+FOLLOW

2. PHYLOGENETIC RELATIONSHIPS
Class Aves have all types of birds. Birds have
adaptations for flight. The major characteristics of this
class are:
1. Their appendages are modified to wings.
2. They body is covered by feathers.
3. Birds are endotherms.
4. They have high metabolic rate.

3. 5. Their vertebral column is modified or flight.
6. Flues are lightened bv numerous air
spaces.
7. Modern birds possess a horny bill and they
lack teeth.
Evolution of birds from reptiles
There are close similarities between birds and
reptiles. That is why, birds are called as
glorified reptiles

4. Archosaurs ancestor: The ancestor of the birds is ancient
archosaurs
These reptiles lost the clavicles long before the appearance of
birds.
Clavicle is an important and used in flight in birds
They have not feather wings. Their flight surface was
composed of membranous fold of skin.e.g Archaeopteryx.

5. ANCIENT BIRDS AND THE EVOLUTION OF FLIGHT
Archaeopteryx fossil was found in Germany in 1861.
Archaeopteryx (archaios, ancient + pteron wing). It lived
during the Jurassic period about 150 million Years ago.

6. 1. It was pigeon-sized animal.
2. It had a long reptilian tail.
3. It has clawed fingers.
4. The complete head .
5. It has rounded wings .
6. It has teeth in beaklike jaws..
• These characters are the main evidence that this was the fossil of an
ancient bird. A complete fossil archaeopteryx was discoverered
sixteen years Later four other fossils of Archaeopteryx were
discovered. These fossils supported the ideas of reptilian ancestry for
birds.

7. Gliding was most primitive than flight.
Archaeopteryx as the oldest bird fossil.
 It is very close to the main line of evolution between the reptiles
and birds.
The clavicles (wish bones) of Archaeopteryx ere well developed.
Clavicle provides points of attachment for wing muscles.
 The sternum, wing, bones and other sites for flight muscle
attachment were less developed than in modern birds.
 These observations indicate that Archaeopteryx as a glider. It used
flapping flight for short distance

8. Evolution of flight
• Flight was more primitive than gliding.
• Some zoologists studied the hind limb structure of the earliest
birds. It suggests that they were bipedal.
• They run and hop on the ground. They used their wings for
capturing flying insects from air and ground.
• Their teeth and claws resembled talons (claw of eagle) of
modern birds.
• They used these teeth and claw for grasping prey.
• They also started flight over short distances.
• This flight led to wing-powered flight.

9. 1. Archaeopteryx, Sinornis and Eoalulovis are transition between reptiles and
birds.
Archaeopteryx
Eoalulovis

10. 2. Many fossils of birds have been found between the period
of 100 million and 70 mya.
Some of these birds were large flightless birds.
Some were adapted for swimming and diving. Some were
fliers.
Most birds like Archaeopteryx, had reptile like teeth. Most
of the lineages of these fossils have become extinct. ‘Ilk.
dinosaurs were also belonged to this lineage. They became
extinct at the end of the Mesozoic era.