Rostrids' diversity in a changing world

Rostrids have never been such widespread and diversified as now: ducktail pressure has pushed these robust geese on the brink of extinction, but after the END they had their chance to shine.
While not as large as brontosparrows, the group includes medium-sized species like the terrarider (Neocursoria acutirostris). Similar to a small ostrich, this grassland-adapted bird can reach extreme speed when running from predators. They are the only rostrids with only two digits on their feet and, like their ancestors, they possess a complex digestive system that can easily assimilate cellulose and even lignin partially.
Terrariders are grazers and feed mainly on fresh grass and low shrubs across the entire year and are widespread in both planitial coldvanna and mediterranean scrub. Chicks and eggs are kept by their parents inside a wingpouch like all rostrids, which is very adipose to reduce impact damage. 

Terrariders are partially sympatric to another rostrid that dwells in cold mountain woodlands but can also breed in the coldvanna: the brumble (Magnaves excavatoria). This moderately large bird has retained some primordial rostrid traits, like the robust beak, a browsing diet and a stocky build. Brumbles have however some important autapomorphies: the inner part of their mouth is filled with small false teeth merged to form a sort of tooth battery analogous to hadrosaurs; due to their proximal position, teeth are partially covered by a novel cheek muscle, the pseudomasseter (already present in ancestral woodclimbers), which reduce the food loss while munching. The result of these adaptations is a highly advanced mastication that, in some respects, is more efficient than ducktails' mastication.
Brumbles live in breeding pairs but often communicate with neighbors' brumbles by producing low-pitched rumbling sounds that can be heard over long distances. Males possess a long feather crest on their heads, which is absent in females.