Have a pteranadon, and only upgrade stamina. Go to the rift, near the redwood, and fly all the way to the back near the big lavafall(?). There are many egg spawns here. Wait until the wyvern go out of range, then quickly take the egg, fly next to the edge and go through the forrest. There is a high chance the wyvern gets stuck, and you may loose it. If not, die and find your body, and you will find the egg in your inventory. Recommended is to take your second-best ptera.
Other tip: Have two players and two ptera’s. Make your friend with a weak ptera stay on the edge, and when you steal the egg fly towards your friend, and pass him. This will make the Wyvern aggro on your friend instead, giving you sufficient time to escape, and leave him to die. You can also do this solo, however, we often do it together, and my friend tries to escape in which he succeed half the time. So it might save you losing another ptera.