a family of dinosaurs of the order Ornith-ischia. Hadrosaurs measured as much as 10 m in height. The largest vertebrates on earth that moved on hind legs, they became adapted to aquatic life. The front part of the head, resembling a huge duck bill, was equipped with a filtering apparatus but retained a complex dental system.
Hadrosaurs fed on tiny organisms, which they filtered from the water, as well as on underwater and terrestrial herbaceous vegetation. Several species had a comblike crest on the upper cranium that contained a group of air cavities; these cavities, connected with the respiratory tract, probably served as a supplemental adaptation enabling the animal to hold its head underwater while obtaining food. The aquatic mode of life of hadrosaurs is evident from the placement of the nostrils far back on the head, the webbed anterior extremities, the long tail, which was set high on the body and served as a powerful swimming organ, and the broad phalanges on the posterior extremities, which facilitated walking on muddy bottoms.
There were more than 40 species of hadrosaurs. Remains are known from Upper Cretaceous deposits, mainly in North America and Asia; some have been found in Europe.
A. K. ROZHDESTVENSKII