172
AN EVOLUTIONARY
LINK BETWEEN BIRDS
AND DINOSAURS
THOMAS HENRY HUXLEY (1825–1895)
I
n 1859, Charles Darwin
described his theory of
evolution by natural selection.
In the heated debates that followed,
Thomas Henry Huxley was the
most formidable champion of
Darwin’s ideas, earning himself
the nickname “Darwin’s bulldog.”
More significantly, the British
biologist did pioneering work
on a key tenet in the evidence
for Darwin’s theories—the idea
that birds and dinosaurs are
closely related.
If Darwin’s theory that species
gradually changed into others was
true, then the fossil record should
show how species that were very
different had diverged from
ancestors that were very similar. In
1860, a remarkable fossil was found
in limestone in a German quarry.
It dated from the Jurassic period,
and was named Archaeopteryx
lithographica. With wings and
feathers like a bird’s, yet from the
time of the dinosaurs, it seemed
to be an example of the kind of
missing link between species that
Darwin’s theory predicted.
One sample, however, was
not nearly enough to prove the
connection between birds and
dinosaurs, and Archaeopteryxcould simply have been one of
the earliest birds, rather than a
feathered dinosaur. But Huxley
began to study closely the anatomy
of both birds and dinosaurs, and for
him, the evidence was compelling.A transitional fossil
Huxley made detailed comparisons
between Archaeopteryx and
various other dinosaurs, and found
that it was very similar to the small
dinosaurs Hypsilophodon and
Compsognathus. The discovery,
in 1875, of a more complete
Archaeopteryx fossil, this time
with dinosaur-like teeth, seemed
to confirm the connection.Eleven fossils of Archaeopteryx
have been discovered. This birdlike
dinosaur lived in the Late Jurassic
period, about 150 million years ago,
in what is now southern Germany.IN CONTEXT
BRANCH
BiologyBEFORE
1859 Charles Darwin
publishes On the Origin
of Species, describing his
theory of evolution.1860 The first Archaeopteryx
fossil, discovered in Germany,
is sold to London’s Natural
History Museum.AFTER
1875 The “Berlin specimen”
of Archaeopteryx, with teeth,
is found.1969 US paleontologist John
Ostrom’s study of microraptor
dinosaurs highlights new
similarities with birds.1996 Sinosauropteryx, the first
known feathered dinosaur, is
discovered in China.2005 US biologist Chris Organ
shows the similarity between
the DNA of birds and that of
Tyrannosaurus rex.