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Notes from the edge

Thursday، 30 July 2020 01:03 AM

After years of searching the Arctic, Southern Methodist University scientists have discovered the fragment of a baby dinosaur’s tiny jawbone, providing what they believe is a significant clue to the behaviour of certain dinosaurs.
The theory: Some meat-eating dinosaurs, called dromaeosaurs, lived year-round in the Arctic.
Decades ago, scientists realised that birds might share a common ancestor with dromaeosaurs. So they thought that some dinosaurs migrated south with the changing seasons in search of food like modern-day birds.
Today, most researchers assume that polar dromaeosaurs made the Arctic their home year-round, because their relatively small sizes would make migration difficult.
Dr Anthony Fiorillo and his team recently published their findings in PLOS One. The presence of this baby dinosaur also suggests that during the Cretaceous Period, the Arctic was rich in prey to support families of these meat-eating dinosaurs.
There would have been enough food available in the harsh Arctic environment to sustain a population of carnivorous dinosaurs, said Fiorillo. “To me, this specimen suggests that dromaeosaurs were thriving in an environment because their prey, the herbivorous dinosaurs, had also successfully adapted to an extreme environment,” he said.
More information on the lives of different polar dinosaurs can help scientists better understand how they adapted to live year-round in these colder, darker regions.
The discovery of this juvenile jawbone could also help in understanding the diversity of animals that lived in the ancient Arctic, said Dr Patrick Druckenmiller, a palaeontologist at the University of Alaska Museum of the North.
During the Cretaceous Period, which occurred between about 66 million and 145 million years ago, the Prince Creek Formation of northern Alaska was an open woodland filled with conifer trees and flowering plants. The ancient Arctic was probably a little warmer than it is today, but there would have been mountains, with peaks both high and cold enough to be topped with fields of snow.
The area was once part of “Beringia,” the land bridge that stretched between present-day Asia and North America, allowing dinosaurs to move freely between the two continents. Dinosaurs likely passed through parts of modern-day northern Alaska in their travels back and forth. For a while, this land was thought of as a “dinosaur highway.”
In the 1970s and 1980s, palaeontologists found similar species of large dinosaurs in both northern Alaska and southern Alberta. Since the dinosaur fossils were found thousands of miles apart, some scientists thought that the dinosaurs might have migrated south from the Arctic in search of food when the weather became colder.
“People thought big dinosaurs used to migrate when we re-envisioned dinosaurs not as lumbering lizards but these dynamic ancestors of birds,” said Druckenmiller.
But dinosaurs would have had to travel 1,000 miles in order to migrate from northern Alaska to Alberta or Montana, both south of the Arctic Circle. That would be a longer distance than any living vertebrate, or an animal with a backbone, can migrate on land. The current migration record for vertebrates on land is held by caribou, which travel in herds about 400 miles every year.
For these reasons, other scientists believed that large dinosaurs might have lived in the Arctic year-round. But experts say they never thought that smaller dinosaurs such as the dromaeosaurs migrated south from the Arctic. Adult dromaeosaurs are only 6- to 8-feet long, and it would be hard for their small bodies to trek thousands of miles without running out of energy.
For 22 years, Fiorillo has travelled from his office at SMU to Alaska, including his field site at Alaska’s Prince Creek Formation.
Fiorillo was in search of fossils to support the theory that dromaeosaurs lived north of the Arctic Circle. He and his team of scientists would assemble inflatable boats and travel up and down the windy Colville River examining the bluffs for fossils.
The researchers thought they found evidence of fossils from the Cretaceous Period at a nearly vertical bluff. As the sun rose during the day, the researchers worked to collect the rocks from the frozen ground and routinely had to dodge falling rocks from the melting ice.
While searching the cliff face in 2007, Fiorillo’s team found the 14-millimetre dinosaur jawbone with pointy teeth. It is most likely from a young dromaeosaur that was the size of a small puppy, said Fiorillo.
Experts agree that the bone suggests some small meat-eating dinosaurs lived north of the Arctic Circle.
“To have such a young individual from this group of dinosaurs means it is likely that it probably lived somewhere nearby, even, if not exactly at the fossil locality,” said Jack Tseng, a palaeontologist at the University of California, Berkeley.
But Druckenmiller is sceptical about whether the jaw fragment is from a dromaeosaur. “Those teeth look quite a bit different from the dromaeosaur teeth I’ve seen, and I am not sure about the identity of them,” he said.
Druckenmiller, along with Dr Jaelyn Eberle, a palaeontologist at the University of Colorado, Boulder, argues that the jaw fragment doesn’t reveal anything new about the role of Beringia as a home for dromaeosaurs.
At the 2019 Annual Meeting for the Society of Vertebrate Paleontology, Druckenmiller’s team reported in a conference abstract that they found teeth from even smaller dromaeosaurs near the Prince Creek Formation.
Fiorillo says that the baby jaw fragment his team found is the first physical evidence that really indicates dromaeosaurs used the Arctic as a place to live. “When I make that claim,” he said, “I go by what is in the published literature, and conference abstracts are generally not considered part of the published literature because they’re opinion pieces that haven’t gone through peer review.” 
         — The Dallas Morning News

Polar bears ‘could be extinct by century-end’


The heating of the planet is pushing Earth’s polar bear population to its limit, and according to a new study, they could have fewer than 100 years left before extinction.
The carnivorous bears live by hunting seals in the Arctic Ocean, but as more and more ice melts in that region, their habitat continues to shrink. Since amounts began to be measured at the end of the 1970s, sea ice that lasts for more than a year in the Arctic has decreased at a rate of 13% per decade.
Studies have long shown that declining sea ice will lead to a decline in polar bears, but new research published in Nature Climate Change models a specific doomsday timeline. Polar bears will be unable to endure the effects of climate change over the next several decades, the scientists believe, and will be wiped out by 2100.
“What we’ve shown is that, first, we’ll lose the survival of cubs, so cubs will be born but the females won’t have enough body fat to produce milk to bring them along through the ice-free season,” said Dr Steven Amstrup, chief scientist of Polar Bears International, to the BBC. “Any of us know that we can only go without food for so long. That’s a biological reality for all species.”
The study estimated that, even in a situation where countries achieve a moderate reduction in greenhouse gases, several populations of polar bears will disappear. But Amstrup emphasised that the animal can still persist if climate change does not continue unabated.
“Showing how imminent the threat is for different polar bear populations is another reminder that we must act now to head off the worst of future problems faced by us all,” he said. “The trajectory we’re on now is not a good one, but if society gets its act together, we have time to save polar bears. And if we do, we will benefit the rest of life on Earth, including ourselves.”   — New York Daily News

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