The article says beaked birds were more fit for the new situation not because they had beaks per se, but because toothed birds were obligate carnivores and beak

The article says beaked birds were more fit for the new situation not because they had beaks per se, but because toothed birds were obligate carnivores and beaked birds evidently weren't. What I've read up to now is that the mammals that survived the K-Pg extinction were largely small, ground-dwelling creatures. Those likely had a similar sort of omnivorous or herbivorous diet and the right kinds of teeth to match.