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|Hadrosaurs are often referred to as “duck bill” dinosaurs because of
the wide tip of their snout.
A hadrosaur (right) is compared to Iguanodon on the left in the adjacent images.
a monophyletic clade with Telmatosaurus
being the most primitive member (Telmatosaurus
is a hadrosaur but it lacks derived characteristics that all other hadrosaurs
have). Another partial specimen
is known which is more advanced than Telmatosaurus
but more primitive than other genera (Casanovas, 1999; Weishampel, 1993). There were at least
25 genera and 40 species of hadrosaurs, mostly
Given the large number of hadrosaur fossils in many areas, it appears that they often
composed as much as 75% of the dinosaur biomass in a region. Hadrosaurs may have
There is a great diversity of hadrosaur species. A number of species may even be known from the same locality, suggesting that many species probably coexisted by specializing for different habitats. Most hadrosaur fossils have been found near coasts and deltas while most lambeosaur fossils have been found more inland. Maiasaurus was found even deeper inland than the lambeosaurs.
The smaller species were primarily bidepal
and the larger ones were capable of both bipedal and quadrupedal
locomotion. It is possible that
they depended more on quadrupedal locomotion as they aged. The hindlimbs were large, twice the length of
the forelimbs. The large species
could achieve perhaps 15-20 km/hr in an extended run but probably couldn’t
gallop. The smaller species may
have achieved up to 60 km/hr. Their
forelimbs were clawed and they could dig up plants and bring plants to
their mouths. All had 4 fingers
on their hands and some had hooves on their feet (Fastovsky,
All had ossified tendons in their tails that held their tails horizontally and the tails were laterally compressed. The tails were too stiff to be used in swimming as was once thought. The brains of hadrosaurs were well developed and their large optic lobes suggest that perhaps good senses were needed to detect predators. Kritosaurus had a nasal horn.
Several mummified hadrosaurs have been discovered
that dried before burial. Twigs,
berries, conifer needles, and plant material were found in the digestive
systems. (An Edmontosaurus specimen
even preserved the skin showing that it was covered with both large and
small bumps.) Small species could
forage 1-2 meters off the ground and the large species could forage up
to 4 meters off the ground. Hadrosaurs
had a beak to crop vegetation and were well prepared for chewing with
a dental battery, a deep set tooth row (indicating cheeks) and strong
coronoid process on the lower jaw. They
could chew back to front and some feel they could also chew side to side.
In hadrosaurs, the premaxillary
and predentary regions of the jaw are even more
expanded than in the iguanodonts and there are
much higher numbers of cheek teeth (
All of the Euornithopoda also had some pleurokinesis of skull–the upper jaw could move a bit relative to nose and skull roof. The ability to chew may indicate that they depended on lower quality fibrous plant material. There were 45-60 tooth positions per jaw plus several rows of replacement teeth and an individual could have 700 exposed teeth at once. Their large gut indicates some fermentation of food material (Fastovsky, 1996).
Gryposaurus and Lambeosaurus had depressions around the nasal area, perhaps indicating the presence of skin flaps. Modern elephant seals possess similar areas which are used in sound production.
Several species probably traveled in herds
which included young and juveniles and some nested in large colonies. Since there are many hadrosaur remains near
rivers but very few juvenile specimens, suggesting that hadrosaurs
went inland to nest. Nests have
been found in the foothills of the
Below are some members of the Hadrosaurinae:
Each of the lambeosaur species had a distinctive crest. It was once thought that their skulls indicated that they were aquatic or that crests were used in a sense of smell. Today, the most common conclusions are that crests were used for vocalizations and visual display. If these crests had roles in visual display or in vocalization, lambeosaurs would have to have good vision and/or hearing. Lambeosaurs (and hadrosaurs in general) had both large eyes and good hearing (known from preserved middle and inner ears). Pararhabdodon is a primitive lambeosaur (Casanovas, 1999b).
|In Hypacrosaurus the vertebrae were lengthened, producing a low sail.|
|Hadrosaur crests enclosed an enlarged nasal cavity.|
|There was sexual dimorphism in crests: each lambeosaur species had sexually dimorphic crests and the differences between genders became pronounced during maturity.|