The Pelagornithidae, also known as pelagornithids, pseudodontorns, bony-toothed birds, false-toothed birds, or pseudotooth birds, were a group of large seabirds that lived long ago. Fossil remains of these birds have been discovered in many parts of the world. These fossils are found in rocks that are between 66 million years old (from the Early Paleocene) and about 2.6 million years old (up to the Pliocene-Pleistocene boundary).
Most of their common names describe their most noticeable feature: small, tooth-like points along the edges of their beaks. These points were not true teeth but had structures called Volkmann’s canals and were part of the upper and lower jaw bones. Even the smaller species of pseudotooth birds were about the size of albatrosses. The largest species had wingspans estimated at 5 to 6 meters (15 to 20 feet), making them some of the largest flying birds in history.
These birds were the main seabirds in most oceans during much of the Cenozoic era. The last known pelagornithids lived at the same time as early humans, such as Homo habilis, and during the early stages of human technology.
Description and ecology
The largest pseudotooth birds were the biggest flying birds known. Most remains from the Neogene period are very large, but in the Paleogene, some pelagornithids were about the size of a great albatross (genus Diomedea) or slightly smaller. A species named "Odontoptila inexpectata," found near the Paleocene-Eocene boundary in Morocco, is the smallest pseudotooth bird discovered so far. It was only slightly larger than a white-chinned petrel (Procellaria aequinoctialis).
Pelagornithidae had bones that were very thin and filled with air sacs from their lungs. Most limb bone fossils are crushed because of this. In life, these features helped the birds grow large without exceeding the maximum weight their wings could support. While 25 kg/m² (5 lb/ft²) is the highest weight wings can handle for powered flight, evidence suggests these birds used dynamic soaring, a flight style that requires little flapping. Their humerus bones had a shape that made typical flapping unlikely. Muscles for holding wings straight were well-developed, and their anatomy allowed them to keep wings rigid at the glenoid joint better than any other bird. This feature was most common in Neogene pelagornithids and less so in older Paleogene species. Their sternum had a deep, short shape typical of dynamic soarers, and bony growths on the keel helped anchor the furcula.
Their legs were short, their feet likely webbed, and their hallux (big toe) was small or missing. Their anklebones resembled those of albatrosses, but their front toes were arranged more like those of fulmars. A second toe on their feet was positioned slightly toward the knee and angled outward. Their "teeth" were probably covered by the rhamphotheca (a hard outer layer of the beak). Two furrows ran along the underside of the upper bill, just inside the ridges that held the "teeth." When their beaks were closed, only the upper jaw's "teeth" were visible, with the lower ones hidden. Some pseudotooth birds had well-developed salt glands in their eye sockets, possibly only in younger species.
Most pelagornithid fossils are single bones, and few complete remains are known. However, some fossils show entire birds, including feathers, that were buried where they died. Skulls and beak parts are found more often. In February 2009, a nearly complete skull of a presumed Odontopteryx from about 9 million years ago was discovered in Peru. Paleontologist Mario Urbina and his team called it the best-preserved pelagornithid skull known at the time.
Unlike the sharp teeth of Mesozoic birds like Archaeopteryx, pseudoteeth were not serrated and were used to hold prey for swallowing, not tearing. Since these teeth were hollow or filled with soft bone, they likely broke easily in life. Their prey probably included soft-bodied animals like cephalopods and soft-skinned fish. Though some reconstructions show them diving like gannets, their fragile bones suggest this was unlikely. Instead, they likely caught prey near the ocean surface while flying or swimming, submerging only their beaks. Their jaw structure allowed them to open their beaks wide, similar to pelicans. Pelagornithids filled an ecological role similar to large fish-eating pterosaurs, which went extinct at the end of the Cretaceous. Like pterosaurs and modern albatrosses, they may have used ocean currents to travel long distances, returning to breed only every few years. Unlike today’s albatrosses, which avoid tropical regions, pelagornithids lived in many climates, with fossils found from Belgium to the Antarctic. They often shared habitats with penguins and plotopterids, suggesting they gathered in upwelling areas for feeding or breeding.
Some claim that the rise of whales and seals outcompeted pseudotooth birds, but this is unlikely for pelagornithids. They thrived for 10 million years after baleen whales evolved and coexisted with early whales and seals in the Miocene. Unlike seals, which live near shore, pseudotooth birds roamed the open ocean. All three groups (pelagornithids, whales, and seals) had low population densities and may have competed for nesting areas. However, pseudotooth birds likely nested on high ground, such as islands or coastal mountains, which were inaccessible to seals. This may have reduced competition for breeding sites. Their need for strong updrafts to take off also favored higher nesting locations, further limiting overlap with seals.
Taxonomy, systematics and evolution
The name "pseudodontorns" refers to the genus Pseudodontornis, which was once the family's namesake. However, the name Pelagornithidae was used earlier than Pseudodontornithidae, and modern scientists now prefer "pelagornithids" over "pseudodontorns." The term "pseudodontorns" is more commonly found in writings from the mid-20th century.
Historically, the bones of pseudotooth birds were divided into six groups. Some leg bones were placed in a family called Cyphornithidae, which was considered closely related to pelicans (Pelecanidae). These groups were later grouped together in a larger category called Pelecanides in the suborder Pelecanae, or later Pelecanoidea in the suborder Pelecani. Some scientists later grouped them with a made-up family called Cladornithidae in a category called Cladornithes. Skull bones were often placed in families like Odontopterygidae or Pseudodontornithidae in the Odontopteryges or Odontopterygia suborder. The Pelagornis species, known from wing bones, was traditionally placed in a family called Pelagornithidae. This family was sometimes grouped with gannets and cormorants in the Sulae suborder or with Odontopterygia. The sternum of Gigantornis was once placed in the albatross family (Diomedeidae) within the tube-nosed seabird order (Procellariiformes).
The most confusing classification issues involved Dasornis. This genus was first described based on a large skull piece, which was mistakenly placed in the Gastornithidae family because of its size. Argillornis, now known to belong to Dasornis, was described from wing bones and was once grouped with Sulae in a made-up family called Elopterygidae. Some ankle bones were placed in a genus called Neptuniavis and assigned to the Procellariidae family in Procellariiformes. These remains were later shown to belong to Dasornis in 2008.
The oldest known pelagornithid is Protodontopteryx.
The classification of bony-toothed birds is still debated. Early scientists grouped them with Pelecaniformes (pelicans, gannets, and frigatebirds) and Procellariiformes (albatrosses and petrels) because of their similar anatomy. Some remains of Dasornis were once mistaken for a ratite or a gastornithid, and this led to incorrect ideas about the relationship between these groups. Today, scientists believe that pelagornithids are more closely related to pelicans than to albatrosses, even though they share some physical traits with albatrosses.
In 2005, a study suggested that pseudotooth birds are closely related to waterfowl (Anseriformes), which are part of the Galloanserae group, a basic lineage of neognath birds. Features like the shape of the skull and jaw bones support this idea. For example, pelagornithids lack a crest on the underside of the palatine bone, unlike other birds. They also have two, not three, condyles on the mandibular process of the quadrate bone, similar to ducks and geese. Their basipterygoid articulation and parasphenoid lamina are also similar to those of waterfowl.
Other skeletal features, such as those in the arms and hands, also show similarities between pelagornithids and waterfowl. The ulna has a strongly curved upper part, a pointed dorsal cotyle, and a wide intercondylar sulcus. The radius has a convex ventral border and a flat, triangular surface near the ulna. The carpometacarpus in both groups has a prominent pisiform process and a specific structure on the underside.
Leg and foot bones show fewer similarities between pelagornithids and waterfowl. The tibiotarsus has a wide gap between condyles, and the tarsometatarsus has a low vascular foramen and an elongated middle toe trochlea.
It is unclear whether the features that link pelagornithids and waterfowl are meaningful. Other bones, like the sternum and leg bones, show traits typical of "higher waterbirds." Skull features shared by both groups might relate to feeding habits, such as skimming the water's surface. Some traits in pelagornithids could be ancient features or traits that reappeared later. The location of salt glands inside the eye sockets of Osteodontornis and Pelagornis suggests that pelagornithids adapted to oceanic life independently of penguins and tube-nosed seabirds, which have salt glands above the eyes.