Giant mushrooms ruled the Earth

Long before the first forests appeared, the skyline belonged to Prototaxites. These were massive, pillar-like organisms that stretched up to twenty-six feet tall and three feet wide. For decades, scientists couldn't agree on what they were, guessing everything from giant lichens to rotting conifer logs. Chemical analysis finally confirmed the truth: they were humongous prehistoric mushrooms.

From about 420 to 350 million years ago, these fungal towers were the tallest living things on land. At the time, plants were tiny, scrubby things that barely reached a person's ankle. If you walked through a Devonian landscape, you wouldn't see leafy canopies. You would see a barren, rocky terrain punctuated by smooth, trunk-like fungus spires that lacked branches or leaves.

This fungal reign lasted for at least 40 million years. They eventually lost the evolutionary arms race when plants figured out how to build complex vascular systems and grow tall enough to compete for sunlight. Once trees arrived, they sucked the nutrients out of the soil and shade-blocked the Prototaxites into extinction, leaving us with the much smaller mushrooms we find on the forest floor today.