1. Evolution of Birds

2. Evolution of birds Kingdom Animalia, Phylum Chordata, Class Aves
Where did they come from?
From the Mesozoic Era, a debate of how they originated.
Two Hypotheses exist:
Thecodont vs.Theropod

3. Evidence to link birds and dinosaurs
Hundreds of similar skeletal features
Hollow bones
Feathers in some dinosaurs
Lungs
Heart
Reproductive and Sleeping Posture

4. More Evidence Similarities:
Gizzard Stones, Brooding and Care of young, Pulmonary Tract
Less DNA repetitions, proposed to aid in flight.
T. Rex bones found with same amino acid sequence (made from DNA) as in chickens. This sequence is for collagen tissue created in common birds.

5. Archaeopteryx
First universally accepted bird. Estimated to be 150 million years old.
Had teeth, flight feathers, long bony tail, wishbone (fused collar bone), and many more theropod features.
At least 10 found by now.

6. So, Reptiles, But Where Birds?
Lizards & Snakes
So, Reptiles, But Where Birds?
Mammals
Turtles
Crocodiles
Tertiary 65
MYA
Cretaceous
CARNOSAURS
COELUROSAURS
135
MYA
SAUROPODS
ORNITHISCHIA
PTEROSAURS
Jurassic
THEROPODS
190
MYA
SAURISCHIA
DINOSAURIA
THECODONTS
Triassic
THERAPSIDS
225
MYA
SYNAPSIDS
ANAPSIDS
Permian
DIAPSIDS

7. Lizards & Snakes Mammals Turtles Crocodiles Tertiary 65 MYA CARNOSAURS
Cretaceous
CARNOSAURS
COELUROSAURS
135
MYA
SAUROPODS
ORNITHISCHIA
PTEROSAURS
Jurassic
THEROPODS
190
MYA
SAURISCHIA
DINOSAURIA
THECODONTS
Triassic
THERAPSIDS
225
MYA
SYNAPSIDS
ANAPSIDS
Permian
DIAPSIDS

10. Theropods(ground runners) give rise to Carnosaurs & Coelurosaurs
Velociraptor is associated with this group.
Theropods(ground runners) give rise to Carnosaurs & Coelurosaurs
Carnosaurs
CARNOSAURS
COELUROSAURS
SAUROPODS
ORNITHISCHIA
THEROPODS
Coelurosaurs
SAURISCHIA
THECODONTS
DINOSAURIA

11. Theropod Hypothesis Theropod has a 3-toed foot similar to modern bird.
Carpal wrist bone in Theropod and Archeaopteryx similar.
Shoulder sockets similar to modern birds and allow “wings” or arms to tuck in close to body.
Lays eggs in nest that were incubated/protected.
This Hypothesis aligns with “Ground Up” model for flight.

12. Thecodonts give rise to crocodilians, dinosauria, & pterosaurs
Theropods’ ancestors: Known for being smaller, long tails, short forelimbs.
Some scientists hypothesize that this group includes the small, lizard-like, flying reptiles.
These were around before Theropods.

13. Thecodonts One example: Microraptor
As seen in DVD “The Four-Winged Dinosaur”

14. Thecodont Hypothesis
Gliding seems more reasonable than “ground-runners” to giving flight.
Birds bodies are flattened top-bottom, Theropods were flattened side-to-side.
Feathers more likely evolved as flight stabilizers instead of a runners warmth.
This hypothesis aligns with “Top Down” model for flight.

15. Evolution of Flight!

16. Two Main, Opposing Hypotheses
Arboreal Model
“Trees Down” Model
(Thecodont)
Cursorial Model
“Ground Up” Model
(Theropod)

17. “Trees Down” Model Ancestors of birds were tree-dwellers (arboreal)
Powered flight evolved from gliding/parachuting:
Tree-dwelling animals jumped from branch to branch
Those with a gliding/parachuting surface could travel further, so selection favored development of increased wings
Eventually, forms modified the gliding surface to give them additional thrust: powered flight
Seems like a reasonable scenario for the origins of the other powered flying vertebrates (pterosaurs, bats)
Makes sense energetically, since the early gliding phases can use gravity to help them fly long before the need for the development of strong arm muscles
Gliders/parachuters are VERY common, and tetrapod gliders/parachuters have consistenly evolved convergently from arboreal animals

18. “Ground Up” Model
Ancestors of birds were ground running animals (cursorial)
Powered flight evolved from activity useful to runners, outside of the context of a tree-dwelling phase
Evolution of the wing stroke evolved in some non-flight context (possibly food capture; possibly as a speed-aid or an aid for leaping and jumping)
Feathers originally evolved in a non-locomotion context, but were exapted for whatever the possible pre-flight use of the forelimbs was
Through enlargement of the proto-wing in the non-flight context, the forelimbs became large enough and developed enough to begin to carry the animal through the air
Birds only got into the trees after having developed the early phases of flight

19. “Ground Up” Model
Birds, unlike bats and pterosaurs, do not make use of a membrane to fly; and there is no fossil evidence that they ever did
Unlike bats and pterosaurs, the hind limb is not part of the flight surface; in fact, most modern and fossil birds have perfectly good running legs (just as their out groups had)
Until recently, all the known member of avialian outgroups (Deinonychosauria, Oviraptorosauria, Therizinosauria, Ornithomimosauria) were fairly large bodied animals that were unlikely to have spent much time in trees
But there was a lack of good modern analogues for whatever the ground use scenario would have been
Also, some questioned whether it would have been energetically feasible for animals to have achieved powered flight directly from a running/leaping behavior

20. Youtube: 1of5--Evolve-Flight by History Channel 1 of 5 (see all 5)