After a whole round on the island I litteraly found a lvl 20 mosa near my base area.

Then knocked it out with toxicant and tranq arrows and tamed it with 2 quetz kibbles(soothing balm also).

And now I'm sure that I'll see those mosa's everywhere cuz I've tamed one¯\_(ツ)_/¯¯\_(ツ)_/¯