April 4, 2022 Scott Kraus

Maiasaura was a Nurturing Duck-billed Herbivore

Maiasaura, pronounced “mah-ee-ah-sawr-uh”, was a large, duck-billed herbivore of average intelligence from the hadrosaur family. It’s name comes from the Greek words meaning “good mother lizard”, which refers to the evidence in the fossils showing that Maiasaura parents were nurturing of their young. This duck billed dinosaur lived in what is now the state of Montana in the United States during the Upper Cretaceous period, about 74 million years ago.

Quick Facts

What Did Maiasaura Look Like?

Long, heavy and stocky, the Maiasaura may have looked like an easy meal to potential predators in the  Cretaceous period, but they flourished through their devotion to their young and by maintaining safety in numbers. Paleontologists believe that large herds played a role in predator defense as well as this dinosaur’s social nature. As part of the Hadrosaur family of dinosaurs, known for the presence of “duck bills”, the Maiasaura’s snout was flattened and, while the overall appearance and shape of the skull is much shorter and blunt, the resemblance to a duck’s bill can easily be seen. It was also unique in that it had a bony crest, possibly to protect the eyes and for head butting rivals.

Maiasaura was large, over 9 meters long as an adult, including a hefty, rigidly extended tail, almost doubling the length of this herbivore’s body. Maiasaura weighed over 3 tons  and could walk or stand on two feet or run on all fours. The hind legs of this herbivore were significantly larger than the front appendages.The four appendages of Maiasaura ended in hoof like feet with three toes and four fingers.

Physical Attributes of Maiasaura

Because Maiasaura were specialized herbivores,  they had highly developed teeth and skull structures designed for handling their food. The Maiasaura’s namesake bill was most likely the support for a beak or mandible like structure used for clipping off plants and small branches. The teeth of the Maiasaura were located solely on the sides of the dinosaur’s skull, with multiple teeth in cheek clusters for the grinding of food.

Maiasaura Nesting Habits

Maiasaura is notable for being the first dinosaur found alongside its young, including a nest and eggs. This indicates that the adult Maiasaura were nurturing of their young. The nests were holes, about 6-7 feet wide (1.8-2m), dug out of the ground. Each nest would hold 20-40 ostrich-sized eggs, and the hatchlings were about 1 foot long (.3m). Instead of sitting on their eggs, Maiasaura parents placed decomposing vegetation into the nests which would produce heat in order to keep the eggs warm.It is likely that the temperature at which eggs were kept played a role in the determining the sex of the young much like modern day crocodiles.

Baby Maiasaura

When Maiasaura eggs hatched, the baby Maiasaura did not yet have sufficiently developed legs or teeth to care for themselves. The parents would have had to bring food to the nest, in addition to protecting them from predators. In the first year, the hatchlings had a rapid growth spurt from 16 to 58 inches, or 41 to 150 cm. Paleontologists believe this high growth rate could suggest that they were warm blooded. Researchers can determine age ranges in Maiasaura because the baby Maiasaura had differently proportioned features from the adults. Hatchlings had a proportionately larger head compared to the body, larger eyes and a shorter snout. These young dinosaurs were likely a lot of work for their parents.

Maiasaura Social Behavior

The close proximity of Maiasaura nests to each other indicate that Maiasaura was a social dinosaur. Their nests were about 25-30 feet apart, or approximately the size of an adult Maiasaura. In Montana fossils were found in groups of up to 40 nests spread over an area of 2.5 acres. Other evidence that Maiasaura was a social, or herding, animal includes a discovery of a huge fossil bed of about 10,000 fossils. Herding behavior would have been beneficial for evading predators and could suggest that the dinosaurs needed to make seasonal migrations in order to feed their large groups.

What Did Maiasaura Eat?

Maiasaura was an herbivore, so its diet consisted of plant material and included leaves, seeds, and berries. It was pretty large for a hadrosaur, so paleontologists estimate that an adult would have to eat about 200 pounds of vegetation a day. However, the Maiasaura would also have to feed its hatchlings, so fully grown Maisaura would have been constantly clipping vegetation.

How Did Maiasaura Move?

Paleontologists believe that Maiasaura alternated between a bipedal stance and quadrupedal movement. Its hind legs were bigger and stronger and used to run, but it would have grazed using its front limbs. Like other hadrosaurs, Maiasaura was probably a fast runner, which was its main defense against predators. Scientists estimate that hadrosaurs like Maisaura could run at speeds up to 28 mph.

Where Did Maiasaura Live?

Maiasaura lived in what is now the state of Montana during the Upper Cretaceous period, in a semi-arid climate. Some of the common plants of the time were conifers, horsetail and ferns. Maiasaura herding patterns have been compared to those of bison, which roam the modern plains of Montana. There are a few differences between herding habits of these two creatures however. There was no grass in Montana during the Cretaceous period and two of the biggest areas of Maiasaura nest groupings, dubbed “egg mountain” and “egg island”, were both islands.

The Discovery of Maiasaura

Maiasaura was first discovered in 1978 by Laurie Trexler and later named and described by Jack Horner (who is best known as the paleontological advisor for the Jurassic Park films) and Robert Makela. The name Maiasaura, meaning “good mother lizard” in Greek, comes from a major discovery of nests with eggs, egg shells, and young dinosaurs as well as the adult female dinosaurs that had been looking after them. The ending of “a” in the name is feminine, as opposed to most dinosaur type specimens which are male and end in “us”. These fossils were found in the Two Medicine Formation of Montana and the specific area has since been called “Egg Mountain”. Over 200 specimens of this herbivore have been found since the initial discovery of Maiasaura.

The Importance of Maiasaura

Maiasaura has the distinction of being the first dinosaur ever found with its young. Prior to that discovery, paleontologists had different theories about how baby dinosaurs were raised. The finding of Maiasaura brought new evidence that dinosaurs were more maternal and nurturing than scientists had imagined them to be. Maiasaura also has the honor of being the first dinosaur in space! No, we haven’t found fossils on the moon but in 1985, astronaut Loren Acton brought bone fragments with her onto Spacelab 2. So Maiasaura was the first dinosaur to orbit the earth.