Megatherium can fit through the entrance to the grave of the tyrants on scorched earth. It is one of the few caves the Megatherium can actually get in and out of with no issues. If you fall in the water just make your way to a ramp and climb out.
Absolute godsend for meat runs in caves. Only things that'll aggro up on it are Pirhana, Megalania and (presumably) Megalosaurus. Otherwise, everything else (including Arthropleura and Sarcos) won't aggro. Have at 'em!