I adopted it using bait. My best dinosaur was a Triceratops. I managed to adopt it, but if you don't have the budget to build stone walls and floors, bring a bait with a full life, tell it not to be aggressive, and attack the megatherium with the dinosaur. Stop with the dinosaur in place and let the megatherium attack your dinosaur while you shoot it with semi-anesthetizer. If you've made it this far, I'd love for you to share this for anyone who needs it. Thanks for reading.