This is a reading comprehension exercise for children. It was written by Susan Fineman, a reading specialist in the New Haven, Conn., school district.

Symbols carved on stones 2,600 years ago in Mexico suggest that the Olmecs, an early North American people, invented the first writing system in the Americas and that the symbols were adopted by later native cultures such as the Mayas.

The symbols were found on chips from a stone plaque and on a cylinder stone used for printing that were unearthed in an archaeological dig near an ancient Olmec city on the Gulf of Mexico.

"These symbols have a very close resemblance to symbols that were found from a later era among Mayan artifacts," said Kevin O. Pope, a study co-author. "We think the writing was developed by the Olmecs and then adopted later by the Mayans."

Age dating suggests the artifacts were deposited on the site around 650 B.C., about 350 years before the date of specimens previously thought to be the earliest examples of Mesoamerican writing.

The Olmecs are thought to have established a large and complex culture starting around 1300 B.C. They built massive pyramids, carved intricate and detailed sculpture and built large cities with thousands of people. The Olmecs are credited with creating a political state, with rulers and royalty, and a formal government.

Pope, a scientist with Geo Eco Arc Research of Maryland, said the Olmec culture collapsed by about 400 B.C., not long after the Mayan culture began to rise farther south.

Mary E.D. Pohl, first author of the study and a researcher at Florida State University, said it was known that the Olmec originated many of the cultural traditions later adopted by other cultures in the Americas. But evidence of writing was missing until now.

Pohl said the artifacts were found in a large deposit that included shards of pottery and drinking vessels, animal bones and hollow figurines. She said those items may have been discarded in a ritual associated with a feast or celebration.

The most complete specimen is a cylinder with raised carvings on the outside. The researchers think it was used as a rolling imprinting device, probably to apply the symbols to cloth or even to human skin, Pope said.

On the cylinder is a symbol of a bird, wings extended, with lines leading from the mouth to additional symbols to one side.