BREEDING: babys need to be in the water. In my testing the babies start to take damage if they're on the land just before 25% raised (part way through the juvenile stage). You can hatch them on land you just need to transfer them into the water before that point. Thank you to everyone else that put up breeding tips about this!

They will eat berries after taming

To tame the Archelon you will need bio-toxin or kibble, once tamed the Archelon can eat mejoberries so you don’t have to keep killing jellyfish

Breeding tip babies either need to be in a gigaraptor saddle or in the water or their health plummits very fast by 0.1 growth. Sorry for the category as I didn't know where to put this under.

TAMING: Have your mount hit the archelon you want to tame (you might do this by accident will trying to save it), it'll aggro for a long time. Kite it onto the land and clear out any threats while you wait for it to catch up. Hop off your mount and whistle passive. The archelon will slowly chase down your tame allowing you to casually feed it bio-toxin or kibble from behind while picturing the steam roller scene from the first Austin Powers movie.

Seen a few in the swallow waters around herbivore island, seems to be a common spawn point for them

To find this wonderful creature, it has a chance to spawn near the Cnidaria. So if you find the jellyfish, you just might be lucky enough to find yourself one of these bad boys. Passive tame using superior kibble or Bio Toxin. Obviously the kibble will take less time, but use what you got.

If staying near the surface, which tbh most already do, you can hop on their back and passively feed biotoxin, especially helpful for higher levels

Baby Archelon in ARK: Survival Ascended must be raised in water to survive and primarily eat Biotoxin to thrive. While they can consume Mejoberries once they reach the juvenile stage, Bio-Toxin is highly recommended for babies to avoid starvation. They must be submerged in water immediately after hatching to prevent suffocating on land.

Raising Archelon needs to be done in water. Also they're bugged similarly to when snow owls came out. They eatt berries and eat more and faster then a baby giga. If you thought you could walk away, you were wrong.