An international team of scientists has discovered that some of the species of dinosaurs were dying even before huge asteroids hit earth, contradicting earlier studies that suggested dinosaurs died because of asteroids.

"Few issues in the history of paleontology have fuelled as much research and popular fascination as the extinction of non-avian dinosaurs," said Steve Brusatte, researcher at the Columbia University and the American Museum of Natural History. "Did sudden volcanic eruptions or an asteroid impact strike down dinosaurs during their prime? We found that it was probably much more complex than that, and maybe not the sudden catastrophe that is often portrayed."

Scientists claimed that species that had large-bodied, bulk-feeding herbivores were declining during the last 12 million years of the Cretaceous Period, which was way before the asteroids that hit earth. They claim that asteroids were one of the major reasons for the extinction of dinosaurs.

Scientists discovered this when they were analysing morphological disparity-the variability of body structure within particular groups of dinosaurs.

By looking at the change in variability within a given dinosaur group over time, researchers can create a rough snapshot of the animals' overall well-being. This is because groups that show an increase in variability might have been evolving into more species, giving them an ecological edge. On the other hand, decreasing variability might be a warning sign of extinction in the long term.

Scientists found that hadrosaurs and ceratopsids, two groups of large-bodied, bulk-feeding herbivores, had experienced a decline in biodiversity in the 12 million years before the dinosaurs ultimately went extinct.

Some of the dinosaurs remained small herbivores relatively stable. Herbivorous dinosaurs like ankylosaurs and pachycephalosaurs, carnivorous dinosaurs like tyrannosaurs and coelurosaurs showed an increase in variability might have been evolving into more species.

Scientists believe that the new study has shown that there a lot more things hidden behind the extinction of dinosaurs. They believe further research will help them know more about the lost world.

"I think our study highlights the fact that we still have a long way to go until we fully understand the extinction of the dinosaurs," Discovery quoted Stephen Brusatte, a Columbia University graduate student affiliated with the American Museum of Natural History's Division of Paleontology, as saying.

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