Gastornis, a large flightless bird from the Eocene of Wyoming. Gastornis were very large birds, &amp; have traditionally been considered to be predators of small mammals. However, several lines of evidence, including the lack of hooked claws in known Gastornis footprints &amp; studies of their beak structure, have caused scientists to re-interpret these birds as herbivores which probably fed on tough plant material &amp; seeds