Description and Classification

Gilmoreosaurus was a plant-eating dinosaur that walked on two legs but could also move on all fours. It grew to be about 6 to 8 meters (20 to 26 feet) long and likely weighed between 1 and 2 tons. Like other hadrosauroids, it had a beak-like mouth good for snipping off plants, and many small teeth packed together in its cheeks, forming “dental batteries” for grinding tough vegetation. Unlike some of its later relatives, such as Parasaurolophus or Lambeosaurus, Gilmoreosaurus did not have a large, bony crest on its head, making it a more primitive or early type of hadrosauroid.

In terms of classification, Gilmoreosaurus belongs to the group Ornithopoda, within the larger clade Hadrosauroidea. It is considered a non-hadrosaurid hadrosauroid, meaning it is closely related to the true Hadrosauridae family (the main group of duck-billed dinosaurs) but sits just outside it or represents an early member. This makes it an important dinosaur for understanding how hadrosaurs evolved. The primary species is Gilmoreosaurus mongoliensis.

Distinguishing Features

• A relatively simple skull structure, lacking the elaborate bony crests seen in many later hadrosaurs.
• A “duck-bill” shaped snout, characteristic of hadrosauroids, used for gathering plant food.
• Dental batteries, or collections of closely packed teeth, designed for efficiently grinding tough plant material.
• A body plan that allowed it to walk on two legs (bipedal) for running and on four legs (quadrupedal) for slower movement or feeding.

Paleoenvironment and Diet

Fossils of Gilmoreosaurus have been found in rock formations like the Iren Dabasu Formation in Mongolia. During the Late Cretaceous, this area was likely a mix of plains and woodlands with rivers and lakes. Gilmoreosaurus shared this environment with other dinosaurs, including the small, feathered predator Velociraptor, the horned dinosaur Protoceratops, and early tyrannosaurs like Alectrosaurus.

As a herbivore, Gilmoreosaurus fed on the plants available in its habitat. Its diet probably included conifers (like pine trees), ferns, and early flowering plants. It would have used its beak to crop leaves and stems, and then its powerful dental batteries would grind the food before swallowing, similar to how cows chew cud.

Significance and Ongoing Research

Gilmoreosaurus is significant because it helps scientists understand the early stages of evolution for the hadrosauroid group of dinosaurs. By studying its features, paleontologists can learn how these “duck-billed” dinosaurs diversified and became so successful during the Cretaceous period. Its more basic anatomy compared to later, crested forms like Edmontosaurus or Corythosaurus shows the steps in their evolutionary journey. Discoveries of Gilmoreosaurus also add to our knowledge of the types of dinosaurs that lived in Asia.

Ongoing research on Gilmoreosaurus includes re-examining existing fossils with new technology to better understand its anatomy and how it lived. Scientists are also working to clarify its exact position in the hadrosauroid family tree and to determine if all fossils currently assigned to Gilmoreosaurus truly belong to this genus. New fossil finds could provide more complete skeletons, offering further insights into this important early duck-billed dinosaur.