> Students >
What is a hadrosaur?
(Greek for "bulky lizard") are also known as the "duck-billed
dinosaurs" because of their
long flattened snouts. They first appeared during the
Cretaceous period, near the end of the Age of Dinosaurs. Hadrosaurs
were very common dinosaurs and fossils have been found throughout
North America, Europe, and
Asia. Based on their teeth,
paleontologists believe that hadrosaurs were herbivores. Their
teeth were mostly small and leaf-shaped, but there were plenty of
them. Some hadrosaurs had almost 900 teeth! The hadrosaurs ranged
in size from about 10 feet long (the size of a small car) to 40 feet
long (the size of a school bus). They weighed up to 3 ˝ tons, about
as much as two cars!
feet had three toes, covered in a hoof-like material. Hadrosaurs
could walk (or run if a Tyrannosaurus rex was near!) on their
large muscular hind legs, but may have occasionally used all four
legs while grazing for food. Their long thick tails helped them
balance while running. Without spikes, plates, or teeth to defend
themselves, the hadrosaurs probably relied on keen senses of sight
and smell, as well as their legs, to get out of trouble fast.
of the hadrosaurs
into two major groups based on the type of hips they have. The
Saurischia, or lizard-hipped, and the Ornithischia, or bird-hipped.
Despite the names, there are dinosaurs that walk on two legs and
ones that walk on four legs in both groups. The Saurischia species
dominated during the Triassic Period, then the Ornithischia
dominated later in the Cretaceous Period.
include two suborders: Sauropoda, or reptile-footed, and the
Theropoda, or beast-footed. Different sources break Ornithischia
into 3 to 5 suborders (the three suborders described here are as
presented by the University of
California, Berkeley, Museum of
Paleontology). The Ornithopoda are bird-footed. The Thyreophora includes the plated
Stegasauria and the armored Ankylosauria. The Marginocephalia, or
fringe-headed, dinosaurs includes the horned Ceratopsia, and the
All of the
Ornithischia were plant eaters who had evolved cheeks. Prior to
these dinosaurs, the flesh along the side of the head ended at the
back of the jaw. Imagine the profile of a Tyrannosaurus; you can
see all of the teeth, not just those in front. While this is
effective for animals that use their jaws for killing, it is not
effective for animals that chew plants for food. A lot of the food
simply fell out the sides of their mouths. The Ornithischia were
small to medium-sized dinosaurs (usually less than 30 feet long) but
very successful. It was just at the beginning of the Cretaceous
period that the number of species of flowering plants began to
multiply dramatically. Perhaps because of these cheeks and the many
new plant food sources, the Ornithischia flourished.
Maiasaura, Edmontosaurus, Lambeosaur
or bird-footed dinosaurs were one branch (suborder) of the
Ornthischia that lived for some 140 million years, during the better
part of both the Jurassic and the Cretaceous periods. Dinosaur
species from other branches of the Ornithischia include the
stegosaurus, ankylosaurus, and triceratops. The Ornithopoda were
medium to large in size, by dinosaur standards. They walked on
their back legs with three-toed, bird-like feet for which they were
named. Four families make up the Ornithopoda, including the
Iguanodons and the Hadrosaurs. The Iguanodon was one of the first
dinosaurs to be discovered. A Hadrosaur footprint was recently
discovered in Aniakchak National Monument and Preserve
in southwest Alaska.
are the members of the Hadrosauridae family, or the “duck-billed”
dinosaurs that evolved probably in Asia during the Jurassic or early
Cretaceous period, and by the late Cretaceous period had spread to
Europe and North America as well. These
were some of the later dinosaurs, living 80 million years after the
Stegosaurus of the Jurassic period. They died out during the mass
extinction that took place at the end of the Cretaceous period.
Hadrosaurs had a wide duckbill like snout with no front teeth.
They did have teeth
further back for chewing vegetation. In fact, they had teeth that
were continually being replaced. Their jaws were able to move up
and down as well as side to side. These two adaptations, along with
the cheeks common to all Ornithopoda, helped to make them
particularly well adapted to chewing and eating even the toughest of
the vegetation flourishing at the time.
family consists of two subfamilies, the hadrosaurine duckbills and
the lambeosaurine duckbills. The hadrosaurine had flat heads and
bony ridges on their snout, whereas the lambeosaurine had high domed
heads with hollow air passages in crests atop their heads. The
lambeosaurine evolved in North America and have so far only been
found there. The hadrosaurine were very successful, long-lived and
were some of the last dinosaurs before the mass extinction at the
end of the Cretaceous period. Common hadrosaurs include:
Hadrosaurus (bulky lizard), Edmontosaurus (Edmonton lizard),
Maiasaurus (good mother lizard), Lambeosaurus (Lambe's lizard).
might have roamed the earth in giant herds and so have been called
the "cows of the Cretaceous." One fossil site found the bones of
over ten thousand hadrosaurs, clearly a very large group!
Hadrosaurs were likely a favored food of the Tyrannosaurus Rex,
which lived at the same time. Hadrosaurs had powerful back legs
and smaller front legs. They probably grazed on all fours, but ran
(or fled) upright on their back two legs.
Nests of some
species of hadrosaurs have been found, including a parent dinosaur
sitting on a nest of eggs. Paleontologists discovered a particularly
interesting Maiasaura (a dinosaur in the hadrosaurine subfamily)
nesting area in Montana in 1978. The site showed that the mother
made a crater-like nest with the eggs carefully arranged in a
circular pattern. Several nests were grouped together showing that
they were social animals, and the females were nesting in groups.
Along with the mothers were Maiasaura of various ages, young ones,
hatchlings, and intact eggs. This is fossil evidence that
Maiasaura mothers cared for their young even after they hatched, rather than leaving the
babies to hatch and grow on their own.
hadrosaurs, called Lambeosaurs, had large crests on the tops of
their heads with built-in air passages. These air passages in
Lambeosaurinae crests are a matter of speculation for scientists.
Scientists think that Lambeosaurs could blow air through their
crests, making tuba-like noises. Maybe they used these sounds to
warn other members of the herd or as a mating ritual. Some of these
air passages were quite large and connected with the hadrosaur’s
nasal passages but did not connect directly to the outside. The
theory that most scientists now ascribe to is that the
Lambeosaurinae used these as resonating chambers to make very loud,
deep sounds that would carry far. In other words, they might have
used them a bit like megaphones to call to others in their herd, to
keep track of one another, or to attract mates or to warn of
predators. The crests themselves are large and unusual looking, and
another theory is that they used these crests to attract a mate,
just like peacocks use their fancy feathers.