I'm the madlad who hatched one of these bad Bois at lvl 47 here is my experience.

1-you need a tame with 5000 health and above a parcer is recommended(cuz your tame will start losing health).

2-you need a spy glass to see the rhynios health and gender.

3-you need a pteranodon so you can lure the rhynio in a safe area.

4-kill a male rhynio to get the pheromone and feed it to your 5000 health tame when the female rhynio is at 10% of it's health and then it will pregnate your tame.

5-get food for your tame (Incase the health is not enough) about 10000 batches of berries if your tame is a herbivore(a carnivore tame is not recommended).

And that is how to get a rhynio at low level.