A research team focused on examining North America’s fossil records from 18 million years before the mass extinction at the end of the Cretaceous period. According to the new analysis, evidence is mounting that dinosaurs were in good shape before an asteroid struck Earth.

There has been a long-standing debate in paleontology: were dinosaurs still alive when an asteroid hit Earth on a spring day 66 million years ago, or were they already on the brink of extinction? To find answers, a research team examined North America’s fossil records from 18 million years before the mass extinction at the end of the Cretaceous period. A new analysis published in Current Biology adds to the growing evidence that dinosaurs were in good condition before the asteroid’s fatal impact.

However, fossils available for study from that period show that the number of over 8,000 dinosaur species peaked around 75 million years ago and declined in the 9 million years before the asteroid impact.

FOUR DINOSAUR FAMILIES STUDIED

Researchers in the new study focused on four major dinosaur families: Ankylosauridae (armored herbivores like Ankylosaurus with clubbed tails), Ceratopsidae (large three-horned herbivores including Triceratops), Hadrosauridae (duck-billed dinosaurs), and Tyrannosauridae (carnivores like Tyrannosaurus rex).

The data was input into a computer model, and Dean and colleagues compared the physical fossil records with the model’s predictions, finding a discrepancy.

HABITATS REMAINED CONSTANT

The model suggests that over the 18 million-year period, the overall landmass likely occupied by the four dinosaur clades remained steady, implying that potential habitats remained stable, and the risk of extinction remained low.

One factor that could obscure the true diversity patterns of dinosaurs was the absence of rocks exposed on the Earth’s surface during that time frame, which is something not available for scrutiny by fossil hunters today.

“NOT DOOMED TO EXTINCTION”

Co-author of the study and Royal Society Newton International Fellow at the Department of Earth Sciences at University College London, Alfio Alessandro Chiarenza, stated, “In this study, we show that the likely cause for this notable decline in fossil specimens in the final layers of the Mesozoic is more probably a result of the decreasing sampling window driven by geological changes in these late Mesozoic fossil-bearing deposits, rather than true fluctuations in biological diversity.”

Chiarenza added, “Dinosaurs were not inevitably doomed to perish at the end of the Mesozoic. If it weren’t for that asteroid, they might still be sharing this planet with mammals, reptiles, and their surviving descendants, birds.”