A team of French and Bolivian paleontologists reported last week that it has discovered the oldest known remains of a vertebrate -- a fossilized school of 30 animals called "jawless fish" in the mountains of southern Bolivia.

The flattish fishlike fossils, which measure up to 18 inches long and six inches wide, lived about 470 million years ago, when the land was under an ancient sea. Previously the oldest known vertebrates were jawless fish that lived 20 million years later.

The Bolivian finds are the first jawless fish from outside North America and Australia. They are the most complete specimens known and appear to represent a new species.

The zoological subphylum Vertebrata includes all animals with spinal columns: fish, amphibians, reptiles, birds and mammals. As the earliest example of a vertebrate, the Bolivian specimens are the closest known relative of the common ancestor of all vertebrates.

"This is one of the most exciting and important discoveries in lower-vertebrate studies in the last 50 years," said David K. Elliott, a specialist on ancient fish at Northern Arizona University.

Jawless fish, represented by today's lampreys and hagfishes, have long been considered the earliest known vertebrates. Although most vertebrates have a spine of bony vertebrae, jawless fishes had a simpler structure called a notochord. It was a stiff but flexible rod similar to cartilage that gave the animal leverage for more efficient swimming.

The fossils were found by Philippe Janvier of the French National Research Center in Paris; Pierre-Yves Gagnier, a Canadian graduate student; and Ramiro Suarez-Sorruco, a Bolivian paleontologist. Their discoveries were announced by the National Geographic Society, the sponsor.