Follow the branching family tree for all modern-day ant species, and it will lead you back 115-135 million years before you come to the most recent common ancestor, say researchers at UC Davis, the California Academy of Sciences and the Smithsonian Institution's National Museum of Natural History. That's a long time ago, but previous estimates, based on DNA differences, had placed the divergence among ants even earlier, during the Jurassic period that dates back roughly 140 to 200 million years ago.

This is just one of the findings of the research team, which recently assembled the largest ever molecular data set on the evolutionary history of ants. The findings of their study are published online this week in the Proceedings of the National Academy of Sciences of the U.S.A.

"Ants are among the most successful of all insects," said Philip Ward, a professor of entomology at UC Davis and co-author on this study. "Because of that, we would like to understand how and when they evolved the characteristics that led to their dominance."

Ward and colleagues also noted that ants make up 15-30 percent of all living material in tropical rainforests, are the leading predator of invertebrates in most ecosystems, and are major plant-eaters in the tropical regions of the Americas. And ants have developed their own social agricultural practices including cultivating fungi, harvesting seeds, and herding and milking other insects.

To better understand how ants developed their present dominance, the researchers analyzed DNA sequences from 152 species representing all 20 ant sub-families, as well as 10 species of stinger-bearing insects from related wasp families.

While the molecular data gathered in this study identified the range of time when current ant species diverged from a common ancestor, it left many questions unanswered regarding the ancient lineage of ants.

"We have shown that the currently available molecular data allow for several alternative hypotheses on how the first ant lineages evolved and acquired their distinctive physical and behavioral characteristics," Ward said.

This study was funded by the National Science Foundation.