Dinosaurs are not extinct - they just just evolved into birds, according to Oxford University scientists.
The reptiles that ruled the world for almost 200 million years never went away, the theory says.
Researchers have shown that shrinking was key to survival, which became one of the most diverse and abundant families of animals alive today.
Only those dinosaurs destined to be birds broke the lower body weight limit of one kilogram seen in their relatives.
Lead scientist Dr Roger Benson, from the Department of Earth Sciences at Oxford University, said: "Dinosaurs aren't extinct; there are about 10,000 species alive today in the form of birds."