Get the Longneck Rifle and some simple rifle ammo and with your Argentavis or Pteranodon fly to the most tallest rock where he can’t damage you and your pet shot that mf and that’s the most easy way

If you ride a trike you can kill with knockback, just be on level ground or above it. Right before you kill it hop off your mount, whistle passive, then kill it yourself to get lots of exp. Hope this helps, enjoy!😁

Alpha Carnos will attack and kill anything it sees, so when your close to one, either run away, or attempt to kill it and get the Alpha Carno arm.