Dinosaurs have always fascinated me. I thrilled
to "One Million B.C." with Raquel Welch and the great animated
dinosaurs. To be completely accurate, dinosaurs have been
extinct for 66 million years, so the movie's title is off
by a few million years. Of course, everyone knows people didn't
live during those days either, but I liked the movie in spite
of its errors. Interest in the dinosaurs is bigger today than
ever. Just look at the success of such movies as "Jurassic
Park." More new findings and species are being dug up now
than ever before. I guess the popularity of dinosaurs is due
to the fact that these kind of amazing creatures actually
existed. Over the years, theories have changed, discoveries
have been made, and science has given the dinosaurs a makeover.
Once thought to be cold blooded, sluggish reptiles, the image
of dinosaurs today is one of vital, hot-blooded beasts, much
more dramatic than the plodding behemoths of my youth. Somehow,
in my mind, I must have always known this to be true. How
could these creatures have captured my imagination so completely?
How could they have dominated the earth while other animal
forms hid in the shadows? Rather than being the evolutionary
failure most people stereotype them as, they are, on the contrary,
one of the most successful forms of life to have come along.
Their kind ruled the earth for 155 million years, while people
have been around for perhaps 4 million (modern humans even
less). Descendents of the dinosaurs live among us today in
the form of birds.
Here is some basic information about what we know about dinosaurs
AGE OF REPTILES
Dinosaurs lived in a block of time
called the Mesozoic Era, which began about 248 million
years ago an lasted 182 million years. The Mesozoic era is
divided into three smaller blocks of time called Periods.
The earliest period was the Triassic, which lasted
from 248 million years ago to 208 million years ago. This
period saw the beginning of the dinosaurs (towards the end
of the period), and was actually dominated by other animal
forms that, at the time, were larger and more numerous than
the primitive dinosaur forms.
Next came the Jurassic Period, which lasted until 144
million years ago. This was the age when dinosaurs really
took over, with animal forms reaching immense size and incredible
shapes. The first bird forms are believed by most paleontologists
to have evolved in this period.
The last age of dinosaurs was the Cretaceous Period, which
started 144 million years ago and lasted to 66 million years
ago. Some of the most familiar dinosaurs forms evolved and
lived during this time, including the ceratopians (Triceratops),
and hadrosaurs (duck-billed dinosaurs). Probably the
most famous dinosaur of all, Tyrannosaurus Rex, lived
during this period.
At the end of the Cretaceous period, all fossil evidence of
the dinosaurs disappears. Throughout Earth's history species
have vanished during happenings called mass extinction
events. All through the history of the earth, including
the Mesozoic Era, and Cenozoic Era (the age
of mammals, which includes the present day), mass extinctions
have wiped out many forms of life, which were then replaced
by other forms. The mass extinction event at the end of the
Cretaceous wiped out many forms of life, including the dinosaurs,
pterosaurs, and the huge marine reptiles. What caused these
extinctions is still in dispute, and may never be truly solved.
The most recent popular theory is that the extinctions were
triggered by a large asteroid or comet smashing into the earth's
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WHAT ARE DINOSAURS?
Dinosaurs were a group of animals, now extinct,
which lived during the Mesozoic Era. Some were quite small,
chicken or dog sized, while others reached incredible size,
becoming the largest land animals to exist on the earth. Although
they are called reptiles, most scientists today believe that
at least some dinosaurs were warm-blooded. Fossil evidence
indicates that they laid eggs, and some may have fed their
young by bringing food to their nests, as birds do today.
They ruled the earth for about 155 million years, finally
dying out 66 million years ago during a mass extinction at
the end of the Cretaceous Period.
came in two forms or groups. One group is called saurischia(reptile-hipped),
which includes the theropods (all carnivorous dinosaurs
were theropods), and the sauropods (the largest of
all land animals were sauropods). The other group is known
as ornithischia (bird-hipped), and all species in this
group were herbivores.
The ornithicians can be further divided into five sub-groups,
the ankylosaurs (armored dinosaurs), ceratopians
(with parrot-like beaks, most had bony shields and horns),
ornithopods (which include Iguanodon and the duck-billed
dinosaurs), pachycephalosaurs (similar to the ornithopods,
but with bony, domed heads), and the stegosaurs (another
armored group, with bony back plates and spiked tails). Interestingly,
birds seem to have developed from the reptile-hipped group
(specifically, the theropods).
All dinosaurs lived exclusively on the land, no specimen has
been found that could fly or swim in the ocean. Many animals
that lived in and around the time of the dinosaurs have been
mistaken by people as being dinosaurs. Here are some of the
most popular examples:
Dimetrodon was a dinosaur-like creature that lived in the
Permian Period at the end of the Paleozoic Era. A flesh eater,
it was more closely related to mammals than to dinosaurs,
which didn't evolve until millions of years later.
Pterosaurs were a group of reptiles that developed a thin
membrane of skin that stretched from elongated fingers to
its back legs, allowing them to fly. Evolving from a group
of early archosaurs during the Triassic Period, they existed
for longer than the dinosaurs, finally dying out in the mass
extinction event at the end of the Cretaceous along with the
dinosaurs. Birds did not evolve from pterosaurs, as some may
The marine reptiles were a varied group that lived in much
the same ways as whales and dolphins do today. Ichthyosaurs,
plesiosaurs and mosasaurs ruled the seas and oceans
as the dinosaurs did the land. The ichthyosaurs in particular
were incredibly dolphin-like, even giving birth to live young
while swimming in the oceans.
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