Giant monitor lizards roamed Australia during the Pleistocene. Scientists are aware of 3 species of giant lizards that lived in Australia: the Komodo dragon (Varanus komodensis), a larger undescribed species, and megalania (Varanus priscus). Komodo dragons still occur as a relic species confined to a remote island owned by Indonesia. They grow to 6 feet long and have a venomous bite. The undescribed species is poorly known from just 1 fossil site. Megalania is an extinct species that grew to over 20 feet long and also had a venomous bite. Megalania remains have been excavated from 5 sites–Wyandotte, Cuddie Springs, Darling Down, Lake Eyre basin, and Colosseum Chamber. Archaeologists are interested in knowing whether humans overlapped in time with megalania. Humans arrived in Australia about 50,000 years ago. The megalania remains from Cuddie Springs and Wyandotte may be less than 50,000 years old, but the dating at these sites is considered unreliable. Now for the first time, scientists have found remains of giant lizards that unequivocally overlapped in time with humans.
Photo taken inside the Capricorn Cave System, Australia. The Colosseum Chamber, where the youngest reliably dated remains of a giant monitor lizard were found, is part of this cave system.
The Capricorn Cave system is located near Mt. Etna.
Size comparison between human and megalania, the extinct giant lizard that roamed Australia until humans colonized the continent.
Scientists excavated a bony osteoderm of a giant lizard from a cave deposit inside Colosseum Chamber. This hard skin plate could’ve belonged to any of the 3 species of giant monitor lizards mentioned above, but was 4x larger than the osteoderm of the largest species of monitor lizard found in Australia today. Komodo dragon remains are not known from Australian sites younger than the mid-Pleistocene, so this specimen likely belonged to 1 of the even larger species of Varanus lizards. Most of the fossil remains in this cave deposit consist of owl prey–the inside of the cave served as an owl’s roost for thousands of years. But bones of kangaroos and wallabies are mixed with the ancient owl pellets. Scientists used carbon dating of charcoal and uranium-thorium dating of straw stalactites to estimate an absolute age for the level of the deposit where the giant lizard specimen was found. The age of the deposit ranges between 51,000 BP-30,000 BP. The giant lizard skin plate was found closer to the deeper older level of the deposit.
Although the temporal co-occurrence of humans and giant lizards in Australia doesn’t prove humans were responsible for the extinction of megalania, it shows overhunting by or competition with humans can’t be ruled out. I have no doubt humans were the cause of megalania’s extinction. Megalania existed for millions of years, yet didn’t become extinct until man arrived on the continent. This species survived dozens of dramatic climatic changes, but they didn’t become extinct until man shows up. That can’t be coincidence.
Environmental changes resulting from Ice Age aridity may have made it more likely that humans came into conflict with giant lizards. I hypothesize that during mid-Pleistocene arid climate cycles, megalania outcompeted Komodo dragons for dwindling resources, explaining why there are no certain remains of Komodo dragons younger than 283,000 BP in Australia. However, during the late Pleistocene when environmental conditions deteriorated, this time humans outcompeted megalania for the dwindling resources. Moreover, megalania feared nothing–a disastrous behavior pattern for a large animal when confronted by men with projectile weapons.
Hominids did co-exist with Komodo dragons for 900,000 years in the region of what today is Indonesia. These islands are lush and surrounded by abundant seafood. Humans had no need to hunt big lizards for food here. But the interior of Australia, especially during dry climate stages, was an harsh environment where humans were forced to hunt giant lizards for food. Australian aborigines were the real dragon hunters. A few men with atlatls could’ve easily dispatched the former top predators of Australia. But I’m sure some people were killed and eaten by giant lizards before the real life dragons were eradicated from the land.
Gilbert, Price; et.al.
“Temporal Overlap of Humans and Giant Lizards (Varanidae; Squamata) in Pleistocene Australia”
Quaternary Science Reviews October 2015