Powered flight has evolved in insects, bats, birds and the extinct pterosaurs.

Today's fliers are among the most widespread, diverse and successful animals on Earth.

But let's narrow our focus to one particular flying group—birds.

Two hundred million years ago, birds did not yet exist.

Today they are the most diverse terrestrial vertebrates, with nearly 10,000 known species.

Click on the hummingbird to see a sample of bird diversity.

What happened during the last 200 million years to account for the evolution and diversification of birds?

Let's look at some clues in the fossil record.

The first clues about the origin of birds came in 1861, when an odd-looking fossil was found in a German quarry in Solnhofen.

This was the first of many such specimens found in the same location, at the site of a 150-million-year-old tropical lagoon.