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scarcely noticed. The first flight-worthy birds appeared and shared the skies
with flying reptiles called pterosaurs.
THE EARLY BIRDS
Birds first appeared in the Jurassic about 150 million years ago, although some
accounts push their origin as far back as the late Triassic 225 million years ago.
By about 135 million years ago, early birds began to diversify. They diverged
into two lineages. One led to archaic birds, and the other led to modern birds.
The birds are believed to have descended from the diapsid reptiles called the-
codonts, the same ancestors of dinosaurs and crocodiles. Consequently, birds
are often referred to as “glorified reptiles.” Alternatively, they could have
Figure 144Marine flora
and fauna of the late
Jurassic.
(Courtesy Field Museum of
Natural History)197JURASSIC BIRDS