Size and Weight:
Aside from the crocodiles, very few prehistoric reptiles after the age of dinosaurs achieved enormous sizes--the notable exception being Megalania, the giant monitor lizard. Depending on reconstructions, Megalania measured anywhere from 12 to 25 feet long and weighed in the neighborhood of 500 to 4,000 pounds--a wide discrepancy, to be sure, but one that would still put it in a bigger weight class than the largest lizard alive today, the Komodo Dragon (a relative lightweight at "only" 150 pounds).
Some paleontologists speculate that Megalania was the "apex predator" of Pleistocene Australia, feasting at leisure on mammalian megafauna like Diprotodon (better known as the Giant Wombat) and Procoptodon (the Giant Short-Faced Kangaroo). This giant monitor lizard would have been relatively immune from predation itself, unless it happened to spar with Thylacoleo, the Marsupial Lion. Whatever, the case, Megalania is one of the few recent, giant animals the demise of which can't be traced directly to early humans; it was probably doomed to extinction by the disappearance of the gentle, herbivorous, oversized mammals that early Australians preferred to hunt instead.