Maiasaura: Discovery of the 'Good Mother Lizard' Nesting Site Reveals Parental Care in Dinosaurs

Maiasaura [mah-yah-SAWR-uh] was a hadrosaur, a type of duck-billed dinosaur, that lived during the late Cretaceous Period. The name comes from Greek, with "maia" meaning mother and "saura" meaning lizard, thus "good mother lizard." The name was given because the first Maiasaura fossils were found at a nesting site, providing evidence of parental care. Adult Maiasaura could grow to be 25 to 30 feet long and weigh around 4 tons. These herbivorous dinosaurs had hundreds of tiny teeth designed for grinding plants. They likely grazed on leaves, ferns, fruits, and small branches. Maiasaura is famous for a nesting site discovered in Montana, containing dozens of individuals of all ages. This site included not only eggs and hatchlings, but also older juveniles and subadults. Many paleontologists believe this indicates a herding behavior of family groups with members of all ages. Maiasaura eggs were about the size of ostrich eggs, but oval-shaped, and nests contained 30-40 eggs arranged in a spiral. Adult Maiasaura were too large to sit on the eggs for incubation. It's believed they used vegetation to keep the nests protected and warm. The name "good mother lizard" comes from evidence of parental care at the nesting site. Hatchlings' legs were underdeveloped for walking, but their teeth showed wear patterns, suggesting adults brought them food. Studies suggest Maiasaura may have walked on two legs when young, switching to four legs as they grew larger.