It is tamed in the same way as the Hesperornis, where you have to carry a dead fish to it. Larger fish, and those caught by Ichthyornis, apparently work better. Piranha are better than coelacanths for taming, and salmon are better than piranha.
Just push this cute lil creature in front of a giga and it'll have an existential crisis. Realising the path of destruction it left in its wake and deteriorate in front of the otters blue sparkly marble eyes
They move pretty fast and you can loose them easily, so I suggest making a pen to put them in. Having a Ichthynoris is quite useful to catch salmon as you don't need to be in the water fighting them, the bird will snatch it right out of the water and bring it to you.