Maiasaura Peeblesorum

Science Daily: Largest dinosaur population growth study ever shows how Maiasaura lived and died - Decades of research on Montana's state fossil -- the 'good mother lizard' Maiasaura peeblesorum -- has resulted in the most detailed life history of any dinosaur known

summary - Research into a vast bone bed in western Montana has yielded the most complete life history of any dinosaur known.