I didn’t see a Rex so I picked it up. Suddenly, a Rex burst through the trees looking for blood. It hit me, which got my argent ( #prayfortoriel) to attack it. While the Rex was distracted, I shot at it with my apprentice longneck and it was soon dead. There’s also a pursuit on mobile single player called keep your distance where you have to make Rex kibble. If you want a Rex egg without taming a female, make sure there’s no Rex