Origin of the world’s largest lizard

Unravelling the origins of the Earth’s largest living lizard, the Komodo dragon, scientists have found that its ancestors bred with sand monitor lizards from Australia and southern New Guinea millions of years ago.

“The Komodo dragon and sand monitors share more genetic variants between them than expected, suggesting they bred with each other in the past,” says lead researcher Carlos Pavón Vázquez, from Australian National University.

“Also, the sand monitors are more similar in their physical appearance to the Komodo dragon than what you would expect if hybridisation had not occurred.”

The comprehensive study, published in the journal Systematic Biology, adds to evidence that the giant lizards (Varanus komodoensis) likely originated in Australia – not their current home in Indonesia, as originally surmised.

Their large size had been attributed to conditions on the islands, such as lack of competition with other predators and sizeable prey such as now-extinct dwarf elephants. 

The researchers suggest they crossed the sea to get into Indonesia before becoming extinct in Australia – independently confirming previous suggestions based on fossil records.

“In Australia there weren’t any dwarf elephants, and the Komodo dragon lived alongside other large predators such as the marsupial lion, the Megalania (an even larger monitor lizard) and terrestrial crocodiles,” says Pavón Vázquez.

“Thus, we need to rethink the reasons behind the uniqueness of the Komodo dragon, as it didn’t originate in those tiny islands where it now lives.”

In shedding new light on the dragon’s origins, the team’s primary focus was hybridisation – successful interspecies breeding. Because past studies have shown conflict between evolutionary stories told by different genes in the Komodo dragon and other closely related monitor lizards, Pavón Vázquez and team wanted to check if hybridisation was at play.

Technical advances are revealing this is more widespread in nature than previously thought, they say, suggesting it has played an important role in evolution.

They collected genetic data from the dragon and other species of monitor lizard. They also obtained measurements such as head, leg and tail length from valuable specimens in natural history collections to test whether the conflict between genes was due to hybridisation or other evolutionary phenomena.

They also reconstructed ancient geographic ranges of the lizards based on their current distributions and relationships between them – which support the view that the dragon and sand monitors lived together in northern Australia millions of years ago. 

Learning about the dragon’s evolution has important conservation implications. The powerful three-metre-long lizard, which can slay large prey including pigs, deer, buffalos and even the random human, is under threat.

“By learning more about the Komodo dragon’s past and how it responded to changes in its environment,” says Pavón Vázquez, “we can be better prepared to design conservation strategies that will safeguard this iconic animal from the catastrophic effects that human activities have on our planet and its inhabitants.”