The material made from dinosaur eggshells shows that the species range decreased in the area of central China at the end of the Cretaceous period.
Dinosaurs the end of the era due to an asteroid impact 66 million years ago is the most famous single events in natural history.
The Cretaceous period changed to the Paleocene period as if cutting with a knife, and three quarters of the diversity of life on Earth was destroyed in one fell swoop. At the same time, all the dinosaurs went except for birds.
Anyone no denying the destruction caused by the meteor. However, this could only be the last nail in the coffin of the dinosaur population, which is already in decline, according to a recent Chinese study.
It was led by a researcher from China University of Geosciences Fei Hanand research published by the scientific journal Pnas.
The study looked at more than a thousand dinosaur egg shell samples found in Shanyang, central China. The shells were excavated from a 150-meter-thick rock layer that had formed 66.4–68.2 million years ago, i.e. just before the mass extinction that ended the Cretaceous period.
The sedimentary basin is one of the richest deposits of dinosaur remains in the world. Even so, researchers found eggshells from only three types of dinosaurs. This was clearly less than in other well-known, more varied occurrences.
Of the types of dinosaur eggs found, two belonged to toothless, parrot-like dinosaurs, the third to flat-beaked hadrosaurs. The finds match bone finds from other Shanyang areas of the same period.
“Our findings support the view that the species spectrum of dinosaurs had been declining for a long time. We believe this predisposed the dinosaurs to a final mass extinction,” the researchers write.
Vertebrate paleontologist Mikko Haaramo The University of Helsinki says that the new study confirms previous observations.
“It has been known for a long time that the dinosaur species collapsed during the last five million years of the Cretaceous period. For example, there was a 30 percent drop in North America,” Haaramo commented.
There have probably been two reasons for the decrease. First, the climate became colder and drier at the end of the Cretaceous period. At the same time, the level of the oceans decreased. This was probably the fate of some species.
Secondly, in the earlier Cretaceous period, a lot of new species were born, the most efficient of which displaced the others and narrowed the species spectrum.
Haaramo does not subscribe to the Chinese view that the dinosaurs would have been on the path to destruction even without the meteor.
“The growth and contraction of species is natural as millions of years pass. There is no reason to assume that diversity has not turned to growth again.”
However, the things are connected in that the meteor struck at the worst possible moment for the dinosaurs.
“The reduction of the range of species weakens the ability to adapt. If the meteor had hit five million years earlier, maybe there would have been species that adapted to the world after the impact.