You can’t tranq these guys, they are like dragons you have to steal eggs. You can find their caves in the volcano area on Lost Island. Once you have some eggs you need to feed it Amber Gris as there is a glitch at the moment that won’t allow it to eat sulfur. You can only get the Amber Gris on Genesis so you will have to admin spawn it in if your playing unofficial. To get them to breed you need to breed them in lava

Magmasaur egg stealing: On Fjordur, head to the volcano with an Andrewsarchus. Beware Fire Wyverns and X Rock Elementals. Search for some magmasaur nests and grab the egg. Then run as fast as you can. There is some sulfur you can feed the baby magmasaur so it doesnt die. It smells metal and cooks raw meat. I don't know how to hatch it other then an incubator.

Hope this helps, Best luck to those who try.

If trying to get one on the switch version they instantly respawn literally as you kill them. Here is a tip on how to get the eggs on switch: take a gasbag or whatever you use to get in the volcano (I prefer gasbag) and bring a velo or really any passive tame. With the magmasuars attention land on a safe cliff and toss out your passive tame within agro of the magmas: leave the passive tame, fly off out of render and come from the back side and grab your egg. They will chase you etc but leave render and repeat. Recommended to use a passive dodo in case the volcano erupts before you can grab it.

For some reason this works. Just hang from above a nest and then drop it there aren’t any ON the nest. Then grab and then quickly escape ( do all these on a bloodstalker ) in the time it takes for them to first Agro animation, then there ai says don’t swipe just charge a ball. It’s surprising how much time you have to grab a egg and get away is much larger than you think. Want proof, watch AxeMan’s idea when he gets his. He uses this strategy