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Edmontosaurus saskatchewanensis

Commonly called "duck-billed" dinosaurs, Hadrosaurs were a very prolific and diverse group of plant eating dinosaurs whose 30 million year evolutionary heritage ended, suddenly, like so many others 65 million years ago. Edmontosaurus was a hadrosaur and its name means "Reptile from Edmonton", a city in Alberta, Canada near where it has been found. Imagine this huge herbivore. It was over 10 meters (30 feet) long from end to end, half of which was its tail. This tail was suspended off the ground, counter balancing the chest, neck and head. Edmontosaurs walked on two pillar-like legs and had enormous three-toed feet that measured up to a meter (3 ft.) wide. As they browsed their way through the dense conifer forests of what is now western North America, their wide, duckbill-shaped beaks cropped coarse needles and small twigs.

We probably know more about hadrosaurs than any other group of dinosaurs. Not only do we have an extensive fossil record with many complete skeletons of both young and old animals, we have eggs, footprints and even two mummified specimens complete with skin and stomach contents. Our evidence today suggests that Edmontosaurus and other hadrosaurs traveled in large herds and possibly migrated seasonally.

Taxonomy

The last major group of ornithopod dinosaurs to evolve before the extinctions at the end of the Cretaceous were the hadrosaurs. This is a large group of herbivores that is thought to have evolved from the Iguanodon dinosaur family of the Early Cretaceous. In fact, the rise of the hadrosaurs marks the decline of these earlier dinosaurs except in isolated pockets in Western Europe. While the many skeletal similarities between hadrosaurs and their iguanodontid ancestors represent a strong evolutionary link, hadrosaurs have their own group of distinguishing characteristics which include broad toothless beaks (giving them the name duck-billed) and large complex batteries of teeth. These batteries often had hundreds of teeth, all fitted together to form four (2 top and 2 bottom) massive grinding surfaces. Each chomping bite rotated the top rows of teeth outward just enough to create the grinding action against the lower teeth that was necessary to break down the tough plants on which it fed. Among the skeletal differences that sets them apart, is the lack of a thumb on its four-fingered hand.

Most hadrosaurs fall into one of two groups: those without ornate skulls, but with large nasal areas (hadrosaurines) and those with fancy crests and bony, tubular protrusions (lambeosaurines). Edmontosaurus was a hadrosaurine like Anatosaurus, Kritosaurus, Hadrosaurus and Shangtungosaurus. Hadrosaurs all have very similar skeletons and it is the skulls that are the primary resource determining the species.

Anatomy
Notice the broad beak of Edmontosaurus, it is about 25 cm(~1 ft.) wide. The beak would have been covered with a tough horn-like material for nipping off vegetation. The teeth are set in from the outside edges of the skull allowing "cheeks" to hold food while it was being chewed. The grinding (chewing) surfaces are on the outsides of the lower teeth and the insides of the uppers.

Next look at the nasal areas on either side of the snout. They are quite large and may indicate a well developed sense of smell. Recent studies have led scientists to propose that hadrosaurines may have had large fleshy coverings for their nostrils that could have been brightly colored and inflatable. These display attributes when coupled with noisy snorting or hooting are thought to have been part of the creatures signaling language for both mating and social communication.

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