With no explanation, label text_A→text_B with either "DON'T KNOW", "NO" or "YES".
text_A: Early in the Cenozoic, following the K-Pg event, the planet was dominated by relatively small fauna, including small mammals, birds, reptiles, and amphibians. From a geological perspective, mammals and birds were able to greatly diversify because dinosaurs that had dominated during the Mesozoic had died off. Some flightless birds grew larger than humans. These species are sometimes referred to as "terror birds," and were formidable predators. Mammals came to occupy almost every available niche (both marine and terrestrial), and some also grew very large, attaining sizes not seen in most of today's terrestrial mammals.
text_B: Does the K-Pg event allow mammals to benefit, in that dinosaurs can't compete with them?
YES.