Dinosaurs were failures that went extinct due to poor adaptation

Dinosaurs were extraordinarily successful, dominating terrestrial ecosystems for approximately 165 million years (Jurassic and Cretaceous periods). In contrast, mammals have existed for only 66 million years since the K-Pg extinction. Non-avian dinosaurs did not fail due to poor adaptation, they went extinct as a result of a catastrophic asteroid impact combined with massive volcanism. Avian dinosaurs (birds) did survive and diversified, proving the lineage's remarkable adaptive capacity. By any measure of evolutionary success (longevity, diversity, ecological dominance), dinosaurs were one of the most successful groups of animals ever.