Non-avian dinosaurs began to lose in the struggle for survival millions of years before the Cretaceous-Paleogene extinction, and the reason for this is the cooling and the appearance of more advanced competitors.

All non-avian dinosaurs became extinct during the Cretaceous-Paleogene extinction event, about 66 million years ago. It is believed that it was launched by the fall of a massive celestial body that hit the Earth, on the territory of present-day Mexico. However, some data suggest that the era of dinosaurs would have come to an end without this catastrophe: by that time they were experiencing far from the best period of their evolutionary history, and the meteorite put only a fat dot at the end.

The state of the dinosaurs before the asteroid hit remains controversial: many scientists believe that they could have thrived for a long time. However, this possibility is rejected by the results of a new work by French paleontologists led by Fabien Condamine (Fabien Condamine). After comparing data on more than 1,600 remains of ancient reptiles, scientists found that they began to lose the race for survival long before the asteroid hit.

The authors collected information on the known remains of key families of non-avian dinosaurs, dated to the age of 66 million to 150 million years. Representatives of ankylosaurids, hadrosaurids, ceratopsids, dromaeosaurids, troodontids and tyrannosaurids, once widespread around the world, were considered. Scientists have traced how their diversity changed up to extinction, at what rate new species appeared and old ones disappeared.

The work showed that for a long time both processes continued in a balanced manner, without sharp changes in speed. However, about 76 million years ago-about 10 million years before the asteroid hit — the rate of extinction of species began to increase sharply, and the formation of new ones slowed down in all the families considered. This indicates that the dinosaurs stopped keeping up with the pace of environmental changes, and more adapted species did not appear quickly enough to replace those that failed to adapt.

The authors associate these processes with the appearance of a group of hadrosaurs — one of the most advanced non-avian dinosaurs, which began to displace herbivorous competitors everywhere. This could trigger whole "chains of extinctions", affecting the state of the predators that hunted them and destabilizing entire ecosystems. An equally important factor could be the global cooling, the first signs of which appeared about 100 million years ago. According to scientists, these reasons could start the process of extinction long before the meteorite hit the Earth.

The article was published in the journal Nature Communications

Photo-The graph on the left shows the rates of speciation in blue, and extinction in red. On the right, changes in biodiversity are depicted and key representatives of six groups of non-avian dinosaurs are shown. © Fabien Condamine, ISEM, CNRS

Certificate of registration of mass media ЭЛ № ФС 77 - 78868 issued by Roskomnadzor on 07.08.2020