Osteodontornis: a Miocene seabird with pseudo-teeth

Osteodontornis orri is the traditional name for a large Miocene member of the pelagornithids, the extinct birds with tooth-like bony projections along the beak. A 2010 revision proposed placing Neogene species of the family in one genus, so the same species may be called Pelagornis orri. The dispute concerns its classification, not whether the bird existed.

The Californian type material preserves a flattened skull, parts of the limbs and shoulder, and impressions associated with feathers. It provides unusually useful evidence for a giant seabird, but compression complicates measurements and the exact length of the flight feathers is unknown. The jaw and wings are directly informative; its precise diet and take-off method are not. The extinct bird catalogue also includes Pelagornis, whose fossils help explain both the shared pseudo-teeth and the changing genus name.

Quick facts

A fossil with a disputed generic name

Hildegarde Howard described Osteodontornis orri in 1957 from late Miocene deposits in California. The type includes parts of the skull, limbs and shoulder girdle, preserved largely as mineralised fragments and impressions. Feather traces were noted nearby. The association makes the find informative, although flattening means that measurements taken from the slab do not always represent the original three-dimensional shape.

For decades, similar fragments from across the Pacific were placed in Osteodontornis. A more complete pelagornithid from Chile led Gerald Mayr and David Rubilar-Rogers to argue in 2010 that differences among Neogene genera had been overstated. They proposed combining them in Pelagornis. Under that view, Osteodontornis orri becomes Pelagornis orri. The species name remains while the genus assignment changes. Researchers may continue to use the familiar older name when discussing the historical literature.

Why the “teeth” were not teeth

The pointed structures along the jaws were bony projections continuous with the premaxilla and other jaw bones. They did not sit in individual sockets, had no enamel crowns and were not replaced like true teeth. Larger and smaller projections alternated along the edge of the long beak, creating a comb-like gripping surface.

That arrangement could help retain slippery prey near the sea surface, especially fish or squid. It was not designed to crush large bones. No stomach contents preserve the bird's last meal, and a useful gripping shape cannot identify an exclusive menu. The feeding interpretation remains a functional inference from anatomy and marine ecology.

Wings, soaring and uncertain measurements

Older illustrations often gave Osteodontornis a wingspan of five or six metres. More cautious comparisons found that its preserved bony wing was shorter than that of Pelagornis chilensis, whose minimum span has been estimated at about 5.2 metres. The length of Osteodontornis's primary feathers is not known, however, so a shorter bony wing does not translate into a definitive total span.

Thin-walled bones, an elongated wing and the shoulder structure are consistent with flight. Pelagornithids probably spent long periods soaring above the ocean, making use of wind and moving air rather than continuously flapping. How O. orri launched from the water, where it nested or how far it travelled in a day are not recorded by the fossil.

Its mass was probably below that of the terrestrial South American Argentavis, even if their wingspans may have approached one another under some estimates. Similar dimensions do not imply the same flight style: an ocean-going seabird and a terrestrial soaring bird had different bodies and surroundings.

What the Miocene record can and cannot show

Pelagornithids are known from marine deposits on several continents and persisted through much of the Cenozoic. A broad distribution is compatible with long-distance flight over water, but it does not mean that every species lived at the same time or shared one route. Fossils attributed to Osteodontornis come from different regions and deposits, and their assignment has changed as comparative material improved.

The type specimen establishes the presence of a large bird with bony pseudo-teeth and flight-capable wings. It does not establish a precise body mass, a six-metre wingspan, one feeding technique or a nesting site. Plumage colour and the visual pattern of the bill covering are also unknown. A reconstruction may show a giant ocean glider, but the particular scene remains an artistic choice built around a limited skeleton.