feather fossils
One of the spectacular feather fossils that has been sitting in a museum's sample collection for decades.
Researchers have described ten fossil feathers from the polar regions of the former continent Gondwana for the first time. The collection, documented in a recent paper in Gondwana Research, contains a highly diverse array of feathers collected from the 118 million-year-old Koonwarra Fossil Bed in Victoria, Australia.

The paper describes what is potentially the earliest evidence of a flight feather, and the first-ever non-avian dinosaur feathers found within the Antarctic Circle. It also documents dark coloration and insulating branching structures on some of the feathers, providing valuable insight into how polar dinosaurs might have stayed warm during long, dark winters.

The fossils were initially discovered in the 1960s, but most of the technologies and knowledge used to understand the feathers described in this study didn't yet exist at that point. Since then, they were tucked away in a drawer in the Melbourne Museum for decades, until lead author Martin Kundrát happened across an old paper in 2012 that described one of the feathers.

"It caught my attention immediately," said Kundrát, a paleontologist at the University of Pavol Jozef Šafárik in Slovakia. "I would say the fossil feathers were waiting for me. It seems I was the first one who paid attention."

An unlikely (re)discovery

In 1961, highway construction workers near the small Australian town of Koonwarra stumbled upon something unexpected: the fossilized remains of a Cretaceous lakebed. The lake had formed for just a few thousand years some 118 million years ago and would have been located farther south than Antarctica's Ross Sea today.

It was nestled in a lush rift valley between the continents of Antarctica and Australia, surrounded by mountains covered in ferns, conifers, and ginkgo trees. The nearby forests were populated by small mammals, dinosaurs, and a giant crocodile-like amphibian called Koolasuchus. Plants and animals alike would have coped with "prolonged periods of polar darkness with winter freezing," Kundrát said.

The first two fossil feathers found at the site were unearthed soon after its discovery in 1962. One of these was tufted, like a tiny feather duster. Over the next two decades several more feathers were discovered, but interest in the Koonwarra Fossil Bed waned in the 1980s after it failed to turn up many fossil bones. Luckily, the little collection of feathers survived, tucked away in a museum archive.

In the meantime, the field of paleontology was changing. The first feathered non-avian dinosaur fossil was discovered in China in 1996, and China became a hotbed of feathered dinosaur research. In 2010 came another breakthrough — researchers discovered that some fossil feathers contained microscopic evidence of their former color in the form of specialized organelles called "melanosomes."

Since then, techniques for interpreting microscopic detail preserved in soft tissue fossils have become more and more refined. "Technology to analyze and study different aspects of fossils is always advancing," said Lisa Buckley, a vertebrate paleontologist who specializes in Cretaceous trace fossils. "The specimens stored in archives of the past are the basis for discoveries of the future."

So when Kundrát happened across a decades-old paper mentioning a fossil feather in Australia, he knew he had to track it down. "My curiosity was well paid off by getting access to these fantastic forgotten specimens," he said.

A detective in a micro-paleo world

To provide new insights into polar feathered dinosaurs and primitive birds, Kundrát and his team employed a number of modern techniques to analyze them at the microscopic level. He described the process as akin to "becoming a detective in a micro-paleo world."

To study the overall structure and function of the small feathers, the team used scanning electron microscopy to view each feather in minute detail. The tufted, duster-like feathers were probably body feathers from a small carnivorous dinosaur like a dromaeosaur, with their branching structure providing useful insulation for cold winters. Feathers with more structure would have belonged to primitive birds.

One avian feather in particular stood out. It has a thick central rachis (the part of the feather you would use as a quill), with vanes on either side that appear to be "zipped" closed with little hooks called barbicels. In modern birds, barbicels are the structures that allow flight feathers to retain their shape as birds flap their wings. If the microscopic hooks are indeed barbicels, this is the earliest evidence of a flight-capable feather that has ever been found.

Such a find is particularly interesting in a cold polar region, as a "bird of this size with a capacity to actively fly in the Cretaceous freezing environment had to possess very high metabolism comparable to those of modern birds," Kundrát said.

The team also looked for the tiny melanosomes that could give an indication of the feathers' former colors. The color produced by melanosomes is determined by their shape — round ones indicate a color anywhere from yellow to brown, while elongated ones are grayscale. Kundrát found tightly packed elongated melanosomes on several of the fluffy non-avian protofeathers, indicating dark coloration comparable to the iridescent plumage previously described in small carnivorous dinosaurs like Microraptor. One of the bird-like feathers, meanwhile, appears to have been patterned with dark bands.

Evidence of patterning indicates that the color of the feathers might have been used for camouflage or communication, while the very dark feathers may have been used to help insulate the dinosaurs during cold winters.

The feathers represent "a surprising morphological and functional diversity," said Benjamin Kear, a paleontologist at Uppsala University and principal investigator of the study. "The microscopic and spectroscopic techniques that we employed provide insights into coloration and preservation that are at the cutting edge of modern paleontology."

More to Discover

The micro-structural details discovered in the Koonwarra fossils help researchers understand how Cretaceous dinosaurs and birds might have used these early feathers to survive polar conditions. It also provides insight into the kind of lifestyle these creatures might have had and hints at the possibility of more discoveries to come.

No one has yet found a fossil dinosaur with feathers intact from polar Gondwana, but now researchers have evidence that such a fossil might yet exist, just waiting to be uncovered. New remote sensing techniques could be used to find other fossil beds in the area near the Koonwarra site — ones that might have formed in conditions more favorable to preserving fossil bones.

"This study is an excellent example of why well-funded, stable, and fully supported museum archives are critical to the study of natural history," said Buckley. "Studying fossil feathers like the wonderful specimens collected from the Koonwarra Fossil Bed helps us flesh out the picture we have of Australian and polar paravian dinosaurs."