Australia: The Land Where Time Began

A biography of the Australian continent 

Beware the The Demon Duck of Doom

The Dromornithidae

In Aboriginal legend of the people from western Victoria there is mention of a giant emu called Mihirung. The legend has now been found. It is Genyornis newtoni, the last member of the family Dromornithidae or thunderbirds to survive in Australia, apparently until the arrival of the Aboriginal People. This bird looked very much like a heavy ostrich.

They ranged from about the size of a cassowary up to possibly the largest bird that ever lived. Their appearance was similar to an emu, with powerful legs, reduced wings, and no sternum. The skulls, however, were very different from those of emus. Another difference was that the end bones of the toes looked more like small hooves than the claws expected in flightless birds. So far there are 5 genera and 7 species recognised. At the time of writing there is one new genus being studied but not yet named. 

They have been found only in Australia, though some foot bones have been found in Antarctica that may be dromornithid but have yet to be classified. They are mostly found in the eastern half of Australia, but there is some evidence that they were also in Tasmania and Western Australia. At some Northern Territory sites their remains are so common that they comprise about 65 % of all fossils. 

The earliest evidence of dromornithids are footprints in southeast Queensland that could be from these birds, but so far it's not certain. They have been dated to the Early Miocene, about 50 million years ago. The oldest identified bones of this family are found at Riversleigh, Queensland, from the Late Oligocene, about 25 million years ago. The most recent species to be found was Genyornis newtoni, from Caddie Springs north-central New South Wales that have been dated to 31,000 years ago. At this age they almost certainly inspired the Aboriginal legend of the Mihirung, as they would have been present when the first Aboriginal People arrived. From the fossil evidence so far it seems they were probably at the peak of their diversity in the Late Miocene when 3 species lived at the same time. 

The skulls are often missing from the fossils so there has been some confusion over the type of skull and beak, which in turn made it difficult to speculate on what they ate. The skull of some species, such as Bullockornis and Dromornis, have now been studied sufficiently to show that they were much larger and heavier than an emu skull. The narrow, deep bill made up 2/3 of the skull, with the front part being specialised for cutting and the back part for crushing. The muscle attachments showed that the muscles that operated the beak were large. They had a powerful bite. 

Other evidence of Dromornithids found include trackways, cranial endocasts, almost complete eggs and eggshell fragments, and gizzard stones.

The belief that Dromornithids were herbivores is based on the following points:

• the lack of a hook at the end of the bill
• the lack of talons on the toes
• the association of gizzard stones with some specimens
• the large number of individuals occurring together, suggesting flocking behaviour.

Amino acid analysis of Genyornis eggshells also indicates that this species was herbivorous.

The size and heavy construction of the skulls of Bullockornis and Dromornis argue for something other than the normal herbivorous diet. It is possible that these 2 species were either carnivores or scavengers. The multi-part make-up and heavy structure of their beaks, as well as the heavy musculature, make it at least possible that they weren't herbivores. A problem with classifying these 2 species as herbivores is that no source of vegetable food requiring such large and powerful beaks is known from their environment. 

It is known that while the vast majority of kangaroos are exclusively herbivores, at least a few became carnivores, so why not a few of the Dromornithids. 

One of the arguments put forward as evidence against the hypothesis that they were carnivores is that they were too heavy to run down prey, so must have been either herbivores or scavengers. The emu, a known fast runner, has long, slender legs, though still powerful enough to disembowel an attacking dingo. But the legs of Dromornithids were much more heavily built. Biomechanical studies have been carried out on the legs of known Dromornithids and the conclusion drawn, based on the size of the muscle attachments and the estimated size of the muscles, was that they could indeed run much faster than originally assumed, and that at least some of the middle-sized species may have been able to outrun an emu. The emu achieves its speed by making its legs lighter, but the Dromornithids achieved the same goal by making the muscles larger. 

Relationships

For some time it was thought that the dromornithids were related to the ratites, the large flightless birds that include emus, cassowaries, and ostriches. It is now mostly accepted the similarities in appearance between dromornithids and ratites is a case of parallel evolution resulting from their adopting of a similar lifestyle. As more research has been done on the skulls, which were not always present in the earlier discovered fossils, it is now thought that they branched off from the line that eventually led to the anseriformes, which includes ducks and geese, at an early stage of their evolution.

Because of this combination of its large skull and possible carnivorous habits and its probable waterfowl relationships, Bullockornis was nicknamed 'The Demon Duck of Doom'!!

Dromornithidae

Dromornithidae indeterminate
Remains that can only be identified as belonging to this family are known from a number of localities. Some of these of particular interest are listed below.

Early Eocene (Redbank Plains Formation). QLD: Redbank Plains [foot impression] Mid-Tertiary. TAS: Endurance Tin Mine pit, 5 miles north of Pioneer [trackway] Late Oligocene/Early Miocene. SA: Muloorina Station: Snake Dam Locality [eggshell] Pleistocene. WA: Mammoth Cave

Barawertornis tedfordi Rich, 1979
Late Oligocene-Early Miocene. QLD: Riversleigh

Undescribed new genus and species
Late Oligocene-Middle Miocene. QLD: Riversleigh

Bullockornis planei
Rich, 1979 Middle Miocene. NT: Bullock Creek

Dromornis australis Owen, 1872
Pliocene. QLD: Peak Downs

Dromornis stirtoni Rich, 1979
Late Miocene. NT: Alcoota Station

Ilbandornis woodburnei Rich, 1979
Late Miocene. NT: Alcoota Station

Ilbandornis lawsoni Rich, 1979
Late Miocene. NT: Alcoota Station

Genyornis newtoni Stirling & Zietz, 1896
Pleistocene. SA: Lake Callabona; Baldina Creek; Mt Gambier; Naracoorte; Salt Creek. NSW: Cuddie Springs

Bullockornis

It was assumed that the earlier and the smaller Bullockornis and Ilbandornis were also herbivorous. Then in 1997 a 38.5 cm long skull of Bullockornis planei was discovered. Birds have heads that are big enough to match the size of the food they normally, so if Bullockornis ate fruit they must have been enormous. Some think they ate tough plant material. It is thought by some that they may have been carnivorous. 

Stirton's Thunder Bird (Dromornis stirtoni)

These flightless birds from the Late Miocene have been found on Alcoota Station in the Northern Territory. They grew to 3 m plus, with a skull 46 cm long and 14 cm deep, and may have gone up to 50 cm long. They lived in open woodlands. They were taller than the Madagascan elephant bird and at 500 kg were heavier than the New Zealand Moa. They were thought to have eaten tough fruit until a skull was studied. They are thought to have been the largest, tallest and heaviest, bird that ever lived. They also may have been carnivores, though this is not proven. .

The Dromornithidae are actually more closely related to the anseriformes, ducks and geese, than to the emus as the appearance indicates.

Links

1. http://www.newscientist.com/article/mg 16622404.800-the-demon-duck-of-doom.html
2. http://www.amonline.net.au/birds/factsheets/thunder_birds.htm
3. http://www.washington.edu/burkemuseum/events/duck/
4. http://www.lostkingdoms.com/snapshots/miocene_late_animals_birds.htm
5. http://en.wikipedia.org/wiki/Bullockornis

Sources & Further reading