Montana State Fossil

Duck-billed Dinosaur

(Maiasaura peeblesorum)

Adopted on February 22, 1985.

Because of its scientific importance, a group of middle school students and rockhounds led a drive to crown the Duck-billed Dinosaur, Maiasaura peeblesorum, as the state fossil. The legislature passed Bill 130 with a unanimous "yea," and it was signed into law by the governor on February 22, 1985.

Scientists digging in Choteau, Montana, found "Egg Mountain." The mountain, and the area surrounding it, was filled with fossilized eggs, babies, and adult dinosaurs from 80 million years ago. It was the first proof that some dinosaurs took care of their babies the way birds do now. That's how the Maiasaur got its name, which means "good mother lizard."

Their round nests were six or seven feet wide and could hold 25 eggs. The hatched babies weighed about as much as a phonebook and were about one foot long. Adult Maiasaurs weighed almost 6,000 pounds (or about the same as a car with six people in it) and were almost 30 feet long (about as long as the inside of most movie theaters). This plant-eater had a toothless beak, cheek pouches, and many self-sharpening cheek teeth. Hard enamel was found on both the outer surface of the upper teeth and the inner surface of the lower teeth. Maiasaura's hands each had four fingers, and its feet had hoof-like claws. Maiasaura walked on four legs, and was a moderately fast dinosaur. Its front legs were much shorter than the rear legs. When Maiasaura ran, it probably only used the back legs, with the tail providing balance. Running was this dinosaur's only means of escaping carnivores like Albertosaurus and Troodon.

This dinosaur was first discovered in Montana. Since then, thousands of Maiasaura fossils (adults, hatchlings, juveniles, nests, eggs and embryos) have been found in western Canada and the United States. Marion Brandvold and her son David Trexler found one huge bone bed in Montana dubbed Egg Mountain. Jack R. Horner & Robert Makela named Maiasaura in 1979.

Maiasaura lived during the late Cretaceous period. It was among the last of the dinosaur species to evolve before the Cretaceous-Tertiary extinction 65 million years ago. Other dinosaurs of this time were Velociraptor, Albertosaurus and Troodon (carnivores that probably preyed upon Maiasauras), Tyrannosaurus rex (a larger version of Albertosaurus), Ankylosaurus (an armored herbivore), Parasaurolophus, Corythosaurus (a crested dinosaur), and Dryptosaurus (a meat-eating dinosaur).