Through the process of evolution, few species of reptiles were transformed into modern birds. This ppt describes about the similarities between reptiles and modern birds.

1. Abhi giri
M.Sc. –I / Sem –II

2. Class Aves – Birds
 Birds (class Aves) are
archosaurs but almost every
feature of their reptilian anatomy
has undergone modification in
their adaptation to flight.

3. Classification
 The first classification of birds
was developed by Francis
Willoughby and John Ray in
their 1676
 Most taxonomist classify the
nearly 9,000 species of Class
Aves into 27 orders
 To classify birds into orders and
families taxonomists most often
use morphological evidence
from beaks, feet, plumage, bone
structure, and musculature.

4. Characteristics
 Feathers- composed of keratin, essential for flight, insulate
body
 Wings- modified forelimbs, covered by feathers
 Lightweight, rigid skeleton- bones are thin & hollow
 Endothermic metabolism- high body temperature
 Unique respiratory system- rapid metabolism, lungs
connected to air sacs, oxygen-rich
 Beak- no teeth, horny sheath made of keratin
 Oviparity- lay amniotic eggs- eggs are incubated by both
parents

5. Bird evolution
• Birds arose in the Jurassic period
• Birds evolved from reptiles.
• Thomas H. Huxley: Birds are
“merely glorified reptiles”.
• J.Z. Young described birds as
‘Masters of air’.

6. Birds and Reptile Homologies
 Scales- birds’ feet.
 Yolked, polar eggs
 Nucleated red blood cells. In mammals the red
blood cells lack nuclei.
 A single middle ear bone: the stapes. Mammals
have three.
 The lower jaws (mandibles) have five or six bones
on each side.

7. The Connecting Link!

8. Archaeopteryx
• Fossil found in Bavaria in 1861
dated at 135 to 155 mya.
• Clearly showed: Wing bones,
Flight feathers, Pairs of feathers
attached to each vertebra of the
tail
• Immensely important for the
theory of evolution.
– Found only two years after
Darwin published Origin of
Species (1859)

9. Archaeopteryx
 Archaeopteryx was a crow-sized, bipedal “reptile” with a blunt
snout and many small, reptilian teeth.
– Feathers on wings and tail
– A strong-running terrestrial “bird” that could leap into
trees, jump among branches and make short flights.
– Capable of gliding, not long sustained flight.
– Strong, curved claws, like those of perching birds.
– Could not launch from the ground because it lacked the
principal muscles that lift the wing rapidly in the recovery
stroke.
– Vanes were asymmetrical, like that of strong fliers.

10. Birds are Dinosaurs

11. Evolution of Flight
 Two Competing Theories
1. Arboreal Theory- Started from trees
down
2. Cursorial Theory- Started from
ground up

12. The Arboreal Theory
 originally proposed in
1880 by Othniel C. Marsh
 suggest that the ancestors
of Archaeopteryx lived in
trees and glided into
flapping flight.

13. Arboreal Theory
 Evolution of flight started with the
parachuting and gliding from elevated
perches.
 The extensions of the bones of the forelimb
enhanced by elongated (flight) feathers
enabled the ancestors of Archaeopteryx to
parachute and glide between trees.
 The favored theory for many years.

14. The Cursorial Theory
 Proposed by Samuel Wendell
Williston in 1879
 It states that “Flight evolved in
running bipeds through a
series of short jumps”

15. Cursorial Theory
suggest that these ancestors used their long, powerful
legs to run fast with their arms outstretched, and were
at some point lifted up by air currents and carried into
flapping flight
As the length of the jumps extended, the wings were
used not only for thrust but also for stability, and
eventually eliminated the gliding intermediate.
Flight would be a logical extension of the first small
jumps by this little dinosaur.

16. Evolution of Flight

17. What were the changes that
lead to the glorification of birds
over reptiles ?

18. Amazing Physiology
 Higher metabolism & temperature regulation
Red fibers of avian flight muscles have an extraordinary
capacity for sustained work.
– can also produce heat by shivering.
 Endothermy
To help conserve body heat, birds fluff out there
feathers to insulation.
– Enables birds to inhabit both cold and hot climate

19. Incredible Circulatory & Respiratory
Systems
 The highly adapted respiratory system of birds is adapted
for the high metabolic demands of flight.
 Circulatory system is also well developed with complete
separation of oxygenated & Deoxygenated blood.

20. Circulatory System
 Birds have a four-chambered heart.
– Separate systemic and respiratory circulations.
 Fast heartbeat – faster in smaller birds.
– Hummingbird-600 times a minute
 Red blood cells are nucleated and biconvex.
– Mammals are enucleated and biconcave.

21. Respiratory System
 Air follows a one way journey.
 Do not have Diaphragm.
– Allows birds to fly at high altitude
– The finest branches of the bronchi are
developed as tubelike parabronchi
through which air can flow continuously
– instead of ending in saclike alveoli as
in mammals.
– The result is that there is an almost
continuous stream of oxygenated air
passing through the highly vascularized
parabronchi.
– Air flows - posterior air sacs - to the
lung - anterior air sacs and out.

22. Bird Brains
 Large well, developed brains 6 to
11 times larger than that of
similarly sized reptiles
• Bird brains exhibit functional
lateralization, with left
hemispheric dominance
associated with learning and
innovation in vocal repertoires.

23. Bird Neural Systems
 Highly developed neural systems and acute senses
mediate feats of communication and navigation.
• Birds (esp. song birds) have the greatest sound-
producing capabilities of all vertebrates.
• Birds can navigate using patterns of the Earth’s
magnetism, celestial cues, and perhaps polarized
light.
• Birds can see into the near-ultraviolet and can hear
infrasound's-sounds below the range of human
hearing.

24. Nervous System
 Birds have well developed
cerebral hemispheres,
cerebellum (important for
coordinating movement &
balance), and optic lobes.

25. Reproduction
 Much elaborate for mating purposes
behavior include nest building,
dancing, singing & colorful displays
 Requires dedicated parental care.
 Most birds form monogamous pairs,
though many engage in additional
sexual liaisons.

26. Skeleton
 Modern birds are toothless.
– Instead they have a keratinized
beak.
 Most birds have kinetic skulls.
– They have a wide gape.
– Upper jaw is attached loosely
increasing the gape.

27. Skeleton System
 All birds that can fly have a
large, thin Heel on their
sternum that provides area
for the large flight muscles
to attach.

28. Skeleton
 The sternum supports the large breast muscles
 The humerus, ulna, and radius, along with the pectoral girdle
and the sternum, support the wing.
 Bones are strong but hollow hence light weight filled with air
allowing increased respiration efficiency
copyright cmassengale

29. Efficient Digestive & Excretory
system
 Digestive system has a Crop which stores food
 The avian excretory system is also efficient and
light weight

30. Digestive and Excretory system
 Food passes from the mouth cavity
straight to the esophagus.
 Enlargement of the esophagus
called the crop stores and
moistens food.
 In the first chamber, The
proventriculus, gastric
fluids begin breaking down the
food.
 Then passes through the gizzard, a
muscular organ that kneads and
crushes the food

31. Excretory System
 Urine is formed in large, paired metanephric kidneys.
 Shows two specialization not found in reptiles
1- Uriniferous tubules are relatively longer
2- U-shaped piece called the loop of henle is usually inserted in
the middle.
– There is no urinary bladder.
– Nitrogenous wastes are secreted as uric acid rather than
urea.
– Bird kidneys can only concentrate solutes to 4-8 times that
of blood concentration.

32. Excretory System
 Some birds, including
marine birds, have a salt
gland to help rid the body of
excess salts.
– Salt solution is excreted from
the nostrils.

33. Senses
 Birds usually have poor sense of smell & taste.
– Some, carnivores, waterfowl, flightless birds have
well developed sense of smell & taste.
 Birds have the keenest eyesight in the animal
kingdom and also very good hearing.
– A hawk can clearly see a crouching rabbit a mile
away!

34. Flight
 To fly, birds must generate
lift forces greater than their
own mass and they must
provide propulsion to move
forward.
 Bird wings are designed to
provide lift.

35. Flight - Wings are Specialized for
Particular Kinds of Flight
 Elliptical wings are good for maneuvering in forests.
 High speed wings are used by birds that feed during flight or that make long
migrations.
 Dynamic soaring wings are used by oceanic birds that exploit the reliable
sea winds.
 High lift wings are found in predators that carry heavy loads. Soaring over
land with variable air currents.

36. Migration
 Many species of birds undergo
long migrations using well
established routes.
– Some species make the trip
quickly, others stop along the
way to feed.
– Often, they follow landmarks
such as rivers and coastlines.

37. Migration
 Birds navigate using a number of cues:
– Visual cues – landmarks.
– Accurate sense of time.
– Some may use the Earth’s magnetic field.
– Celestial cues – sun by day, stars at night.

38. And thus is the end of our tale

39. References
 A Life of Vertebrate by J.Z.Young.
 Riseof Birds by Dr. ShankarChatterjee.
 http://people.eku.edu/ritchisong/554notes2.html.
 http://originoflight.bio54.html
 scienceblogs.com/tetrapodzoology/.../luis-chiappes-
glorified-dinosaurs/