Description and Classification

Anatosaurus was a large, plant-eating dinosaur. It could grow to be about 9 to 12 meters (30 to 40 feet) long and may have weighed several tons. Like other hadrosaurs, it could walk on two legs (bipedal) or all four (quadrupedal). Its most noticeable feature was its wide, flattened beak at the front of its mouth, which was toothless. Further back in its jaws, Anatosaurus had hundreds of tightly packed teeth arranged in “dental batteries.” These teeth were excellent for grinding up tough plant material.

Anatosaurus belongs to the family Hadrosauridae, commonly known as duck-billed dinosaurs. Within this family, it is classified as a hadrosaurine, meaning it did not have the large, hollow, bony crests on its head that are seen in other hadrosaurs like Parasaurolophus. The scientific classification of Anatosaurus has been a subject of debate. Many paleontologists today consider the species once called Anatosaurus annectens to be a species of Edmontosaurus (Edmontosaurus annectens). However, the name Anatosaurus is still recognized in older classifications and helps us understand the history of dinosaur discovery.

Distinguishing Features

• A broad, duck-like bill that was toothless at the front, used for cropping vegetation.
• Complex dental batteries in the cheeks, containing hundreds of teeth that constantly replaced themselves, perfect for grinding tough plants.
• The lack of a hollow bony crest on its skull, distinguishing it from lambeosaurine hadrosaurs like Corythosaurus.
• A relatively long and low skull compared to some other hadrosaurs.
• Some specimens, historically associated with names like Anatosaurus or Edmontosaurus, have been found mummified, showing impressions of their scaly skin.

Paleoenvironment and Diet

Anatosaurus lived in what is now western North America during the very end of the Cretaceous period, just before the mass extinction event that wiped out the non-avian dinosaurs. It shared its environment with famous dinosaurs such as Tyrannosaurus rex, which likely preyed on it, and Triceratops. Its fossils are often found in formations like the Hell Creek Formation and Lance Formation.

The paleoenvironment was a mix of coastal plains, river systems, and forests. As an herbivore, Anatosaurus would have eaten a variety of plants. Its strong beak could clip off branches and leaves, while its powerful dental batteries could grind down tough material like pine needles, twigs, and seeds from conifers, ferns, and early flowering plants. It was likely a browser, feeding on vegetation at low to medium heights.

Significance and Ongoing Research

Anatosaurus, along with the closely related Edmontosaurus, is one of the best-understood hadrosaurs due to the large number of fossils discovered. These include nearly complete skeletons and even rare “mummy” specimens that preserve skin impressions and other soft tissues. These finds have provided invaluable information about hadrosaur anatomy, how they moved, what their skin looked like, and their biology.

Ongoing research continues to refine our understanding of these dinosaurs. While most scientists now classify specimens previously known as Anatosaurus under the genus Edmontosaurus, the historical context of Anatosaurus is important. Studies on bone histology help researchers learn about their growth rates and life stages. The predator-prey relationship between duck-billed dinosaurs like Anatosaurus/Edmontosaurus and large theropods like Tyrannosaurus rex is also an active area of study, with some fossils showing bite marks. These dinosaurs remain crucial for painting a picture of the ecosystems at the very end of the Age of Dinosaurs.