Two University scientists have found and identified a tiny yellow ant as a key link in the evolution of the ant family.

Edward O. Wilson, member of the Society of Fellows, and William L. Brown, curator of Insects at the Museum of Comparative Zoology, said yesterday that the species was common over the earth 50,000,000 years ago.

The ant, found only in the jungles of Ceylon, is a direct evolutionary link between the oversized, stinging, primitive ants of Australia and the highly developed ant subfamilies familiar in this country.

Fossil examples and old, now unusable specimens previously showed the existence of the discovered ant, but scientists knew practically nothing about its habits or evolutionary status. "Now its importance has been confirmed," Wilson said, "and we have studied it in virtually all possible aspects."

Wilson collected the "missing-link" specimens, among thousands of others, on a 10-month expedition in the Southwest Pacific. He air-mailed them to Brown, who analyzed, mounted, and mailed them back. Wilson, by then in Europe, checked the species he had found against the classic type speciments in European museums to prove their idenity.

About 1000 species were collected on the expedition, including 100 unknown before. In addition to the discovery of the Ceylon ant, the expedition fulfilled two major purposes; expanding the insect holdings of the Museum of Comparative Zoology, and collecting and studying data on the distribution and behavior of ants from Fiji to Australia.

Wilson and Brown have also sought another "missing-link" ant, believed to be living somewhere in a 10,000 square-mile patch of Australia.