Web Site

The Age of Dinosaurs
The Mesozoic Era | What Were Dinosaurs?
The Great Extinction | The Fossil Remains of Dinosaurs

   View printable page version.

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.)

Blood Temperature
Many dinosaurs may have been warm-blooded, just like modern mammals and birds. The evidence that they were warm-blooded is significant and growing.

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 against predators.

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.

 Jurassic Art
  Database Home
  Order Software

  © 2005 Arts & Letters Corporation
Translate to:   Chasque aquí para traducir inglés a español. Cliquetez ici pour traduire l'anglais en Français. Klicken Sie hier, um Englisch in Deutschen zu übersetzen. Scattisi qui per tradurre l'inglese in italiano. Estale aqui para traduzir o inglês no português.