It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
IMAGE: GREG ERICKSON AND PAT DRUCKENMILLER PLACE A PLASTER JACKET ON A BONE FOUND ALONG THE COLVILLE RIVER ON ALASKA'S NORTH SLOPE. view more
CREDIT: PHOTO BY KEVIN MAY
Images of dinosaurs as cold-blooded creatures needing tropical temperatures could be a relic of the past.
University of Alaska Fairbanks and Florida State University scientists have found that nearly all types of Arctic dinosaurs, from small bird-like animals to giant tyrannosaurs, reproduced in the region and likely remained there year-round.
Their findings are detailed in a new paper published in the journal Current Biology.
"It wasn't long ago that people were pretty shocked to find out that dinosaurs lived up in the Arctic 70 million years ago," said Pat Druckenmiller, the paper's lead author and director of the University of Alaska Museum of the North. "We now have unequivocal evidence they were nesting up there as well. This is the first time that anyone has ever demonstrated that dinosaurs could reproduce at these high latitudes."
The findings counter previous hypotheses that the animals migrated to lower latitudes for the winter and laid their eggs in those warmer regions. It's also compelling evidence that they were warm-blooded.
For more than a decade, Druckenmiller and Gregory Erickson, a Florida State University professor of biological science, have conducted fieldwork in the Prince Creek Formation in northern Alaska. They have unearthed many dinosaur species, most of them new to science, from the bluffs above the Colville River.
Their latest discoveries are tiny teeth and bones from seven species of perinatal dinosaurs, a term that describes baby dinosaurs that are either just about to hatch or have just hatched.
"One of the biggest mysteries about Arctic dinosaurs was whether they seasonally migrated up to the North or were year-round denizens," said Erickson, a co-author of the paper. "We unexpectedly found remains of perinates representing almost every kind of dinosaur in the formation. It was like a prehistoric maternity ward."
Recovering the bones and teeth, some no larger than the head of a pin, requires perseverance and a sharp eye. In the field, the scientists hauled buckets of sediment from the face of the bluffs down to the river's edge, where they washed the material through smaller and smaller screens to remove large rocks and soil.
Once back at their labs, Druckenmiller, Erickson and co-author Jaelyn Eberle from the University of Colorado, Boulder, screened the material further. Then, teaspoon by teaspoon, the team, which included graduate and undergraduate students, examined the remaining sandy particles under microscopes to find the bones and teeth.
"Recovering these tiny fossils is like panning for gold," Druckenmiller said. "It requires a great amount of time and effort to sort through tons of sediment grain-by-grain under a microscope. The fossils we found are rare but are scientifically rich in information."
Next, the scientists worked with Caleb Brown and Don Brinkman from the Royal Tyrrell Museum of Palaeontology in Alberta, Canada, to compare the fossils to those from other sites at lower latitudes. Those comparisons helped them conclude that the bones and teeth were from perinatal dinosaurs.
Once they knew the dinosaurs were nesting in the Arctic, they realized the animals lived their entire lives in the region.
Erickson's previous research revealed that the incubation period for these types of dinosaurs ranges from three to six months. Because Arctic summers are short, even if the dinosaurs laid their eggs in the spring, their offspring would be too young to migrate in the fall.
Global temperatures were much warmer during the Cretaceous, but the Arctic winters still would have included four months of darkness, freezing temperatures, snow and little fresh vegetation for food.
"As dark and bleak as the winters would have been, the summers would have had 24-hour sunlight, great conditions for a growing dinosaur if it could grow quickly enough before winter set in," said Brown, a paleontologist at the Royal Tyrrell Museum.
Year-round Arctic residency provides a natural test of the animals' physiology, Erickson added.
"We solved several long-standing mysteries about the dinosaur reign, but opened up a new can of worms," he said. "How did they survive Arctic winters?"
"Perhaps the smaller ones hibernated through the winter," Druckenmiller said. "Perhaps others lived off poor-quality forage, much like today's moose, until the spring."
Scientists have found warm-blooded animal fossils in the region, but no snakes, frogs or turtles, which were common at lower latitudes. That suggests the cold-blooded animals were poorly suited for survival in the cold temperatures of the region.
"This study goes to the heart of one of the longest-standing questions among paleontologists: Were dinosaurs warm-blooded?" Druckenmiller said. "We think that endothermy was probably an important part of their survival."
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The research team's camp sits on the banks of the Colville River on Alaska's North Slope, with the bluffs rising in the background.
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Photo by Patrick Druckenmiller
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Illustration showing a pair of adult tyrannosaurs and their young living in the Arctic during the Cretaceous Period.
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Art by James Havens
Multiple dinosaur species not only lived in the Arctic, they also nested there
IMAGE: THIS PHOTOGRAPH SHOWS PERINATAL (BABY) DINOSAUR BONES AND TEETH FROM THE PRINCE CREEK FORMATION, NORTHERN ALASKA (PENNY IS 19 MM IN DIAMETER). view more
CREDIT: PATRICK DRUCKENMILLER
In the 1950s, researchers made the first unexpected discoveries of dinosaur remains at frigid polar latitudes. Now, researchers reporting in the journal Current Biology on June 24 have uncovered the first convincing evidence that several species of dinosaur not only lived in what's now Northern Alaska, but they also nested there.
"These represent the northernmost dinosaurs known to have existed," says Patrick Druckenmiller of the University of Alaska Museum of the North. "We didn't just demonstrate the presence of perinatal remains--in the egg or just hatched--of one or two species, rather we documented at least seven species of dinosaurs reproducing in the Arctic."
Previous studies at a handful of other sites provided tantalizing bits of evidence that one or two species of indeterminate dinosaurs were capable of nesting near or just above the Arctic or Antarctic circles, he says, but this study is the first to show unequivocal evidence of nesting at extremely high latitudes. Environmental conditions at this time and place indicate challenging seasonal extremes, with an average annual temperature of about 6 degrees Celsius (about 40 degrees Fahrenheit). There also would have been about four months of full winter darkness with freezing conditions.
Druckenmiller and co-author Gregory Erickson from Florida State University have a longstanding project to document the ancient Arctic ecosystem of the Prince Creek Formation in Northern Alaska, including its dinosaurs, mammals, and other vertebrates. They also want to know how they lived there, given the challenging environment. The environment is also a difficult place to work.
"The field season is short in the Arctic and access is very difficult--aircraft and small boats are required," Druckenmiller says. "To make matters more challenging, the only way to see the rocks is in river-cut steep bluffs along the largest river in Northern Alaska, the Colville. These bluffs are dangerous, prone to catastrophic collapses, making it hard to safely find and extract fossils. As such, we have focused on finding discrete bonebed horizons where we can more efficiently excavate many bones. In the process, we've also discovered numerous new microfossil deposits that have provided for a wealth of new knowledge about the whole ecosystem that lived in the Arctic over 70 million years ago."
Over the course of about a decade of painstaking work, the researchers, aided by many students they've enlisted over the years, have now found hundreds of small baby dinosaur bones, including tiny teeth from individuals that were either still in the egg or had just hatched out. The Arctic dinosaurs they've uncovered include small- and large-bodied herbivorous species including hadrosaurids (duck-billed dinosaurs), ceratopsians (horned dinosaurs and leptoceratopsians), thescelosaurs and carnivores (tyrannosaurs, troodontids, and dromaeosaurs).
"It wasn't that long ago that the idea of finding any dinosaurs in such extreme latitudes and environments was a surprise," Druckenmiller says. "To then find out that most if not all of those species also reproduced in the Arctic is really remarkable. We have long been asked, 'Have you found any eggs?' To that we have, and still answer 'no.' But, we have something much better: the actual baby dinosaurs themselves."
The findings add to evidence that the dinosaurs didn't just spend time at these extreme latitudes, but they most likely lived there as year-round residents. Their evidence suggests both smaller dinosaurs and larger species, such as duck-billed dinosaurs, horned dinosaurs, and a tyrannosaur that more likely could have migrated to warmer climes, resided in the Arctic.
"Year-round residency in the Arctic provides a natural test of dinosaurian physiology," Erickson says. "Cold-blooded terrestrial vertebrates like amphibians, lizards, and crocodilians have yet to be found, only warm-blooded birds and mammals--and dinosaurs. I think that this is some of the most compelling evidence that dinosaurs were in fact warm-blooded."
Erickson says they now have new questions about how dinosaurs survived Arctic winters. It's likely they had unique strategies to cope with darkness, cold temperatures, and food limitation, the researchers say.
Current Biology (@CurrentBiology), published by Cell Press, is a bimonthly journal that features papers across all areas of biology. Current Biology strives to foster communication across fields of biology, both by publishing important findings of general interest and through highly accessible front matter for non-specialists. Visit http://www.cell.com/current-biology. To receive Cell Press media alerts, contact press@cell.com.
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This photograph shows researcher Greg Erickson excavating along the Colville River, northern Alaska.
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