Lambeosaurinae
   Corythosaurus
   Lambeosaurus
   Parasaurolophus
Hadrosaurinae
   Anasazisaurus
   Anatotitan
   Edmontosaurus
   Hadrosaurus
   Maiasaura
   Prosaurolophus
   Saurolophus
   Shantungosaurus

Hadrosaurids or duck-billed dinosaurs are members of the family Hadrosauridae, and include ornithopods such as Edmontosaurus and Parasaurolophus . They were common herbivores in the Upper Cretaceous of Asia, Europe, and North America. They are descendants of the the Upper Jurassic/Lower Cretaceous iguanodontid dinosaurs, and have similar body plans.

Hadrosaurids are divided into two subfamilies. The lambeosaurines (Lambeosaurinae) have large cranial crests or tubes, and are less bulky. The hadrosaurines (Hadrosaurinae) lack the cranial crests or tubes, and are larger.

Discoveries

Hadrosaurids were the first dinosaur family to be identified in North America, the first traces being found in 1855-1856 with the discovery of fossil teeth. Joseph Leidy examined the teeth, and erected the genera Trachodon and Thespesius (others included Troodon, Deinodon and Palaeoscincus). One species was named Trachodon mirabilis. Now it seems that the teeth genus Trachodon is a mixture of all sorts of cerapod dinosaurs, including ceratopsids. In 1858 the teeth were associated with Leidy's eponymous Hadrosaurus foulkii, named after the fossil hobbyist William Parker Foulke. More and more teeth were found, resulting in even more (now obsolete) genera.

A second duck-bill skeleton was unearthed, and was named Diclonius mirabilis in 1883 by Edward Drinker Cope, which he incorrectly used in favor of Trachodon mirabilis. But Trachodon, together with other poorly typed genera, was used more widely, and when Cope's famous "Diclonius mirabilis" skeleton was mounted at the American Museum of Natural History it was labeled as "Trachodont dinosaur". The duck-billed dinosaur family was then named Trachodontidae.

A very well-preserved complete hadrosaurid specimen (Edmontosaurus annectens) was recovered in 1908 by the fossil collector Charles Hazelius Sternberg and his three sons, in Converse County, Wyoming. It was known as the "Trachodon mummy". This specimen's skin was almost completely preserved, together with some muscles and was analysed by Henry Osborn in 1912. Sternberg was in Cope's camp during his famous competition to name new species with Othniel Charles Marsh. This discovery was a victory for Cope in the Bone Wars.

Lawrence M. Lambe erected the genus Edmontosaurus ("lizard from Edmonton") in 1917 from a find in the Edmonton Rock Formation , Alberta. Hadrosaurid systematics were a mess until 1942, when Richard Swann Lull and Nelda Wright proposed the genus Anatosaurus. Cope's famous mount at the AMNH became Anatosaurus copei. In 1975, Anatosaurus was moved to Edmontosaurus, because the species were just too similar to the Edmontosaurus type species, E. regalis and because Edmontosaurus was older, it had precedence. The original sample was probably a young Edmontosaurus. In 1990 the AMNH mount became known as Anatotitan copei.

Characteristics

The hadrosaurids are known as the duck-billed dinosaurs due to the similarity of their head to that of modern ducks. The whole front of the skull was flat and broadened out to form a beak, ideal for clipping leaves and twigs from the tropical forests of Asia, Europe, and North America. However, the back of the mouth contained literally thousands of teeth suitable for grinding food before it was swallowed. Hadrosaurids, like their their iguanodontid cousins, had a rudimentary dentary specialisation in incisors and molars and this probably was a crucial factor in the success of this group in the Cretaceous, compared to the sauropods who were still largely dependent on gastroliths.

External links

• UCMP Tree of Life
• Trachodon