Return to my Biology pages
Go
to my home page
© Copyright 1997, Jim Loy
The age of dinosaurs (the Mesozoic era, in which reptiles dominated the entire earth) lasted for about 160 million years. It began about 225 million years ago, and ended about 65 million years ago. The current age of mammals, which followed, has only lasted 65 million years. Small mammals existed throughout much of the age of dinosaurs.
Dinosaurs are divided into two very different orders, the
saurischians (lizard-hipped dinosaurs), and the ornithischians (bird-hipped
dinosaurs). The saurischians were of two types, the carnivores like
Tyrannosaurus (right) and Velociraptor, and the large herbivores like
Apatosaurus ((left) sometimes called Brontosaurus). Some of the carnivores were
very small.
The
ornithischians were all herbivores, and were mainly the duck-billed dinosaurs
(like Maiasaurus), and the armored dinosaurs (like Triceratops (left) and
Stegosaurus (right)). The "bill" of a duck-billed dinosaur was not much like
that of a duck. And the Stegosaurus is often shown together with these other
dinosaurs, but it lived earlier.
The flying reptiles (Pterosaurs (left)) and swimming reptiles
(Plesiosaurs (right) and Ichthyosaurs) were not dinosaurs. Crocodiles and their
relatives were also among the ruling reptiles (archosauria) which were not
dinosaurs.
Apparently, some smaller dinosaurs were warm-blooded, and very quick and agile. And some dinosaurs actively raised their young (maiasaurus for example). Dinosaurs walked, and ran, upright, seldom dragging their tails. A few of the herbivores formed vast herds.
Apparently, a large meteor struck the earth, at the end of the age of dinosaurs. It seems that there is no evidence that other mass extinctions were caused by such meteors. So, even though this meteor may be a handy explanation for the extinction of the dinosaurs, it confuses the subject of extinctions in general. Regardless of the initial cause, changes in climate probably were involved.