Multiple genomic and paleontological studies refute the claim that the most recent common ancestor of all living birds lived after the Cretaceous-Paleogene extinction event, instead pointing to a Cretaceous origin for modern avian lineages.
The claim states that the most recent common ancestor of all living birds (crown-group Aves) lived after the K-Pg boundary. However, multiple recent studies and well-known molecular clock analyses provide strong evidence that major modern bird lineages originated deep within the Cretaceous period, meaning the claim is refuted by current evidence.