THIS IS SO COOL! So animals can get fungal infections, as can plants and even other fungi. We've seen fungi like Cordyceps produce fruiting bodies on insect hosts postmortem. But this is the first known observation of a fruiting body on a live host! And the frog apparently seemed to be in good health otherwise.
It's likely a situation with an opportunistic spore of Mycena landing in a wound or other small vulnerability on the frog's skin, and since amphibians have to stay wet, the fungus had plenty of water. I'm not sure what it's been consuming since Mycena normally is a decomposer of dead plant tissue; maybe dead skin cells and bacteria?
Before people start leaping to conclusions, this is NOT the start of some sort of zombie apocalypse. Mycena and Cordyceps engage with their hosts in very different ways, and neither are anywhere near related to any fungi that parasitize human hosts and which do not cause any sort of altered mental state of that sort. I find it kind of sad when people have to sci-fi a new scientific discovery in order to find it interesting enough to think about, instead of just appreciating how awesome, weird, and scary nature is all on its own.
Regardless, this is a really spectacular find, and we'll see if any other crop up or whether this was one of those once-in-a-lifetime discoveries.