Flying dinosaurs is the correct answer.

A recent German-U.S. research project concluded that most dinosaurs were already under gradual extinction long before a large asteroid fell to Earth about 65 million years ago. This asteroid event served as the final blow for their disappearance.

Led by paleontologist Stephen Brusatte (born 1984) from Columbia University and the American Museum of Natural History, the large land-based herbivorous-eating dinosaurs like Triceratops were already going through the process of a slow extinction during the last 12 million years of the Cretaceous period.

In contrast, land-based meat-eating dinosaurs including Tyrannosaur Rex and some species of herbivorous-eating dinosaurs did not enter the phase of gradual extinction at that time- the impact of the celestial body triggered their sudden destruction and extinction. One exception to this was the flying dinosaurs that survived after this cataclysmic event. A few examples include the Pteranodon, Pterodactylus and the Haopterus.

According to Brusatte, “the world of dinosaurs already knew many changes before the asteroid hit the Earth”.

Stephen Brusatte specializes in the anatomy and the evolution of dinosaurs. He received his undergraduate Bachelor of Science degree at the University of Chicago, Masters of Science at the University of Bristol, and his Doctorate degree from Columbia University.

More Info: