Taming these actually isn't too hard if you know the method. I personally had the assistance of a Tropical Crystal Wyvern, though. Quick heads up: They WILL attack Crystal Wyverns on their own, and likely many other fliers (eg Argentavis, Maewing, Pteranodon.) This tip also includes controls, if you have the default ones.

Wear Ghillie, and find your croc. They're bigger than a Sarco and their head shape is different. Have your taming food (I used mutton, I don't remember which kibble they like) in your last item slot. When it lays down with it's mouth open, sneak up to it's head and feed it. You'll know its been fed if it's mouth closes abruptly. Then, RUN, preferably back to a flier. It has a short animation/roar after being fed which gives you time to run. Repeat until tamed.

It doesn't need an interval or to have it's food drain, it can be fed every time it lays down with it's mouth open. Please don't try fight them in the wild! A 135 did over 700 damage and a nasty bleed to my Wyvern with it's Giga-bite. Just avoid them, unless taming.

Controls (PC)

Left click: Normal melee

Right click (hold and release:) Giga-bite

C: Tailwhip. Stuns things and knocks them back.

Space: Seems to be turn on the spot in the direction the camera is facing.

Left control: Roar, no special effect.

With their left click, they can turn immediately like a Sarco.