DO NOT breed Megatherium for the Swamp Cave, they are too large to navigate between most chambers. A Chalicotherium is a much wiser choice, being able to reach all parts of the cave except the entrance itself and the artifact tunnel; Their boulder attacks can dispatch Arthropleuras without collateral damage and their swipe/bite attack have a large AoE.
As a surprising bonus, Chalicos do not harvest any bodies, including Meganeuras, so you can have a tribe mate using a Beelzebufo collecting tons of cement while you clean the room of other bugs. Beware the huge knockback of their melee attacks, however, as they can and will scatter bodies all around the walls, making your mate's work harder. If possible, stick with boulders until the cement sources are collected.
Oh wait, this is about the Megatherium, right? But yeah, their own tip will go elsewhere.
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!