Anserimimus

Though my flat-bed scanner's fucked right now (making it kind of a pain to scan artwork that's oversized or on watercolour paper), I've got a document scanner that's working juuuust dandy. I present to you - the Anserimimids!

Rising from a lineage of early troodontid herbivores, the anserimimids only rose from the role of marginal herbivores to their current role of grazing megaherbivore in the miocene as a drying climate helped shrink forests and expand grasslands. Along with the more diverse grass-eating mammalian herbivores, the anserimimids largely supplanted the avimimid lineages (the avititans [link] , etc) that had previously dominated the forested earth.
The anserimimids have a very similar digestive system to the avititans, but one that differs greatly, as well. They independently developed the enlarged crop (which acts as a rumen), like the avititans, but have larger, more muscular gizzards and much longer intestines for gleaning nutrients from the grasses. These beasts live very social lives, traveling in herds anywhere from ten to several hundred strong.

I saw these guys having a role somewhere between that of an elephant and a buffalo - large-scale herd animals that would act as keystone species in grassland environments. What do you think - too duck-y? (they're based, again, off of some of those lovely aussie giant birds...)