Sickle-clawed bird discovered

Jeff Poling

Scientists have announced discovery of a fossil that shines more light on the origins of birds.

Scott Sampson, David Krause and Catherine Forster write in the March issue of Natural History that they discovered the limbs, parts of the shoulder and hip bones, and numerous vertebrae of a bird duing their 1995 expedition to Madagascar. The scientists describe the bird as extremely primitive, occupying a position close to the first branch of the avian family tree.

The bird, about the size of a large hawk, has many modern avian characteristics, such as bony bumps on the forearms that serve as the attachment points for flight feathers. It also has many characteristics of non-avian dinosaurs, including a long, robust tail and unfused bones in the upper part of the foot. The most spectacular dinosaurian characteristic of the bird is a large, retractable, sickle claw on the second toe of the hind foot (click on the thumbnail image at right to view the picture; click on your browser's "back" button to return). The claw is a smaller but identical version of the slashing claws of dromaeosaurids such as Deinonychus and Velociraptor.

The bird dates to the Late Cretaceous, approximately 75 million years ago. Although much younger than Archaeopteryx, the oldest known bird in the fossil record, this new bird nonetheless provides further strong evidence of the close relationship between birds and dromaeosaurids. Scientists believe that the first birds may have looked very much like the Madagascan bird, and the existence of such a bird bolsters the theory. Its late appearance in the fossil record may indicate that it was an evolutionary holdover, possibly due to Madagascar's relative isolation beginning 120 million years ago.

Addendum: The official description of the bird was published in the March 20, 1998, issue of the journal Science. The fossil has been named Rahona ostromi, "Ostrom's menace from the clouds." The name honors Dr. John Ostrom, the discoverer of the sickle-clawed Deinonychus and early proponent of the dinosaur-bird link. In addition to the information above, press releases note that Rahona was found with the fossils of more advanced birds, indicating they co-existed.

Note: George Olshevsky announced several days after publication that the genus Rahona is preoccupied by a Madagascan butterfly. A new name was chosen by the authors, Rahonavis ostromi, "Ostrom's menace-from-the-clouds bird."