They can only mate in the water. The egg looks like a ball of jelly and floats on the water surface. You can't pick it up! It doesn't spoil either.
This dino is excellent for getting the deep sea loot crates. Be aware that your own stamina runs down very slowly when you're riding.
Can ride but only underwater. In order to ride, hold whatever your ride button is and click the option that says ride. Level up in oxygen, health, and movement speed if using this for underwater dives. Really fast underwater, and can outspeed megalodons.