The dinosaurs were already in decline 50 million years before the asteroid strike that finally wiped them out, a new study suggests. The assessment adds further fuel to a debate on how dinosaurs were doing when a 10km-wide space rock slammed into Earth 66 million years ago. A team suggests the creatures were in long-term decline because they could not cope with the ways Earth was changing. Researchers analysed the fossil remains of dinosaurs from the point they emerged 231 million years ago up to the point they went extinct. To begin with, new species evolved at an explosive rate. But things started to slow about 160 million years ago, leading to a decline in the number of species which commences at about 120 million years ago.