CHICAGO, Illinois (Reuters) -- Scientists have identified the Godzilla of fungi, a giant, prehistoric fossil that has evaded classification for more than a century, U.S. researchers said on Monday. A chemical analysis has shown that the 20-foot-tall organism with a tree-like trunk was a fungus that became extinct more than 350 million years ago, according to a study appearing in the May issue of the journal Geology. Known as Prototaxites, the giant fungus originally was thought to be a conifer. Then some believed it was a lichen, or various types of algae. Some suspected it was a fungus. "A 20-foot-fungus doesn't make any sense. Neither does a 20-foot-tall algae make any sense, but here's the fossil," C. Kevin Boyce, a University of Chicago assistant professor of geophysical sciences, said in a statement.