Today's #mega...er... organisms...are prototaxites. These large, columnar fossils date to 240-350 million years, and stood 24 feet tall and 3 feet wide when they were alive. During this time period, both plants and animals on land were still quite small--meaning that #prototaxites formed the dominant feature of the land during the #Silurian and #Devonian periods.

But what exactly were these giant spires? First described in 1859, they were originally thought to be very early trees. However, their internal structure of tiny, criss-crossing tubes suggests that this is not correct. Chemical analysis also indicates that prototaxites gained their energy from diverse sources--ruling out the idea that they were plants.

This leads to the conclusion that prototaxites were giant, spire-like mushrooms--and the researchers who completed the analysis suggested that their height helped them to spread spores in an otherwise low-laying landscape.

An alternative explanation--perhaps attempting to account for the prototaxites' unusual height--suggests that they were a matted mixture of liverworts, fungus, and cyanobacteria that got rolled up by external forces and never stood upright. This has been disputed based on the fossils' anatomy and chemical makeup.