Some scientists had previously thought that dinosaurs were flourishing right up until they were wiped out by a massive asteroid impact 66 million years ago, Xinhua news agency reported.
However, in the new study published on Monday, British researchers found dinosaur species were actually going extinct at a faster pace than new ones were emerging from 50 million years before the asteroid hit what is now the Gulf of Mexico.
The findings, published in the US journal Proceedings of the National Academy of Sciences, were based on a sophisticated statistical analysis and information from the fossil record.
"We were not expecting this result. While the asteroid impact is still the prime candidate for the dinosaurs' final disappearance, it is clear that they were already past their prime in an evolutionary sense," Manabu Sakamoto of the University of Reading, who led the research, said.
"This suggests that for tens of millions of years before their ultimate demise, dinosaurs were beginning to lose their edge as the dominant species on Earth."
The study also showed that while the long-necked giant sauropod dinosaurs were in the fastest decline, theropods, the group of dinosaurs that include the iconic Tyrannosaurus rex, were in a more gradual decline.
Factors that may possibly have influenced the decline of dinosaurs included the break-up of continental land masses, sustained volcanic activity and other ecological factors.
The researchers said the prolonged demise of dinosaurs likely favoured the rise of mammals on Earth.
"The decline of the dinosaurs would have left plenty of room for mammals, the group of species which humans are a member of, to flourish before the impact, priming them to replace dinosaurs as the dominant animals on earth," said co-author Chris Venditti, an evolutionary biologist from the University of Reading. (IANS)