How plausible is my creature?

Question

My creature, called the Kurbish, inhabits a wasteland-world, in my universe.

Recently, I have been wondering; "How plausible is this thing, really?"

A description: Large, Elephant-like creatures that photosynthesise. They feature intelligence not unlike Humans. They grow a number of precious minerals in the crevices in their shell-like back, along the length of the spine.They can grow to be 125 feet tall, and can be up to 3 kilometers in length. They don’t have to traditionally eat, but they can eat and digest several types of rock and metal. The crystals on their backs grow as they age, and grow in various colors and types to represent the diets and emotions of the Kurbish. They have large tails, on which very precious minerals grow. The Kurbish have anywhere from 6 to 18 legs, and are able to communicate subsonically(around the same level as a black hole). They grow crystal tusks as they age, and they are able to regenerate if damaged or destroyed. They have around 28 eyes, with around 14 being on each side of the head. They are able to have multiple heads, albeit rare for it to happen.Their shells feature microbiomes, which changes according to the emotions, health, and age of the Kurbish. These microbiomes grow and change with the Kurbish.

Aside from the sizes, which is impossible for a normal, living, creature, how plausible would this creature be?

Answer 1

Slightly less probable than a unicorn that rides dragons (which, come to think of it, could possibly outsell Harry Potter as a YA series).

The way I see it, your main problem isn't that this thing communicates subsonically like a black hole (which, you might want to scale that up a little, the soundwaves from a black hole are bigger than the Earth). It could manage infrasound pretty easy.

It's not even that they grow precious minerals and gems. There are microorganisms that process gold, and some theories even say that is the reason we find gold in veins instead of smatterings (the paths of ancient microorganisms). Quartz crystals are easy to make, especially when processed from sandy soil. So if these things have a massive interaction with their microbiome, that changes based on their emotions (also not hard, since there is evidence that this is also true of humans), then the microbiome could be helping with the crystal growing.

No, your only unbeatable problem here is size. No land animal can be that big in Earth like gravity. Because mass increases as a power of three, but the size of bones and muscles increases as a power of two. Your weight simply outpaces the ability of legs to sustain it past a certain size size limits. I mean a redwood can manage it, but they can't walk.

And speaking of the walking, an elephant has to cover something like 80 miles a day looking for food. If this thing ate plants, it would have to have a thresher mouth in front of a race car to get enough. But energy absorption from sunlight is only about 3% efficient ( Wiki ). So this thing really can't afford to move. Or even to really think, because intelligence takes a massive amount of calories.

But, they sound pretty awesome. So, maybe twist the facts some and make it so the crystals help gather sun? Or the minerals they eat have uranium and they are part nuclear powered? Or their shape involves very wide and squat legs that can support more weight, moving very slowly?

Answer 2

They don’t have to traditionally eat, but they can eat and digest several types of rock and metal.

Not plausible

Every living thing needs energy from somewhere in order to live. No exceptions, ever. This is not plausible. And, unfortunately, as you haven't given me an alternate range for your creatures size of 125ft tall, 3 klicks longs, I can't tell how plausible this could be if I assumed that it had a functional digestive system.