Were the dinosaurs Already on the disappearance course before the asteroid impact? This question has been the subject of discussion among scientists for more than 30 years. A group of researchers, led by the Univercity College Londonhe suggests that the view that dinosaurs were already in decline before the asteroid disappeared most of them 66 million years ago can be explained by the limited fossil record of that time and not by the actual decrease in dinosaur species.

The study, published in Current Biology, analyzed the North America’s fossil archives between the period between 66 and 84 million years ago, ie 18 million years before an asteroid impact at the end of the Cretaceous period. Four dinosaur families were examined: Akylosaurids (armor with armor, such as Agylosaurus), kerats (including triceps), hunts (herbivores with papas beak, such as Edmontosaurus).

These fossils suggest that the number of dinosaur species culminated about 75 million years ago and then decreased in the nine million years that preceded the asteroid impact. However, the research team found that this trend was due to the fact that fossils from that time are less likely to be discovered, mainly due to the smaller number of seats with exposed and accessible rocks from the late Cretaceous period. This reduced sampling capability is associated with geological changes in layers that encompass fossils, such as mountain lifting and declining sea levels.

The researchers have adopted a technique, the housing modeling, which was previously used in ecology and biodiversity studies, to assess how likely it is to be a species to reside in a particular area during the last 18 million years of the Crete period.

“We have analyzed the fossil record and found that the quality of the four dinosaur teams is getting worse in the last six million years before the asteroid. The likelihood of finding dinosaur fossils decreases, and the likelihood of dinosaurs living in these areas at that time remains stable. This shows that we cannot receive the fossil record for granted, “notes the lead author of the study, Chris Dean, a researcher at UCL.

As they found, during this time the ratio of the land probably occupied by the four dinosaur families remained overall stable, suggesting that the possible extent of the natural environment in which they lived was constant and the risk of extinction was low. At the same time, they appreciated the possibility of detecting the four types of dinosaurs in each area, based on factors such as how much land is accessible to researchers (eg if covered by vegetation), how much relative rock is exposed and how many times the researchers had tried to find it.

The team found that the possibility of tracking was reduced and the most important factor was the degree of exposure and accessibility of the relevant rocks. They also found that unlike the other three families, the kerats were more likely to be detected later in this period, and to occupy more areas. They assumed that this was due to that they preferred the green plains away from rivers at a time when this kind of natural environment was the main type of environmental environment. This is related to the retreat of a large inner sea that divided North America into two and to dry the river systems that supplied this sea.