These bad boys have insanely high hp, weight and damage aswell as a bubble breath which can push back enemies super far on land and can push enemies to the surface and stun em when in water. To top it all off they also have a platform saddle and are stupidly good at climbing things so you can use them for fights and holding a ton of stuff such as a base without being too restricted on where you can go
Probably the best platform dino to live on, the megachelon can fit a 5 by 7 of foundations on its shell, and many structures, like chemistry benches, grinders, and even industrial forges can be built on it while staying there when underwater. You don't even need scuba gear when going underwater, staying above one provides oxygen. Not only this, but they actually have surprisingly good melee damage, as well as being one of, if not the best fiber harvester in the game. Different resources will constantly build up in its inventory, including rare mushrooms and flowers. They also automatically irrigate any crops placed of them. Get an imprinted one for extra speed, damage, and resistance, then give it an good armor saddle from the frog escort mission in the bog, and you have an extremely tanky resource gathering portable base, war machine, greenhouse, and water exploration mount!