They were possibly twenty-four feet tall and three feet wide
How was there enough organic matter in the soil to support such large fungal organisms?
I think it's still up in the air what the Prototaxites actually ate. Currently, researchers think they fed on algae and bacteria in nearby pools of water.
https://www.unh.edu/unhtoday/news/release/2010/03/25/giant-fungus-fed-aquatic-microbes-not-plants-research-shows-1#:~:text=Chemical%20and%20anatomical%20analysis%20by,photosynthesis%20by%20algae%20and%20bacteria.
How was there enough organic matter in the soil to support such large fungal organisms?
I think it's still up in the air what the Prototaxites actually ate. Currently, researchers think they fed on algae and bacteria in nearby pools of water.
https://www.unh.edu/unhtoday/news/release/2010/03/25/giant-fungus-fed-aquatic-microbes-not-plants-research-shows-1#:~:text=Chemical%20and%20anatomical%20analysis%20by,photosynthesis%20by%20algae%20and%20bacteria.