Hadrosaurs

When I lived in Montana, it seemed that everyone was familiar with the hadrosaur Maiasaura ("the good mother lizard"), discovered by local paleontologist Jack Horner of the Museum of the Rockies in Bozeman, Montana.

The Hadrosauridae, also known as the duck-billed dinosaurs, were members of the ornithischian ("bird-hipped") dinosaurs. They were herbivorous (plant eating), and could probably switch easily from walking bipedally (on two legs), to walking quadrupedally (on all four legs) depending on whether they were feeding or running from predators. (Be sure to read my article "Dinosaur Primer" for more information about the difference between ornithischian and saurischian dinosaurs.)

The hadrosaurs became the most common and well-adapted group of the ornithopod dinosaurs throughout the world. They probably first appeared in central Asia during the Cretaceous Period (140 to 65 million years ago). By the late Cretaceous Period, they had spread all over the Northern Hemisphere, migrating into North America across the Bering Land Bridge. From North America, they travelled into South America. The southern landmass of Gondwanaland had broken up by this time, so hadrosaurs have not been found in Africa, Asia, or the Indian subcontinent. Be sure to visit the Paleomap Project to see the positions of the continents throughout geologic history.

The most noticeable feature of the hadrosaurs was their broad, flattened snout which resembled the bill of a duck, resulting in their being called the duck-billed dinosaurs. Hadrosaurs did not have teeth in the front of their mouths, but they had batteries of cheek teeth arranged in their upper and lower jaws in such a way as to form a grinding surface. One of the factors that led to the success of the hadrosaurs was that they developed at the same time as the angiosperms (flowering plants). This meant that in addition to ferns, horsetails, cycads, and conifers (evergreen plants), the hadrosaurs were also able to feed on flowering plants. Grasses, however, did not appear until the late Eocene Epoch (55 to 36 million years ago). (Be sure to read my article "Grasses and Grazers" for more information.) The success of the hadrosaurs may have been a factor in the decline of other herbivorous dinosaurs, such as the iguanodonts (such as Iguanodon) and the sauropods.

In the photos of the hadrosaur teeth, you can see a part of the tooth that is black, while the rest of the tooth is brown. The black part of the teeth is the chewing surface. The teeth then come together in off-set positions, to form a grinding surface.

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