Dinosaurs were in decline even before extinction

Dinosaurs were not very diverse and had declined overall even before their extinction nearly 66 million years ago, a study of fossilised eggs in China suggests.

The long-term decline in global dinosaur diversity and sustained low number of their lineages for the last few million years may have resulted from climate fluctuations and massive volcanic eruptions from the Deccan Traps in India, the researchers said.

These factors may have led to ecosystem-wide instability, thus making non-bird dinosaurs vulnerable to mass extinction coincident with the asteroid impact, they said. A large asteroid that hit Earth at the end of the Cretacious period - 145 to 66 million years ago - is believed to have contributed to the global extinction of dinosaurs, leaving birds as their only living descendants.

It has been widely debated whether dinosaurs were at their peak or already in decline prior to their demise. Most of the scientific data on the last days of the dinosaurs come from North America. Although some published studies suggest that dinosaur populations there were thriving quite well before extinction, other more detailed research has suggested that dinosaurs were in decline, which set the stage for their eventual mass extinction.

Researchers from the Chinese Academy of Sciences studied over 1,000 fossilised dinosaur eggs and eggshells from the Shanyang Basin in central China. These fossils came from rock sequences with a total thickness of about 150 meters.