Sat. Sep 24th, 2022
Image of a rock with a spring fossil that preserves many fine branches.
enlarge One of the spectacular feather fossils that has been in a museum’s sample collection for decades.

Researchers have described ten fossil feathers from the polar regions of the former continent of Gondwana for the first time. The collection, documented in a recent article in Gondwana Researchcontains a very diverse array of feathers collected from the 118 million year old Koonwarra Fossil Bed in Victoria, Australia.

The article describes what may be the earliest evidence of a battle spring and the very first non-avian dinosaur feathers found within the Antarctic Circle. It also documents dark coloring and insulating branching structures on some feathers, providing valuable insight into how Arctic dinosaurs may 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 did not exist at the time. They had been tucked away in a drawer in the Melbourne Museum for decades, until lead author Martin Kundrát came across an old paper in 2012 describing one of the feathers.

“It immediately caught my attention,” 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 to pay attention.”

An unlikely (re)discovery

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

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

The first two fossil feathers found at the site were unearthed shortly after its discovery in 1962. One was tufted, like a small feather duster. Several more feathers were discovered over the next two decades, but interest in the Koonwarra Fossil Bed waned in the 1980s after it failed to yield many fossil bones. Fortunately, the small collection of feathers survived, tucked away in a museum archive.

Meanwhile, the field of paleontology changed. The first feathered fossil of non-avian dinosaurs was discovered in China in 1996, and China became a hotbed of feathered dinosaur research. In 2010, another breakthrough came: Researchers found that some fossil feathers contain microscopic evidence of their former color in the form of specialized organelles called “melanosomes.”

Since then, techniques for interpreting microscopic details preserved in soft tissue fossils have become increasingly sophisticated. “The technology to analyze and study different aspects of fossils is always advancing,” said Lisa Buckley, a vertebrate paleontologist who specializes in trace fossils from the Cretaceous. “The specimens stored in archives of the past provide the basis for discoveries of the future.”

So when Kundrá came across a decades-old paper that mentioned a fossil feather in Australia, he knew he had to track it down. “My curiosity was well rewarded by accessing these fantastic forgotten specimens,” he said.

A detective in a micropaleo world

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

To study the overall structure and function of the tiny feathers, the team used scanning electron microscopy to look at each feather in great detail. The tufted, duster-like feathers were likely the body feathers of 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 bird feather in particular stood out. It has a thick central spindle (the part of the feather you would use as a quill pen), with vanes on either side that appear to be “zipped” with small hooks called barbicels. In modern birds, barbicels are the structures that allow flight feathers to hold their shape while birds flap their wings. If the microscopic hooks are indeed barbicels, it will be the earliest evidence of a flyable feather ever found.

Such a find is especially interesting in a cold polar region, because a “bird of this size with the ability to fly actively in the freezing Cretaceous environment would have to have a very high metabolism comparable to that of modern birds,” Kundrát said. .

The team also looked for the small melanosomes that could provide an indication of the feathers’ earlier colors. The color produced by melanosomes is determined by their shape – round ones indicate a color from yellow to brown, while elongated ones are shades of gray. Kundrá found densely packed elongated melanosomes on several of the fuzzy non-avian proto feathers, indicating a dark color similar to the iridescent plumage previously described in small carnivorous dinosaurs such as Micro bird of prey. One of the bird-like feathers, meanwhile, appears to be patterned with dark bands.

Evidence from patterns indicates that the color of the feathers may 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 the study’s principal investigator. “The microscopic and spectroscopic techniques we have used provide insights into staining and conservation that are at the forefront of modern paleontology.”

More to discover

The microstructural details discovered in the Koonwarra fossils are helping researchers understand how Cretaceous dinosaurs and birds used these early feathers to survive polar conditions. It also provides insight into the kind of lifestyle these creatures may have had and hints at the possibility of more discoveries.

No one has yet found a fossil dinosaur with intact feathers from the polar region of Gondwana, but now researchers have evidence that such a fossil may still exist, waiting to be discovered. New remote sensing techniques could be used to find other fossil beds in the area near the Koonwarra site — which may have formed in conditions more favorable to fossil bone preservation.

“This study is an excellent example of why well-funded, stable and fully supported museum archives are critical to the study of natural history,” Buckley said. “By studying fossil feathers, such as the beautiful specimens collected from the Koonwarra Fossil Bed, we can shape the picture we have of Australian and polar Paravian dinosaurs.”

By akfire1

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