We all have in mind the fall of a huge asteroid twelve kilometers wide that, 66 million years ago, caused the extinction of the dinosaurs on the face of the Earth. However, the scientific community is not clear if, before the impact, these animals were already in decline. “We have studied the six most abundant families of dinosaurs from the Cretaceous, between 150 to 55 million years ago”Explains Fabien Condamine, lead author of the work and researcher at the French National Center for Scientific Research (CNRS). “They were all evolving and expanding successfully until 76 million years ago, when there was a sudden fall. Their extinction rates increased and, in some cases, even the rate of formation of new species decreased”.
Scientists used Bayesian statistical techniques to account for several types of uncertainties: both incomplete fossil records and uncertainties about the dating of fossils and about evolutionary models. Each of the models was run millions of times to consider all of these possible sources of error and to determine whether the analyzes would converge on the agreed most probable outcome.
Why were the dinosaurs disappearing?
“The decline of the dinosaurs in their last ten million years makes sense and, in fact, this is the best-sampled part of their fossil record, as our study shows,” explains Phil Currie, co-author of the study and researcher at the University of Edmonton (Canada).
In the analyzes carried out, the authors explored the different possible causes of the decline that the dinosaurs were already suffering: “There are two main factors, the first is that the climate was getting colder, and this made it difficult for these animals adapted to warmer temperatures to survive”Explains Mike Benton, a researcher at the University of Bristol. “Subsequently, the extinction of herbivores made ecosystems more unstable and prone to cascading extinctions. Another of the results showed us that the oldest dinosaur species were also more prone to extinction, this could reflect that they were incapable to adapt to the new conditions of the Earth ”.
As we already know, the extinction of the dinosaurs was a key moment in the evolution of life on Earth. “The world had been dominated by dinosaurs for more than 160 million years, and as dinosaurs declined, other groups began to emerge, including mammals,” explains Condamine. “The dinosaurs were, for the most part, so large that they would hardly interbreed with the small furry mammals that were already around. But mammals began to increase in number of species before the dinosaurs disappeared. and later, after the impact, they had the opportunity to build the new types of ecosystems that we see today. “
Reference: Condamine et al. 2021.’Dinosaur biodiversity declined well before the asteroid impact, influenced by ecological and environmental pressures’ Nature Communications.