Video Assignments
Microraptor—PBS
The Four-winged Dinosaur—Mark Davis
SUNY Cortland Library Online
Radiolab Apocalyptical
http://www.youtube.com/watch?v=K52vD4WBdLw&feature=youtu.be
Minute 13 through minute 60
Link to this video will be emailed—but you can search on Youtube for
“Radiolab Apocalyptical”
Evolutionary Origin of Birds Outline
• Why birds are reptiles
• Archaeopteryx—the link to reptiles
• Birds as dinosaurs
• What kind of dinosaur
• Theropods as bird precursors
• Feathered dinosaurs
• Molecular evidence
Characteristics that Define Birds
• Feathers
• Bills
• Lightweight Bones
• Furcula
• Opposable Hallux
• Efficient Respiratory
System
• External Eggs & Parental
Care
• Finely-tuned Nervous
Systems
Why Birds are Reptiles
Thomas Huxley—19th Century Naturalist regarded birds
as “Glorified Reptiles”
Cladistics—classification application that attempts
to group organisms based on shared derived traits.
(i.e., novel traits that were inherited through a common ancestor)
Species A
Species B
Species C
Ancestor of A, B, & C
Ancestor of A & B
Evolutionary Origins
Species A Species B Species C
Ancestor of A, B, & C
Ancestor of A & B
Why Birds are Reptiles Shared Derived Traits
• Single Occipital Condyle
• Single Middle Ear bone
• Fused Jaw Bones
• Epidermal Scales
• Female Heterogametic Sex
• Sclerotic Eye Ring
• Nucleated Red Blood Cells
Archaeopteryx as a Missing Link
• Archaeopteryx
lithographic fossil
from lithographic rock
quarries in Germany
• 150 MYA
• Reptile-like traits
– Reptilian teeth
– Long tail
– Separate pelvic, hand,
head, and foot bones
– Dinosaur-like hip
– Skull osteology of
reptiles
– Floating gastric ribs
Archaeopteryx as a Missing Link
• Bird-like traits – Asymetrical feathers on wings
– Furcula
– Reversed hallux (?)
• What was the life-style of Archaeopteryx? – Arboreal or ground-dweller?
– Volant?
Archaeopteryx as a Missing Link
More Specimens of Archeopteryx 2005--Science 310:1483
• Pterosaurs
• Pre-dinosaur, pre-crocodilian ancestor
(Archosaurs)?
• Theropod dinosaurs
Who were the
direct
ancestors to
birds?
Ornithischians (Stegosaurus, Ankylosaurus,
Corythosaurus, Iguanodon)
Saurischians—Lizard-hipped (Brachiosaurus, T. rex,
Velociraptor, Deionychus)
DINOSAURS
Thecodonts--Archosaurs
Birds????
Dinosaur-Bird Connection
Backward tilted pelvis,
Predentary bone,
Ossified vertebral tendons
Hands rotate around digits
III, IV, and V
Pelvis tilted forward,
No predentary
No ossified tendons
Digits II, III, and IV
Ornithischians (Stegosaurus, Ankylosaurus,
Corythosaurus, Iguanodon)
Saurischians—Lizard-hipped (Brachiosaurus, T. rex,
Velociraptor, Deionychus)
DINOSAURS
Potential Theropod Precursors
Hollow bones
Three-toed foot (digit I rotated backwards)
Semilunar carpal
Pectoral girdle enlargement
Bipedal
Reduction in digits and arms
Feathers???
Caudipteryx
Elongated feathers
worthy of flight
Arms and legs of
equal length
Enlarge pectoral girdle
Fusion and reduction of bones
Reduction in tail
Motor system development
Beak development
Respiratory efficiency
Why Birds are Reptiles Cladistics of Morphology and Molecular Data
Shark
Mammals
Amphibians
Turtles
Crocodilians
Birds
Reptiles
Snakes
Lizards
Habits of Archaeopteryx (Feduccia, 1993)
Glen & Bennett, 2007.
Cuckoos and Road Runners Pigeons
The first birds (Mesozoic) were very
likely ground foragers and not arboreal foragers.
Feathered Dinosaurs
Hot bed of dinosaur fossils in
Chinese Liaong Province
New species of feathered
theropod dinosaurs-120 MYA
Sinosauropteryx
(first Chinese dragon feather)
Caudipteryx
Caudipteryx zoui
Filamentous
tail feathers
Other specimens that blur the line
between dinosaurs and birds include
Protoarchaeopteryx, Confuciusornis
Birds as Theropods
• Feathered Theropods
– Feathers evolved
before flight
– Feathers are no longer
a novel feature of birds
• Share large numbers of
advanced traits
• Evolutionary trends in
theropods are consistent
with bird evolution
The Four-winged Dinosaur
Microraptor
Significance?
What about non-avian
dinosaur feet and Chukars?
Opposition to Theropod-bird lineage
• Feduccia--birds share an ancestor
with an Archosaur
• Bird-theropod similarities are due to
convergent evolution
– Bipedalism
• Flight evolved from the trees down.
• Deinonychus is 40 MY more recent
than Archaeopteryx. “Temporal
Paradox: you can’t be your own
grandmother”
Comparative Embryology
Feducia’s strongest argument.
• Assume: Digit IV forms the
central axis of modern hands in
birds, turtles, and crocodiles
• Counting backward it appears
that birds retain digits II, III,
and IV and not digits I, II, and
III as in Theropods
Photo from Burke and Fedducia, 1997
Top row-alligator
Middle row-chicken
Bottom row-turtle
Who cares about finger number? (Pennisi-2005, Science 307:195)
• Digit I in terrestrial vertebrates
has unusual development
• Digit I depends on the
developmental gene Hoxd13
and not Hoxd12
• Molecular genetics suggests
that Digit I in birds is indeed
Digit I
Amino Acid Sequence from Bone
Collagen of Dinosaurs
C, G, I are from Ostrich
Amino Acid Sequence
of Dinosaur Collagen
Birds share a more recent common ancestor
with dinosaurs than to early reptiles.
Concluding Remarks • The origin and evolution of birds is
one of the greatest modern day debates in evolutionary biology
• Birds are reptiles
• Theropod origin of birds is gaining strength from many biological disciplines
• Remaining Questions; How did flight arise and & why did feathers evolve?
