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

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The Great Extinction
The various theories of the extinction of dinosaurs have only one thing in common: the fact that, all of the dinosaurs died out completely and suddenly 66 million years ago, after having been very successful animals for about 160 million years. (In contrast, the human family dates back only four million years.)

The geologic moment when dinosaurs died out is known as the K-T boundary. The K stands for Cretaceous (C having already been used for Carboniferous); the T stands for Tertiary Period, when mammals began their rise to dominance.

“Geologic moment” is a relative term; in this case, it might mean hundreds of thousands of years. In other words, the dinosaurs died out “suddenly” only in the sense that they had already been around for 160 million years.

Curiously, other reptile lines, such as crocodiles and turtles survived. They were not dinosaurs, but dinosaurs or not, when theories are proposed they must account for the survival of these reptiles.

In addition to the great land-based extinctions, many marine species perished at the end of the Cretaceous Period. Any explanation of why the dinosaurs perished must also include these marine extinctions as well.

What happened to the dinosaurs? There are many theories that have been advanced over the years and argued about from a supernova to excessive size. No one knows for sure. Each theory has something to recommend it; each theory has its critics. Even the extinction of dinosaurs is debated -- the predatory dinosaurs (Tyrannosaurus and his relatives) may have left a line of descendants that evolved into our modern birds. This means that essentially, birds are living dinosaurs. The lineage becomes apparent when you forget about sparrows and think about ostriches and emus.

But isn't it nice that, with all the things that have been discovered and invented already, there is still a great, puzzling mystery to be solved?

See Theories and Controversies, for a summary of each theory, along with the objections that are generally raised to each.

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