Maiasaura peeblesorum fossil (juvenile) Cretaceous (144-65 million years ago), Montana; photo by alan madrid on Flickr (noncommercial use permitted with attribution / share alike).
Official State Fossil of Montana
Montana designated the duck-billed dinosaur (Maiasaura peeblesorum) as the official state fossil in 1985, influenced directly by Montana's schoolchildren (guided by Helen Peterson, a sixth-grade teacher from Livingston Middle School). All State Fossils
"Maiasaura" means "good mother lizard." Fossil skeletons of this dinosaur have been found with nests of eggshells and hatchlings, proving for the first time that some dinosaurs lived in herds and fed and raised their offspring. So far fossil remains of this Late Cretaceous dinosaur have been found only in Montana.