Build a smal open air base and fly with your argentavis and bring the megalo... in the base

They are are eating demophordon kibble and vegetables like potatos and carrots

Easy tame. Bola, tranq darts or arrows, then tame with crops or mejo berries if you don't have the kibble.

If you're lucky you'll find one at the coast in the snow biome. So it's near your raft.

Do pop hhahahhhahahahahahhahhahahahaahhahahahahahhaahahha