A new discovery suggests Prototaxites, a giant organism once believed to be a massive fungus, may have belonged to an unknown branch of the tree of life that vanished without explanation. Estimated to have lived between 420 and 375 million years ago, Prototaxites was the first known giant terrestrial life form on Earth, growing up to 8 meters tall and 1 meter wide.
Its fossils were first discovered in the early 20th century, leading scientists to assume it was a fungus due to its unique structure. However, this assumption may be incorrect, as recent research reveals that Prototaxites may have been an undiscovered species of organism that went extinct mysteriously.
Source: https://www.newscientist.com/article/2473272-bizarre-fossil-may-have-been-an-entirely-new-type-of-life