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New Fossil Links Birds and Dinos
17 March 1998 7:00 pm
Paleontologists digging in the sandstone of Madagascar have uncovered an ancient, raven-sized bird with a slashing claw fit for a Velociraptor. The 65-million- to 70-million-year-old fossil is one of the most primitive birds known, and is strong evidence that birds evolved from dinosaurs. But skeptics say it's possible that the researchers found not one, but two skeletons: a bird's wing and a dinosaur's hindquarters.
The new find, to be reported in Friday's issue of Science, is called Rahona ostromi (Rahona, for menacing cloud in Malagasy, and ostromi in honor of Yale University paleontologist John Ostrom). The fossil was dug up by Catherine Forster of the State University of New York, Stony Brook, and Scott Sampson of the New York College of Osteopathic Medicine in Old Westbury on a 1995 dig led by Stony Brook's David Krause. The team found a long, slender lower wing bone with quill knobs for feather attachment lying just above, though not attached to, several hind-limb bones that fit together, as well as a long, bony tail like that belonging to Archaeopteryx, one of the first known birds.
They also unearthed a "wicked-looking" sickle claw, says Forster, like those seen on Velociraptors and other dromaeosaurid dinosaurs. And the bird's last six dorsal vertebrae have an extra face, as seen in theropod dinosaurs but not in modern birds. These features make R. ostromi look even more like a theropod dinosaur than does Archaeopteryx, says Forster. The best way to explain this half-bird, half-dinosaur appearance is that birds evolved from dinosaurs, and R. ostromi retained many vestigial dinosaurian traits for millions of years. "It's a great discovery," says Archaeopteryx expert Peter Wellnhofer of the Bavarian State Collection of Paleontology and Historical Geology in Munich, Germany. "This fossil is very strong support for the theropod ancestry of birds."
But researchers such as John Ruben of Oregon State University in Corvallis say that the reason R. ostromi looks like a dinosaur is that its hind limbs actually come from a small dinosaur. "I think it's a chimera--a little dinosaur hindquarter, with a bird's forelimbs," Ruben says. Forster can't rule out that the wing bones and hind limb come from two different animals. But she contends that the hind limbs themselves are clearly bird legs, possessing avian traits such as an opposable big toe and a small fibula, or lower leg bone. It's "a really primitive bird, walking in the gray area between bird and dinosaur," she says.