Alaska dinosaur fossils hint at a wetter, wilder future | Polarjournal
(Artist’s conception: SMU)

Think of large, plant-eating dinosaurs, and the setting that comes to mind is likely an ancient tropical swamp, not a coastal environment that is akin America’s Pacific Northwest. That, though, appears precisely to have been the type of habitat that a number of types of dinosaur called home some 75 million years ago in what is today Alaska. And now, scientists say, the fact that some types did better than the other there could offer some suggestions for how the climate of Alaska and other Northern regions might look in a warmer, wetter world.

The knowledge that dinosaurs lived in Alaska between 100 million and 66 million years ago, during a period known as the Late Cretaceous, dates only to the 1980s. But, as scientists uncover more about where they lived and the way that many appear to have died, they believe they are able to draw conclusions about what Alaska was like at the time, and what it may someday be like again.

“The reason we’ve been looking at Cretaceous environments up here is because Earth was in a greenhouse state at that point in time, and it offers the potential to provide analogues to what we might see, eventually, if global warming continues,” said Paul McCarthy, a geologist with the University of Alaska Fairbanks, and one of the authors of a recent paper laying out their findings after comparing fossil remains of two types of dinosaurs two of these type of dinosaurs — the duck-billed hadrosaurs (above left) and the horned, beaked ceratops (above right) — found at the Prince Creek Formation along the Colville River in the northern part of Alaska, the Lower Cantwell Formation in the Central Alaska Range and the Chignik Formation on the Alaska Peninsula.

Dr McCarthy specialises in fossilised soil, which can tell us what type of vegetation grew in a certain area in the past, and how the soil was formed. Both provide an indication of what the local climate was the time, and, by combining those findings with the fossil record of dinosaur bones, scientists are able to deduce that the climate in Alaska during the Late Cretaceous was wetter than it is today.

“We can’t simulate the rates of change, which are likely to have been totally different in the Cretaceous,” he said. “But we can simulate what an ice-free coast would look like and also see how rivers and floodplains would respond to spring snowmelt from the mountains if everything’s not frozen. And we can look at the distribution of plants and animals.”

The distribution of the fossilised dinosaur remains, in particular, has told us two things: firstly, that the hadrosaurs did better than the ceratops, and, secondly, that many of them probably died in huge floods.

The first is important because of the different type of environment each preferred. As indicated in the top picture, certatops was more at home in drier, forested areas. Hadrosaurs, on the other hand, preferred the wetter, marshier environment and stable year-round temperatures that would have predominated in Alaska at that time. That there appeared to have been fewer ceratops serves as evidence that more of the area was covered by an environment that was favourable to hadrosaurs.

The evidence is piled up (Photo: Anthony Fiorillo / SMU)

But while wetter may have been better for hadrosaurs, it was also associated with one big problem that future inhabitants of the Alaska coast may want to take note of: major seasonal floods capable of overwhelming an animal weighing five tonnes and measuring perhaps 10 metres in length that turned the the ancient Alaskan coastal plain into what a 2010 paper co-authored by Dr McCarthy described as a “killing field”.

The floods appear to have been the product of the seasonal melting of snow and ice from adjacent mountain ranges. Whereas today the climate is cold enough for the precipitation that falls on Alaska’s ranges to remain frozen year round, when they were just being formed, it did not, and the runoff this created, scientists say, swept down to the coastal areas where dinosaurs were living.

Evidence of the floods and their force can been seen in the bones that scientists have found in the bonebeds — accumulations of fossilised bones (see image above) — where many of the fossils have been found. Bonebeds can be left by rivers, but had the bones been transported in water over long distances they would show signs of wear, and it would be unlikely that entire skeletons would be found in the same spot, as was the case with the Alaska bonebeds. Likewise, had they been left on the ground to be buried gradually, they would show signs of exposure, and, though this would likely have lead to the collections of bones belonging to single individuals that were found, had the dinosaurs lain undisturbed, their fossils would have been neatly arranged. Instead, the bones were discovered in a jumbled pile, as if groups of dinosaurs had been swept away and covered by sediment almost immediately.

Kevin McGwin, PolarJournal
Featured image: James Havens

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