Dinosaurs were land-dwelling reptiles that walked with an erect stance.
Their unique hip structure caused their legs to stick out from under their
bodies, and not sprawl out from the side (like other reptiles ). When dinosaurs first
evolved from more primitive archosaurs, they were bipedal (walked on two
legs). Much later, some dinosaur groups returned to a four-legged stance, having
hind legs much larger than their front legs .
There were lots of different kinds of dinosaurs that lived at different
times. Some were HUGE, some were small. Some walked on
two legs, some walked on four . Some were speedy , and some were slow
and lumbering . Some were carnivores and some were herbivores . Some
were armor-plated, some had thick, bumpy skin, some had horns , some even had primitive feathers.
No one knows what colors or patterns they were, how they
sounded, how they behaved, how they mated, or even how to tell whether a fossil
came from a male or a female dinosaur.
Dinosaurs suddenly became extinct about 65 million years ago, at the
end of the Cretaceous period, which was a time of high volcanic and tectonic
activity. There are a lot of theories why the extinction occurred. The most
widely accepted theory is that an asteroid impact caused major climactic
changes which the dinosaurs couldn't adapt to.
All that's left of the
dinosaurs are fossils.
Although dinosaurs' fossils have been known since 1818, the term dinosaur
(deinos = terrifying; sauros = lizard) was coined by the English anatomist Sir
Richard Owen in 1842. The only three dinosaurs known at the time were
Megalosaurus, Iguanodon, and Hylaeosaurus, very large dinosaurs.
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