Scientists discovered and described a new ancient fungus called Harristroma eboracense that lived on plant leaves about 170 million years ago during the Jurassic period. This fungus helps us understand how fungi diversified and evolved over time. By studying this fossil and comparing it with modern fungi, researchers learned that fungi began developing specialized structures for infecting plants during the Mesozoic era, and that they likely first thrived on broad-leaved plants in warm, wet forests.