MAY 12, 2022 10:00 AM PDT

Precipitation helped drive distribution of Alaska dinosaurs

Dinosaurs are fascinating creatures, and everyone has their favorite one, most notably the Tyrannosaurus Rex, rightfully named the “king of the tyrant lizards”. While the T. rex is possibly the most well-known dinosaur, approximately 700 species of dinosaurs have been named, with recent estimates suggesting that about 700 to 900 more dinosaur genera may remain to be discovered. Members of these current 700 include hadrosaurids and ceratopsids -- the megaherbivores of the Late Cretaceous Period, 100.5 million to 66 million years ago, who have been studied to roam the vast landscape of what is now Alaska, aka The Last Frontier. But how could dinosaurs survive this frozen tundra known to reach temperatures as cold as -30°F (-35°C), and was it in fact temperature that drove their distribution in this climate?

A recent study published in Geosciences discusses hadrosaurids and ceratopsids and how precipitation, not temperature, helped drive their distribution within Alaska. This is because Alaska had a much different climate than it does today.

"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 analogs to what we might see, eventually, if global warming continues," said Dr. Paul McCarthy, who is a geology professor with the University of Alaska Fairbanks Geophysical Institute and co-author on this study. Studying dinosaur fossils and other fossils from that time period help teach us not only about Earth’s climate back then, but how it might be in the future.

"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."

McCarthy, a sedimentologist and a fossil soils specialist, led the analysis of the depositional environments and ancient soils of three rock formations: the fossil-rich Prince Creek Formation along the Colville River in northern Alaska, the Lower Cantwell Formation in the Central Alaska Range and the Chignik Formation on the Alaska Peninsula.

The three formations are close enough to one another on the geologic time scale to allow for a climate comparison, according to the research paper. They all contain Late Cretaceous rocks that were deposited approximately 83 million to 66 million years ago.

Through analysis at UAF and elsewhere, scientists studying the three Alaska formations found a correlation between the amount of precipitation and the distribution of hadrosaurids and ceratopsids. They also found a lesser correlation between temperature and the distribution of those two groups of dinosaurs.

Hadrosaurids, the duck-billed family of dinosaurs, preferred climates that were wetter and had a narrower annual temperature range. Adults weighed about 3 tons and reached about 30 feet in length. Their percentage dominance over the ceratopsids in the three studied formations increased in the more-favorable climate.

Ceratopsids, a family with beaks and horns, preferred a milder and drier climate but never became dominant in percentage over the hadrosaurids in the three formations. Triceratops is perhaps the best known ceratopsid, at a length of about 25 to 30 feet and weighing 4.5 to 5.5 tons.

The finding for greater influence of precipitation than temperature was based in part on prior research that looked at dinosaur teeth from the Prince Creek Formation, including teeth of hadrosaurids and ceratopsids. That study was led by Celina A. Suarez of the University of Arkansas and included work by McCarthy.

Results from that dental study, authors of the new paper write, suggest that ceratopsids preferred the drier, better-drained regions of the Late Cretaceous Arctic landscape and that hadrosaurids preferred wetter regions of the landscape.

What further secrets of Earth’s past will we learn from studying fossils? Only time will tell, and this is why we science!

As always, keep doing science & keep looking up!

Sources: National Geographic, United States Geological Survey, Britannica, Alaska Tours, Geosciences

MS in Geological Sciences
Laurence Tognetti is a six-year USAF Veteran who earned both a BSc and MSc from the School of Earth and Space Exploration at Arizona State University. Laurence is extremely passionate about outer space and science communication, and is the author of “Outer Solar System Moons: Your Personal 3D Journey”.
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