Ornithopods are a group of bird-hipped dinosaurs
that started out as small, bipedal running grazers, and grew in
size and numbers until they became one of the most successful
groups of herbivores in the Cretaceous world, and dominated the
North American landscape. Their major evolutionary advantage was
the progressive development of a chewing apparatus that became
the most sophisticated ever developed by a reptile, rivaling that
of modern mammals like the domestic cow. They reached their apex
in the duck-bills, before they were wiped out by the Cretaceous-Tertiary
extinction event along with all other non-avian dinosaurs. Members
are known from all seven continents, although the Antarctic remains
are unnamed, and they are generally rare in the Southern Hemisphere.
 |
The
pictures of ornithopods are grouped alphabetically on tabbed
pages. |
Ornithopoda means "bird feet", from
the Greek ornis ("bird") and pous ("feet");
this refers to their characteristic three-toed feet, although
many early forms retained four toes. They were also characterized
by having no armor, the development of a horny beak, an elongated
pubis that eventually extended past the ilium, and a missing hole
in the lower jaw.
The early ornithopods were only about 1 meter
(3 feet) long, but probably very fast. They had a stiff tail,
like the theropods, to help them balance as they ran on their
hind legs. Later ornithopods became more adapted to grazing on
all fours; their spines curved, and came to resemble the spines
of modern ground-feeders like the bison. As they became more adapted
to eating while bent over, they became semi-quadrupedal; still
running on two legs, and comfortable reaching up into trees; but
spending most of their time walking or grazing while on all fours.
Later ornithopods became larger, but never rivaled
the incredible size of the long-necked, long-tailed sauropods
that they partially supplanted; the largest, like the Edmontosaurus
and Shantungosaurus, never grew far beyond 15 meters
(50 feet).
|
