The idea that dinosaurs were already declining before an asteroid exterminated most of them for 66 million years can be explained by a deterioration of fossil registration over the past 6 million years.
The idea that dinosaurs were already declining before an asteroid had exterminated the vast majority of these animals for 66 million years can be explained by a fossil registration deterioration over the past 6 million years.
A new study led by researchers at University College London, published in Current Biology, analyzed the North America Fossil Registration that covers the 18 million years that preceded the impact of the asteroid at the end of the Cretaceous period (between 66 and 84 million years ago).
Taking this into account, These fossils (over 8,000) suggest that the number of dinosaur species reached peak about 75 million years ago and then decreased in nine million years prior to the impact of the asteroid.
But the research team found that this trend was due to the fact that fossils of this period are less likely to be discoveredmainly because there were fewer places with exposed and accessible rocks from the end of the Cretacic.
The main author of the investigation, Chris Dean (UCL Earth Sciences), explained that his team analyzed the fossil record and found that the Quality of registration of four groups of dinosaurs (Clados) deteriorated during the last 6 million years before the asteroid.
“The likelihood of finding dinosaurs fossils decreases, while the probability that dinosaurs have lived in these areas at this time remains stable. This shows that we cannot accept fossil registration for its nominal value,” he said.
According to the expert, Half of the fossils of this period were found in North America.
“Our findings suggest that at least in this region dinosaurs may have had a better life than previously suggested before the impact of the asteroid, possibly with a greater diversity of species than the one we see in the gross rock record,” he said.
For the study, the investigation team analyzed the clades of dinosaur ankylosauridae (shielded herbivores such as the ankylosaurus of Clava’s tail), keratopsidae (large herbivores with three horns, including triceratops), Hadrosauridae (herbivores with duck -beak such as Edmontosaurus) and Tyrannosauridae (carnivores such as Tyrannosaurus rex).
They adopted a technique, the model model, previously used in ecology and biodiversity studies to estimate the likelihood of a species inhabiting a specific area.
Deep investigation in North America
They divided North America into a grid and, based on geology, geography and climate of the time, estimated how many of these grid cells the four types of dinosaurs probably occupied in four different moments during the last 18 million years of Cretacic.
Thus, they found that, during this period, the proportion of land probably occupied by the four clads of dinosaurs was usually constantsuggesting that its potential habitat area remained stable and the risk of extinction remained low.
At the same time, they estimated the Probability of detecting the four types of dinosaurs in each area, based on factors such as the amount of land accessible to investigators (That is, if it is covered by vegetation), the amount of relevant rock exposed and how many times the investigators tried to find fossils in this area.
The team found that the probability of detection decreased over the four periods of timethe most influential factor being the amount of relevant rock exposed and affordable.
The work concludes that The dinosaurs were probably not inevitably condemned to extinction at the end of the Mesozoic.
If it weren’t for this asteroid, they could still share this planet with mammals, lizards and their surviving descendants: the birds.
