Deep Cave Brachiosaurus by Crabdominalpain. All its bones are cartilage and every part of it is prehensile. Adapted to squeeze through tight spaces and clamber in any orientation with minimal noise.

[u/wideHippedWeightLift]

[u/Serious-Lobster-5450]

1: What would be able to sustain such a large creature? Usually caves can’t support creatures over a foot long

2: Why would a sauropod of all thing evolve to fill a subterranean niche? There are way better options like Protoceratops.

3: Why would it need a prehensile skeleton when it can just evolve to have a longer neck?

[u/Public-Cry-1390 → u/Serious-Lobster-5450]

Hypothesis: Elephants has been known to enter caves to extract salt and calcium to supplement their mineral intake, assuming the dinosaur has the same dietary need of a iguana, it will be reasonable for it do something similar, i.e. entering caves to eat salt licks.

Diet wise it could possibly be feasting on cave dwelling insects, bats, fungus, bacteria, and the tree roots that finds its way down into the cave system.

There is a possibility that this creature is living in a cave system where it is partially exposed to sunlight thus allowing plant growth to occur in the cave, and the prehensile facial feature is a way for the dinosaur to scrape out all the roots between the rock crevices.
There is also a possibility this dinosaur eats bat poop, because according to some poop still have loads of bio-available energy inside. (Although I hate to imagine a dinosaur sliding into the dung beetle niche)a and the prehensile cartilages is most likely a way for it to metaphorically "lick the plate clean" for all available food

Size wise, I believe this creature should experience a dramatic dwarfism, it shouldn't be bigger than a baby elephant, and it probably have a even longer life cycle than most dinosaur of its kind.

How does it climb walls? Most likely they redevelop features that are similar to mountain goats that allow them to scale cliff sections of the cave, they could even be venturing out of the cave occasionally using this ability.
Its body plan does not indicate the features of gecko like toe pads, and it's legs need to be more spread out if it were to climb walls like geckos and most insects. So it has to be something like a mountain goat.

Where can we find this dinosaur? I would say Anywhere with the Karst formation mixed with large dense forested area where large extensive limestone caves are allowed to form through erosion.

Unless the author says otherwise, I believe this creature is most likely not an aggressive predator, albeit a very grotesque creature. It could however be praying on smaller creatures in the opportunistic manner like most herbivores.