The causes, rate, and selectivity of the end-Cretaceous mass extinction continue to
be highly debated [1-5]. Extinction patterns in small, feathered maniraptoran dinosaurs
(including birds) are important for understanding extant biodiversity and present
an enigma considering the survival of crown group birds (Neornithes) and the extinction
of their close kin across the end-Cretaceous boundary [6]. Because of the patchy Cretaceous
fossil record of small maniraptorans [7-12], this important transition has not been
closely examined in this group. Here, we test the hypothesis that morphological disparity
in bird-like dinosaurs was decreasing leading up to the end-Cretaceous mass extinction,
as has been hypothesized in some dinosaurs [13, 14]. To test this, we examined tooth
morphology, an ecological indicator in fossil reptiles [15-19], from over 3,100 maniraptoran
teeth from four groups (Troodontidae, Dromaeosauridae, Richardoestesia, and cf. Aves)
across the last 18 million years of the Cretaceous. We demonstrate that tooth disparity,
a proxy for variation in feeding ecology, shows no significant decline leading up
to the extinction event within any of the groups. Tooth morphospace occupation also
remains static over this time interval except for increased size during the early
Maastrichtian. Our data provide strong support that extinction within this group occurred
suddenly after a prolonged period of ecological stability. To explain this sudden
extinction of toothed maniraptorans and the survival of Neornithes, we propose that
diet may have been an extinction filter and suggest that granivory associated with
an edentulous beak was a key ecological trait in the survival of some lineages.