Filling in fossil record gaps The model suggested that, during the 18 million-year time period in question, the proportion of land the four dinosaur clades likely occupied remained constant overall, suggesting their potential habitat area remained stable, and the risk of extinction stayed low. renzo One of the factors that could have clouded the true diversity patterns of dinosaurs was the lack of rock exposed at the Earth’s surface during that window of time — and thus available for fossil hunters today to scrutinize.

“In this study, we show that this apparent decline is more likely a result of a reduced sampling window, caused by geological changes in these terminal Mesozoic fossil-bearing layers — driven by processes such as tectonics, mountain uplift, and sea-level retreat — rather than genuine fluctuations in biodiversity,” said study coauthor Alfio Alessandro Chiarenza, a Royal Society Newton International Fellow at University College London’s department of Earth sciences, in a statement.

“Dinosaurs were probably not inevitably doomed to extinction at the end of the Mesozoic,” Chiarenza said. “If it weren’t for that asteroid, they might still share this planet with mammals, lizards, and their surviving dscendants: birds.” The study helped to highlight what biases may affect scientists’ understanding of the true pattern of dinosaur diversity leading up to the extinction event, said Darla Zelenitsky, a paleontologist at the University of Calgary in Alberta who wasn’t involved in the research.

“Because of the nature of the rock record, (paleontologists have) found it was more difficult to detect dinosaurs and thus understand their diversity patterns in that window of time just before the mass extinction,” she said.

“It certainly makes sense as we know there are biases related to the rock record that can obscure true biological patterns. The more rock that is exposed at the surface (today), the better our chance of finding dinosaurs in that rock, which in turn leads to a better understanding of their diversity patterns.”

Mike Benton, a professor of vertebrate paleontology at the UK’s University of Bristol, called the paper “thorough and detailed” but said it doesn’t prove there was no reduction in dinosaur diversity ahead of the extinction event. Benton’s work has suggested that dinosaurs were in decline before the asteroid wiped them out. He wasn’t involved in the new study.

“The current paper suggests that the ‘reduction’ can be explained as a statistical artefact,” Benton said via email. “What it shows is … simply that the reduction could be real or could be explained by reduced sampling, in my opinion.”