This is probably the most powerful creature in Ark. You probably want to be a high level and have good armor and equipment before confronting one of these. They are pretty rare and are usually found in the ocean or flying around in colder areas.
I was trying to tame a dodo and built the gate trap too close to base. When I shot it with the first dart it went crazy and destroyed half our base. We lost a Rex in the chaos that followed. When attempting to tame this build the trap as far from base as possible.
Imagine A chicken on steroids this thing will lay around 25-50 eggs every hour and that's about all it's good for. A must have for any tribes looking to take to the sky however, as their eggs make getting a Ptera much easier.