Kritosaurus Willardii

Kritosaurus Willardii is an extinct species of Hadrosaur part of the extinct genus, Kritosaurus. It was slightly smaller than most other species of Kritosaurus, but was also the most common of any Kritosaurus species, being almost as common as the Lumbergosaurus, the most common Hadrosaur species. It was a herbivore and like all species of Kritosaurus, it fed mainly on ferns, cycads, leaves, and horsetails, but unlike most other Hadrosaur species of its time, it fed on grass, which first appeared in the Middle Cretaceous but was not very abundant during that time nor at the end of the Cretaceous period, but being a primitive browser and grazer meant that this species of Hadrosaur did survived the mass extinction, since grass weren't very much effected by the asteroid during that time, so Kritosaurus Willardii was the last species of Kritosaurus and the last ever native North American Hadrosaur. It lived from the Late Cretaceous around 71.5 million years ago to the Eocene period around 36 million years ago, when it finally became extinct for some unknown reason, probably due to competition from newer mammal herbivores related to, but not the ancestors to, today's mammals such as Brontotheres or maybe it was killed off by new mammal predators such as Hyaenodonts, or a bit of both.