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Giant birds with false teeth

By Hans-Dieter Sues

The oldest known birds, classified in the genus Archaeopteryx, lived near the end of the Jurassic Period (145.5 to 150.8 million years ago).  Although Archaeopteryx has a fully developed plumage its skeleton still retains many features of its dinosaurian precursors, one of which is jaws with teeth. With the exception of some Cretaceous-age forms, all later birds lack teeth.

In 1873 the Victorian paleontologist Sir Richard Owen described the incomplete skull of a new fossil bird from the early Eocene (48.6-55.8 million-year-old) London Clay of southeast England. What makes this fossil special is the presence of tooth-like structures along the margins of its bill, which led Owen to name the new bird Odontopteryx–“toothed wing.”  Its “teeth” are actually pointed projections of the jawbone.

Subsequently, fossils of such false-toothed birds have been discovered in other parts of Europe, Japan, New Zealand, and especially North America. In 1957 the American paleontologist Hildegard Howard reported an incomplete skeleton of a false-toothed bird, Osteodontornis, from Miocene rocks exposed in a quarry near Santa Barbara, California. She estimated its wingspan at an impressive 16 feet (4.87 m).

In the September issue of the Journal of Vertebrate Paleontology, the German ornithologist Gerald Mayr and his Chilean colleague David Rubilar-Rogers have described much of an exceptionally well-preserved skeleton of a giant false-toothed bird. The specimen had been collected from a sequence of Miocene rocks in northern Chile, the top of which has been dated radiometrically at 6.8±1.3 million years before present. The researchers placed this remarkable fossil, along with all other Miocene-age false-toothed birds (including Howard’s Osteodontornis), in the genus Pelagornis but classified it as a new species, Pelagornis chilensis.

GIANT_BIRDS_FALSE-TEETH_FIG1.jpg

Skull of Pelagornis chilensis in side view. Note the tooth-like bony projections in the upper and lower jaws. Length of skull 45 cm (1.48 feet). 

Photograph by S. Tränkner; courtesy and copyright of Dr. Gerald Mayr (Sektion für Ornithologie, Forschungsinstitut Senckenberg, Frankfurt am Main).

The new species attained a wingspan of at least 5.2 m (17.1 feet)–the largest wingspan of any known bird and rivaled only by the extinct teratorn vulture Argentavis. By comparison, present-day albatrosses attain wingspans of about 3.4 m (11.2 feet).

The structure of the upper arm bone (humerus) in Pelagornis rules out flapping of the wings. Mayr and Rubilar-Rogers suggest that takeoff relied on spreading those enormous wings against headwinds. The birds may have also held their wings horizontal during landing, using their short, robust legs for braking.

The bones of Pelagornis chilensis are remarkably thin-walled. Using various methods for calculating body weight from bone dimensions in birds, the researchers obtained weight estimates ranging from 15.6 to 28.6 kg (34.3 to 62.9 pounds)–not much heavier than the heaviest flying bird alive today, the mute swan, which can attain weights of up to 20 kg (44 pounds) in males. Together with the limb proportions, these figures suggest that Pelagornis was a highly proficient long-distance soarer.

GIANT_BIRDS_FALSE_TEETH_FIG2.jpg

Preserved elements of the skeleton of Pelagornis chilensis. Scale equals 1 m (3.29 feet).

Photograph by S. Tränkner; courtesy and copyright of Dr. Gerald Mayr (Sektion für Ornithologie, Forschungsinstitut Senckenberg, Frankfurt am Main).

The beak of Pelagornis chilensis has 22 variously sized tooth-like projections on the front three fourths of its upper bony cutting edge. Presumably the false teeth helped to maintain a grip on slippery prey such as fish and squid on which these giant birds fed.

A living Pelagornis must have been a truly spectacular sight as it cruised offshore, now and then plucking prey from the ocean surface with its “toothed” bill.  Why these remarkable seabirds vanished cannot yet be ascertained.  Perhaps climate change following the formation of the Isthmus of Panama and the resulting major changes in ocean currents accounts for the disappearance of these animals.

Hans-Dieter-Sues.jpgHans-Dieter (Hans) Sues is a vertebrate paleontologist based at the National Museum of Natural History in Washington, D.C. He is interested in the evolutionary history and paleobiology of vertebrates, especially dinosaurs and their relatives, and the history of ecosystems through time.

A former member of the National Geographic Committee for Research and Exploration, Hans has traveled widely in his quest for fossils and loves to share his passion for ancient life through lectures, writings, and blogging.

Blog entries by Hans-Dieter Sues >>

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