Page 26 - The Dinosaur Book and Other Wonders of the Prehistoric World (DK-Smithsonian)

What is a

Introduction dinosaur?

Dinosaurs were a diverse and successful group
Saurischians
of reptiles that dominated life on land for about Saurischian (“lizard
140 million years. Humans, for comparison, have hipped”) refers to the typical
existed for less than 1 million years. Ranging saurischians that had hip bones
like those of lizards. This group
in size from animals no bigger than pigeons included the sauropodomorph

to lumbering giants the size of trucks, they plant-eaters. It may also have included
the meat-eating theropods, but some
were reptiles, but very different from modern scientists think that theropods are
reptiles. Dinosaurs can be split into two groups: more closely related to
ornithischians.
lizard-hipped dinosaurs (saurischians) and
bird-hipped dinosaurs (ornithischians). These
can be split further, as shown.

Ancestral
dinosaurs Eoraptor
The first dinosaurs were small,
agile animals that ran on two
legs—they would have looked like this
Marasuchus, an early, dinosaurlike
archosaur. During the late Triassic Period,
early dinosaurs evolved in different
ways. Most became specialized for
eating plants, but some were to
become dedicated hunters.
Ornithischians
This group is made up of
beaked plant-eaters with
Marasuchus relatively short necks. The name
means “bird hipped,” because their
hip bones resembled those of birds
(even though birds were small
saurischians and so not
closely related).

Hypsilophodon
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