Biology Reference
In-Depth Information
Fig. 4.18
The flight feathers are well developed and asymmetrical, like those of modern birds.
Archaeopteryx
was probably a glider rather than a flapping animal because it lacks
a large breastbone required for the anchoring of the powerful muscles necessary for
flight, and the anatomy of its shoulder suggests it was unable to lift its wings above
its back. Reconstructions of its skull by computer tomography (CT scanning) of the
skulls show that the regions of the brain concerned with vision were well developed.
The structure of the inner ear closely resembles that of modern birds rather than that
of reptiles. These observations are interpreted to indicate that
Archaeopteryx
had
good vision, hearing and balance, but whether it lived as a tree-dwelling glider or
evolved flight by running along the ground is the subject of continuing debate.
In China in the last 15 years, eight different feathered dinosaur fossils have been
discovered (Fig. 4.18, right hand panel). From their anatomy, these were probably
not capable of flapping flight, so their feathers may have evolved to act as insulation
as these animals evolved warm-bloodedness, and only later were used for flight.
This is a recurring theme in evolution - one thing leads to another. Natural selection
is a very powerful opportunistic process - even a slight variation will be selected
if it aids survival and reproduction, so traits selected for one purpose can form the
basis for the subsequent development of quite different traits.
Figure 4.19 shows some fossils that bridge the gap between fish and tetrapods -
animals with four limbs.
