Pelagornis is a group of ancient birds that no longer exist. These birds were a type of extinct seabird. They lived from the Oligocene to the Early Pleistocene. Pelagornis birds were some of the largest pseudotooth birds. One species, P. sandersi, had the largest wingspan of any bird ever found.
Taxonomy
Four species of pseudotooth birds have been officially named, but other named groups might also belong to the Pelagornis genus. The type species, Pelagornis miocaenus, was found in 23-million-year-old Aquitanian (Early Miocene) sediments in Armagnac, France. The original fossil used to name this species was a left humerus (upper arm bone) nearly as large as a human arm. The name "Pelagornis miocaenus" means "Miocene pelagic bird" and does not reflect the bird's large size. Initially, scientists thought it was related to albatrosses, but later studies placed it in the Pelecaniformes group, either with cormorants and gannets or with other pseudotooth birds in the Odontopterygia suborder.
Pelagornis miocaenus was the first pseudotooth bird species to be scientifically described. Its relative, Pelagornis mauretanicus, was named in 2008 and is slightly different, with remains found in 2.5-million-year-old Gelasian (Late Pliocene/Early Pleistocene) deposits in Morocco.
Many other fossils have been placed in the Pelagornis genus, though they are often not assigned to specific species. These fossils are usually large and from the Miocene period. In the United States, such fossils have been found in the Middle Miocene Calvert Formation of Maryland and Virginia, and the Pungo River Formation in North Carolina. A tarsometatarsus fragment (a foot bone) from South Carolina was assigned to P. miocaenus, as was a slightly smaller tarsometatarsal bone. A broken but mostly complete sternum (breastbone) from Portugal, near the Serravallian-Tortonian boundary (Middle to Late Miocene), is also likely from this genus. Similar fossils have been found in Chile’s Bahía Inglesa Formation and Peru’s Pisco Formation, dating to the Late Miocene to Early Pliocene.
It is unclear whether the South American fossils, which are similar in size and age, belong to one or two species. Some fossils from Oregon and California, as well as material from the North Pacific, have been mistakenly assigned to Pelagornis. These may instead belong to a different species or even to Osteodontornis, another pseudotooth bird. Some older fossils from Chile’s Bahía Inglesa Formation were initially thought to be from Pseudodontornis longirostris, but later studies suggest they might be from Pelagornis. A humerus from New Zealand, found near the Waipara River, is similar to both Osteodontornis orri and P. miocaenus. The Pisco Formation fossils in Peru may be from the same species as those in Chile or a closely related descendant. However, during the Miocene, the Isthmus of Panama had not yet formed, which may explain differences in species between the Atlantic and Pacific regions.
Pelagornis sandersi, a species dating to 25 million years ago in the Oligocene’s Chattian age, was described in 2014. Its only known fossil was discovered in 1983 at Charleston International Airport, South Carolina, by James Malcom during construction. At the time, the area was an ocean, and global temperatures were higher. The fossil was stored at the Charleston Museum until 2010, when paleontologist Daniel T. Ksepka rediscovered it. The bird is named after Albert Sanders, a former museum curator who led the excavation. The fossil remains at the Charleston Museum, where Ksepka identified it as a new species in 2014.
A humerus from the Muséum d'Histoire naturelle de Bordeaux was labeled "Pelagornis Delfortrii 1869." However, this name is not valid and may refer to a different species, Plotornis delfortrii, described in the 1870s. Pseudodontornis is a Paleogene genus of large pseudotooth birds, and its species are often considered synonyms of other, earlier-described groups. The type species, Pseudodontornis longirostris, may belong to Pelagornis, but further study is needed. Similarly, Palaeochenoides mioceanus may also be related to Pelagornis, but comparisons are required.
Few studies have focused on the relationships of Pelagornis, as most pseudotooth bird fossils are rare or poorly preserved. The large Gigantornis eaglesomei from the Middle Eocene Atlantic was based on a damaged sternum and may belong to Dasornis. While Gigantornis and the slightly smaller LHNB (CC-CP)-1 share similarities, they differ in features like the shape of the sternum and the spina externa (a bone near the sternum). Despite these differences, the two fossils are likely closely related.
The family name Pelagornithidae has replaced the older Pseudodontornithidae. Some scientists suggest Pseudodontornis may belong to a separate lineage, which could lead to the revalidation of the family name. However, similarities between Dasornis and Odontopteryx are likely shared traits and not informative about their relationships. It is likely that large pseudotooth birds form a group (clade), and families like Pseudodontornithidae, Cyphornithidae, and Dasornithidae are correctly grouped under Pelagornithidae.
Description
The only known example of P. sandersi has a wingspan estimated to be between approximately 6.06 and 7.38 meters (19.9 and 24.2 feet), making it the largest flying bird discovered so far. This wingspan is twice that of the wandering albatross, which has the largest wingspan of any living bird (up to 3.7 meters (12 feet)). In this regard, P. sandersi replaces the previous record holder, the also extinct Argentavis magnificens. The skeletal wingspan (excluding feathers) of P. sandersi is estimated at 5.2 meters (17 feet), while that of A. magnificens is estimated at 4 meters (13 feet).
Although smaller than P. sandersi, P. chilensis was estimated to weigh between 16 and 29 kilograms (35 to 63 pounds) and have a wingspan of more than 5.2 meters (17 feet), making it one of the largest flying birds.
Fossil evidence shows that P. miocaenus was one of the largest pseudotooth birds, nearly as large as Osteodontornis or the older Dasornis. Its head was likely about 40 centimeters (16 inches) long in life, and its wingspan was probably more than 5 meters (16 feet), possibly as large as 6 meters (20 feet).
Like all members of the Pelagornithidae family, P. sandersi had tooth-like or knob-like structures along the edges of its beak, called "pseudo-teeth." These features would have helped the bird grip and hold slippery prey. According to Ksepka, P. sandersi's "pseudo-teeth" "do not have enamel, they do not grow in sockets, and they are not lost or replaced during the creature’s lifetime." Unlike Osteodontornis, but similar to the older Pseudodontornis, each large "tooth" on Pelagornis was separated by a single smaller one. The salt glands inside the eye sockets of Pelagornis were extremely large and well-developed.
Pelagornis differed from Dasornis and its smaller contemporary Odontopteryx in several ways. It lacked pneumatic foramina in the fossa pneumotricipitalis of the humerus, had a single long attachment site for the latissimus dorsi muscle on the humerus instead of two separate segments, and did not have a prominent ligamentum collaterale ventrale attachment knob on the ulna. Additional differences between Odontopteryx and Pelagornis are found in the tarsometatarsus: in Pelagornis, the first metatarsal bone of the hallux has a deep fossa, while the middle-toe trochlea is not noticeably expanded forward. From the humerus pieces of specimen LACM 127875, found in the Eo-Oligocene Pittsburg Bluff Formation near Mist, Oregon (United States), P. miocaenus differs in an external tuberosity that is not as far toward the shoulder and is separated from the elbow end by a wider depression. The head of the humerus is turned more inward, and the large protuberance there is not as far toward the end. The Waipara River humerus mentioned above agrees with P. miocaenus in this regard. If the Oregon fossils are related to Cyphornis and/or Osteodontornis, and if the traits found in P. miocaenus and the New Zealand specimen are apomorphic, the latter two may indeed be closely related.
Paleobiology
P. sandersi had short, thick legs and likely flew by jumping from cliff edges. This is supported by its discovery near coastal areas. Scientists once debated whether P. sandersi could fly. Earlier, it was believed that flying birds could not have wingspans larger than 5.2 meters (17 feet) because the energy needed to flap wings at that size would exceed the strength of a bird’s muscles. However, this idea assumes birds flap their wings constantly, while P. sandersi probably glided on ocean air currents near the water, which requires less energy. Scientists estimate it could fly at speeds up to 60 km/h (37 mph). Its long wings and gliding ability likely helped it travel far without landing while hunting. Because of its large size, P. sandersi likely lost all its flight feathers at once, like a grebe, since larger feathers take longer to regrow. Scientists believe P. sandersi glided and traveled like a modern albatross, though its closest living relatives are chickens and ducks.
P. sandersi was unlikely to feed by skimming the ocean surface like skimmers (a type of bird in the genus Rynchops) because it could not generate enough energy to pick prey from the water. This raises questions about whether this bird could hunt near the ocean’s surface.
Some scientists were surprised that P. sandersi could fly at all because its weight, between 21.9 and 40.1 kg (48 and 88 lb), would make it too heavy for traditional flight methods. Dan Ksepka, a scientist who discovered fossils of this species, believes P. sandersi could fly due to its small body and long wings, and it likely spent much of its time over the ocean, like an albatross. As of 2014, Ksepka was studying how P. sandersi evolved and what caused the species to become extinct.