Osteodontornis - Description

Description

With a wingspan of 5.5 to 6 metres (18 to 20 ft) and a height of 1.2 metres (3.9 ft) when on the ground, Osteodontornis orri and similar giant pseudotooth birds were the second-largest flying birds known, surpassed only by the teratorn Argentavis magnificens. The head, from neck to bill-tip, measured about 40 centimetres (1.3 ft), and the eyesockets were about 5.3 centimetres (2.1 in) wide. The humerus, though about as long as a human's, was only about 3.5 centimetres (1.4 in) wide at the shoulder end. The skull's quadrate bone measured almost 30 millimetres (1.2 in) at its widest and was nearly 45 millimetres (1.8 in) high.

Like its relatives, O. orri had a stout but extremely light-boned body, feet that were presumably webbed as in its aquatic relatives, and long and probably very narrow wings resembling those of an albatross. Its beak made up about three-quarters of the head's length and had bony tooth-like serrations that were hollow or maybe filled with cancellous bone. The beak was so heavy the creature probably held it between its shoulders while in flight, just like modern pelicans do. The arrangement of its bony serrations is characteristic for this genus: one small "tooth", flanked by small points or even smaller "teeth", is placed between each pair of large ones. However, the "tooth" pattern of pseudotooth birds changed along the length of the beak, and is not considered a very reliable way to distinguish genera.

In general lifestyle, it was probably most similar to the albatrosses, tropicbirds and frigatebirds of today, with long slender wings adapted for soaring vast distances over the open seas. Due to its size, the bird is presumed to have been an excellently adapted dynamic soarer. It probably built its nest on high plateaus or similar places, where it could easily take flight by simply walking into the wind with wings spread. It was a seabird that apparently lived mainly off squid and other soft-bodied prey; the "teeth" were less saw-like than the horny serrations on the beak of the fish-eating saw-billed ducks (Merginae), pointing straight downwards instead and in the fossils often very abraded or broken. The downward-pointing "teeth" were ideal for digging into and holding slippery, soft-skinned pelagic animals such as cephalopods that were probably snatched out of the water in flight or while swimming. Lightly built as it was, O. orri was probably not a good diver and may have found it impossible to dive at all.

Osteodontornis is one of the pseudotooth birds of which rather comprehensive remains are known, but the lack of good fossils of most other Odontopterygiformes allows for few direct comparisons between genera. Still, the distal humerus of the present genus (e.g. the Barstovian specimen LACM 50660 from Kern County, California) can be compared to that of a smaller and older fossil tentatively assigned to Odontopteryx. Osteodontornis has a wider and deeper notch between the external condyle and the ectepicondylar prominence, with the pit between these farther from the bone's end, than did the smallish Paleogene species. Its quadrate bone differed from that of Odontopteryx toliapica in a more narrowly grooved dorsal head, and a larger and less forward-pointing orbital process. The forward center of the ventral articulation ridge extends upwards and forward, and the pterygoid process is conspicuously expanded to the upper center in Osteodontornis. The socket for the quadratojugal has an intermediate position and the lateral ridge of the slender main shaft is straight and fairly thin. The quadrate of the mysterious Pseudodontornis longirostris skull (which some consider to belong in Pelagornis) is not very well preserved; it agees with Odontopteryx in a broad main shaft and with Osteodontornis in the straight main shaft ridge and its upward-directed ventral articulation ridge's forward center. Otherwise, it differs from both.