Make a small building without a roof, preferably thatch, then get an argie or a pteranodon, go to the redwood river and scout around for the and otter, they don’t live in the swamp section though, then once found pick up the otter with your flying dino, then drop it into the small building you made, then kill a lot of sabertooth salmon, and then feed your otter raw prime fish meet, then soon you have a noodle!
If you have an Argy, fly over the otter and pick it up with the argy's beak ('C' on pc). Land the argy and let the otter hang out in its beak while you bring fish over. I found I needed to drop the fish and pick it back up to target the otter. After having done this by following around a scampering otter with a dead fish pinwheeling wildly in my hands for 10 minutes the first time, I will never ever attempt it again without my argy.
These little guys are so much easier to tame in mobile, but harder to find. You still need to kill a megipirahna, but you don’t need to grab its corpse to feed the otter. After harvesting its meat you can easily walk up to it and feed it until it’s tamed. It doesn’t run away in mobile, and I’m sure you can use any fish meat.