The demise of Australia’s thunder birds 40,000 years ago has previously been blamed on human nest raiders and crippling bone disease.
However new research reveals the extinction of dromornithids may have been down to something far more mundane: that they were just too slow to adapt to a changing environment.
Big bones from the mighty birds excavated in the northern Flinders Ranges and near Alice Springs have yielded fresh insights into their time-heavy breeding patterns.
Microstructure studies of the fossil finds by vertebrate palaeontologists indicate the size and reproduction cycle of dromornithids gradually changed over millennia.
Yet they failed to keep pace with the world around them.
“Sadly these amazing animals … faced rising challenges of climate change as the interior of Australia became hotter and dryer,” said Prof Anusuya Chinsamy-Turan from South Africa’s University of Cape Town.
“Their breeding biology and size couldn’t match the more rapid breeding cycle of modern day emus to keep pace with these more demanding environmental conditions.”
Prof Chinsamy-Turan said determining how long the birds took to reach adult size and sexual maturity were key to understanding their evolutionary success and ultimate failure to survive alongside humans.
The earliest and largest species, Dromornis stirtoni, lived seven million years ago, stood three metres tall and weighed 600kg.
It also took up to 15 years to fully grow and become sexually mature.
The smallest and last of the flightless mihirung, Genyornis newtoni, lived in the late Pleistocene era when the climate was far drier with greater seasonal variation and unpredictable droughts.
With a body mass of 240kg, it still grew six times larger than emus but reached adulthood faster than the first thunderbirds, likely within one or two years, and started breeding soon after.
However Genyornis newtoni needed several extra years to fully grow and so its progression was still slow compared to most modern birds, that reach adult size in a year and can breed in the second year of life.
Our Australian morning briefing email breaks down the key national and international stories of the day and why they matter.
Co-author of the paper, Flinders University Prof Trevor Worthy, said dromornithids lived alongside emus long before extinction.