It's assumed they grew that way because that's what the fossils look like.
If a fungus had a photosynthetic symbiont, it would have a good reason to compete for height. In fact, an algal symbiont is a leading theory, based on chemical traces that point to algae in the fossils.
Interestingly, lichens do this today: they are composite organisms of fungus and photosyth (algae or cyanobacteria). They don't currently get very high, but perhaps that's just because plants are so much better at height that all tall forms have gone extinct.
If there's no photosynthesis going on, it's harder to explain. Perhaps it's handy in a very low-growing world to lift most of your energy-storage mass or hard-won water above the ground, away from predators?
If a fungus had a photosynthetic symbiont, it would have a good reason to compete for height. In fact, an algal symbiont is a leading theory, based on chemical traces that point to algae in the fossils.
Interestingly, lichens do this today: they are composite organisms of fungus and photosyth (algae or cyanobacteria). They don't currently get very high, but perhaps that's just because plants are so much better at height that all tall forms have gone extinct.
If there's no photosynthesis going on, it's harder to explain. Perhaps it's handy in a very low-growing world to lift most of your energy-storage mass or hard-won water above the ground, away from predators?