T-Rex meets an old enemy: A Triceratops that does not want to
be dinner. (Copyright Lee Krystek, 2003)
Dinosaurs, contrary to what many people think,
are not just big lizards. While it is true that the name dinosaur
(coined by Sir Richard Owen in 1842) means "terrible lizard"
in Greek, dinosaurs are quite a distinct group from lizards.
The first dinosaur bones
were discovered in 1822 in Sussex, England, by Gideon Mantell.
It was a herbivore (plant eating) dinosaur later given the name
Iguanodon. Shortly after the Sussex discovery the first carnivorous
dinosaur, a Megalosaurus, was found.
It is believed that
from about 230 million years ago, to 65 million years ago (The
Mesozoic Era) dinosaurs were the dominant form of life on Earth.
At the end of the Mesozoic, dinosaurs, and many other species
of life, went extinct. The cause
of this extinction is a mystery.
Dinosaurs are considered to be reptiles. Unlike
most reptiles dinosaurs all walked with their legs directly
below their hips. This is different than a lizard or a crocodile
where the top section of the limb is splayed out horizontally
from the body and the lower section goes from the "knee" joint
straight down to the ground. Because of this lizards and crocodiles
move low to the ground and almost appear to be dragging themselves
around on their bellies. In contrast, dinosaurs walked in an
upright manner (Though a few species, like Triceratops,
did retain the lizard-like sprawl on it's front legs as it lumbered
We can tell dinosaurs walked with their feet
under their hips by carefully examining the way their bones
go together. Everything we know about these ancient creatures
is based on the few fossilized skeletal
remains we find. None of the soft tissue of the dinosaur's bodies
have survived the past 65 million years of time except for a
few, rare skin and footprint impressions left in rock.
Also, unlike other reptiles, many scientists
believe that dinosaurs were at least partly, "warm-blooded."
(Though new evidence has called this
theory into question.) That is, they used their metabolism
to control their temperatures, instead of depending on the environment.
Snakes and other reptiles adjust their body heat by moving into
the sun or moving into the shade as need be. If a reptile gets
too cold he will slow down or even go into a state of hibernation.
Warm blooded animals, like mammals and birds, maintain a constant
temperature (in the case of people it's 98.6 degrees Fahrenheit)
no matter their activity or environment. This allows mammals
and birds to be active and quick moving in even cold climates.
To maintain a constant temperature requires tremendous amount
of energy, though. Much more energy, per pound of animal, than
cold blooded animals use.
The Mesozoic Era was divided into three smaller
periods: The Triassic, from 254 to 204 million years
ago; the Jurassic, from 204 to 140 million years ago;
and the Cretaceous, from 140 to 65 million years ago.
During these periods a huge variety of different dinosaurs developed.
A common misconception is that all dinosaurs were on Earth at
the same time. Dinosaurs living during the Triassic, like the
plant eating Plateosaurus, are actually further distant
in time from the Cretaceous Tyrannosaurus
Rex than we are today.
Dinosaurs came in many sizes. One of the smallest,
Compsoganthus, was the size of a chicken. The largest
were the Sauropods (Four legged dinos with long tails and long
necks) like the Apatosaurus
and the Diplodocus and could grow to be 90 feet long.
The largest meat eating was the famous Tyrannosaurus
Rex which stood upright on two legs. His head was 20
feet in the air and his body stretched some 46 feet in length.
Other dinosaurs came in unusual shapes. The plant
eating Triceratops had three sharp horns on it's bony
head for defense. Others like the stegosaurs used a club, covered
with sharp spikes, on the end of their tails to protect themselves.
Ankylosaurus also had a club, but without spikes. He
got additional protection from heavy armor plating that covered
his entire body turning him into a living tank.
A couple of other things about dinosaurs: They
had neither flippers or wings. Animals that lived in the sea
during the age of the dinosaurs were marine reptiles, like the
plesiosaur, not dinosaurs.
The flying reptiles, like the pterodactyl,
are not considered dinosaurs either.
Even though dinosaurs didn't fly they do seem
to be closely related to modern birds. Theropod dinosaurs (those
that walk upright on two feet like Tyrannosaurus Rex)
share some bone structures with birds that are seen in no other
group of animals.
So what is a dinosaur? A reptile that lived between
220 million years ago and 65 million years ago, walked with
its feet below it's hips, was maybe warm-blooded, had neither
flippers or wings, and is closely related to modern birds. They
just aren't oversized lizards.
"The Humongous Book of Dinosaurs"
Stop on Dinosaur Safari
Copyright Lee Krystek 1996.
All Rights Reserved.