History of Birds Evolution

2. Advanced Ornithology
by
Maryam Riasat
HISTORY OF BIRDS EVOLUTION

3.  Avian history starts more than 150 million years ago
 Birds diversified in the Mesozoic era
 Reptiles are ancestors of birds
 Thomas H. Huxley asserted that birds were
“ merely glorified reptiles”
Reptiles
Therapsids Thecodonts
Mammals
Birds
Birds as Reptiles
Theropods
Birds

4.  At the beginning of Pleistocene epoch climate
changes caused extinction of reptile like birds
 Climatic changes continue to alter their
habitats which in turn changed distribution
and viabilities of bird populations
 In past century, humans have become the
primary force changing and threatening the
natural world

5.  Occipital condyle
o Round projection present
on the posterior end of skull
o Birds and reptiles contain only one occipital
condyle while mammals contain two, Which
allows movements i.e. forward and backward
nodding of head
Common shared characters of birds
and reptiles

6.  Ear
Birds and reptiles have a simple middle ear with
only one ear bone – Stapes
 Mandible
The lower jaws or mandible of both are
composed of five or six bones on each side
 Ankles
Ankles of both are sited in the tarsal bones
 Scales
Scales on the legs of birds are similar in
structure to the body scales of modern reptiles

7.  Eggs
Both lay a yoked egg in which the embryo
develops by shallow divisions of cytoplasm
 Sex Chromosomes
In birds and in some reptiles females are
heterogametic – ZW
Male are homogametic – ZZ
 Nucleated RBC’s
Both have nucleated RBC’s

8. Archaeopteryx: The original link
between birds and reptiles
• In 1861 during the digging of limestone an
impression of a single feather found in Bavarian
quarry
• The impression was brought to the attention of
German naturalist Hermann Von Meyer
• A complete skeleton of a small reptile like organism
(Intermediate between reptiles and birds) near
Eichstatt bavaria were also found and brought to Von
Meyer’s attention
• He named the fossil creature “Archaeopteryx
lithographica”

9. Archaeopteryx lithographica
 Archaeopteryx
Archaios ancient
Pteryx wings
 Lithographica
Printing
o Discovery of a second complete specimen of
archaeopteryx followed in 1877
o Archaeopteryx contained characteristics of both reptiles
and birds i.e.
o Snout, Feathers and wings, three digits, S shape neck,
teeth, bony tail, scapula and furcula (for flight)

10. Reptiles
Thecodonts
Birds
Birds as Dinosaurs
Theropods
Birds
Dinosaurs

11. Thecodont Hypothesis
Diverse group of reptiles gave rise to dinosaurs
Characteristics
 Four digits
 S shaped neck
 Snout
 Arboreal
 Flying reptiles
 Had elongated scales that seemed like natural
precursors of feathers

12. But the size of wings and long 4th digit attached
to wings are not bird’s character

13. Theropods Hypothesis
Theropods
Compsognathus Dromaeosaurs
More similar
Less similar

14. Dromaeosaurs Characteristics
• Body size similar to early birds (Archaeopteryx)
• Bipedal
• Wings
• Feather
• Furcula
• Scapula
• Three digits
• Bill
• Ventilation of lungs

15. These characters were similar with birds but
flight was not so healthy as birds
Modern birds are probably descended from
dinosaurs theropods