Free dinosaur games

The term 'dinosaur', derived from the Greek, meaning "terrible lizard," refers to the gigantic proportions of some of these beasts. Dinosaurs belonged to two distinct but related orders-the Saurischia and the Ornithischia-that were distinguished from each other chiefly by differences in the structure of their pelvic girdles.

The dinosaurs belonged to the Archosauromorpha infraclass of reptiles. Among the other archosaurs (Greek: "ruling reptiles") were the early crocodilians and extinct flying reptiles. A considerable number of dinosaurs were flesh eaters, but many others abandoned this primitive reptilian mode of life for a plant diet. The early dinosaurs may have descended from archosaurs that were bipeds; many dinosaurs remained bipedal throughout the group's history. In both dinosaur orders, however, many of the herbivore types developed a four-footed mode of locomotion.

Most types of dinosaurs continued to flourish until the very latest phases of the Cretaceous Period. Then, within the next million years, they disappeared completely from the geologic record, and succeeding rock strata show not the slightest trace of a dinosaur. The cause of this sudden demise is not at all clear. One widely accepted explanation for their mass extinction has been that a major geologic cycle of mountain building at the end of the Cretaceous Period reduced the lowland areas in which dinosaurs flourished and also changed the world's climate, thus stimulating evolutionary changes in the plant life upon which dinosaurs fed.

A more recent theory postulates an astronomical catastrophe as the cause: a collision between an asteroid and the Earth generated a huge dust cloud that caused a period of darkness lasting as long as three years. This blockage of sunlight made photosynthesis virtually impossible, and the resulting collapse of the food chain led to the worldwide extinction of the dinosaurs and many other life forms. Although this hypothesis has been partially substantiated by geologic evidence, the apparent survival of some types of dinosaurs for as long as 1 million years after the presumed asteroid impact raises doubts that this catastrophe was the primary cause of the dinosaurs' eventual disappearance. It is possible that both climatic change and an asteroid impact played a part in the extinction of dinosaurs.