Maiasaura

Phylogeny: Dinosauria > Ornithischia > Genasauria > Neornithischia > Cerapoda > Ornithopoda > Iguanodontia > Ankylopollexia > Styracosterna > Hadrosauriformes > Hadrosauroidea > Hadrosauridae > Saurolophinae > Brachylophosaurini

Overview: In the late 1970’s, at a site later called “Egg Mountain” in Montana, fossil hunters came across a remarkable bone bed. Among the fossils recovered were those of a fairly large “duck-bill”, or hadrosaurid dinosaur, which was recognized as a genus new to science. Maiasaura was officially described as such in 1979 by paleontologists John “Jack” R. Horner and Robert R. Makela. Its name, meaning “good mother lizard”, refers to another, more remarkable find made at “Egg Mountain” – a massive nesting site. Multiple nests full of egg clutches were found at the site, along with remains of hatchlings and juvenile Maiasaura. Maiasaura was named the “good mother lizard” in reference to strong evidence that the parents of these young specimens and eggs were actively attentive and invested in their offspring. Traces of vegetation that were placed around eggs to insulate them are observable and the fact that some juveniles, even a while after hatching, were still present at the nesting site reveals that they were being cared for and, most likely, would later join large herds.

Maiasaura is significant as one of the first non-avian dinosaurs found with undisputed evidence of parental care for their young. To be more accurate, it was the first to be recognized as such. Fossils of oviraptorids brooding over their nests had been found decades prior, though researchers would mistake this as evidence of preying on the nests of other animals. Parental care, on top of famously occurring in modern birds, is actually fairly widespread among some archosaurs. Crocodilians are also known to care for their young to some degree. In adulthood, Maiasaura was similar to most of its hadrosaur kin, being a mostly low-browsing herbivore with strong, grinding teeth. The animal’s skull was large and rectangular in shape, bearing a small crest just in front of the eyes, possibly used for visual display. Maiasaura belonged to the hadrosaurid subfamily Saurolophinae, and specifically, to the tribe Brachylophosaurini. Fossils are known from the Two Medicine and Oldman Formations, so it probably had to contend with predatory dinosaurs like Daspletosaurus and Gorgosaurus.