather than a derived feature of neognaths. The authors noted that among the groups often regarded as galloanserans based on their pterygoid morphology (pelagornithids, and ), some might instead constitute early-diverging crown-birds outside Galloanserae, or even be outside the avian crown group altogether.
Tentatively, the following genera are recognized:Olson (1985: pp.195–199), Mlíkovský (2002: pp. 81–84), Mayr (2009: pp. 55–59)
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