What Were Dinosaurs?
Ask the average person what dinosaurs were, and he might tell you that
dinosaurs were huge, cold-blooded, slow-moving, dim-witted reptiles
that ruled the Earth millions of years ago and became extinct
suddenly and completely in some sort of catastrophe.
Actually, the only undisputed truth in this commonly-held view is that
the dinosaurs became extinct suddenly in some sort of catastrophe -- and
that may not be true, either!
Dinosaurs ranged in size from smaller than a chicken to larger than
most whales. When the word “dinosaur” is mentioned, many people think of
the gigantic Apatosaurus, placidly
munching prehistoric treetops, or of Tyrannosaurus, enthusiastically pursuing
a tank-like Triceratops. Most dinosaurs, however, were smaller, and many
were very small indeed. Compsognathus, as much a carnivore as was Tyrannosaurus,
measured only about 2' 5" (.7 meters) from his nose to the tip of
his tail. Just as there is great diversity in the size of modern mammals,
from the tiny shrew to the hundred-ton blue whale, so was there diversity
in the size of dinosaurs.
It is curious how large dinosaurs grew to be, considering the size that
modern land animals grow to be. Why were dinosaurs so large? What purpose
did their extreme size serve? In the case of the sauropods, it has been
suggested that their gigantic dimensions were nothing more than a passive
defense against predators; lacking effective armor, speed, or fangs, they
grew larger and larger until they towered over predators. (This might also
explain why some theropods, like Tyrannosaurus, grew as large as they did:
perhaps they were responding to the ever-greater size of their prey.)
Many dinosaurs may have been warm-blooded, just like modern mammals
and birds. The evidence that they were warm-blooded is significant and
One clue is the rapid rate at which their bones grew. Another clue is finding
the fossil remains of dinosaurs in what were very cold climates. Cold-blooded
animals, like snakes and lizards, do not function well when the weather
is very cold. If dinosaurs were cold-blooded, what were they doing in extremely
cold areas where they couldn't function well? Another argument for dinosaurs
being warm-blooded is the speed at which they were apparently able to move.
Far from being slow, some dinosaurs moved as fast as many modern mammals.
Again, there are several reasons for thinking this, but one firm piece
of evidence is the finding of widely-spaced dinosaur tracks in fossilized
prehistoric riverbeds. Knowing the size and structure of the dinosaur that
made the tracks, paleontologists can easily measure the distance between
left footprint and right footprint to calculate the speed at which the
dinosaur was moving. (When a grown man is walking, his stride measures
about two to three feet (.6 - 1.0 meter); when he runs, it increases to
four or five feet (1.2 - 1.5 meters)).
There is evidence at a trackway in Texas of a predatory dinosaur thought
to be Acrocanthosaurus that ran at 25 miles per hour (40 km/h), and it
is believed that Allosaurus and Tyrannosaurus could run faster than a man.
Armored dinosaurs and the extremely large sauropods probably were slower-moving;
they relied on their armor and their size, respectively, for protection
In general, smaller dinosaurs were more active than larger dinosaurs, just
as today's small mammals are more active than large mammals.
Far from being dim-witted, some dinosaurs had a brain-to-body mass
ratio comparable to that of modern species. Recent findings indicate that
some dinosaurs lived in herds, some may have hunted in packs, and most
may have cared for their young. Nowadays, these behaviors are found in
flocks of birds, herds of buffalo, packs of wolves, prides of lions, and
schools of fish.