© Illustration by Peter Trusler A cache of fosslized feathers found in Australia provides solid evidence that small carnivorous dinosaurs, l...
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| © Illustration by Peter Trusler A cache of fosslized feathers found in Australia provides solid evidence that small carnivorous dinosaurs, like the one illustrated here, sported insulating plumage to help them survive life within the southern polar circle. |
Ten exquisitely preserved fossil feathers found in Australia represent the first solid evidence that feathered dinosaurs lived at Earth’s poles, paleontologists report in an upcoming study in the journal Gondwana Research.
The feathers date back 118 million years to the early Cretaceous period, when Australia was much farther south and joined with Antarctica to form Earth’s southern polar landmass. Although the environment would have been warmer than Antarctica today, the dinosaurs that sported this plumage probably endured many months of darkness and potentially freezing temperatures during winter. (By the late Cretaceous, Antarctica was warm enough for South American sauropods to trek across the south polar region and into Australia.)
“Fossils feathers have never been found in polar settings before,” says study coauthor Benjamin Kear, a paleontologist at Uppsala University in Sweden. “Our discovery … shows for the first time that a diverse array of feathered dinosaurs and flight-capable primitive birds inhabited the ancient polar regions.”
While the delicate bones of dinosaur-era birds have been found in polar places before, none have so far sported fossilized feathers. Fossils of an extinct type of penguin found in Peru included plumage, but they date to about 36 million years ago, when that landmass was seated farther north. (Find out why today’s birds are the dinosaurs that didn’t die.)
Finding Cretaceous feathers in this part of Australia is therefore a vital clue to the many uses ancient animals found for these distinct body coverings, from mating displays to flight. In this case, feathers may have been important for insulation, allowing small carnivorous dinosaurs to survive the difficult winter months.
“It makes perfect sense that these feathers would have helped to keep dinosaurs and primitive birds warm at high latitudes during the Cretaceous,” says Ryan McKellar, an expert on fossil feathers and a curator at the Royal Saskatchewan Museum in Regina, Canada.
“It is spectacular to see data from rocks this old and this far south,” he adds. “The report provides a really important snapshot of early Cretaceous polar plumage.”
Lost to the lake
The newly described feathers were all found at a site called Koonwarra, about 90 miles southeast of Melbourne in the state of Victoria. A road cut into a hillside in the 1960s revealed a rich seam of fossils, and over the past 60 years, digs there have uncovered numerous fossil fish and plants, as well as the array of well-preserved plumage.
None of the feathers are currently associated with distinct dinosaur or bird bones. Instead, they were probably lost during molting or preening and drifted on the wind onto the surface of an ancient lake, where they sank to the bottom and were preserved in the fine mud. (Also find out about a huge pterosaur that once soared over the Antarctic Peninsula.)
For the new study, Tom Rich of the Melbourne Museum and Patricia Vickers-Rich of Monash University, who have led digs at Koonwarra over the past 37 years, worked with an international team to analyze the finds, showing that the 10 feathers are highly diverse. The fossils include downy feathers for insulation, a fluffy protofeather that most likely belonged to a nonavian dinosaur, and one complex flight feather like those on the wings of modern birds.
Most of these feathers are an inch or less in length and perhaps belonged to enantiornithines, an extinct group of primitive birds that were very diverse during this time in the early Cretaceous, Kear says. Some of the feathers are so tiny that there is the tantalizing possibility they came from hatchlings, he adds.
However, all but one of the feathers could not have sustained any kind of flight, further hinting that some of them may have belonged to ground-dwelling carnivorous dinosaurs, says lead author Martin Kundrát, a paleontologist at of Pavol Jozef Šafárik University in Slovakia.
The protofeather “is entirely consistent with some of the tufted [dinosaur] protofeathers identified from the early Cretaceous rocks of China, and from Canadian Cretaceous amber,” McKellar says. (See a whole dinosaur-era bird found trapped in amber.)
Based on its size, the protofeather was probably left by a relatively small dinosaur like a dromaeosaur, the group of speedy carnivores that includes Velociraptor and Deinonychus. A few fossil bones and teeth have been found in Victoria that belonged to slender-snouted dromaeosaurs called unenlagiids, which are well known from South America and may have eaten fish. It makes sense, then, for similar dinosaurs to have been hunting next to a Cretaceous lake.
“We know from the abundant fossil fish in the lake that there would have been possibly a food source for them,” says Stephen Poropat, a paleontologist at Swinburne University in Melbourne.
Seasonal colors?
The study authors also found fossilized traces of packets of pigment called melanosomes in the feathers, suggesting that many of the animals would have been black, grey, or brown, or that they had dark stripes.
This is somewhat surprising for polar animals, since dark coloration wouldn’t have been good camouflage in snowy, wintery environments, Poropat noes. Maybe these dinosaurs and birds were changing color seasonally, as Arctic ptarmigans do today, he says.
“But it’s also possible that it wasn’t getting that cold at the South Pole during this part of the Cretaceous, and they didn’t need to be pale-colored to blend in with snowdrifts,” he says.
Solving the puzzle will require more fossils, and Rich is hopeful that one day the team may find entire fossilized dinosaurs or birds at Koonwarra similar to the beautifully preserved feathered dinosaurs of northeastern China.
“To actually find the skeleton of a feathered dinosaur here in Australia would be amazing,” Poropat says. “And as far as we know, Koonwarra is the site from which it is likely to come.”
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