Life as a human on this planet before the dawn of modern industrial civilization was probably pretty tough. Especially if you lived in Australia, where the wildlife is giant, scary, and unforgiving.

According to a report from the Sydney Morning Herald, researchers from the University of Queensland have found evidence that some of the earliest inhabitants of the continent likely had to go about their business watching out for massive predatory lizards, some of which weighed up to half a ton.

Vertebrate paleoecologist Gilbert Price explains how researchers in central Queensland made a shocking discovery when they realized that the earliest human residents of Australia were likely sharing the same turf with “giant apex predator lizards.”

Dr. Price and his research team were excavating one of the Capricorn Caves near Rockhampton when they found they found something strange – a tiny fossil from the lizard buried two meters deep. The bone was only a centimeter long, but it was likely an osteoderm, which came from beneath the lizard’s skin. It is the youngest record of one of the giant lizards on the entire continent of Australia.

The research team used radiocarbon and uranium thorium dating to determine the bone’s age. They found that it was roughly 50,000 years old, which was around the same time when Australia’s first aboriginal settlers arrived on the continent.

“We can’t tell if the bone is from a Komodo dragon, which once roamed Australia, or an even bigger species like the extinct Megalania monitor lizard, which weighted about 500 kilograms and grew up to six meters long,” Dr. Price mused.

Megalania has been extinct for roughly 30,000 to 40,000 years. They were native to Australia, and flourished during the Pleistocene era. The name Megalania prisca was given to the massive beast by Sir Richard Owen, and refers to the “great Saurian.” It translates to “ancient great romer.”

There is currently a lack of complete fossil skeletons, so researchers only have partial individuals by which to learn about the beasts. Conservative estimates reveal that the beast reached an average length of 11 feet and a weight of 350 pounds, but other guesses place the lizard as being much bigger. Regardless of the range of size estimates, it was undoubtedly the largest land lizard that is known to have existed.

Megalania probably didn’t bother early human settlers too much, as it had a plethora of easier prey to hunt. It likely fed on giant marsupials like Diprotodon, in addition to other lizards, small mammals, and birds. It was build like a predator, with stocky limbs, a large skull, and a jaw full of razor-like serrated teeth.

Megalania had another tool to ensure that it captured its prey with ease – venom. It joins the Komodo dragon and lace monitor in the class Toxicofera, which includes all other reptiles that have oral glands that secrete toxin. They are closely related to the non-venomous Iguana, Anguimorpha, and Serpentes reptiles. It was likely the largest venomous vertebrate ever discovered.

The finding is significant because it represents the biodiversity present on the island at the time the first human inhabitants arrived. Today, the largest lizard left in Australia is the perentie, which reaches a length of two meters. Dr. Price said that during the last ice age, Australia was likely home to giant killer lizards and inland crocodiles that reached lengths of up to nine meters. The discovery may help researchers begin to figure out what happened to these massive lizards, which no longer walk the continent.

“It’s been long-debated whether or not humans or climate change knocked off the giant lizards, alongside the rest of the megafauna,” Price said.

As of now, humans can explain a part of the giant lizards’ extinction, but there is still much information that scientists don’t have. The Capricorn Caves are famous for their massive underground cache of fossils, and researchers have been returning to them for decades to sift through the millions of bones left behind by predators over the years. The manager of Capricorn Caves, Ann Augusteyn, takes great care with her team to ensure the caves are left undisturbed for the purposes of research. Augusteyn was thrilled by the finding in the caves. “The study also begs the question – what else is entombed in our caves and what else can we learn?” she asked.