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 ID: 376003
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Slide1
Evolution of BirdsSlide2
Evolution of birds
Kingdom
Animalia
, Phylum Chordata, Class AvesWhere did they come from?From the Mesozoic Era, a debate of how they originated. Two Hypotheses exist: Thecodont vs.TheropodSlide3
Evidence to link birds and dinosaurs
Hundreds of similar skeletal features
Hollow bones
Feathers in some dinosaursLungsHeartReproductive and Sleeping PostureSlide4
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.Slide5
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.Slide6
190
MYA
135
MYA
65
MYA
225
MYA
Turtles
Lizards & Snakes
Crocodiles
Mammals
ANAPSIDS
DIAPSIDS
SYNAPSIDS
THERAPSIDS
THECODONTS
SAUROPODS
THEROPODS
CARNOSAURS
COELUROSAURS
ORNITHISCHIA
PTEROSAURS
DINOSAURIA
SAURISCHIA
So, Reptiles, But Where Birds?
Tertiary
Cretaceous
Jurassic
Triassic
PermianSlide7
190
MYA
135
MYA
65
MYA
225
MYA
Turtles
Lizards & Snakes
Crocodiles
Mammals
ANAPSIDS
DIAPSIDS
SYNAPSIDS
THERAPSIDS
THECODONTS
SAUROPODS
THEROPODS
CARNOSAURS
COELUROSAURS
ORNITHISCHIA
PTEROSAURS
DINOSAURIA
SAURISCHIA
Tertiary
Cretaceous
Jurassic
Triassic
PermianSlide8Slide9
Slide10
DINOSAURIA
SAUROPODS
THEROPODS
CARNOSAURS
COELUROSAURS
ORNITHISCHIA
SAURISCHIA
Theropods
(ground runners)
give
rise to
Carnosaurs
&
Coelurosaurs
THECODONTS
Carnosaurs
Coelurosaurs
Velociraptor
is associated with this group.Slide11
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.Slide12
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
.Slide13
ThecodontsOne example:
Microraptor
As seen in DVD “The Four-Winged Dinosaur”Slide14
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.Slide15
Evolution of Flight!Slide16
Two Main, Opposing Hypotheses
Arboreal Model
“
Trees Down” Model(Thecodont)Cursorial Model“Ground Up”
Model
(
Theropod
)Slide17
“Trees Down
”
Model
Ancestors of birds were tree-dwellers (arboreal)Powered flight evolved from gliding/parachuting:Tree-dwelling animals jumped from branch to branchThose with a gliding/parachuting surface could travel further, so selection favored development of increased wingsEventually, forms modified the gliding surface to give them additional thrust: powered flightSeems 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 animalsSlide18
“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 phaseEvolution 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 wasThrough 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 airBirds only got into the trees after having developed the early phases of flightSlide19
“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 didUnlike 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 behaviorSlide20
Youtube: 1of5--Evolve-Flight by History Channel 1 of 5 (see all 5)