‘Thunder’ bird brains rock

FOSSIL hunters are thunderstruck by the latest discoveries of a ‘demon duck’ that went extinct in Australia about 50,000 years ago.
Weighing up to 600kg with a head and powerful beak up to half a metre long, the flightless bird also called ‘demon ducks of doom’ and ‘thunder birds’ stood up to 3m tall and lived for millions of years in forests around river channels and lakes across Australia.

PENTAX Image

It was heavier than the Giant Moa of New Zealand and taller than the Elephant Bird of Madagascar.
In a new study published in the journal Diversity, palaeontologists found the brains of Dromornis stirtoni, the largest of the dromornithid or ‘mihirungs’ (Aboriginal word for ‘giant bird’ from the Tjapwuring people of western Victoria), are similar to modern chickens and Australian mallee fowl.
“Together with their large, forward-facing eyes and very large bills, the shape of their brains and nerves suggested these birds likely had well-developed stereoscopic vision, or depth perception, and fed on a diet of soft leaves and fruit,” Flinders University lead author Warren Handley said.
Flinders vertebrate palaeontologist Trevor Worthy added: “The unlikely truth is these birds were related to fowl, chickens and ducks, but their closest cousin and much of their biology still remains a mystery. While the brains of dromornithids were very different to any bird living today, it also appears they shared a similar reliance on good vision for survival with living ostrich and emu.”
Researchers compared the brain structures of four mihirungs, from the earliest Dromornis murrayi (24Ma) to Dromornis planei and Ilbandornis woodburnei (12Ma) and Dromornis stirtoni (7Ma).
“This bird had the largest skull but behind the massive bill was a weird cranium. To accommodate the muscles to wield this massive bill, the cranium had become taller and wider than it was long, and so the brain within was squeezed and flattened to fit,” Associate Professor Worthy said. “It would appear these giant birds were probably what evolution produced when it gave chickens free reign in Australian environmental conditions and so they became very different to their relatives the megapodes, or chicken-like land fowls which still exist in the Australasian region.”

Inside their head

While bones of giant birds are relatively common in the fossil record, their skulls are extremely rare. The most complete skull known, of Dromornis planei, was discovered in the late 1980s. Neutron CT scanning technology enabled the Flinders researchers to ‘see’ inside the skull to reveal the shape of the brain for the first time since it was discovered.
Brain models also were made from CT scans of five other dromornithid skulls from fossil sites in Queensland and the Northern Territory. The oldest Dromornis murrayi (25Ma) was found in the Riversleigh World Heritage Area in Queensland.
Palaeontologists have unearthed dromornithid foot impressions from southeastern Queensland. The most recent evidence, of Genyornis newtoni, including carved footprints and cave paintings, has surfaced at Cuddie Springs in north-central NSW and dated at 31,000 years old when Aboriginal people occupied the megafauna-filled continent (Megafaunal species include animals weighing more than 47kg, such as the extinct marsupial lion Thylacoleo carnifex; herbivorous diprotodons and giant land lizards).
Palaeontologists have also discovered fossil stones found in the birds’ gizzards (gastroliths) to help the digestion of coarse and solid foods.
Many palaeontologists are convinced they were herbivores, but others think at least some dromornithids may have eaten meat based on the shape and size of their skulls and beaks. Analysis of eggshells in Genyornis supports a plant diet.
Today, Australia is home to two species of giant flightless bird, the emu and the cassowary. These two species are closely related to other giant flightless birds that evolved on the former southern landmass of Gondwanaland including the ostrich of Africa; rhea of South America; kiwis of New Zealand; and extinct moa and elephant birds of New Zealand and Madagascar, respectively.