Based on the dinosaur fossil record, dinosaurs died out about 65 million years ago. More recently, many scientists point out that not all dinosaurs disappeared, citing birds as direct descendants of the dinosaur. In fact, a recent study shows that birds may have survived the Cretaceous-Tertiary extinction because they had larger and more complex brains than many other contemporary animals, including the dinosaurs. Such physical features probably made survival—and competition—that much easier for the birds, allowing them to better adapt to the environmental changes associated with the mass extinction.