Like it’s predecessors, the Magmasaur is a simple “Grab the egg and get the hell out” tame, however this one CAN be breed with each other, but only in lava. Don’t bother trying it on Val or Rag, as it won’t work. The only lava source it works on is Genesis, so build a base near lava if you want as many Magmasaurs as possible.
So after losses.. I've worked out the magmasaurs food drops at a rate of 15 (rounded up from around 13.7) per minute, 900 food per hour. Feed your mag 1 ambergris every half hour to keep a happy healthy lil magma blob
I’ve found the eggs. The eggs are located inside the volcano in an amethyst cave. There are lava pools with groups of magmasaurs in them. There are small islands with craters in them, within those craters the eggs are nestled within. But be careful there are lots of magmasaurs, magma, and what look like varient rock elementals.