If your on the lost island you can possibly find one in swamp areas. If your on the island probably check redwoods or swamps. If your taming one kill a male since the females don’t drop pheromones, find a female, use a harpoon gun ( put the net ammo in ) use something to get the female low. Get a dinosaur ( I recommend giga or carcha to get higher chance of it inheriting the stats ) feed it to your dinosaur . And let the female to impregnate your dinosaur. And there you have it a rhyniognatha. Just don’t cryo your Dino or you lose the rhy.