Dinosaurs Were Unaffected by Climate Change, Flourished before Asteroid Strike, Paleontologists Say

Paleontologists largely agree that the Chicxulub asteroid impact, possibly coupled with intense volcanic activity in India’s Deccan Traps, wiped out non-avian dinosaurs (all dinosaurs except birds) at the end of the Cretaceous period, approximately 66 million years ago. However, there is debate about whether dinosaurs were flourishing before this, or whether they had been in decline due to in climate change. Now, in a study that modeled the changing environment and dinosaur species distribution in North America, a team of researchers has shown that dinosaurs were likely not in decline before the Chicxulub strike.

Reconstruction of Late Maastrichtian (66 million years ago) paleoenvironment in North America, where a floodplain is roamed by dinosaurs like Tyrannosaurus rex, Edmontosaurus and Triceratops. Image credit: Davide Bonadonna.

Reconstruction of Late Maastrichtian (66 million years ago) paleoenvironment in North America, where a floodplain is roamed by dinosaurs like Tyrannosaurus rex, Edmontosaurus and Triceratops. Image credit: Davide Bonadonna.

“Dinosaurs were likely not doomed to extinction until the end of the Cretaceous, when the asteroid hit, declaring the end of their reign and leaving the planet to animals like mammals, lizards and a minor group of surviving dinosaurs: birds,” said study lead author Alessandro Chiarenza, a PhD student at Imperial College London.

“The results of our study suggest that dinosaurs as a whole were adaptable animals, capable of coping with the environmental changes and climatic fluctuations that happened during the last few million years of the Late Cretaceous.”

“Climate change over prolonged time scales did not cause a long-term decline of dinosaurs through the last stages of this period.”

The study shows how the changing conditions for fossilization means previous analyses have underestimated the number of species at the end of the Cretaceous period.

Chiarenza and colleagues focused their study on North America, where many Late Cretaceous dinosaurs are preserved.

During this period, the continent was split in two by a large inland sea. In the western half there was a steady supply of sediment from the newly forming Rocky Mountains, which created perfect conditions for fossilizing dinosaurs once they died. The eastern half of the continent was instead characterized by conditions far less suitable for fossilization.

This means that far more dinosaur fossils are found in the western half, and it is this fossil record that is often used to suggest dinosaurs were in decline for the few million years before the asteroid strike.

“Most of what we know about Late Cretaceous North American dinosaurs comes from an area smaller than one-third of the present-day continent, and yet we know that dinosaurs roamed all across North America, from Alaska to New Jersey and down to Mexico,” said co-author Dr. Philip Mannion, a paleontologist at University College London.

Instead of using this known record exclusively, the researchers employed ‘ecological niche modeling.’

This approach models which environmental conditions, such as temperature and rainfall, each species needs to survive.

The scientists then mapped where these conditions would occur both across the continent and over time.

This allowed them to create a picture of where groups of dinosaur species could survive as conditions changed, rather than just where their fossils had been found.

The team found habitats that could support a range of dinosaur groups were actually more widespread at the end of the Cretaceous period, but that these were in areas less likely to preserve fossils.

Furthermore, these potentially dinosaur-rich areas were smaller wherever they occurred, again reducing the likelihood of finding a fossil from each of these areas.

The findings appear today in the journal Nature Communications.

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Alfio Alessandro Chiarenza et al. 2019. Ecological niche modelling does not support climatically-driven dinosaur diversity decline before the Cretaceous/Paleogene mass extinction. Nature Communications 10, article number: 1091; doi: 10.1038/s41467-019-08997-2

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