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Fossil skeleton gets seabird size record.

Fossil skeleton sets seabird size record

Extensive fossil remains of the largest known seabird, weighing close to 90 pounds with a wingspan of between 18 and 19 feet, have been chipped out of a 30-million-year-old block of hardened sand and mud and identified by scientists at the Charleston (S.C.) Museum and the Smithsonian Institution in Washington, D.C.

The bird represents a new species of an extinct family known as "bony-toothed birds,' or pseudodontorns, that lived from 50 million to 5 million years ago, says Smithsonian paleontologist Storrs L. Olson. Pseudodontorns are thought to be related to modern pelicans and cormorants. They appear to have glided over the ocean with little or no flapping of the wings, much as albatrosses--the largest living seabirds, weighing 22 pounds with a wingspan of up to 11 feet--now do.

Remains of the bony-toothed birds have been found throughout the world, but their fragile bones do not perserve well. "Usually just the ends of bones have been found,' says Olson. "A few fairly complete skulls have turned up as well as a two-dimensional impression in rock.' The new fossil find includes virtually the entire skull, a complete lower jaw, most of one wing, all of one leg with one toe bone and fragments of the clavicle, or wishbone. It is a much larger creature than any previously known pseudodontorn.

"This specimen will permit a reevaluation of all other species of pseudodontorns described from single or isolated remains,' says Olson. In most places where these fossils are found, there appears to be a bigger and a smaller pseudodontorn species, he adds, "but up to now we haven't had any way to know which feet go with what skull.'

The structure of the large bird's wing and shoulder bones indicates that it could raise and lower its wings, but the rotational movement necessary to flap the wings was restricted. Pseudodontorns appear to have glided long distances using oceanic winds. The wing construction of the pseudodontorns was similar to that of albatrosses, notes Olson, but the pseudodontorns probably possessed longer necks.

The bony "pseudo-teeth' of the specimen were intact and, in some cases, were as long as three-quarters of an inch. Although lacking the dentin and enamel of real teeth, the tooth-like bones may have enabled pseudodontorns to feed on soft marine life, such as squids, and possibly fish, says Olson. No other known group of birds, alive or extinct, has bony teeth.

Several anatomical features, however, link pseudodontorns to modern pelicans. For example, says Olson, the two groups of birds have salt glands located between the eyes and the skull, whereas the salt glands on most other seabirds--including albatrosses--are found in deep grooves on top of the skull.

"We simply don't know why these birds became extinct,' says Olson. Their demise, he suggests, may have been related to changes in ocean currents and wind patterns that curtailed their movement. Another possibility is that their nesting areas along coastlines and island shores were overrun by competing animals, such as seals. "But this is pure speculation,' adds Olson.

The new specimen was recovered in a block of hardened sand and mud excavated in 1984 during construction of an airport in Charleston. Fragments of another, smaller pseudodontorn were visible on the surface of the block, but the extensive skeleton it encased was not revealed until Smithsonian scientists began to chip away the hardened material early this year. Olson and his colleagues plan to return to the South Carolina site, which they believe may once have been a large nesting ground for pseudodontorns.
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Author:Bower, Bruce
Publication:Science News
Date:Nov 14, 1987
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