Insect nest predates dinos.

While hunting for traces of extinct freshwater crayfish in Arizona's Petrified National Forest, researchers found this fossilized insect burrow in 200-million-year-old sedimentary deposits. The finding pushes back by more than 100 million years the emergence of social behavior in insects, they say.

The preserved nest, excavated in sandstone by termites, is about 3 inches wide and 4 inches deep and contains a number of tiered chambers connected by spiral ramps, notes co-discoverer Russell F. Dubiel of the U.S. Geological Survey in Denver. Most significantly, says Dubiel, "the construction of the nest tells you about the behavior of the organism." Although the termites were not preserved along with their handiwork, the nest shows that the creatures lived a communal existence.

Termites, wasps, ants, and some bees work together for the survival of the group. Termites make the most complex nests of all social insects. Until now, the earliest such nests dated back 65 to 70 million years, near the end of the dinosaurs' reign.

Dubiel and Stephen Hasiotis, a doctoral student at the University of Colorado at Boulder, presented their findings to colleagues at a May 19-21 regional meeting of the Geological Society of America in Reno, Nev.