Giant flightless birds called mihirungs are the largest birds to ever span what is now Australia. These animals, weighing hundreds of kilograms, went extinct about 40,000 years ago. Now researchers may have a better understanding of why.
These birds may have grown and reproduced too slow to bear The researchers reported on August 17 at Anatomical records.
Mihirungs are sometimes called “devil ducks” because of their large size and close evolutionary relationship with today’s waterfowl and game birds. This flightless, plant-eating bird has a lifespan of more than 20 million years.
During that time, some species evolved into Titans. Take Stilton’s Thunderbirds for example (praying mantis). It lived about 7 million years ago, stood 3 meters tall and probably weighed more than 500 kilograms, making it a contender for the largest known mihirung and the largest bird ever recorded.
Most research on mihirungs has focused on their anatomical and evolutionary relationship to living birds. Little is known about the biology of these animals, such as how long it takes them to grow and mature, says paleontologist Anusuya Chinsamy-Turan of the University of Cape Town in South Africa.
So Chinsamy-Turan and colleagues at Flinders University in Adelaide, Australia, collected samples from 20 fossilized leg bones. D.stirtonianimals from different life stages.
“Even after millions of years of fossilization, the microstructure of fossil bones is often still intact,” which can be used to decipher important clues about the biology of extinct animals, Chinsamy-Turan said.
The team examined thin bone sections under a microscope, detailing whether there were any traces of growth. These markers provide information about the rate of bone growth when the bird is alive.
D.stirtoni The team found that it would take 15 years or more to reach full size. Depending on the timing of the transition from fast-growing bones to the slow-growing form thought to be associated with reaching reproductive age, it may have reached sexual maturity several years earlier.
These results differ from the team’s Early analysis Another mihirung bone, Gadfly. That species – the last known mihirung – was less than half its size. D.stirtoni. It lived about 40,000 years ago, a contemporary of the continent’s earliest human inhabitants. G. Newton It grows much faster than its giant relatives, reaching adult size within one to two years, and grows more over the next few years before possibly breeding.
This difference in the rate of development of mihirung species separated by millions of years may be an evolutionary response to Australia’s development of a drier, more volatile climate over the past few million years, the researchers said. Rapid growth and reproduction may be advantageous when resources are unpredictable.
Even so, this seemingly inspiring pace of development in recent mihirungs is slower than the emus with which they live. Emus grow quickly, reaching adult size in less than a year, and they reproduce shortly after, laying a large number of eggs.
This difference could explain why G. Newton Hungry humans went extinct soon after arriving in Australia, but emus continue to thrive today, the team said. The researchers concluded that while mihirungs as a group appeared to have adapted over millions of years to grow and reproduce faster than ever, it was not enough to survive the arrival of humans, who may have eaten the birds and their eggs. .
“Slow-growing animals face dire consequences because of their reduced ability to recover from environmental threats,” Chinsamy-Turan said.
Scientists’ work on other giant, extinct, flightless birds is thought to have come to an end with the help of humans – such as dodo bird in mauritius (knotweed) and Madagascar’s largest elephant bird (Dragon Beast Titan) — indicating that they also grow relatively slowly (serial number: August 29, 2017).
“It’s very interesting to see this pattern repeated time and time again in many large groups of flightless birds,” said Thomas Cullen, a paleoecologist at Carleton University in Ottawa, who was not involved in the new study.
Modern ratites appear to be an exception in handling similar pressures, he said. In addition to the emu, other surviving ratites—such as cassowaries and ostriches—also grow and reproduce rapidly (SN: April 25, 2014).