11 Of Ancient Earth’s Most Unbelievable Prehistoric Animals

Published December 2, 2021
Updated February 7, 2025

Megalania Prisca: The World’s Largest Lizard

Megalania

Wikimedia CommonsA skeleton of the enormous megalania.

Today’s Komodo Dragons can weigh up to 150 pounds, but their ancestor, Megalania prisca — also called Varanus priscus or Giant Monitor Lizard — could grow to between 500 and 4,000 pounds. It’s the largest known lizard to have ever walked the Earth.

Between two million and 40,000 years ago, these intimidating creatures easily reigned over present-day eastern Australia. Up to 25 feet long, they likely feasted on a wide variety of animals, including kangaroos, pygmy elephants, and tortoises.

Though they could certainly use their size to subdue and kill prey, the M. prisca also had another tool at their disposal: toxic saliva. Scientists believe that they used venom from glands in their lower jaw to kill.

That said, it’s possible that M. prisca occasionally faced predators of its own. During its life, it shared an environment with The Marsupial Lion (called Thylacoleo) and a 500-pound crocodile (known as the Quinkana). It’s hard to predict if the Giant Monitor Lizard could win a bout with these dangerous prehistoric animals.

Varanus Priscus Skull

Wikimedia CommonsA skull of the Giant Monitor Lizard.

English naturalist Richard Owen first described M. prisca in 1859. He’s the one who gave it its name (which means giant roamer) but contemporary scientists believe he mislabeled it, which is why it also goes by the name Varanus priscus.

Since Owen’s discovery, however, scientists have found very few fossilized remains of the Giant Monitor Lizard. That means that there’s still a lot to learn about this prehistoric animal.

There are some theories out there about why the M. prisca died out, however. Although humans didn’t seem to hunt it directly, they did hunt animals that the M. prisca relied on as prey. As such, people may have played an indirect role in its extinction.

Then again, as with the giant sloth, some believe that the Great Monitor Lizard never went extinct at all. Rumor has it that the beast simply crept into the Australian wilderness and lives there to this day.

author
Kaleena Fraga
author
A senior staff writer for All That's Interesting since 2021 and co-host of the History Uncovered Podcast, Kaleena Fraga graduated with a dual degree in American History and French Language and Literature from Oberlin College. She previously ran the presidential history blog History First, and has had work published in The Washington Post, Gastro Obscura, and elsewhere. She has published more than 1,200 pieces on topics including history and archaeology. She is based in Brooklyn, New York.
editor
Leah Silverman
editor
A former associate editor for All That's Interesting, Leah Silverman holds a Master's in Fine Arts from Columbia University's Creative Writing Program and her work has appeared in Catapult, Town & Country, Women's Health, and Publishers Weekly.
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Fraga, Kaleena. "11 Of Ancient Earth’s Most Unbelievable Prehistoric Animals." AllThatsInteresting.com, December 2, 2021, https://allthatsinteresting.com/prehistoric-animals. Accessed July 27, 2025.