Once upon a time, there was a supercontinent named Gondwana. Around 85 million years ago, during its fragmentation, the country we now know as Australia began to form – and around 30-35 million years ago, its segregation from Antarctica was complete.
As revealed in a new study by the Australian National University, it appears that this tectonic shift coincided with mass extinction on the brand new continent, wiping out a decent swath of the nation’s lizards.
Writing in the journal Evolution, the team explain how they took a comprehensive look at the evolutionary history of the Pygopodoidea, a superfamily of ecologically diverse lizards that have long occupied various niches across Australia.
Using molecular genetics, fossil evidence, and complex algorithms to predict how these geckos would have responded to the sudden isolation of Australia, they came to the conclusion that their diversity bottomed-out around that time.
Pinning down the causes of such enormous extinction events are always quite tricky, and there’s rarely just one primary antagonist. The non-avian dinosaurs’ final chapter may have been marked by a catastrophic asteroid impact, but the rise of opportunistic mammals and prolonged volcanism also played key roles long before the coup de grace took place.
In this case, however, it appears that there was indeed one villainous phenomenon above all others – rapid climate change. In this case, over 100,000 years, the region cooled by 5°C (9°F) – extremely quickly by any measure – and Australia began to transition from being a tropical rainforest-covered landmass to a cold, arid one.
To be fair, the entire world at the end of the Eocene Period (around 33 million years ago) was cooling down, and no one is entirely sure why. Preserved climate records suggest that there was a rather significant drawdown in the amount of carbon dioxide in the atmosphere, and some have suspected this was related to several as-of-yet unconfirmed asteroid impacts around the world.
Whatever the cause, Earth in general became decided chilly, and around 12 percent of all marine life died out – a huge extinction event to be sure, but nothing like that which finished off the non-avian dinosaurs, or the Great Dying event 252 million years ago that wiped out up to 96 percent of all life.
Australia ain't what it used to be. FiledIMAGE/Shutterstock
In any case, the isolation of Australia appears to have left these geckos stranded on a continent they couldn’t live in. With their traditional environments disappearing all over the continent, plenty of them were unable to adapt and died out.
Those sneaky few that did manage to adapt went on to occupy the eventual hot deserts of Australia, and ultimately evolved into the myriad of species you can still find there today. Many died, and some thrived – the history of natural selection in a nutshell, really.