Question Regarding Shows with Realistic Animals like 'The Lion King' and 'Game of Thrones'

I've only started my vfx and animation journey and I'm currently watching reels for inspiration. So far, I've only modeled, sculpted, rigged, and animated humanoids but my goal was always to create nonhuman characters especially wyverns and quadrupeds. And so I was watching MPC's videos on 'The Lion King' and Pixomondo's videos on 'Game of Thrones' and there's one thing that boggles me. Did they actually modeled rigged AND ANIMATED THE SKELETON AND INTERNAL ORGANS?! Like even if you're an expert with that in science or traditional art, how long does it take to translate that into software? I'm basically asking for resources/courses on how to do that.