Maiasaura
my-uh-SORE-uh
"good mother lizard"
- Lived
- 84 to 72 million years ago, Late Cretaceous
- Diet
- Herbivore
- Length
- about 9 m (30 ft)
- Group
- Ornithopods, Hadrosauridae
- Found in
- United States
- Named by
- Horner and Makela 1979
Size comparison
To scale
Scale in meters
Where its fossils were found
The evidence
Today
80 million years ago
Habitat
Rivers crossed a floodplain in Montana, with conifer woodland and seasonal dry intervals. Orodromeus and Troodon lived in the region.
Field notes
About Maiasaura
What it was like
Maiasaura was a duck-billed plant eater with a broad, flat beak and rows of grinding teeth for chewing tough plants. It grew to about 9 meters (30 feet) long and likely moved on two legs or four, depending on its speed.
It is best known for evidence of parental care: nests, eggs, and young at different growth stages found together suggest that Maiasaura fed and protected its hatchlings in the nest rather than leaving them to fend for themselves.
Its world
Maiasaura lived in what is now Montana about 84 to 72 million years ago, during the Late Cretaceous, on a floodplain crossed by rivers and dotted with conifer forests. Its fossils come from the Two Medicine Formation.
It shared its floodplain habitat with the horned Achelousaurus and Einiosaurus, the armored Euoplocephalus, and predators including Daspletosaurus and Troodon.
How it was found
Horner and Makela named Maiasaura in 1979, after finding a nesting site in Montana with eggs, hatchlings, and adults together. Only 5 finds of the genus are formally recorded, but the original nesting site remains one of the most important discoveries in dinosaur research.
Field gallery
More views of Maiasaura
Scenes reconstructed from the available fossil evidence.
1 of 7
Lived alongside
Found in the same rock formations
A rock formation can hold fossils laid down millions of years apart, so not every animal here met Maiasaura.
The evidence
The science behind Maiasaura
Which parts of the picture come from its own bones, and which come from its relatives.
From its own fossils
- Skulls show a broad beak, grinding tooth batteries and a low, solid bump above the eyes.
- Nests preserve eggs and groups of very young skeletons with shorter faces than adults.
- Growth marks in limb bones trace rapid early growth and slower growth near maturity.
Borrowed from relatives
- Most of the skeleton is known from its own bones.
- Scaly skin is inferred from other duck-billed dinosaurs, including Edmontosaurus.
Still unknown
- Its color and detailed skin covering.
- How adults protected nests or supplied food to young.
- How long young stayed with adults after leaving a nest.
Often drawn wrong
- A tall or hollow crest replaces its low, solid skull bump.
- Newly hatched young should have shorter faces rather than scaled-down adult heads.
Discovery timeline
- 1979Named itHorner & Makela
- 1990Fossil sitesHirsch & Quinn
- 2015Growing upWoodward et al.
- 2018Growing upPrieto-Marquez & Guenther
- 2024Its worldRogers et al.
Key papers
The research behind what we know of Maiasaura
Named it
Named Maiasaura from a nesting site in Montana and proposed parental care from groups of young preserved in a nest.
Nest of juveniles provides evidence of family structure among dinosaurs. Nature 282: 296-298
Read the paper : Nest of juveniles provides evidence of family structure among dinosaurs (opens in a new tab)Fossil sites
Examined eggshell structures and used embryos and nest-associated young to connect some eggs with Maiasaura.
Eggs and eggshell fragments from the Upper Cretaceous Two Medicine Formation of Montana. Journal of Vertebrate Paleontology 10: 491-511
Read the paper : Eggs and eggshell fragments from the Upper Cretaceous Two Medicine Formation of Montana (opens in a new tab)Growing up
Studied growth marks across a large bone sample, reconstructing rapid growth and a high risk of death early in life.
Maiasaura , a model organism for extinct vertebrate population biology: a large sample statistical assessment of growth dynamics and survivorship. Paleobiology 41: 503-527
Read the paper : Maiasaura , a model organism for extinct vertebrate population biology: a large sample statistical assessment of growth dynamics and survivorship (opens in a new tab)Growing up
Described very young skeletons and showed how the face lengthened and parts of the forelimbs changed proportions during growth.
Perinatal specimens ofMaiasaurafrom the Upper Cretaceous of Montana (USA): insights into the early ontogeny of saurolophine hadrosaurid dinosaurs. PeerJ 6: e4734
Read the paper : Perinatal specimens ofMaiasaurafrom the Upper Cretaceous of Montana (USA): insights into the early ontogeny of saurolophine hadrosaurid dinosaurs (opens in a new tab)Its world
Revised the formation timeline, separating Maiasaura nesting and bonebed levels from later dinosaur communities.
Updating the Upper Cretaceous (Campanian) Two Medicine Formation of Montana: Lithostratigraphic revisions, new CA-ID-TIMS U-Pb ages, and a calibrated framework for dinosaur occurrences. Geological Society of America Bulletin 137: 315-340
Read the paper : Updating the Upper Cretaceous (Campanian) Two Medicine Formation of Montana: Lithostratigraphic revisions, new CA-ID-TIMS U-Pb ages, and a calibrated framework for dinosaur occurrences (opens in a new tab)
Close relatives
Other members of Hadrosauridae
Sources: Wikidata