acrylics, digital & photography, 2015 &2018
ca.13 million years ago, mid-Miocene, Bullock Creek, Northern Territory, Australia
At the onset of the breeding season, two Dromornis planei drakes warily size each other up. The closer bird utters a booming warning call while the other male examines his rival’s brightly coloured bill, a reliable indicator of health and strength.
Dromornis planei is the bird formerly known as Bullockornis the Demon Duck of Doom. As it turns out, these magnificent 2.5m tall birds were neither ducks nor the bringers of doom.
Mihirungs (Dromornithidae) were once considered to be giant flightless members of the waterfowl clade Anseriformes. Recent analyses have revealed that they belong to an extinct radiation of stem-Galloanserae, basal to both waterfowl and the Galliformes.
A popular 1990s hypothesis presented these birds as hypercarnivores, which used their enormous beaks to slice up their prey. Subsequent research has failed to support this model and these animals were probably herbivores or generalist omnivores. Arguments against the “duck of doom" model include =
* Absence of a hooked bill or sharp talons for tearing meat.
* The bill, while deep, is also extremely thin with limited attachment areas for biting musculature.
* Small eyes that face to the sides of the head.
* High relative abundance to potential prey. Large mihirungs are often the most abundant big animals in their fossil assemblage.
Multiple phylogenetic analyses have resolved Bullockornis as being deeply nested within Dromornis as the sister-taxon of D.stirtoni. The mid-Miocene D.planei (= Bullockornis) is so similar to the late Miocene D. stirtoni that the two are likely an example of anagensis within a single population over time. “Bullockornis” differs from D. stirtoni in having stockier, shorter legs while the bones in the back of the skull are a bit less squished together. Together, this pair clusters with later D. australis, the type species from the early Pliocene, and the Oligocene-Miocene D. murrayi, the oldest member of the genus.
So what did Dromornis use its gigantic bill for? Recent research by Warren Handley and Trevor Worthy at Flinders Uni has shown the uppermost parts of the upper bills of many specimens are both roughened and highly porous, pitted with numerous blood vessels. It is possible that this surface acted as an anchor for a soft-tissue structure, so with Worthy's guidance I've reconstructed a greatly enlarged cere covering most of the upper mandible, similar to that of the modern Cape Barren Goose (Cereopsis). So perhaps the remarkable bills of Dromornis evolved to maximise a brightly coloured display surface.