English: A cast of an embryonic Maiasaur emerging from an egg, on display at the Museum of the Rockies in Bozeman, Montana.

Maiasaura were a very large duck-billed dinosaur, and lived (as far as known) exclusively in Montana. They were first discovered near Choteau, Montana, in 1979 in the Two Medicine Formation. Marion Brandvold found a huge nest of eggs, hatchlings, and juveniles -- and suddenly a lot of interest was expressed in the dusty, ignored, out-of-the-way, unexciting Two Medicine Formation. (Thereafter, a wide number of new dinosaur species were found there!)

More than 200 Maiasaura specimens have been unearthed, and it is one of the best-described dinosaurs today. We know they laid a huge number of eggs in nests, that their nests were close together, that they used rotting vegetation to incubate their eggs, and that they nutured their young for at least a year (maybe two). Hatchlings were unable to walk for several months, and there is clear evidence that adults brought food to the next for the young to eat. Maiasaura moved in large herds, too.