2. • These are birds and are believed to have evolved
from some reptiles called Archosauria some 140
million years ago.
• This is evident by some similarities between birds
and reptiles.
• e.g.:
1. Both have scales at the feet.
2. Both have single ear ossicle
3. Both possess occipital condyle.
3. • However, there are some differences
between them.
(a)Birds are warm blooded but reptiles are
cold blooded.
(b)Birds have right systemic arch.
• The earliest fossil bird is Archaeopteryx sp
which is extinct.
• The Archaeopteryx had teeth but lost them
in the course of evolution.
• Its skeleton was close to that of the reptiles.
4. FLIGHT IN BIRDS
• Some of the modification made for effective flight
were:
(i) Changes in the vertebral column, e.g. Formation of
the synsacrum for rigidity.
(ii) Loss of teeth and some vertebrae/bones to reduce
weight.
(iii)Pneumatization of bones (hollowing of bones)
reduces weight and promotes buoyancy in birds.
(iv)Improved respiratory system to provide continuous
flow of air to obtain enough oxygen especially at
high altitude.
5. 5. They have aerofoil wings which are convex above
and concave below. They also have thick leading edge
and thin trailing edge.
6. They have specialized flight muscles attached to a
huge keel/carina.
• Keel is reduced in flightless birds and causes them
not to fly. E.g. ostrich.
6. TYPES OF FLIGHT
• There are 3 types of flight in birds. These are:
(i) Gliding
(ii) Soaring
(iii)Flapping
7. Reasons why some birds cannot fly
(I) Undeveloped wings
(II) Reduced keel
(III) Heavy weight
• The keel is the modification of the sternum.
• A bird that has keel present is called a
carinate/keeled bird. i.e. a flying bird.
• The sternum projects into a huge keel to which the
flight muscles anchor.
• Deeply enlarged pectoral muscles originate from the
sternum and insert on the humerus.
8. • Flight has helped birds to radiate.
• But some birds are flightless, e.g. ostrich which
evolved from flying birds.
• They are mostly found on small oceanic islands.
• They are large in size and lack predators.
9. CLASSIFICATION OF BIRDS
Sub-class Archaeornithes
• These are ancient birds and they include reptile-like
birds.
Sub-class Neornithes
• Neornithes- modern birds.
• These include all other birds and they have fused
metacarpals.
• They have 13 or less vertebrae.
10. Archaeopteryx
• Archaeopteryx spp is a pigeon-sized Jurassic bird.
• They had teeth, long reptilian tail consisting of about
21 vertebrae.
• They had three free hand digit bearing curved
talons/claws.
• But all these features disappeared in the latter birds.
11. • The Neornithes has two super orders.
(i) Super-order Neognathae
• They have about 19 orders and all have keeled
sternum. Their wings are well-developed and used
for flying in air. Their bones are hollowed or
pneumatized.
(ii) Super-order Paleognathae.
• They are ratites (running birds).
• They mostly cannot fly because they have unkeeled
sternum, weak wings or solid bones.
12. • Examples;
(i) Rhea, i.e. Rhea americana also known as
American ostrich.
(ii) Struthio camelus i.e. African ostrich.
• Both have unkeeled sternum.
• The cassowaries of Australia and New Guinea and
the emus of New Zealand have unkeeled sternum
and weak wings.
• The kiwis of New Zealand have unkeeled sternum
with wings extremely degenerated and remiges
absent.
13. • There are 3 groups of feathers depending on their
attachment.
1. On digit (I) are tertiary feathers called Alula or
bastard wings.
2. Primary feathers on digits (II) and (III) and the
metacarpals.
3. Secondary feathers on the ulna.
• Primary and secondary feathers are called remiges.
And both remiges and tail feathers have the quill.
14. • In primary feathers, the inner side of the vane is
broader than the outer side.
• In secondary feathers, the two parts (inner and outer)
of the vane are nearly equal.
• The feather of the Alula is oval in shape.
15. • Muscles that move the wing are situated on special
part of the sternum called keel or carina.
• Two types of muscles move the wing.
(i) Pectoralis major (on top).
(ii) Pectoralis minor/ supercoracoideus(beneath).
• These are antagonistic muscles that bring about
movement of the wing; when one contracts, the
other relaxes and vice versa.
• Tendons from pectoralis major contract, the wing is
pulled down.
16. • Tendons for the pectoralis minor passes through the
foramen triosseus (an enclosed hole between three
bones; clavicle, coracoid and scapula) to insert on
the dorsal part of the humerus.
• When the pectoralis minor contracts, the wing is
pulled up.
