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78 Nature

Dinosaurs

This group of land-living reptiles appeared around 230 million years

ago. Like reptiles today, dinosaurs had a scaly, waterproof skin, and

young that hatched from eggs. For 165 million years, in the Mesozoic

era, they dominated life

on Earth. Most dinosaurs

became extinct

65 million years

ago (mya), while

others have

evolved into what

are modern birds.

Ornithischians

had two pairs of

backward-pointing

hip bones, similar

to a modern bird’s

Saurischians

mostly had a pair

of hip bones that

pointed forwards,

similar to a

modern lizard’s

WHY WERE MANY

DINOSAURS SO BIG?

The large size of many plant-eating

dinosaurs helped protect them from

fearsome meat-eaters. This led to

the evolution of larger predators,

big enough to tackle their

prey, which in turn resulted

in an increase in the size

of plant-eaters. Over millions

of years, both prey and predator

grew bigger and bigger.

HOW MANY DIFFERENT TYPES OF DINOSAUR WERE THERE?

Dinosaurs fall into two groups. The ornithischian dinosaurs

were all plant-eaters, but the saurischian dinosaurs included

plant-eaters and meat-eaters. Other reptiles that lived at this

time, but were not actually dinosaurs, included flying reptiles

called. PTEROSAURS, and marine reptiles

such as. ICHTHYOSAURS

and plesiosaurs.

GALLIMIMUS

HYPSILOPHODON

GIGANOTOSAURUS 3

A pair of Giganotosaurus dinosaurs charge through a South American

forest 95 mya. Weighing as much as 125 people, or about 7 tonnes

(6.9 tons), and bigger than Tyrannosaurus rex, Giganotosaurus was

probably the largest predator ever to walk the Earth.

dinosaurs