In 2007, isotopic analyses by a team including Hueber and Kevin Boyce of the University of Chicago concluded that Prototaxites was a giant fungus. They detected a highly variable range of values of carbon isotope ratios in a range of Prototaxites specimens; autotrophs (organisms such as plants and algae, that make a living via photosynthesis) living at the same time draw on the same (atmospheric) source of carbon; as organisms of the same type share the same chemical machinery, they reflect this atmospheric composition with a constant carbon isotope trace.
In 2007, an investigation by Hueber and Boyce's team at the University of Chicago revealed that Prototaxites was a massive fungus. The researchers found significant differences in carbon isotope ratios among various specimens, indicating that these organisms had unique metabolic pathways.