Megalania was a large monitor-like lizard that lived in australia during the Pleistocene Era, about 2.5 million years ago. The massive reptile was about 23 feet (7 meters) long, the size of a Saltwater Crocodile, the largest reptile alive today. It also had a poisonous bite just like its relative, the Komodo Dragon.
Megalania would normally prey on on Australia's large Marsupials, such as Diprotodon and Procoptodon. It would have used its veneomous bite to take down these large animals. Megalania shared it's habitat and rivaled with the marsupial lion Thylacoleo, crocodiles, and other monitor lizards. A Study of modern-day Monitor Lizards prove that Megalania was most likely very noisy when it walked or moved, so chasing down prey likely wasn't an option. What it most likely did was, like modern lizards, lay in wait for prey to pass by, and then jump out in ambush and bite down using its powerful jaws and venom to take them down.
One theory of how Megalania became extinct is that after Diprotodon and Procoptodon died off, there was not enough food to sustain such a large reptile, and slowly the population died to extinction. Another theory is that the first humans who colonised Australia hunted the gigantic lizard to extinction. There's also a theory of the combined two, that early man burned the once plentiful forested areas to protect themselves from this mighty reptile, and doing so not only helped directly kill off Megalania, but also indirectly, since it ran out of places to hide in ambush and the prey andimals it once fed on had no more food. There is one last, very unlikely theory that a small population of Megalania still lives on in the outback, stories of cattle savidged in the night by mysterious killers and large footprints in the sand. But as of yet, it cannot be proved and is highly unlikely that Megalania lives on.
Megalania had a large role in Mega Beasts, where they talk about how it might have lived and interacted in its environment, even when early man came into the picture. It shows how it had a venomous bite, how it took down prey like the short-Procroptodon, Diprotodon, and the marsupial lion. It also shows how it might have gone extinct by early man. Megalania also featured in an episode by BBC called Monsters We Met, where it shows how early men in Australia lived alongside this monstrous lizard. It was shown to have killed an aboriginal, and the leader, determined to get revenge on the reptile, found out how to use Megalania's cold-blooded nature to their advantage, and they got up early while the lizard was still sluggish, and burned it. It made an appearance in Jeff Corwin's Giant Monsters, where Jeff was chased around by one. It was also in an episode of Lost Tapes, where a herpetologist gets lost in the jungles of Australia and was killed by a Megalania or "Devil Dragon".