Way back in the 50s -- the 1850s, that is -- a scientist named discovered fossils of an Australian lizard he dubbed Megalania prisca. Measuring around 20 feet long, and suspected of living at the same time as early humans arrived on Australia, he was one big scary lizard.

Or not.

From the NatGeo blog of self-described "fossil killjoy" Brian Switek:

...Megalania ain’t what it used to be. For one thing, the lizard’s bones are so similar to those of other monitor species – belonging to the genus Varanus – that paleontologists have taken to calling it Varanus priscus. And while it seems likely that the big lizard was venomous, recent size estimates have shrunk this “dragon in the dust.”

Let’s have a look at the traditional baseline first. In 2004, working with the relationship between vertebrae size and body length, paleontologist Ralph Molnar proposed that mature Varanus priscus could have been between 23 and 26 feet long, depending on the anatomy of the tail. But other researchers think such sizes are major overestimates. In a 2002 study that critiqued “the myth of reptilian domination” in prehistoric Australia, anatomist Stephen Wroe reanalyzed old body size data and calculated that the lizard probably averaged about 11 feet in total length and, citing earlier estimates from Molnar, wouldn’t have grown much longer than 15 feet.

Size estimates in a 2012 paper by paleontologist Jack Conrad and colleagues came out in between the extremes. While describing a new, large Varanus species that once lived in Greece, the researchers also took a look back at Australia’s ever-contentious lizard. Without the tail, the Varanus priscus specimen in their study had an estimated body length of almost seven feet, meaning that this individuals total length was almost certainly longer than the 11 foot average Wroe suggested. Especially large specimens, Conrad and coauthors noted, could have had bodies almost 10 feet long with the tails trailing behind, although these animals still would have been smaller than the monstrous lizards paleontologists used to reconstruct.

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Photo: Cas Liber/NatGeo