Introduction

Maiasaura was a large herbivorous ornithopod dinosaur that lived during the Late Cretaceous Period. It is classified within the hadrosaurid group, commonly known as duck-billed dinosaurs. Fossils of this species have been found primarily in North America and date to approximately 76–74 million years ago. Maiasaura is known from abundant fossil material, including adults, juveniles, and nesting sites, providing significant insight into hadrosaurid biology and reproductive behavior.

Quick Information

Field	Information
Common Name	Maiasaura
Scientific Name	Maiasaura peeblesorum
Meaning of Name	“Good mother lizard”
Geological Period	Late Cretaceous
Lived	~76–74 million years ago
Diet	Herbivore
Locomotion	Quadrupedal and facultatively bipedal
Estimated Length	~8–9 meters
Estimated Weight	~2.5–3 metric tons
Habitat	Floodplains and coastal lowlands
Fossil Regions	North America (Montana, USA; Alberta, Canada)
Extinction Status	Extinct

A large duck-billed dinosaur walking on four legs along a forest floor with ferns and tall conifer trees, showing a robust body and long tail. — Maiasaura peeblesorum
Late Cretaceous (Campanian), ~76–74 million years ago
Two Medicine Formation ecosystem

Reconstruction of an adult Maiasaura within a conifer-dominated forest environment. The body proportions and quadrupedal stance reflect skeletal evidence from numerous well-preserved specimens.

Taxonomy and Classification

Maiasaura belongs to the family Hadrosauridae, a diverse group of ornithischian dinosaurs characterized by complex dental batteries and beaked snouts. Within Hadrosauridae, it is classified in the subfamily Saurolophinae (formerly referred to as Hadrosaurinae), which includes hadrosaurs that generally lacked large hollow cranial crests.

The type and only recognized species is Maiasaura peeblesorum. Its classification is supported by numerous well-preserved skeletal remains that exhibit diagnostic features consistent with saurolophine hadrosaurs. Phylogenetic analyses consistently place Maiasaura among derived hadrosaurids within Late Cretaceous North American assemblages.

Geological Period and Age

Maiasaura lived during the Campanian stage of the Late Cretaceous Period. Fossil evidence places it approximately between 76 and 74 million years ago. Most specimens have been recovered from sedimentary formations dated to this interval, particularly those associated with the Western Interior Basin of North America.

This time period was characterized by widespread inland seas, fluctuating sea levels, and extensive coastal plains that supported diverse dinosaur faunas.

Physical Characteristics

Orthographic scientific size comparison showing a human, horse, African elephant, giraffe, and Maiasaura scaled accurately to a 0–10 meter metric bar, with Maiasaura measuring 8.5 meters in total length. — Size comparison chart of Maiasaura peeblesorum (8.5 m total length) alongside a human (Homo sapiens), domestic horse (Equus ferus caballus), African elephant (Loxodonta africana), and giraffe (Giraffa camelopardalis). All figures are shown in true orthographic lateral view and scaled to absolute metric dimensions (0–10 m).

Maiasaura was a large-bodied ornithopod measuring approximately 8 to 9 meters in length. Like other hadrosaurids, it possessed a broad, flattened snout with a keratinous beak at the front of the jaws. Behind the beak, it had extensive dental batteries composed of hundreds of tightly packed teeth arranged in vertical columns. These teeth were continuously replaced and were well-suited for processing fibrous plant material.

The skull lacked a large hollow crest but featured a modest bony ridge above the eyes. The body was robust, supported by strong forelimbs and hind limbs. Maiasaura is interpreted as primarily quadrupedal in posture, although it likely retained the ability to move bipedally when necessary.

The tail was long and stiffened by ossified tendons, contributing to balance and locomotion. Skin impressions attributed to hadrosaurids indicate a scaly integument, though direct skin evidence for Maiasaura is limited.

Juvenile specimens show proportionally larger eye sockets and shorter snouts compared to adults, reflecting typical ontogenetic changes observed in dinosaurs.

Discovery and Fossil Record

Orthographic side-view skeletal diagram of Maiasaura peeblesorum labeled with major bones, including skull, vertebrae, scapula, pelvis, femur, tibia, and metatarsals, with a 0 to 9 meter scale bar showing a total length of about 8.5 meters. — Maiasaura peeblesorum Skeletal Reconstruction
Late Cretaceous (Campanian), approximately 76–74 million years ago
Length: approximately 8.5 meters

Orthographic lateral reconstruction of the articulated skeleton of Maiasaura peeblesorum, a saurolophine hadrosaurid from the Two Medicine Formation of Montana. Major skeletal elements are annotated, including the predentary bone, dental battery, vertebral regions (cervical, dorsal, sacral, and caudal), and limb bones. The scale bar below indicates metric length in 1-meter increments.

Maiasaura was formally described in 1979 by paleontologist Jack Horner and colleagues. The type material was recovered from the Two Medicine Formation of Montana, USA. The species name peeblesorum honors the Peebles family, who assisted in the discovery.

The fossil record of Maiasaura is notable for the discovery of nesting grounds containing eggs, hatchlings, juveniles, and adults in close association. These nesting sites, often referred to as “Egg Mountain,” provide extensive evidence of reproductive behavior and growth stages.

Additional fossils have been found in Alberta, Canada, further supporting its distribution across parts of western North America. The abundance of specimens makes Maiasaura one of the better-documented hadrosaurids.

Habitat and Paleoenvironment

Maiasaura inhabited low-lying floodplains and coastal environments within the Western Interior region of North America. During the Late Cretaceous, this area was influenced by the Western Interior Seaway, which divided the continent into eastern and western landmasses.

The Two Medicine Formation, where many Maiasaura fossils have been found, represents a semi-arid to seasonally dry floodplain environment with rivers, lakes, and vegetated plains. Plant life likely included conifers, ferns, cycads, and early flowering plants (angiosperms).

Associated fossil fauna includes other dinosaurs, small vertebrates, and invertebrates, indicating a diverse terrestrial ecosystem.

Behavior and Ecology

Evidence from nesting sites indicates that Maiasaura reproduced in colonial nesting grounds. Fossilized nests are arranged in patterns suggesting organized spacing. Hatchlings found within nests show partially developed limb bones, which have been interpreted as evidence that they remained in the nest for a period after hatching.

Growth series derived from multiple individuals allow paleontologists to study developmental changes from hatchling to adult. Bone histology studies indicate relatively rapid growth rates compared to many modern reptiles.

As a herbivore, Maiasaura likely fed on a variety of low-growing and mid-height vegetation. Its dental structure suggests efficient processing of tough plant material. Locomotion was primarily quadrupedal, supporting a stable grazing posture, though facultative bipedal movement is generally inferred from hadrosaurid anatomy.

While social structure cannot be determined with certainty, the fossil record supports at least seasonal aggregation at nesting sites.

Extinction Context

Maiasaura became extinct approximately 74 million years ago during the Late Cretaceous. Its extinction predates the Cretaceous–Paleogene (K–Pg) mass extinction event. The reasons for its disappearance are not clearly established but may relate to ecological turnover and faunal changes within Late Cretaceous ecosystems.

There is no direct evidence linking Maiasaura to a specific extinction event.

Reference Summary

Maiasaura was a Late Cretaceous saurolophine hadrosaurid dinosaur from North America, known primarily from the Two Medicine Formation of Montana and related deposits. Measuring approximately 8–9 meters in length, it was a large herbivorous dinosaur with advanced dental batteries and a primarily quadrupedal stance. Its extensive fossil record, including nesting sites and multiple growth stages, provides valuable information about hadrosaurid reproduction and development. It is represented by the species Maiasaura peeblesorum and lived approximately 76–74 million years ago.

Educational Disclaimer

This page is intended for educational and reference purposes only and presents information based on current paleontological research.