Everyone knows that a massive asteroid impact with the Earth was ultimately responsible for the extinction of the dinosaurs. A new study was recently published by an international team of scientists, including researchers from the University of Bristol, that shows dinosaurs were in decline for as much as 2 million years before the asteroid impact. Researcher Fabian Condamine says that the researchers looked at the six most abundant dinosaur families during the Cretaceous ranging from 150 to 66 million years ago.
The team found that they were all evolving and expanding and were successful, but 76 million years ago, they showed a sudden downturn. The rate of extinction for the creatures rose, and in some cases, the rate of origin for new species declined. The team used Bayesian modeling techniques to account for several uncertainties, including incomplete fossil records, uncertainty over the age dating of the fossils, and uncertainties about evolutionary models.
Each of the models was run millions of times to consider all the possible sources of error to determine whether the analysis would converge on an agreed and most probable result. Other researchers on the project looked at how the dinosaur ecosystems function, and it was clear that the plant-eating species tended to disappear first. That made the dinosaur ecosystem unstable and liable to collapse if environmental conditions became damaging. Meat-eating dinosaurs tended to consume the plant-eating dinosaurs, and a decline in one group meant a decline in the other.
Researchers on the study say it became clear that there were two main factors, with the first being overall climates were becoming cooler, making life harder on dinosaurs that required warm temperatures. The loss of herbivores made the ecosystem unstable and prone to an extinction cascade. The team also found that longer-lived dinosaurs species were more liable to go extinct, potentially reflecting that they could not adapt to new conditions on Earth.